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Essays on Chemical Reaction

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N-methyl-d-aspartate by Memantine

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Negative Effects of Chemicals Can Be Found in Commercial Powdered-pigment for Paint

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Synthesis and Characterization of Bioactive Heterocyclic Molecular Hybrids

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Examples of Chemical Reactions in Everyday Life

Chemical reactions occur everywhere in the world around you, not just in a chemistry lab. Here are 20 examples of chemical reactions in everyday life and a closer look at what’s happening on a molecular level.

How to Recognize a Chemical Reaction

The first step to recognizing chemical reactions in the world around you is identifying when a reaction is taking place. Chemical reactions cause chemical changes . In other words, substances interact and form new products . Not every change in matter is a chemical reaction . For example, melting ice, tearing a sheet of paper into strips, and dissolving sugar in water are physical changes that don’t change the chemical identity of matter .

Here are some signs of a chemical reaction. If more than one sign is present, it’s likely a reaction has occurred:

• Temperature change
• Color change
• Bubbling or gas production
• Formation of a solid called a precipitate when liquids are mixed

20 Examples of Chemical Reactions in Everyday Life

Here are some broad examples of chemical reactions in daily life:

Photosynthesis

• Aerobic cellular respiration
• Anaerobic respiration (including fermentation )
• Oxidation (including rust)
• Metathesis reactions (such as baking soda and vinegar)
• Electrochemistry (including chemical batteries)
• Soap and detergent reactions
• Acid-base reactions
• Rotting of food
• Electroplating metals
• Disinfecting surfaces and contact lenses
• Leaves changing color with seasons
• Salt keeping ice off roads and helping to freeze ice cream

Examples of Organic Compounds

Some chemicals are inorganic, while those with carbon and hydrogen are organic. Here are examples in everyday life.

A Closer Look at Chemical Reactions in Daily Life

Here is a closer look at some everyday reactions, along with some chemical equations.

You experience combustion reactions when you strike a match, burn a candle, start a campfire, or light a grill. In a combustion reaction, a fuel reacts with oxygen from air to produce water and carbon dioxide. Here is the reaction for the combustion of propane, a fuel used in gas grills and some fireplaces: C 3 H 8  + 5O 2  → 4H 2 O + 3CO 2  + energy 

Plants use a chemical reaction called photosynthesis to convert carbon dioxide and water into food (glucose) and oxygen. It’s a key reaction because it generates oxygen and yields food for plants and animals. The overall chemical reaction for photosynthesis is: 6 CO 2  + 6 H 2 O + light → C​ 6 H 12 O 6  + 6 O 2

Aerobic Cellular Respiration

Animals use the oxygen provided by plants to perform essentially the reverse reaction of photosynthesis to get energy for cells. Aerobic respiration reacts glucose and oxygen to form water and chemical energy in the form of adenosine triphosphate ( ATP ). Here is the overall equation for aerobic cellular respiration: C 6 H 12 O 6  + 6O 2  → 6CO 2  + 6H 2 O + energy (36 ATP)

Anaerobic Cellular Respiration

Organisms also have ways of getting energy without oxygen. Humans use anaerobic respiration during intense or prolonged exercise to get enough energy to muscle cells. Yeast and bacteria use anerobic respiration in the form of fermentation to make everyday products, such as wine, vinegar, yogurt, bread, cheese, and beer. The equation for one form of anerobic respiration is: C 6 H 12 O 6  → 2C 2 H 5 OH + 2CO 2  + energy

Rust, verdigris, and tarnish are all examples of common oxidation reactions. When iron rusts, it changes color and texture to form a flake coating called rust. The reaction also releases heat, but it usually occurs too slowly for this to be noticeable. Here is the chemical equation for the rusting of iron: Fe + O 2  + H 2 O → Fe 2 O 3 . XH 2 O

Electrochemistry

Electrochemical reactions are redox (oxidation and reduction) reactions that convert chemical energy into electrical energy. The type of reaction depends on the battery. Spontaneous reactions occur in galvanic cells, while nonspontaneous reactions take place in electrolytic cells.

Digestion is a complex process that involves thousands of chemical reactions. When you put food in your mouth, water and the enzyme amylase breaks down sugar and other carbohydrates into simpler molecules. Hydrochloric acid and enzymes break down proteins in your stomach. Sodium bicarbonate released into the small intestine neutralizes the acid and protects the digestive tract from dissolving itself.

Soap and Detergent Reactions

Washing your hands with water isn’t a chemical reaction because you’re just mechanically rinsing away grime. But, when you add soap or detergent, chemical reactions occur that emulsify grease and lower surface tension so you can remove oily grime. Even more reactions occur in laundry detergent, which may contain enzymes to break apart proteins and whiteners to prevent clothes from looking dingy.

Just mixing dry ingredients usually doesn’t result in a chemical reaction. But, adding a liquid ingredient often results in a reaction. Cooking with heat also causes reactions. Mixing flour, sugar, and salt is not a chemical reaction. Neither is mixing oil and vinegar. Cooking an egg is a chemical reaction because heat polymerizes proteins in egg white, while the hydrogen and sulfur in the yolk can react to form hydrogen sulfide gas. When you heat sugar, a reaction called caramelization occurs. When you heat meat, it browns due to the Maillard reaction . Baked goods rise due to carbon dioxide bubbles formed by the reaction between baking powder or soda and liquid ingredients.

Acid-Base Reactions

Acid-base reactions occur anytime you mix an acid (e.g., lemon juice, vinegar, muriatic acid, battery acid, carbonic acid from carbonated beverages) with a base (e.g., baking soda, ammonia, lye). A good example of an acid-base reaction is the reaction between baking soda and vinegar to form sodium acetate, water, and carbon dioxide gas: NaHCO 3  + HC 2 H 3 O 2  → NaC 2 H 3 O 2  + H 2 O + CO 2 In general, a reaction between an acid and a base produces a salt and water. For example, if you react muriatic acid (HCl) and lye (NaOH), you get table salt (NaCl) and water (H 2 O): HCl + NaOH → NaCl + H 2 O In this reaction, two clear liquids form another clear liquid, but you can tell a reaction occurs because it releases a lot of heat.

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Historical overview

• The conservation of matter
• Energy considerations
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• Gas-forming reactions
• Precipitation reactions
• Oxidation-reduction reactions
• The Arrhenius theory
• The Brønsted-Lowry theory
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• Decomposition reactions
• Substitution, elimination, and addition reactions
• Polymerization reactions
• Solvolysis and hydrolysis
• Chain reactions
• Photolysis reactions

What are the basics of chemical reactions?

What happens to chemical bonds when a chemical reaction takes place, how are chemical reactions classified.

• What are acids and bases?
• How are acids and bases measured?

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• Table Of Contents

• A chemical reaction is a process in which one or more substances, also called reactants, are converted to one or more different substances, known as products. Substances are either chemical elements or compounds .
• A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products. The properties of the products are different from those of the reactants.
• Chemical reactions differ from physical changes, which include changes of state, such as ice melting to water and water evaporating to vapor. If a physical change occurs, the physical properties of a substance will change, but its chemical identity will remain the same.

According to the modern view of chemical reactions, bonds between atoms in the reactants must be broken, and the atoms or pieces of molecules are reassembled into products by forming new bonds. Energy is absorbed to break bonds, and energy is evolved as bonds are made. In some reactions the energy required to break bonds is larger than the energy evolved in making new bonds, and the net result is the absorption of energy. Hence, different types of bonds may be formed in a reaction. A Lewis acid-base reaction , for example, involves the formation of a covalent bond between a Lewis base, a species that supplies an electron pair, and a Lewis acid, a species that can accept an electron pair. Ammonia is an example of a Lewis base. A pair of electrons located on a nitrogen atom may be used to form a chemical bond to a Lewis acid.

Chemists classify chemical reactions in a number of ways: by type of product, by types of reactants, by reaction outcome, and by reaction mechanism. Often a given reaction can be placed in two or even three categories, including gas -forming and precipitation reactions. Many reactions produce a gas such as carbon dioxide , hydrogen sulfide , ammonia , or sulfur dioxide . Cake batter rising is caused by a gas-forming reaction between an acid and baking soda (sodium hydrogen carbonate). Classification by types of reactants include acid-base reactions and oxidation-reduction reactions , which involve the transfer of one or more electrons from a reducing agent to an oxidizing agent. Examples of classification by reaction outcome include decomposition, polymerization , substitution , and elimination and addition reactions. Chain reactions and photolysis reactions are examples of classification by reaction mechanism, which provides details on how atoms are shuffled and reassembled in the formation of products.

chemical reaction , a process in which one or more substances, the reactants , are converted to one or more different substances, the products. Substances are either chemical elements or compounds . A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products.

Chemical reactions are an integral part of technology, of culture , and indeed of life itself. Burning fuels, smelting iron , making glass and pottery , brewing beer , and making wine and cheese are among many examples of activities incorporating chemical reactions that have been known and used for thousands of years. Chemical reactions abound in the geology of Earth , in the atmosphere and oceans , and in a vast array of complicated processes that occur in all living systems.

Chemical reactions must be distinguished from physical changes. Physical changes include changes of state, such as ice melting to water and water evaporating to vapour. If a physical change occurs, the physical properties of a substance will change, but its chemical identity will remain the same. No matter what its physical state, water (H 2 O) is the same compound , with each molecule composed of two atoms of hydrogen and one atom of oxygen . However, if water, as ice, liquid, or vapour, encounters sodium metal (Na), the atoms will be redistributed to give the new substances molecular hydrogen (H 2 ) and sodium hydroxide (NaOH). By this, we know that a chemical change or reaction has occurred.

The concept of a chemical reaction dates back about 250 years. It had its origins in early experiments that classified substances as elements and compounds and in theories that explained these processes. Development of the concept of a chemical reaction had a primary role in defining the science of chemistry as it is known today.

The first substantive studies in this area were on gases . The identification of oxygen in the 18th century by Swedish chemist Carl Wilhelm Scheele and English clergyman Joseph Priestley had particular significance. The influence of French chemist Antoine-Laurent Lavoisier was especially notable, in that his insights confirmed the importance of quantitative measurements of chemical processes. In his book Traité élémentaire de chimie (1789; Elementary Treatise on Chemistry ), Lavoisier identified 33 “elements”—substances not broken down into simpler entities. Among his many discoveries, Lavoisier accurately measured the weight gained when elements were oxidized, and he ascribed the result to the combining of the element with oxygen . The concept of chemical reactions involving the combination of elements clearly emerged from his writing, and his approach led others to pursue experimental chemistry as a quantitative science.

The other occurrence of historical significance concerning chemical reactions was the development of atomic theory . For this, much credit goes to English chemist John Dalton , who postulated his atomic theory early in the 19th century. Dalton maintained that matter is composed of small, indivisible particles, that the particles, or atoms , of each element were unique, and that chemical reactions were involved in rearranging atoms to form new substances. This view of chemical reactions accurately defines the current subject. Dalton’s theory provided a basis for understanding the results of earlier experimentalists, including the law of conservation of matter (matter is neither created nor destroyed) and the law of constant composition (all samples of a substance have identical elemental compositions).

Thus, experiment and theory, the two cornerstones of chemical science in the modern world, together defined the concept of chemical reactions. Today experimental chemistry provides innumerable examples, and theoretical chemistry allows an understanding of their meaning.

Basic concepts of chemical reactions

When making a new substance from other substances, chemists say either that they carry out a synthesis or that they synthesize the new material. Reactants are converted to products, and the process is symbolized by a chemical equation . For example, iron (Fe) and sulfur (S) combine to form iron sulfide (FeS). Fe(s) + S(s) → FeS(s) The plus sign indicates that iron reacts with sulfur. The arrow signifies that the reaction “forms” or “yields” iron sulfide, the product. The state of matter of reactants and products is designated with the symbols (s) for solids , (l) for liquids , and (g) for gases .

Essays on Chemical Reaction

Faq about chemical reaction.

Chemical Reactions and Equations

Chemical reactions, what is a chemical reaction.

A chemical reaction is in which the bonds are broken within reactant molecules, and new bonds are formed within product molecules in order to form a new substance.

Chemical reactions are all around us, from the metabolism of food in our body to how the light we get from the sun is the result of chemical reactions. Before beginning with chemical reactions, it is important to know about physical and chemical changes.

A burning candle is the best example of physical and chemical change. Take a candle and light it. As time passes, we can observe that the candle changes to wax. If you cover the candle with a jar, it will extinguish.

In the demonstration, burning of the candle is a chemical change while conversion of the candle to wax is a physical change. In a physical change, there is basically a change of state of the substance but in the case of a chemical change mostly a new substance is formed in which either energy is given off or absorbed. Thus, we can conclude that chemical changes are accompanied by certain physical changes.

Table of Content

Basic concepts of chemical reactions.

• Recommended Videos on Chemical Reactions
• Chemical equations
• Types of Chemical equations

Important Points to Remember

• Frequently Asked Questions – FAQs
• A Chemical Reaction is a process that occurs when two or more molecules interact to form a new product(s).
• Compounds that interact to produce new compounds are called reactants whereas the newly formed compounds are called products.
• Chemical reactions play an integral role in different industries, customs and even in our daily life. They are continuously happening in our general surroundings; for example, rusting of iron, pottery, fermentation of wine and so on.
• In a chemical reaction, a chemical change must occur which is generally observed with physical changes like precipitation, heat production, colour change etc.
• A reaction can take place between two atoms or ions or molecules, and they form a new bond and no atom is destroyed or created but a new product is formed from reactants.
• The rate of reaction depends on and is affected by factors like pressure, temperature, the concentration of reactants.

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Chemical reactions and equations – all activities in one go.

Chemical Equations

Due to the vast amounts of chemical reactions happening around us, a nomenclature was developed to simplify how we express a chemical reaction in the form of a chemical equation. A chemical equation is nothing but a mathematical statement which symbolizes the product formation from reactants while stating certain condition for which how the reaction has been conducted.

The reactants are on the left-hand side whereas the products formed are on the right-hand side. The reactants and products are connected by a one-headed or two-headed arrows. For example, a reaction

A + B → C + D

Here, A and B are the reactants, which react to form the products C and D.  In an actual chemical equation, reactants are denoted by their chemical formula . In order to assure the law of conservation of mass, a chemical equation must be balanced i.e. the number of atoms on both sides must be equal. This is the balancing of the equation.

Let us consider an actual chemical reaction between Methane(CH₄) and Oxygen (O 2 ),

Here we can see how the number of each atom on the left side is balanced on the right side, as stated by the law of conservation of mass.

Types of Chemical Reactions

The basis for different types of reactions is the product formed, the changes that occur, the reactants involved and so on. Different types of reactions are

• Combustion reaction
• Decomposition reaction
• Neutralization reaction
• Redox Reaction
• Precipitation or Double-Displacement Reaction
• Synthesis reaction

1. Combustion Reaction

A combustion reaction is a reaction with a combustible material with an oxidizer to give an oxidized product. An oxidizer is a chemical a fuel requires to burn, generally oxygen. Consider the example of combustion of magnesium metal.

\(\begin{array}{l}2 Mg + O_2 \rightarrow 2 MgO + Heat\end{array} \)

Here, 2 magnesium atoms react with a molecule of oxygen producing 2 molecules of the compound magnesium oxide releasing some heat in the process.

2. Decomposition Reaction

A Decomposition reaction is a reaction in which a single component breaks down into multiple products. Certain changes in energy in the environment have to be made like heat, light or electricity breaking bonds of the compound. Consider the example of the decomposition of calcium carbonate giving out CaO (Quick Lime) which is a major component of cement.

\(\begin{array}{l}Ca C O_3 ( s ) \overset{Heat}{\rightarrow} Ca O ( s ) + CO_2 ( g ) \end{array} \)

Here, the compound Calcium carbonate when heated breaks down into Calcium Oxide and Carbon Dioxide.

3. Neutralization Reaction

A Neutralization reaction is basically the reaction between an acid and a base giving salt and water as the products. The water molecule formed is by the combination of OH –  ions and H +  ions. The overall pH of the products when a strong acid and a strong base undergo a neutralization reaction will be 7. Consider the example of the neutralization reaction between Hydrochloric acid and Sodium Hydroxide giving out sodium chloride(Common Salt) and water.

\(\begin{array}{l}H Cl + NaOH \rightarrow NaCl +H_2O\end{array} \)

Here, an acid and a base, Hydrochloric acid and Sodium Hydroxide react in a neutralization reaction to produce Sodium Chloride(Common Salt) and water as the products.

4. Redox Reaction

A RED uction- OX idation reaction is a reaction in which there is a transfer of electrons between chemical species. Let us consider the example of an electrochemical cell-like redox reaction between Zinc and Hydrogen.

\(\begin{array}{l}Zn+2H^{+}\rightarrow Zn^{2+}+H_2\end{array} \)

Here, A Zinc atom reacts with 2 ions of positively charged hydrogen to which electrons get transferred from the zinc atom and hydrogen becomes a stable molecule and Zinc ion is the product.

5. Precipitation or Double-Displacement Reaction

It is a type of displacement reaction in which two compounds react and consequently, their anions and cations switch places forming two new products. Consider the example of the reaction between silver nitrate and sodium chloride. The products will be silver chloride and sodium nitrate after the double-displacement reaction.

\(\begin{array}{l}Ag N O_3 + Na Cl \rightarrow Ag Cl + Na N O_3\end{array} \)

Here, Silver Nitrate and Sodium Chloride undergo a double displacement reaction. Wherein Silver replaces Sodium in Sodium Chloride and Sodium joins with Nitrate becoming Sodium Nitrate along with the Silver Chloride as the product.

6. Synthesis Reaction

A Synthesis reaction is one of the most basic types of reaction wherein multiple simple compounds combine under certain physical conditions giving out a complex product. The product will always be a compound. Let us consider the Synthesis reaction of sodium chloride with reactants solid sodium and chloride gas.

\(\begin{array}{l}2 Na ( s ) + Cl_{2} (g) \rightarrow 2 Na Cl ( s )\end{array} \)

Here, we have 2 Atoms of solid Sodium reacting with Chlorine gas giving out Sodium Chloride viz. Common Salt as the product.

• In a chemical change, a new compound is formed but in a physical change, the substance changes its state of existence.
• Atoms or ions or molecules which react to form a new substance are called reactants; the new atoms or molecules formed are products.
• A chemical reaction follows the law of conservation of mass. That is no atom is destroyed or created but only a new product is formed from reactants.

BYJU’S helps students by delivering chapter wise and detailed solutions to the questions of NCERT books. They can compare their answers with the sample answers given here – NCERT Solutions for class 10 Science Chapter 1 Chemical reactions and equations .

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Frequently Asked Questions – FAQs

What is meant by a chemical reaction.

A Chemical Reaction is a process that occurs when two or more molecules collide with the right orientation and sufficient force to form a new product. In this process breaking and forming bonds between atoms takes place. Compounds that interact to produce new compounds are called reactants whereas the newly formed compounds are called products.

What is chemical reaction and equation?

A chemical reaction is in which the bonds are broken within reactant molecules, and new bonds are formed within product molecules in order to form a new substance. A chemical equation is nothing but a mathematical statement which symbolizes the product formation from reactants.

What are the chemical reaction types?

On the basis of the product formed, different types of reactions are Combustion reaction, Decomposition reaction, Neutralization reaction, Redox Reaction, Precipitation or Double-Displacement Reaction, Synthesis reaction.

What is a combustion chemical reaction?

A combustion reaction is a reaction in which a substance reacts with oxygen gas, releasing energy in the form of light and heat.

What is a chemical equation?

What is a decomposition reaction, what is a neutralization reaction, what is a redox reaction, what is precipitation or a double displacement reaction, what is a synthesis reaction.

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Types of Chemical Reactions

List of Common Reactions and Examples

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A chemical reaction is a process generally characterized by a chemical change in which the starting materials (reactants) are different from the products. Chemical reactions tend to involve the motion of electrons , leading to the formation and breaking of chemical bonds. There are several different types of chemical reactions and more than one way of classifying them. Here are some common reaction types: 

Oxidation-Reduction or Redox Reaction

In a redox reaction, the oxidation numbers of atoms are changed. Redox reactions may involve the transfer of electrons between chemical species. The reaction that occurs when In which I 2 is reduced to I - and S 2 O 3 2- (thiosulfate anion) is oxidized to S 4 O 6 2- provides an example of a redox reaction : 2 S 2 O 3 2− (aq) + I 2 (aq) → S 4 O 6 2− (aq) + 2 I − (aq)

Direct Combination or Synthesis Reaction

In a synthesis reaction , two or more chemical species combine to form a more complex product. A + B → AB The combination of iron and sulfur to form iron (II) sulfide is an example of a synthesis reaction: 8 Fe + S 8 → 8 FeS

Chemical Decomposition or Analysis Reaction

In a decomposition reaction , a compound is broken into smaller chemical species. AB → A + B The electrolysis of water into oxygen and hydrogen gas is an example of a decomposition reaction: 2 H 2 O → 2 H 2 + O 2

Single Displacement or Substitution Reaction

A substitution or single displacement reaction is characterized by one element being displaced from a compound by another element. A + BC → AC + B An example of a substitution reaction occurs when zinc combines with hydrochloric acid. The zinc replaces the hydrogen: Zn + 2 HCl → ZnCl 2 + H 2

Metathesis or Double Displacement Reaction

In a double displacement or metathesis reaction two compounds exchange bonds or ions in order to form different compounds . AB + CD → AD + CB An example of a double displacement reaction occurs between sodium chloride and silver nitrate to form sodium nitrate and silver chloride. NaCl(aq) + AgNO 3 (aq) → NaNO 3 (aq) + AgCl(s)

Acid-Base Reaction

An acid-base reaction is a type of double displacement reaction that occurs between an acid and a base. The H + ion in the acid reacts with the OH - ion in the base to form water and an ionic salt: HA + BOH → H 2 O + BA The reaction between hydrobromic acid (HBr) and sodium hydroxide is an example of an acid-base reaction: HBr + NaOH → NaBr + H 2 O

A combustion reaction is a type of redox reaction in which a combustible material combines with an oxidizer to form oxidized products and generate heat ( exothermic reaction ). Usually, in a combustion reaction oxygen combines with another compound to form carbon dioxide and water. An example of a combustion reaction is the burning of naphthalene: C 10 H 8 + 12 O 2 → 10 CO 2 + 4 H 2 O

Isomerization

In an isomerization reaction, the structural arrangement of a compound is changed but its net atomic composition remains the same.

Hydrolysis Reaction

A hydrolysis reaction involves water. The general form for a hydrolysis reaction is: X - (aq) + H 2 O(l) ↔ HX(aq) + OH - (aq)

The Main Types of Chemical Reactions

There are hundreds or even thousands of types of chemical reactions ! If you are asked to name the main 4, 5 or 6 types of  chemical reactions , here is how they are  categorized . The main four types of reactions are direct combination, analysis reaction, single displacement, and double displacement. If you're asked the five main types of reactions, it is these four and then either acid-base or redox (depending who you ask). Keep in mind, a specific chemical reaction may fall into more than one category.

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What is a Chemical Reaction?

Instructions, simulations.

Youtube ID: 7UUnRtwQPlc

Lesson Summary Video for teachers

Note: This video is designed to help the teacher better understand the lesson and is NOT intended to be shown to students. It includes observations and conclusions that students are meant to make on their own.

Key Concepts:

• A physical change, such as a state change or dissolving, does not create a new substance, but a chemical change does.
• A chemical change is the result of a chemical reaction.
• In a chemical reaction, the atoms and molecules that interact with each other are called reactants .
• In a chemical reaction, the atoms and molecules produced by the reaction are called products .
• In a chemical reaction, only the atoms present in the reactants can end up in the products. No new atoms are created, and no atoms are destroyed.
• In a chemical reaction, reactants contact each other, bonds between atoms in the reactants are broken, and atoms rearrange and form new bonds to make the products.

The teacher will use a small candle flame to demonstrate a chemical reaction between the candle wax and oxygen in the air. Students will see a molecular animation of the combustion of methane and oxygen as a model of a similar reaction. Students will use atom model cut-outs to model the reaction and see that all the atoms in the reactants show up in the products.

Students will be able to explain that for a chemical reaction to take place, the bonds between atoms in the reactants are broken, the atoms rearrange, and new bonds between the atoms are formed to make the products. Students will also be able to explain that in a chemical reaction, no atoms are created or destroyed.

Be sure you and the students wear properly fitting goggles. Be careful when lighting the candle. Be sure that the match and candle are completely extinguished when you are finished with the demonstration.

Materials for the Demonstration

• Tea light candle or other small stable candle
• Glass jar, large enough to be placed over the candle

Materials for Each Student

• Atom cut-outs from the activity sheet
• Sheet of colored paper or construction paper
• Colored pencils
• Glue or tape

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Standards Alignment

6.1 Next Generation Science Standards (PDF) 6.1 Common Core State Standards (PDF)

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Step 1 Review what happens during a physical change and introduce the idea of chemical change.

Tell students that in previous chapters they have studied different aspects of physical change. When atoms and molecules speed up or slow down, that is a physical change. When they change state from liquid to solid or from gas to liquid, that is a physical change. When a substance is dissolved by water or some other solvent, a new substance has not really been formed. The ions or molecules can still come back together to form the original substance.

Let students know that in this chapter they will explore what happens during a chemical change. In a chemical change, the atoms in the reactants rearrange themselves and bond together differently to form one or more new products with different characteristics than the reactants. When a new substance is formed, the change is called a chemical change .

Step 2 As a demonstration, light a candle and explain what is happening using the terms reactants , products , and chemical reaction .

Explain that in most chemical reactions, two or more substances, called reactants, interact to create different substances called products . Tell students that burning a candle is an example of a chemical reaction.

• Carefully light a tea light candle or other small candle.
• Keep the candle burning as you ask students the questions below. You will put the candle out in the second part of the demonstration

Expected Results

The wick will catch on fire and the flame will be sustained by the chemical reaction.

The following question is not easy, and students are not expected to know the answer at this point. However, thinking about a candle burning in terms of a chemical reaction is a good place to start developing what it means when substances react chemically.

Ask students:

• What do you think are the reactants in this chemical reaction? Wax and oxygen from the air are the reactants.

Students often say that the string or wick is burning. It is true that the string of the wick does burn but it’s the wax on the string and not so much the string itself that burns and keeps the candle flame burning. Explain that the molecules that make up the wax combine with oxygen from the air to make the products carbon dioxide and water vapor.

Point out to students that this is one of the major characteristics of a chemical reaction:

In a chemical reaction, atoms in the reactants combine in new and different ways to form the molecules of the products.

Students may be surprised that water can be produced from combustion. Since we use water to extinguish a fire, it may seem strange that water is actually produced by combustion. You may want to let students know that when they metabolize or “burn” food in their bodies, they also produce carbon dioxide and water.

Step 3 Place a jar over the candle to help students realize that oxygen is a reactant in the burning of a candle.

Remind students that air is a mixture of gases. Explain that when something burns, it reacts with the oxygen in the air.

Ask students to make a prediction:

• Will the candle still burn if one of the reactants (wax or oxygen) is no longer available? Students may guess that the candle will not burn because both reactants are required for the chemical reaction to continue.

• Carefully place a glass jar over the lit candle.

The flame goes out.

• Why do you think the flame goes out when we put a jar over the candle? Placing a jar over the candle limits the amount of oxygen in the air around the candle. Without enough oxygen to react with the wax, the chemical reaction cannot take place and the candle cannot burn.
• When a candle burns for a while, it eventually gets smaller and smaller. Where does the candle wax go? When a candle burns, the candle wax seems to “disappear.” It doesn’t really disappear: It reacts chemically, and the new products go into the air.

Note : Some curious students may ask what the flame is made of. This is a great question and not trivial to answer. The flame is burning wax vapor. The light of the flame is caused by a process called chemiluminescence. Energy released in the chemical reaction makes electrons from different molecules move to a higher energy state. When the electrons come back down, energy is released in the form of light.

Step 4 Introduce the chemical equation for the combustion of methane and explain that atoms rearrange to become different molecules.

Explain to students that wax is made of long molecules called paraffin and that paraffin is made up of only carbon atoms and hydrogen atoms bonded together. Molecules made of only carbon and hydrogen are called hydrocarbons . Tell students that you will use the simplest hydrocarbon (methane) as a model to show how the wax, or any other hydrocarbon, burns.

Project the image Methane and Oxygen React .

Show students that there is methane and oxygen on the left side of the chemical equation and carbon dioxide and water on the right side. Explain that the molecules on the left side are the reactants and the ones on the right side are the products . When the candle was burning, the paraffin reacted with oxygen in the air to produce carbon dioxide and water, similar to the chemical reaction between methane and oxygen.

Explain to students that the chemical formula for methane is CH 4 . This means that methane is made up of one carbon atom and four hydrogen atoms. Show students that the other reactant is two molecules of oxygen gas. Point out that each molecule of oxygen gas is made up of two oxygen atoms bonded together. It can be confusing for students that oxygen the atom, and oxygen the molecule, are both called oxygen . Let students know that when we talk about the oxygen in the air, it is always the molecule of oxygen, which is two oxygen atoms bonded together, or O 2 .

• Where do the atoms come from that make the carbon dioxide and the water on the right side of the equation? The atoms in the products come from the atoms in the reactants. In a chemical reaction, bonds between atoms in the reactants are broken and the atoms rearrange and form new bonds to make the products.

Note : Leave this equation projected throughout the activity in the Explore section of this lesson. Students will need to refer to it as they model the chemical reaction.

Give each student an activity sheet.

• Lesson 6.1 Student Activity Sheet  PDF  |  DOCX  |  Google Doc
• Lesson 6.1 Activity Sheet Answers  PDF  |  DOCX  |  Google Doc

Download the student activity sheet, and distribute one per student.

All Downloads

The activity sheet will serve as the “Evaluate” component of each 5-E lesson plan. The activity sheets are formative assessments of student progress and understanding. A more formal summative assessment is included at the end of each chapter.

Students will record their observations and answer questions about the activity on the activity sheet. The Explain It with Atoms and Molecules and Take It Further sections of the activity sheet will either be completed as a class, in groups, or individually, depending on your instructions. Look at the teacher version of the activity sheet to find the questions and answers.

Step 5 Have students make a model to show that in a chemical reaction the atoms of the reactants rearrange to form the products.

Question to Investigate

Where do the atoms in the products of a chemical reaction come from?

• Atom model cut-outs (carbon, oxygen, and hydrogen)

Prepare the Atoms

• Color the carbon atoms black, the oxygen atoms red, and leave the hydrogen atoms white.
• Use scissors to carefully cut out the atoms.

Build the Reactants

• On a sheet of paper, place the atoms together to make the molecules of the reactants on the left side of the chemical equation for the combustion of methane.
• Write the chemical formula under each molecule of the reactants. Also draw a “+” sign between the reactants.

After you are sure that students have made and written the formula for the reactant molecules, tell students that they will rearrange the atoms in the reactants to form the products.

Build the Products

• Draw an arrow after the second oxygen molecule to show that a chemical reaction is taking place.
• Rearrange the atoms in the reactants to make the molecules in the products on the right side of the arrow.
• Write the chemical formula under each molecule of the products. Also draw a “+” sign between the products.

Tell students that in a chemical reaction, the atoms in the reactants come apart, rearrange, and make new bonds to form the products.

Represent the Chemical Equation

• Have students use their remaining atoms to make the reactants again to represent the chemical reaction as a complete chemical equation.
• Glue or tape the atoms to the paper to make a more permanent chemical equation of the combustion of methane.

Step 6 Help students count the number of atoms on each side of the equation.

Project the animation Combustion of Methane .

Combustion of Methane

Show students that the atoms in methane and oxygen need to come apart like in their models. Also point out that the atoms arrange themselves differently and rebond to form new products. This is also like their model. Be sure that students realize that the atoms in the products only come from the reactants. There are no other atoms available. No new atoms are created, and no atoms are destroyed.

Note: Explain to students that chemical reactions are more complicated than the simplified model shown in the animation. The animation shows that bonds between atoms in the reactants are broken, and that atoms rearrange and form new bonds to make the products.

In reality, the reactants need to collide and interact with each other in order for their bonds to break and rearrange. Also, the animation shows all of the atoms in the reactants coming apart and rearranging to form the products. But in many chemical reactions, only some bonds are broken, and groups of atoms stay together as the reactants form the products.

Read more about the combustion of methane in Teacher Background.

• Lesson 6.1 Teacher Background  PDF

Guide students as you answer the following question together:

• How many carbon, hydrogen, and oxygen atoms are in the reactants compared to the number of carbon, hydrogen, and oxygen atoms in the products? Show students how to use the big number (coefficient) in front of the molecule and the little number after an atom of the molecule (subscript) to count the atoms on both sides of the equation. Explain to students that the subscript tells how many of a certain type of atom are in a molecule. The coefficient tells how many of a particular type of molecule there are. So if there is a coefficient in front of the molecule and a subscript after an atom, you need to multiply the coefficient times the subscript to get the number of atoms. For example, in the products of the chemical reaction there are 2H 2 O. The coefficient means that there are two molecules of water. The subscript means that each water molecule has two hydrogen atoms. Since each water molecule has two hydrogen atoms and there are two water molecules, there must be 2 x 2 = 4 hydrogen atoms. 

Note : The coefficients indicate the ratios of the numbers of molecules in a chemical reaction. It is not the actual number as in two molecules of oxygen and one molecule of methane since there are usually billions of trillions of molecules reacting. The coefficient shows that there are twice as many oxygen molecules as methane molecules reacting. It would be correct to say that in this reaction there are two oxygen molecules for every methane molecule.

Step 7 Explain that mass is conserved in a chemical reaction.

• Are atoms created or destroyed in a chemical reaction? No.
• How do you know? There are the same number of each type of atom on both the reactant side and the product side of the chemical equation we explored.
• In a physical change, like changing state from a solid to a liquid, the substance itself doesn’t really change. How is a chemical change different from a physical change? In a chemical change, the molecules in the reactants interact to form new substances. In a physical change, like a state change or dissolving, no new substance is formed.

Explain that another way to say that no atoms are created or destroyed in a chemical reaction is to say, “Mass is conserved.”

Project the image Balanced Equation . 

Explain that the balance shows the mass of methane and oxygen on one side exactly equals the mass of carbon dioxide and water on the other. When an equation of a chemical reaction is written, it is “balanced” and shows that the atoms in the reactants end up in the products and that no new atoms are created, and no atoms are destroyed.

Step 8 Introduce two other combustion reactions and have students check to see whether or not they are balanced.

Tell students that, in addition to the wax and methane, some other common hydrocarbons are propane (the fuel in outdoor gas grills), and butane (the fuel in disposable lighters). Have students count the number of carbon, hydrogen, and oxygen atoms in the reactants and products of each equation to see if the equation is balanced. They should record the number of each type of atom in the chart on their activity sheet.

Lighting an outdoor gas grill—Combustion of propane

C 3 H 8 + 5O 2 → 3CO 2 + 4H 2 0

Using a disposable lighter—Combustion of butane

2C 4 H 10 + 13O 2 → 8CO 2 + 10H 2 O

After students have counted each type of atom, review their answers to make sure they know how to interpret subscripts and coefficients

What is the 5-E format?

The 5-E instructional model is an approach to teaching and learning that focuses on active engagement, inquiry-based learning, and collaboration.

Simulations for Lesson 6.1

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• Lesson 6.1 Lesson Plan  PDF  |  DOCX  |  Google Doc

Resources for the entire Chapter 6

• Chapter 6 Student Reading  PDF  |  DOCX  |  Google Doc
• Chapter 6 Test Bank  PDF  |  DOCX  |  Google Doc

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This lesson is part of:  Chapter 6: Chemical Change

Lesson 5.9: Temperature Changes in Dissolving

Lesson 6.2: Controlling the Amount of Products in a Chemical Reaction

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Quantitative Biology > Molecular Networks

Title: exact first passage time distribution for second-order reactions in chemical networks.

Abstract: The first passage time (FPT) is a generic measure that quantifies when a random quantity reaches a specific state. We consider the FTP distribution in nonlinear stochastic biochemical networks, where obtaining exact solutions of the distribution is a challenging problem. Even simple two-particle collisions cause strong nonlinearities that hinder the theoretical determination of the full FPT distribution. Previous research has either focused on analyzing the mean FPT, which provides limited information about a system, or has considered time-consuming stochastic simulations that do not clearly expose causal relationships between parameters and the system's dynamics. This paper presents the first exact theoretical solution of the full FPT distribution in a broad class of chemical reaction networks involving $A + B \rightarrow C$ type of second-order reactions. Our exact theoretical method outperforms stochastic simulations, in terms of computational efficiency, and deviates from approximate analytical solutions. Given the prevalence of bimolecular reactions in biochemical systems, our approach has the potential to enhance the understanding of real-world biochemical processes.

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