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Decomposition Reactions

Chemical reaction where one reactant breaks down into two or more products.

You are watching: Which type of reaction has the general formula of ab + cd → ad + cb?

· Write the general chemical equation for a decomposition reaction.

· Describe examples of decomposition reactions.

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Hydrogen peroxide is a widely used disinfectant for minor cuts and scrapes. You may have a bottle of hydrogen peroxide like the one pictured here in your medicine cabinet at home. Did you ever notice that hydrogen peroxide is always kept in a dark brown bottle like this one? Do you know why? The reason is that hydrogen peroxide needs to be protected from light. If it isn’t, it will gradually break down towaterand oxygen. This is a decomposition reaction.  

What Is a Decomposition Reaction?

Adecomposition reactionoccurs when one reactant breaks down into two or more products. It can be represented by the general equation:

AB → A + B

In this equation, AB represents the reactant that begins the reaction, and A and B represent the products of the reaction. The arrow shows the direction in which the reaction occurs.

Q:What is the chemical equation for the decomposition of hydrogen peroxide (H2O2) towater(H2O) and oxygen (O2)?

A:The equation for this decomposition reaction is:

2 H2O2→ 2 H2O + O2

Other Examples of Decomposition Reactions

Two more examples of decomposition reactions are described below. You can see additional examples at this URL:http://www.youtube.com/watch?v=dxlWtsFinTM

· Carbonic acid (H2CO3) is an ingredient in soft drinks. A decomposition reaction takes place when carbonic acid breaks down to producewater(H2O) and carbon dioxide (CO2). This occurs when you open a can of soft drink and some of the carbon dioxide fizzes out. The equation for this reaction is:

H2CO3→ H2O + CO2

· Another decomposition reaction occurs when water (H2O) breaks down to produce hydrogen (H2) and oxygen (O2)gases(seeFigurebelow). This happens when

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an electric currentpasses through the water, as illustrated below. The equation for this reaction is:

2 H2O → 2 H2+ O2


Q:What ratio of hydrogen molecules (H2) to oxygen molecules (O2) is produced in the decomposition of water?

A:Two hydrogen molecules per oxygen molecule are produced because water (H2O) has a ratio of two hydrogenatomsto one oxygen atom.

Summary

· A decomposition reaction occurs when one reactant breaks down into two or more products. This can be represented by the general equation: AB → A + B.

· Examples of decomposition reactions include the breakdown of hydrogen peroxide to water and oxygen, and the breakdown of water to hydrogen and oxygen.

Explore More

Watch the video about decomposition reactions at the following URL, and then answer the questions below.

http://www.youtube.com/watch?v=bQJvbmHD1Lg

1. Why are decomposition reactions the opposite ofsynthesis reactions?

2. What are the products of the decomposition of hydrogen chloride (HCl)?

3. What is missing from each of these balanced equations for decomposition reactions?

a. 2Ni2O3→ 4Ni + ?

b. 2Al2O3→ ? + 3O2

4. What is a general rule for the decomposition of metal hydrogen carbonates?

Review

1. What is a decomposition reaction? What is the general equation for a decomposition reaction?

2. Describe the decomposition of hydrogen peroxide, and write a balanced chemical equation for this reaction.

3. Which of the followingchemical equationsrepresents a decomposition reaction?

a. H2SO3→ H2O + SO2

b. 2Na + Cl2→ 2NaCl

c. 2K + 2H2O → 2KOH + H2

d. NaCl + AgF → NaF + AgCl

Synthesis Reactions

Chemical reaction where two or more reactants combine to form a single product.

· Define synthesis reaction.

· Describe an example of a synthesis reaction.

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In this photo of Los Angeles, California, the air over the city is brown with smog. A major component of smog is nitrogen dioxide, which is a toxic gas with a sharp odor. Nitrogen dioxide can irritate the eyes and throat and trigger asthma attacks. Where does this poisonous gas come from? It forms when nitric oxide—from sources such as car exhaust—reacts with oxygen in the air. This reaction is a synthesis reaction.

What Is a Synthesis Reaction?

Asynthesis reactionoccurs when two or more reactants combine to form a single product. A synthesis reaction can be represented by the general equation:

A + B → C

In this equation, the letters A and B represent the reactants that begin the reaction, and the letter C represents the product that is synthesized in the reaction. The arrow shows the direction in which the reaction occurs.

Q:What is the chemical equation for the synthesis of nitrogen dioxide (NO2) from nitric oxide (NO) and oxygen (O2)?

A:The equation for this synthesis reaction is:

2NO + O2→ 2NO2

Examples of Synthesis Reactions

Another example of a synthesis reaction is the combination of sodium (Na) and chlorine (Cl) to produce sodium chloride (NaCl). This reaction is represented by the chemical equation:

2Na + Cl2→ 2NaCl

Sodium is a highly reactive metal, and chlorine is a poisonous gas. Bothelementsare pictured in theFigurebelow. The compound they synthesize has very different properties. Sodium chloride is commonly called table salt, which is neither reactive nor poisonous. In fact, salt is a necessary component of the human diet. You can see more examples of synthesis reactions at this URL:http://www.youtube.com/watch?v=dxlWtsFinTM.

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Summary

· A synthesis reaction occurs when two or more reactants combine to form a single product. This type of reaction is represented by the general equation: A + B → AB.

· An example of a synthesis reaction is the combination of sodium (Na) and chlorine (Cl) to produce sodium chloride (NaCl). This reaction is represented by the chemical equation: 2Na + Cl2→ 2NaCl.

Explore More

Watch the two-video sequence on synthesis reactions at the following URLs, and then answer the questions below.

http://www.youtube.com/watch?v=HIZoGe-CR5Q

http://www.youtube.com/watch?v=JG121vFEle4

1.Why is it easy to identify synthesis reactions?

2. What is the product of the synthesis reaction in which sodium combines with oxygen?

3. Write a balanced chemical equation for the synthesis reaction in which nitrogen reacts with hydrogen.

4. Complete the following two synthesis reactions by filling in the missing products:

a. 2Al + 3Br2→ ?

b. 2K + S → ?

Review

1. What is a synthesis reaction?

2. Describe the synthesis reaction that produces table salt.

3. Which of the following is a synthesis reaction?

a. 2H2O → 2H2+ O2

b. 2NO + O2→ 2NO2

c. 2K + 2H2O → 2KOH + H2

d. CH4+ 2O2→ CO2+ 2H2O

Combustion Reactions

Commonly called burning, a chemical reaction where a substance reacts quickly with oxygen.

· Write the general formula for a combustion reaction.

· Describe examples of combustion reactions.

See more: How Many Miles From Miami To California From Miami, Miami To Los Angeles Distance (Mia To Lax)

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Don’t try this at home! This performer isn’t really eating fire, but he still puts on an impressive show. You know that fire is dangerous. It’s hot, it can burn you, and it can easily get out of control. But do you know what fire is? Fire is the result of a chemical reaction. Whenever something burns, a type of reaction called a combustion reaction occurs.

What Is a Combustion Reaction?

Acombustion reactionoccurs when a substance reacts quickly with oxygen (O2). For example, in theFigurebelow, charcoal is combining with oxygen. Combustion is commonly called burning, and the substance that burns is usually referred to as fuel. The products of a complete combustion reaction include carbon dioxide (CO2) andwatervapor (H2O). The reaction typically gives offheatand light as well. The general equation for a complete combustion reaction is: