Copy of Decomposition Reactions (with a smidgen of a review of combination reactions) (5/28/2026)

Last updated about 2 hours ago

13 questions

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Copy of Decomposition Reactions (with a smidgen of a review of combination reactions) (5/28/2026)

Last updated about 2 hours ago

13 questions

Sample Problem: Decomposition Reactions
When an electric current is passed through pure water, it decomposes into its elements. Write a balanced equation for the decomposition of water.

Step 1: Plan the problem.

Water is a binary compound composed of hydrogen and oxygen. The hydrogen and oxygen gases produced in the reaction are both diatomic molecules.

Step 2: Solve.

The skeleton (unbalanced) equation:

Note the abbreviation “elec” above the arrow to indicate the passage of an electric current to initiate the reaction. 

Balance the equation.

Step 3: Think about your result.

The products are elements and the equation is balanced.

How does an airbag explode at just the right time in the event of a car accident? Learn more in this simulation:

1

How does a decomposition reaction work?
Antoine Lavoisier is widely known as the “father of modern chemistry.” He was one of the first to study chemical reactions in detail. Lavoisier reacted mercury with oxygen to form mercuric oxide as part of his studies on the composition of the atmosphere. He was then able to show that the decomposition of mercuric oxide produced mercury and oxygen. The diagram above shows the apparatus used by Lavoisier to study the formation and decomposition of mercuric oxide.

Decomposition Reactions
A decomposition reaction is a reaction in which a compound breaks down into two or more simpler substances. The general form of a decomposition reaction is:

Most decomposition reactions require an input of energy in the form of heat, light, or electricity.

Binary compounds are compounds composed of just two elements. The simplest kind of decomposition reaction is when a binary compound decomposes into its elements. Mercury(II) oxide, a red solid, decomposes when heated to produce mercury and oxygen gas.

A reaction is also considered to be a decomposition reaction even when one or more of the products are still compounds. A metal carbonate decomposes into a metal oxide and carbon dioxide gas. For example, calcium carbonate decomposes into calcium oxide and carbon dioxide.

Metal hydroxides decompose on heating to yield metal oxides and water. Sodium hydroxide decomposes to produce sodium oxide and water.

Some unstable acids decompose to produce nonmetal oxides and water. Carbonic acid decomposes easily at room temperature into carbon dioxide and water.

Sample Problem: Decomposition Reactions
When an electric current is passed through pure water, it decomposes into its elements. Write a balanced equation for the decomposition of water.

Step 1: Plan the problem.

Water is a binary compound composed of hydrogen and oxygen. The hydrogen and oxygen gases produced in the reaction are both diatomic molecules.

Step 2: Solve.

The skeleton (unbalanced) equation:

Note the abbreviation “elec” above the arrow to indicate the passage of an electric current to initiate the reaction. 

Balance the equation.

Step 3: Think about your result.

The products are elements and the equation is balanced.

How does an airbag explode at just the right time in the event of a car accident? Learn more in this simulation:

This reaction is classified as:

combination

single displacement

synthesis

decomposition

This reaction is classified as:

displacement

decomposition

combination reaction

synthesis reaction

What form of energy can be used for a decomposition reaction to take place (select all that apply)?

Decomposition reactions form:

Into what does a binary compound often decompose?

Its component elements

A different binary compound

A ternary compound

Two binary compounds

Metal hydroxides often decompose into and _.

a metal oxide and a hydroxide ion

a metallic element and water

a metal oxide and water

a metallic element and a hydroxide ion

Metal carbonates often decompose into _ and __.

a metallic element and a carbonate ion

a metal oxide and carbon dioxide

a metal oxide and a carbonate ion

a metallic element and carbon dioxide

True

False

Which of the following is correctly balanced decomposition reaction for silver oxide?

An element may undergo a chemical decomposition reaction.

True

False

Which of the following is not a decomposition reaction?

Two compounds reacting to form another compound is what type of reaction?

decomposition

combustion

combination

displacement

This is an example of a combination/synthesis reaction.

True

False

How does a decomposition reaction work?
Antoine Lavoisier is widely known as the “father of modern chemistry.” He was one of the first to study chemical reactions in detail. Lavoisier reacted mercury with oxygen to form mercuric oxide as part of his studies on the composition of the atmosphere. He was then able to show that the decomposition of mercuric oxide produced mercury and oxygen. The diagram above shows the apparatus used by Lavoisier to study the formation and decomposition of mercuric oxide.

Decomposition Reactions
A decomposition reaction is a reaction in which a compound breaks down into two or more simpler substances. The general form of a decomposition reaction is:

Most decomposition reactions require an input of energy in the form of heat, light, or electricity.

Binary compounds are compounds composed of just two elements. The simplest kind of decomposition reaction is when a binary compound decomposes into its elements. Mercury(II) oxide, a red solid, decomposes when heated to produce mercury and oxygen gas.

A reaction is also considered to be a decomposition reaction even when one or more of the products are still compounds. A metal carbonate decomposes into a metal oxide and carbon dioxide gas. For example, calcium carbonate decomposes into calcium oxide and carbon dioxide.

Metal hydroxides decompose on heating to yield metal oxides and water. Sodium hydroxide decomposes to produce sodium oxide and water.

Some unstable acids decompose to produce nonmetal oxides and water. Carbonic acid decomposes easily at room temperature into carbon dioxide and water.

This reaction is classified as:

combination

single displacement

synthesis

decomposition

This reaction is classified as:

displacement

decomposition

combination reaction

synthesis reaction

What form of energy can be used for a decomposition reaction to take place (select all that apply)?

Light

Electric

Motion

Heat

Mental

Decomposition reactions form:

Simpler compounds for a complex compound

Complex compounds for a simpler compound

A single product

All of these are correct

None of these are correct

Into what does a binary compound often decompose?

Its component elements

A different binary compound

A ternary compound

Two binary compounds

Metal hydroxides often decompose into __________ and ___________.

a metal oxide and a hydroxide ion

a metallic element and water

a metal oxide and water

a metallic element and a hydroxide ion

Metal carbonates often decompose into ___________ and ____________.

a metallic element and a carbonate ion

a metal oxide and carbon dioxide

a metal oxide and a carbonate ion

a metallic element and carbon dioxide

True

False

Which of the following is correctly balanced decomposition reaction for silver oxide?

An element may undergo a chemical decomposition reaction.

True

False

Which of the following is not a decomposition reaction?

Two compounds reacting to form another compound is what type of reaction?

decomposition

combustion

combination

displacement

This is an example of a combination/synthesis reaction.

True

False