Chapter 9 Laboratory: Introduction to Chemical Reactions and Stoichiometry 161

A chemical reaction is a process during which one or more original substances (called

reactants) are converted to one or more different substances (called products). A chemical

reaction may occur quickly (such as a firecracker exploding) or slowly (such as iron rusting).

Some chemical reactions occur spontaneously at normal temperatures and pressures, as

soon as the reactants are brought into contact with each other. Other chemical reactions

occur only if external energy is supplied in the form of heat, light, or an electrical spark.

Laboratory: 9

Introduction to Chemical Reactions

and Stoichiometry

ComUSTIB oN REACTIoNS

Although it is sometimes considered to be a separate

type of reaction, a combustion reaction is really just a

type of composition reaction. In a combustion reaction,

a substance combines vigorously with oxygen, releasing

energy in the process. For example, when you light a

candle, you initiate a combustion reaction, and the energy

manifests as heat and light, making the flame you see. A

combustion reaction can be thought of as a fast oxidation

reaction, in the sense that a substance is combining

rapidly with oxygen. (Iron rusting or bread growing stale

are examples of slower oxidation reactions.)

However, chemists no longer use the term “oxidation”

to refer exclusively to reactions in which a substance

combines with oxygen. Instead, oxidation is used in a more

general sense to refer to a class of reactions that may not

involve oxygen at all. See Chapter 10 for more details.

There are many different types of chemical reactions. In this

chapter, we examine the following reaction types:

Composition reaction

A composition reaction, also called a combination reaction,

occurs when two or more reactants combine to yield one or

more products. Composition reactions take the general form

A + B → AB, where the reactants A and B may be elements or

compounds and the compound AB is the resulting product. For

example, if you heat a mixture of iron filings (A) and sulfur (B),

those two elements react to form iron sulfide (AB).

decomposition reaction

A decomposition reaction occurs when one reactant is broken

down into two or more products, usually by the application of

heat. Decomposition reactions take the general form AB → A

+ B, where the compound AB is the reactant and the products

A and B may be elements or compounds. For example, if you

heat sodium hydrogen carbonate (sodium bicarbonate or

baking soda, NaHCO 3 ), it breaks down into sodium carbonate

(Na 2 CO 3 ), carbon dioxide (CO 2 ), and water (H 2 O). In this