Section 9-2

Section 9.2 Classifying Chemical Reactions

• Classify chemical reactions.

metal: an element that is a solid at room temperature, a good conductor of heat and electricity, and is generally shiny

• Identify the characteristics of different classes of chemical reactions.

Section 9-2

Section 9.2 Classifying Chemical Reactions (cont.)

synthesis reaction

combustion reaction

decomposition reaction

single-replacement reaction

There are four types of chemical reactions: synthesis, combustion, decomposition, and replacement reactions.

double-replacement reaction

precipitate

Section 9-2

Types of Chemical Reactions

• Chemists classify reactions in order to organize the many types.

• A synthesis reaction is a reaction in which two or more substances react to produce a single product.

Section 9-2

Types of Chemical Reactions (cont.)

• When two elements react, the reaction is always a synthesis reaction.

Section 9-2

Types of Chemical Reactions (cont.)

• In a combustion reaction, oxygen combines with a substance and releases energy in the form of heat and light.

• Heated hydrogen reacts with oxygen to produce heat and water in a combustion reaction. This is also a synthesis reaction.

Section 9-2

Decomposition Reactions

• A decomposition reaction is one in which a single compound breaks down into two or more elements or new compounds.

• Decomposition reactions often require an energy source, such as heat, light, or electricity, to occur.

Section 9-2

Replacement Reactions

• A reaction in which the atoms of one element replace the atoms of another element in a compound is called a single replacement reaction.

A + BX → AX + B

Section 9-2

Replacement Reactions (cont.)

• A metal will not always replace a metal in a compound dissolved in water because of differing reactivities.

• An activity series can be used to predict if reactions will occur.

Section 9-2

Replacement Reactions (cont.)

• Halogens frequently replace other halogens in replacement reactions.

• Halogens also have different reactivities and do not always replace each other.

Section 9-2

Replacement Reactions (cont.)

• Double replacement reactions occur when ions exchange between two compounds.

• This figure shows a generic double replacement equation.

Section 9-2

Replacement Reactions (cont.)

• The solid product produced during a chemical reaction in a solution is called a precipitate.

• All double replacement reactions produce either water, a precipitate, or a gas.

Section 9-2

Replacement Reactions (cont.)

• This table shows the steps to write double replacement reactions.

Section 9-2

Replacement Reactions (cont.)

• This table summarizes different ways to predict the products of a chemical reaction.

A. A

B. B

C. C

D. D

Section 9-2

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Section 9.2 Assessment

Which of the following is NOT one of the four types of reactions?

A. deconstructive

B. synthesis

C. single replacement

D. double replacement

A. A

B. B

C. C

D. D

Section 9-2

Section 9.2 Assessment

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The following equation is what type of reaction?

KCN(aq) + HBr(aq) → KBr(aq) + HCN(g)

A. deconstructive

B. synthesis

C. single replacement

D. double replacement