5.1 Synthesis and Decomposition Reactions

Learning Goals

• Learn how to identify a chemical change

• Learn what is a synthesis reaction and how to create a synthesis reactions

• Learn what is a decomposition reaction and how to create a decomposition reaction

Physical Change• A physical change affects the form of a chemical substance, but does not

change the chemical composition of that substance.

Chemical Change• A chemical change occurs when there is the formation of a new

substance, but it is not always easy to tell.

• Evidence of a chemical change may include one or more of the following:1) Formation of a gas2) Formation of a precipitate3) Change in colour4) Change in odour5) Change in temperature6) Production of light

• A precipitate is an insoluble solid formed in a chemical reaction.

Chemical vs Physical Change

Classifying Chemical Reactions• The new substances, or products, that form during chemical changes

will depend on the type of chemical reaction occurring.

• There are four main types of chemical reactions:

1) Synthesis Reactions

2) Decomposition Reactions

3) Single Displacement Reactions

4) Double Displacement Reactions

Synthesis Reaction• In a synthesis reaction, two or more reactants combine to produce a

new product. This general equation represents a synthesis reaction:

• An example of a synthesis reaction:

2H2(g) + O2(g) 2H2O(l) + thermal energy

Example of Synthesis Reaction

Synthesis ReactionExample: Complete and balance the following synthesis reaction.

Na(s) + Cl2(g)

Synthesis ReactionExample: Complete and balance the following synthesis reaction.

Ca(s) + N2(g)

Decomposition Reaction• In a decomposition reaction, a compound breaks down into two or

more simpler compounds or elements. The general equation is:

• Hint: If you compare this general equation with the one for synthesis reactions, you will see that you can think of decomposition reactions as the opposite of synthesis reactions.

• An example of a synthesis reaction:

H2CO3(aq) CO2(g) + H2O(l)

Example of Decomposition Reaction

Decomposition ReactionExample: Complete and balance the following decomposition reaction.

AgCl(s)

Decomposition ReactionExample: Complete and balance the following decomposition reaction.

AuCl3(s)

Homework

Textbook: • Read Section 5.1• Questions pg 184 # 1 – 2, pg 185 # 1 – 4,

and pg 187 # 1 – 2

Formal Lab Report Due Tuesday!