Chemical Reactions: Synthesis & Decomposition

Types of Chemical Reactions

Learning Target

• I can distinguish between synthesis and decomposition reactions given a chemical equation.

Types of Chemical Reactions

• Chemists classify chemical reactions by their similarities.

• We will examine five types of chemical reactions.

• Today we will look at only two: Synthesis & Decomposition Reactions

Synthesis Reactions

• Definition: In a synthesis reaction, also known as a composition reaction, two or more substances combine to form a new compound.

• General formula: $A + X \rightarrow AX$

• A or X can be elements or compounds, but AX is a compound.

Synthesis Reactions Examples:

• $2Mg(s) + O_2(g) \rightarrow 2MgO(s)$

  • This is a synthesis reaction using a diatomic element and a monatomic element.

• $CaO(s) + H<em>2O(l) \rightarrow Ca(OH)</em>2(s)$

  • This is a synthesis reaction between two compounds.

• Demonstration of Synthesis Reaction

  • $2Mg(s) + O_2(g) \longrightarrow 2MgO(s)$

  • Questions:

    • Where does the oxygen come from?

    • What is left?

    • What evidence do we have that a chemical reaction took place?

Decomposition Reaction

• Definition: In a decomposition reaction, a single compound undergoes a reaction that produces two or more simpler substances or compounds.

• General formula: $AX \rightarrow A + X$

• A or X can be elements or compounds, but AX is a compound

Decomposition Reaction Examples:

• $H<em>2CO</em>3 (aq) \rightarrow CO<em>2 (g) + H</em>2O (l)$

  • This is the decomposition of carbonic acid into carbon dioxide and water.

• $2H<em>2O (l) \rightarrow 2H</em>2 + O_2 (g)$

  • This is the decomposition of water. The decomposition of a substance by an electric current is called electrolysis.

• Demonstration of Decomposition Reaction

  • $C<em>{12}H</em>{22}O<em>{11}(s) + 11H</em>2SO<em>4 \longrightarrow 12C(s) + 11H</em>2SO<em>4* H</em>2O(g)$

  • Questions:

    • Where is the water?

    • What is the black stuff?

    • What evidence do we have that a chemical reaction took place?