Chemical Equations These interactions are called chemical reactions. A substance that undergoes a chemical reaction is called a reactant. A substance that is formed in a chemical reaction is called a product.

The law of conservation of mass states that in any chemical reaction, the mass of the products is always equal to the mass of the reactants. Thus we must balance the reactions.

Balance metals, followed by non-metals, and then polyatomic ions if they are located on both sides. Balance the hydrogens. Finally balance the oxygens. Verify all values.

Synthesis Reactions In a synthesis reaction, two or more elements or compounds combine to form a new substance. A + B → C

Synthesis Reactions 2 H 2(g) + O 2(g) → 2 H 2 O (g) 2 Mg (s) + O 2(g) → 2 MgO (s) 2 K (s) + Cl 2(g) → 2 KCl (s) 4 Fe (s) + 3 O 2(g) → 2 Fe 2 O 3(s)

Synthesis Reactions When a non-metallic oxide reacts with water, the product is an acid. SO 3(g) + H 2 O (l) → H 2 SO 4(aq) Conversely, when a metallic oxide reacts with water, the product is a metal hydroxide. CaO (s) + H 2 O (l) → Ca(OH) 2(aq)

Decomposition Reactions In a decomposition reaction, a compound breaks down into elements or other compounds. Therefore, a decomposition reaction is the opposite of a synthesis reaction. C → A + B

Decomposition Reactions 2 H 2 O → 2 H 2 + O 2 NH 4 NO 3(s) → N 2 O (g) + 2 H 2 O (g) Generally decompose into elemental form, but maybe some compounds.

Decomposition Reactions Carbonates decompose into carbon dioxide and a metal oxide: MgCO 3(s)  CO 2(g) + MgO (s) Hydroxides decompose into water and a metal oxide: Ca(OH) 2(s)  H 2 O (l) + CaO (s)

Decomposition Reactions Chlorates decompose into oxygen and a metal halide: 2 KClO 3(s)  3 O 2(g) + 2 KCl (s)

Combustion Reactions A combustion reaction occurs when a compound reacts in the presence of oxygen to form oxides and energy. S 8(s) + 8 O 2(g) → 8 SO 2(g) Complete combustion of a hydrocarbon occurs when the hydrocarbon reacts completely in the presence of sufficient oxygen. The complete combustion of a hydrocarbon produces only water vapour and carbon dioxide gas as products. C 3 H 8(g) + 5 O 2(g) → 3 CO 2(g) + 4 H 2 O (g)

Incomplete combustion of a hydrocarbon occurs when there is not enough oxygen present for the hydrocarbon to react completely. The incomplete combustion of a hydrocarbon produces water, carbon dioxide, carbon monoxide, and solid carbon in varying amounts. 2 C 3 H 8(g) + 7 O 2(g) → 2 CO 2(g) + 8 H 2 O (g) + 2 CO (g) + 2 C (s)