5.1 THE COMBUSTION OF HYDROCARBONSpp. 192 - 197

COMBUSTION REACTIONSThe reaction of a substance with oxygen,

producing oxides and energy i.e. fuel + oxygen oxides + energy

Complete CombustionA hydrocarbon (fuel made of some

combination of hydrogen and carbon) will react with oxygen to produce carbon dioxide and water e.g. C7H16(l) + 11O2(g) → 7CO2(g) + 8H2O(g) +

energyDepending on the fuel, other oxides (e.g.

NO, NO2, SO2, etc.) may be produced. e.g. 4CH3NH2 + 13O2 4CO2 + 10H2O +

4NO2

INCOMPLETE COMBUSTION Incomplete combustion occurs when there is

insufficient oxygen. When this occurs, CO(g) and/or C(s) are

produced in addition to the usual H2O and CO2.

e.g. combustion of heptane (hydrocarbon in gasoline): C7H16(l) + 7O2(g) → 3C(s) + 2CO(g) + 2CO2(g) +

8H2O(g) + energy 2C7H16(l) + 11O2(g) → 14CO(g) + 8 H2O(g) + energy

Because there are several possible products, incomplete combustion cannot be represented by a single chemical equation

PRACTICE

Predict the products. Then, write and balance the following (complete) combustion reaction equations:

The combustion of methane (carbon tetrahydride) gas: CH4 + O2

The combustion of hydrogen gas: H2 + O2

5.3 ELEMENTS AND THEIR OXIDESpp. 200 - 204

ACIDS & BASES An acid is a compound that produces

Hydrogen ions (H+) when mixed with water Conversely , a base is a compound that

produces hydroxide ions (OH-) when mixed with water In the acids/bases we named in Unit 1 the

Hydrogen or hydroxide was present in the chemical formula

A substance can be an acid without containing any hydrogen or a base without containing any hydroxide.

Non-metal oxides (e.g. CO2) tend to produce acidic solutions when dissolved in water Called acidic oxides

Metal oxides (e.g. MgO) tend to produce basic solutions when dissolved in water Called basic oxides

ACIDIC OXIDES

Carbon Dioxide (CO2)Reacts with water to form carbonic acid:

CO2(g) + H2O(l) H2CO3(aq)Carbonic acid spontaneously decomposes:

H2CO3(aq) H+(aq) + HCO3(aq)There is the hydrogen ion that makes this solution acidic

ACIDIC OXIDES

Nitrogen Oxides (NOx)Nitrogen can be made to react with oxygen

in a car’s engine:N2(g) + O2(g) 2NO(g)

NO(g) further reacts with oxygen in the atmosphere:2NO(g) + O2(g) 2NO2(g)

NO2(g) can then reacts with water to form two acids:2NO2(g) + H2O(l) HNO3(aq) + HNO2(aq)

The hydrogen ions will spontaneously dissociate like they did above

ACIDIC OXIDES

Sulphur Oxides (SOx)Most sulphur reacts with oxygen by

burning fossil fuels: S(s) + O2(g) SO2(g)

SO2(g) will then react with oxygen in the atmosphere:2SO2(g) + O2(g) 2SO3(g)

SO3(g) can then react with water to form an acid:SO3(g) + H2O(l) H2SO4(aq)

The hydrogen ions will again spontaneously dissociate

BASIC OXIDES

Metal oxides are definite in composition and so are easier to predict how they will form a basic solution

e.g. Sodium Oxide4Na(s) + O2(g) 2Na2O(s) + energyNa2O can then react with water to form a basic

solution:Na2O(s) + H2O(l) 2NaOH(aq) + energy

Na+ and OH- can then dissociate resulting in a basic solution.

In general: Metallic oxide + water metallic hydroxide + thermal

energy

BASIC OXIDES

Try Calcium Oxide:CaO(s) + H2O(l) Ca(OH)2(aq) + energy

Try Aluminum Oxide:Al2O3(s) + 3H2O(l) 2Al(OH)3(aq) + energy

HOMEWORK

Read pp. 192 – 197 and pp. 200 – 204 Answer the following questions:

p. 197 # 1 – 3 p. 204 # 3, 4, 9