5.1 T HE C OMBUSTION OF H YDROCARBONS pp

C OMBUSTION R EACTIONS The reaction of a substance with oxygen, producing oxides and energy i.e. fuel + oxygen  oxides + energy Complete Combustion A hydrocarbon (fuel made of some combination of hydrogen and carbon) will react with oxygen to produce carbon dioxide and water e.g. C 7 H 16 (l) + 11O 2 (g) → 7CO 2 (g) + 8H 2 O(g) + energy Depending on the fuel, other oxides (e.g. NO, NO 2, SO 2, etc.) may be produced. e.g. 4CH 3 NH O 2  4CO H 2 O + 4NO 2

I NCOMPLETE C OMBUSTION Incomplete combustion occurs when there is insufficient oxygen. When this occurs, CO (g) and/or C (s) are produced in addition to the usual H 2 O and CO 2. e.g. combustion of heptane (hydrocarbon in gasoline): C 7 H 16 (l) + 7O 2 (g) → 3C(s) + 2CO(g) + 2CO 2 (g) + 8H 2 O(g) + energy 2C 7 H 16 (l) + 11O 2 (g) → 14CO(g) + 8 H 2 O(g) + energy Because there are several possible products, incomplete combustion cannot be represented by a single chemical equation

P RACTICE Predict the products. Then, write and balance the following (complete) combustion reaction equations: The combustion of methane (carbon tetrahydride) gas: CH 4 + O 2  The combustion of hydrogen gas: H 2 + O 2 

5.3 E LEMENTS AND THEIR O XIDES pp

A CIDS & B ASES 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. CO 2 ) 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

A CIDIC O XIDES Carbon Dioxide (CO 2 ) Reacts with water to form carbonic acid: CO 2 (g) + H 2 O(l)  H 2 CO 3 (aq) Carbonic acid spontaneously decomposes: H 2 CO 3 (aq)  H + (aq) + HCO 3 (aq) There is the hydrogen ion that makes this solution acidic

A CIDIC O XIDES Nitrogen Oxides (NO x ) Nitrogen can be made to react with oxygen in a car’s engine: N 2 (g) + O 2 (g)  2NO(g) NO(g) further reacts with oxygen in the atmosphere: 2NO(g) + O 2 (g)  2NO 2 (g) NO 2 (g) can then reacts with water to form two acids: 2NO 2 (g) + H 2 O(l)  HNO 3 (aq) + HNO 2 (aq) The hydrogen ions will spontaneously dissociate like they did above

A CIDIC O XIDES Sulphur Oxides (SOx) Most sulphur reacts with oxygen by burning fossil fuels: S(s) + O 2 (g)  SO 2 (g) SO2(g) will then react with oxygen in the atmosphere: 2SO 2 (g) + O 2 (g)  2SO 3 (g) SO3(g) can then react with water to form an acid: SO 3 (g) + H 2 O(l)  H 2 SO 4 (aq) The hydrogen ions will again spontaneously dissociate

B ASIC O XIDES Metal oxides are definite in composition and so are easier to predict how they will form a basic solution e.g. Sodium Oxide 4Na(s) + O 2 (g)  2Na 2 O(s) + energy Na 2 O can then react with water to form a basic solution: Na 2 O(s) + H 2 O(l)  2NaOH(aq) + energy Na + and OH - can then dissociate resulting in a basic solution. In general: Metallic oxide + water  metallic hydroxide + thermal energy

B ASIC O XIDES Try Calcium Oxide: CaO(s) + H 2 O(l)  Ca(OH) 2 (aq) + energy Try Aluminum Oxide: Al 2 O 3 (s) + 3H 2 O(l)  2Al(OH) 3 (aq) + energy

H OMEWORK Read pp. 192 – 197 and pp. 200 – 204 Answer the following questions: p. 197 # 1 – 3 p. 204 # 3, 4, 9