Chemistry 5070 · O Level · Alkanes

Alkanes — practice question

Aluminium carbide, $\text{Al}_4\text{C}_3$, reacts with water to produce methane, $\text{CH}_4$, and aluminium hydroxide.
(a)[2]

Construct the symbol equation that represents this reaction.

(b(i))[1]

Methane is a saturated hydrocarbon. Explain why methane is a hydrocarbon.

(b(ii))[1]

Explain why methane is saturated.

(b(iii))[2]

Methane reacts with chlorine in the presence of ultraviolet light. State the formulae of two products formed in this reaction.

(b(iv))[1]

Draw a dot-and-cross diagram to show the electronic structure of a methane molecule. Include only the outer-shell electrons.

(c(i))[2]

The equation for the complete combustion of methane is given as $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$. This reaction is exothermic. Explain, using ideas about bond breaking and bond making, why this reaction is exothermic.

(c(ii))[3]

Complete the reaction pathway diagram in Fig. 2.1 for the complete combustion of methane. Add labels for the reactants, products, enthalpy change of the reaction $\Delta H$, and activation energy $E_a$.

Worked solution & mark scheme

This 12-mark question has a full step-by-step worked solution and mark scheme. One marking point: The balanced equation is $\text{Al}_4\text{C}_3 + 12\text{H}_2\text{O} \rightarrow 4\text{Al(OH)}_3 + 3\text{CH}_4$.

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