Chemistry 9701 · AS & A Level · Hydrocarbons

Hydrocarbons — practice question

Butane, $(\text{CH}_3)(\text{CH}_2)_2\text{CH}_3$, has an isomer called methylpropane, $(\text{CH}_3)_2\text{CHCH}_3$.
(a(i))[2]

Explain why methylpropane and butane form a pair of isomers.

(a(ii))[1]

Identify the kind of isomerism shown by methylpropane and butane.

(b)[2]

A sample of butane is heated to $373\,\text{K}$ in the presence of a catalyst and is then left until equilibrium is reached, producing the reaction shown below. $\text{CH}_3(\text{CH}_2)_2\text{CH}_3(\text{g}) \rightleftharpoons (\text{CH}_3)_2\text{CHCH}_3(\text{g}) \quad \Delta H = -8.0\,\text{kJ mol}^{-1}$ State and explain what happens to the composition of this equilibrium mixture when the temperature is increased to $473\,\text{K}$.

(c(i))[1]

Put a $t$ on the graph to indicate the time needed to reach dynamic equilibrium.

(c(ii))[1]

Use the graph to determine the concentration of butane and methylpropane in the mixture at equilibrium. concentration of butane = ....................... $\text{mol dm}^{-3}$ concentration of methylpropane = ....................... $\text{mol dm}^{-3}$

(c(iii))[1]

Write an expression for $K_c$ for this reaction.

(c(iv))[2]

Calculate a value for $K_c$ and state its units.

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: Same molecular formula $C_4H_{10}$ OR same number of carbon and hydrogen atoms

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