Methylpropane, (CH3)2CHCH3, is an isomer of butane, CH3(CH2)2CH3.

1. (a)(i)Explain why methylpropane and butane are a pair of isomers.[2]
2. (a)(ii)Identify the type of isomerism shown by methylpropane and butane.[1]
3. (b)When a sample of butane is heated to 373K, in the presence of a catalyst, and allowed to reach equilibrium the following reaction occurs. CH3(CH2)2CH3(g) <=> (CH3)2CHCH3(g) ΔH = -8.0 kJ mol-1 State and explain the effect on the composition of this equilibrium mixture when the temperature is increased to 473K.[2]
4. (c)1 mole of butane gas was added to a 1 dm³ closed system, at a constant temperature and pressure. The amount of butane and methylpropane was measured at regular time intervals. [Graph showing amount/mol vs time for two species, one decreasing, one increasing, both reaching equilibrium]
5. (c)(i)Label the graph with a t to show the time taken to reach dynamic equilibrium.[1]
6. (c)(ii)Use the graph to find the concentration of butane and methylpropane in the mixture at equilibrium. concentration of butane = .......................... mol dm⁻³ concentration of methylpropane = .......................... mol dm⁻³[1]
7. (c)(iii)Write an expression for Kc for this reaction.[1]
8. (c)(iv)Calculate a value for Kc and state its units. Kc = .......................... units = ..........................[2]

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