11 Turn over 4 Methanol, CH3OH, is a liquid fuel. An experiment was carried out to determine the enthalpy change of combustion of liquid methanol. thermometer beaker methanol spirit burner water The energy obtained from burning 2.08 g of methanol was used to heat 75.0 g of water. The temperature of the water rose from 25.0 °C to 91.0 °C. [Specific heat capacity of water = 4.18 J g−1 °C−1] (a) Use the data to calculate a value for the enthalpy change of combustion of one mole of methanol. Give your answer to an appropriate number of significant figures and include a sign and units. (4) 12 (b) Methanol can be synthesised from methane and steam by a process that occurs in two steps. Step 1 CH4(g) + H2O(g)  3H2(g) + CO(g) ΔH = +206 kJ mol−1 Step 2 CO(g) + 2H2(g)  CH3OH(g) ΔH = −91 kJ mol−1 (i) Explain the effects of increasing the pressure on the yield of the products and on the rate of the reaction in Step 1. (4) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (ii) Step 2 is carried out at a compromise temperature of 500 K. Explain why 500 K is considered to be a compromise for Step 2 by considering what would happen at higher and lower temperatures. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 13 Turn over (c) Calculate a value for the standard enthalpy change of combustion of gaseous methanol using the enthalpy change for Step 2 and the standard enthalpy change of combustion of gaseous carbon monoxide and of hydrogen. Substance Standard enthalpy change of combustion / kJ mol−1 CO −283 H2 −286 (3) (Total for Question 4 = 14 marks)