Edexcel Jun 2010 Paper 1 Q17

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PMT 17 This question is about methanol and the energy changes that accompany some of its reactions. (a) Complete the diagram (using dots and crosses) to show the bonding in methanol, CH3OH. You should show outer electrons only. H C O H (b) The Hess cycle below can be used to calculate the standard enthalpy change of combustion of methanol, using standard enthalpy changes of formation. CH3OH(l) + 1O2(g) Hc CO2(g) + 2H2O(l) H1 H2 (i) Complete the cycle by filling in the empty box. *(ii) Define the term standard enthalpy change of formation of a compound, making clear the meaning of standard in this context. (2) (2) (3)16 *N35691A01628*<br /> PMT (iii) Use your cycle and the data below to calculate the standard enthalpy change of combustion of methanol, Hc . CO2(g) H2O(l) CH3OH(l) Hf /kJ mol1 393.5 285.8 239.1 (2) *N35691A01728* 17 Turn over<br /> PMT (c) An experiment was carried out, using the apparatus below, to estimate the standard enthalpy change of combustion of methanol. thermometer stirrer 200 g of water screen to reduce draughts spirit burner methanol After burning the methanol for a few minutes, the temperature of water in the beaker had risen by 20.7 C and the mass of methanol burnt was 0.848 g. 18 (i) Calculate the amount of energy transferred to the water. Energy transferred (J) = mass of water4.18temperature change (ii) Calculate the number of moles of methanol, CH3OH, burnt during the experiment. (1) (1) *N35691A01828*<br /> PMT (iii) Use your answers to (c)(i) and (ii) to calculate the experimental value for the standard enthalpy change of combustion. Include a sign and units in your answer, which should be given to three significant figures. (iv) Compare your answers to (b)(iii) and (c)(iii) and give TWO reasons to explain any differences. (1) (2)(Total for Question 17 = 14 marks) *N35691A01928* 19 Turn over<br />

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