Edexcel Jun 2014 (IAL) Paper 1 Q23

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23 Alkanes are used as fuels in homes and in industry. It is, therefore, important that the enthalpy changes involving alkanes are known. (a) Define the term standard enthalpy change of formation of a compound. Give the conditions of temperature and pressure that are used when measuring a standard enthalpy change. (3) DefinitionStandard temperature isStandard pressure is(b) Write the equation, with state symbols, that accompanies the enthalpy change of formation of hexane, C6H14(l). (2) *P42976A01724* 17 Turn over<br /> (c) Enthalpy changes can be calculated using enthalpy changes of combustion. Values for some standard enthalpy changes of combustion are shown in the table below. Substance C(s) H2(g) CH4(g) (cid:507)Hc (cid:57) / kJ mol1 394 286 890 Use these data to complete the Hess cycle below for the reaction and then calculate the standard enthalpy change for the reaction, in kJ mol1. C(s) + 2H2(g) (cid:111) CH4(g) (3) Space for working standard enthalpy change for the reaction =kJ mol1 18 *P42976A01824*<br /> (d) The equations for the combination of gaseous carbon atoms and gaseous hydrogen atoms to form methane, CH4, and ethane, C2H6, are shown below. C(g) + 4H(g) (cid:111)(cid:3) CH4(g) (cid:507)H = 1652 kJ mol1 2C(g) + 6H(g) (cid:111)(cid:3) C2H6(g) (cid:507)H = 2825 kJ mol1 Use these data to calculate (i) the mean bond enthalpy of a CH bond in methane, in kJ mol1. (ii) the bond enthalpy of a CC bond, in kJ mol1, clearly showing your working. (1) (2) (Total for Question 23 = 11 marks) *P42976A01924* 19 Turn over<br />

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