AQA Jun 2017 Paper 2 Q4

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When alkanes are burned in an excess of oxygen they produce carbon dioxide and water.. 1 Write an equation for the complete combustion of propane in oxygen. [1 mark] 0 4 0 4 0 4 . 2 An expression can be derived using bond enthalpy data to estimate the enthalpy of combustion (cH) of an alkane. For an alkane with n carbon atoms: cH =(496n + 202) kJ mol1 The enthalpy of combustion of an alkane was calculated to be 6650 kJ mol1 using this expression. 0 4 . 3 Deduce the molecular formula of this alkane. Show your working. [2 marks] Molecular formula of alkane Suggest one reason, other than the use of mean bond enthalpies, why a value for the enthalpy of combustion of a liquid alkane is different from the value obtained using the expression in Question 4.2 [1 mark] *06* IB/M/Jun17/7404/2<br /> 0 4 . 4 Values of the enthalpy change for combustion of 1 g of some alkanes are shown in Table 2. Table 2 Enthalpy change in kJ for combustion of 1 g methane ethane propane butane pentane 55.6 52.0 49.6 48.7 Plot the enthalpy change for the combustion of 1 g against the number of carbon atoms in the alkanes in Table 2. Draw a best fit line and use this to estimate the enthalpy change for combustion of 1 g of propane. Write your answer in Table 2. [3 marks] *07* Turn overIB/M/Jun17/7404/2<br /> Isooctane (2,2,4-trimethylpentane) is an important component of petrol used in cars. When isooctane is burned, the enthalpy change is 47.8 kJ g1 Isooctane is a liquid at room temperature with a density of 0.692 g cm3 Calculate the heat energy released, in kJ, when 1.00 dm3 of isooctane burns in excess oxygen. Give your answer to the appropriate number of significant figures. [2 marks] 0 4 . 5 Heat energy released kJ *08* IB/M/Jun17/7404/2<br />

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