OCR A Jan 2010 Paper 2 Q3

Answers available below

3 Glucose, C6H12O6, can be completely combusted to give carbon dioxide and water. C6H12O6(s) + 6O2(g) 6CO2(g) + 6H2O(l) (a) In the body, the conversion of glucose into carbon dioxide and water takes place in a number of stages catalysed by enzymes. What name is given to this oxidation process in the body?[1] (b) A student carries out an experiment to determine the enthalpy change of combustion of glucose. In the experiment, 0.831 g of glucose is burned. The energy released is used to heat 100 cm3 of water from 23.7 C to 41.0 C. (i) Calculate the energy released, in kJ, during combustion of 0.831 g glucose. The specific heat capacity of water = 4.18 J g1 K1. Density of water = 1.00 g cm3. (ii) Calculate the amount, in moles, of glucose that is burned. energy =kJ [2] (iii) Calculate the enthalpy change of combustion of glucose. Give your answer to three significant figures. amount =mol [2]OCR 2010 Hc =kJ mol1 [2]<br /> 1 (c) The standard enthalpy change of combustion of glucose can also be determined indirectly. Calculate the standard enthalpy change of combustion of glucose using the standard enthalpy changes of formation below. substance C6H12O6(s) CO2(g) H2O(l) Hf O / kJ mol1 1250 394 286 C6H12O6(s) + 6O2(g) 6CO2(g) + 6H2O(l) answer =kJ mol1 [3] (d) Suggest two reasons why standard enthalpy changes of combustion determined experimentally are less exothermic than the calculated theoretical values.[2] [Total: 12]OCR 2010 Turn over<br />

Show answer