AQA Jun 2010 Paper 2 Q8

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section b answer all questions in the spaces provided do not write outside the box glucose produced during photosynthesis in green plants is a renewable source from which ethanol can be made ethanol is a liquid fuel used as a substitute for petrol the processes involved can be summarised as follows process photosynthesis in green plants co h o c h o o process fermentation of glucose to form ethanol process complete combustion of ethanol ch ch oh o co h o a state three essential conditions for the fermentation of aqueous glucose in process write an equation for the reaction that takes place during this fermentation marks extra space wmp jun chem do not write outside the box b it has been claimed that there is no net carbon greenhouse gas emission to the atmosphere when ethanol made by process is used as a fuel state the term that is used to describe fuels of this type use the equations for processes and to show why it can be claimed that there is no net emission of carbon containing greenhouse gases marks extra space question continues on the next page turn over wmp jun chem do not write outside the box c use the information from the equation for process on page and the mean bond enthalpies from the table below to calculate a value for the enthalpy change for this process c h c c c o o h c o o o mean bond enthalpy kj mol give one reason why the value calculated from mean bond enthalpies is different from the value given in a data book marks extra space wmp jun chem do not write outside the box d a student carried out a simple laboratory experiment to measure the enthalpy change for process the student showed that the temperature of g of water increased by c when g of pure ethanol was burned in air and the heat produced was used to warm the water use these results to calculate the value in kj mol obtained by the student for this enthalpy change the specific heat capacity of water is j k g give one reason other than heat loss why the value obtained from the student s results is less exothermic than a data book value marks extra space turn over for the next question turn over wmp jun chem

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