AQA Jan 2013 Paper 5 Q3

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do not write outside the box the feasibility of a physical or a chemical change depends on the balance between the thermodynamic quantities of enthalpy change h entropy change s and temperature t a suggest how these quantities can be used to predict whether a change is feasible marks b explain why the evaporation of water is spontaneous even though this change is endothermic in your answer refer to the change in the arrangement of water molecules and the entropy change marks question continues on the next page turn over wmp jan chem c this table contains some thermodynamic data for hydrogen oxygen and water do not write outside the box s j k mol hf kj mol h g o g h o g h o i c i calculate the temperature above which the reaction between hydrogen and oxygen to form gaseous water is not feasible marks c ii state what would happen to a sample of gaseous water that was heated to a temperature higher than that of your answer to part c i give a reason for your answer what would happen to gaseous water reason marks wmp jan chem do not write outside the box d when hydrogen is used as a fuel more heat energy can be obtained if the gaseous water formed is condensed into liquid water use entropy data from the table in part c to calculate the enthalpy change when one mole of gaseous water is condensed at k assume that the free energy change for this condensation is zero marks turn over for the next question turn over wmp jan chem

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