Anthony T. answered • 10/06/20
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A heat capacity for the calorimeter of 5.86 kJ/ºC means that it takes 5.86 kJ of heat to raise the temperature of the calorimeter one degree Celsius. So, if the temperature of the calorimeter goes from 23.5º to 39.8º, the heat required to do that is 5.86 kJ x (39.8 - 23.5)º = 95.5 kJ. The energy to do this came from the combustion of cyclohexane. The number of moles of cyclohexane is 4.25 g / 84g/mole = 0.119 moles. As we want heat of combustion per mole, we divide 95.5 kJ by 0.119 moles = 803 kJ/mole.
J.R. S.
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If you took the time to go over the answer provided by Anthony T. you have seen that 0.119 moles is incorrect, since 4.25 g/84 g/mol equals 0.05 moles, not 0.119 moles. If you then take 95.5 kJ/0.05 moles you get the correct answer. Can you do that? Oh, and by the way, the correct answer will have a negative sign as it is exothermic.
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10/07/20
Anthony T.
I checked my physical chemistry textbook and couldn't find any other way to do this problem. What is even more perplexing is that the values for the heat of combustion of cyclohexane online are a little more than 3900 kJ/mol which is way off from the choices you have. The closest answer you have to the -1910 kJ/mol is -1890 kJ/mol.
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10/07/20
Abigail E.
Hello! Than you for your speedy response. The only answer choices I have are: a: -1890 kJ/mol b: 1890 kJ/mol c: -95.5 kJ/mol d: 95.5 kJ/mol There is no 803 kJ/mole answer choice. I'm not sure what to do?10/07/20