heat capacity question

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Katherine Wu 1H
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heat capacity question

Postby Katherine Wu 1H » Mon Feb 10, 2020 12:54 am

The enthalpy of combustion of benzoic acid, C6H5COOH, which is often used to calibrate calorimeters, is -3227 kJ/mol. When 1.453 g of benzoic acid was burned in a calorimeter, the temperature increased by 2.265 celsius. What is the heat capacity of the calorimeter?

The answer says to use q=CΔT to solve the problem.
I'm confused as to why q=CΔT is preferred in this case over q=nCΔT.
I'm also confused as to why the answer would multiply the moles of benzoic acid (after converting it from grams) with the enthalpy of the benzoic acid and using that as the q instead of just 3227.

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Re: heat capacity question

Postby nicolely2F » Mon Feb 10, 2020 1:10 am

C equals n.C(molar), so when the exercise solution says it prefers q=CΔT I think it's just skipping the step where you plug in C = n.C(molar)

You'd use -3227 kJ if you had only one mole of benzoic acid. However, you have 1.453 g (which does not equate to 1 mole of benzoic acid). Thus, to get the enthalpy of 1.453g, you convert it to moles and multiply the result by the molar enthalpy.

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