Midterm 2011 question 1

$\Delta U=q+w$

904638389
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Midterm 2011 question 1

In the winter 2011 midterm question one says:

The enthalpy of combustion of benzoic acid, C6H5COOH, which is often used to calibrate calorimeters, is -327 kj x mol-1. When 1.453 g of benzoic acid was burned in a calorimeter, the temperature increased by 2.265 degrees C. What is the heat capacity of the calorimeter?

Why in the calculation, it says q=CcaldeltaT, and then when it has the values put in, why is there the conversion to mols in the numerator and why is it negative?

Ani Galfayan 1H
Posts: 27
Joined: Fri Sep 25, 2015 3:00 am

Re: Midterm 2011 question 1

From what I understand, because q(sys) = -q(surr) we can say that the system is the reaction and the surrounding is the calorimeter. This is where the negative comes from.
The conversion to moles comes into play because we're using the enthalpy to get q. the need for conversion can also be noticed when looking at the units. since we want to be left with kJ C for heat capacity, moles would need to be canceled out and so we convert the grams of benzoic acid to moles and multiply by the given enthalpy.