Where Ccal= heat capacity of calorimeter delta t = change in temperature Practic

Question

Where Ccal= heat capacity of calorimeter delta t = change in temperature Practice Exercise 6.7: A quantity of 1.435g of naphthalene C10H8, a pungent-smelling used in moth repellants, was burned in a constant-volume bomb calorimeter. Consequently, the temperature of the water rose from 20.28C to 25.95C. If the heat capacity of the bomb plus water was 10.17KJ/ degree C, calculate the heat combustion of naphthalene on a molar basis; that is, find the molar heat of combustion. (molar mass of C10H8= 128.2g)

Explanation / Answer

We know Q = mCp (change in temp)

So Q = 1.435g x 10.17KJ/oC x (25.95oC -20.28oC )

Q = 82.75 kJ

This means 1.435g releases heat of 82.75kJ.

So, 128.2 g releases heat = (82.75 / 1.435) x 128.2 = 7392.52kJ/mol of heat

so molar heat of combustion of naphthalene is  7392.52kJ/mol

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