The enthalpy of combustion of benzoic acid (C6H5COOH) is commonly used as the st

Question

The enthalpy of combustion of benzoic acid (C6H5COOH) is commonly used as the standard for calibrating constant-volume bomb calorimeters; its value has been accurately determined to be -3226.7 kJ/mol. When 3.1871 g of benzoic acid are burned in a calorimeter, the temperature rises from 20.84 degree C to 25.67 degree C. What is the heat capacity of the bomb? (Assume that the quantity of water surrounding the bomb is exactly 2250 g.) A piece of silver with a mass 419 g has a heat capacity of 99.3 J/degree C. What is the specific heat of silver?

Explanation / Answer

4)
moles of benzoic acid burnt = mass/molar mass
= 3.1871 / 122.12
= 0.0261 mol

heat released, Q = number of mol * H
= 0.0261 * (-3226.7)
= -84.21 KJ

this heat is absorbed by calorimeter and water
Q = C*delta T + mw*cw*delta T
84210 J = C*(25.67 - 20.84) + 2250*4.184*(25.67 - 20.84)
84210 = 4.83*C + 45469.61
C = 8020.8 J/oC
= 8.021 KJ/oC
Answer: 8.021 KJ/oC

5)
specific heat capacity = heat capacity / mass
= 99.3 /419
= 0.237 J/g.oC

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