2.00 g of Benzoic Acid are burned in a bomb calorimeter. The temperature increas

Question

2.00 g of Benzoic Acid are burned in a bomb calorimeter. The temperature increases from 17.84 degree C to 23.34 degree C.

a) What is the heat capacity of the calorimeter?

b) You burn 4.08 g of Arginine in the bomb calorimeter. The temperature increases from 17.49 degree C to 23.83 degree C. Determine the enthalpy of combustion and the enthalpy of formation of Arginine.

c) Arginine has a standard molar entropy of 250.6 J/mol K. Determine the entropy of reaction for the combustion of 4.08 g Arginine.

d) Calculate the entropy change of the surroundings and the universe for the combustion of 4.08 g Arginine.

e) Calculate the Gibbs energy of reaction for the combustion of 4.08 g Arginine.

f) Predict the enthalpy of combustion for 4.08 g of Arginine at 373 K. Arginine has a heat capacity of 232.8 J/mol K which you may assume is constant.

Explanation / Answer

a)

The equation for the combustion is,

C7H6O2(s) + 7.5 O2(g) -> 7CO2(g) + 3H2O(l), dH° = 3227 kJ

Since 7.5 moles of O2 gas is needed, and 7 moles of CO2 is produced, some pressure-volume work is done, to the calorimeter:

P V = dn R T, where dn = (7 - 7.5) = - 0.5 mol
dE = dH - dn R T
= - 3227 - (-0.5*8.314298*298)
= - 3226 kJ/mol (a small correction)

The amount of heat produced by 0.1025 g benzoic acid is

q = 2.0/122.13 mol x 3226 (kJ/mol) = 52.83 kJ

Thus, the heat capacity is

C = q / dT = 52.83 / (23.34-17.84) = 9.605 kJ / K.

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