Question

The heat of combustion of benzene in a bomb calorimeter is found to be 3263.9kj/mole at 25 degree celsius. Calculate the heat of combustion of benzene at constant temperature

Answer 1

Let us first write reaction of combustion in benzene.

C6H6 + 7½O2 (g) -----> 6CO2 (g) + 3H2O (l)

In the above reaction O2 and CO2 are the only gases.
g = no. of moles of products – no. of moles of reactants
= 6 - 7½ = - 1 ½ = -3/2

Given valuesU = 3263.9 kJ/mol; T = 298 K;
As we know,
H =U +ng RT R = 8.314

As this is an exothermic reactionH is negative.

H = (- 3263.9 kJ/mol) + (-3/2) (298 K)
= (- 3263.9 kJ/mol) + (-3/2) (2.477)
= (- 3263.9 kJ/mol) – 3.716 kJ/mol
H = - 3267.6 kJ/mol

Answer 2

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