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 (a) When 0.9862 g of benzoic acid was oxidized, the temperature rose from 21.84 C to 25.67 C What was the heat capacity of the calorimeter? (b) In a separate experiment, 0.4654 g of -D- glucose (C6H1206) was oxidized in the same calorimeter, and the temperature rose from 21.22 0C to 22.28 C Calculate the enthalpy of combustion of glucose and the value of change in internal energy of the rxn for the combustion. (Hint: Be sure to write a balanced equation for each reaction first and assume the Drodu . ct H20 is a liauid)

Explanation / Answer

a.

Molecular weight of Benzoic Acid: 122.12 g/mol

No. of moles in .9862g = .9862/122.12 = .008075 mol

Therefore, heat of combustion = .008075 mol * 3226.7 kJ/mol = 26.05kJ

We know, Heat = mass * sp. heat capacity * change in temperature

therefore, sp. heat capacity = heat / (mass * change in temperature)

Heat Capacity of Calorimeter = 26.05 / (0.9862 * (25.67 - 21.84)) = 6.9 kJ/g.C

now, if we want to convert it into kJ/mol.C, we can do it by multiplying it by molecular weight of benzoic acid, then we get: 6.9*122.12 = 842.23 kJ/mol.C

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