In a constant volume calorimeter, 3.5 g of a gas with molecular weight 28 g/mol was burnt in excess of oxygen at 298 K. The temperature of the calorimeter was found to Increase from 298 K to 298.45 K due to the combustion process. Given that the heat capacity of the calorimeter is 2.5 kJ/K. The Numerical value for the enthalpy of combustion of the gas in kJ/mol is
9
Given, Cv = 2.5 kJ/K = 2500 J/K
ΔT = T2 − T1 = 298.45 − 298 = 0.45 K.
ΔH, due to combustion of 3.5 g of gas
= Cv × Δ T = 2500 × 0.45 = 1125 J
1 mole = 28 g (Mol wt of gas = 28 g/mol)
Hence, ΔH due to combustion of 1 mol of gas
= 11253.5 × 28 = 9000 J = 9 kJ/mol