At 300 K, delta_f H° of C6H5COOH(s), (g) and (l) are -408, -393 and -286 kJ/mol respectively. The enthalpy of combustion of benzoic acid at 300 K is

Question

At 300 K, delta_f H° of C6H5COOH(s), $CO_2$(g) and $H_2O$(l) are -408, -393 and -286 kJ/mol respectively. The enthalpy of combustion of benzoic acid at 300 K is

Prashant Kotian · Accepted Answer

Correct answer: A,D. Combustion: C6H5COOH(s) + 15/2 (g) -> 7(g) + 3(l). δ H = [7*(-393) + 3*(-286)] - (-408) = -2751 - 858 + 408 = -3201 kJ/mol (A correct). δ n_g = 7 - 7.5 = -0.5. δ E = δ H - δ n_g * RT = -3201 - (-0.5)*8.314e-3*300 = -3201 + 1.247 = -3199.75 ≈ -3199.76 kJ/mol (D correct).

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