Question

At 300 K and constant volume, 7.8 g benzene releases 327 kJ heat on complete combustion. Calculate the enthalpy of combustion at constant pressure for benzene.

Answer 1

Enthalpy of combustion of 7.8 g benzene = - 327kJ 

Heat released by 1 g of benzene = imm = 3270 kJ

\(C_6H_{6(g)} + \frac{15}{2}O_{2(g)}\longrightarrow6CO_{2(g)} + 3H_2O_{(l)}\)

ΔU = - 3270 kJ; Δng = 6 - 7.5 = (- 1.5) 

R = 8.314 × 10^-3 kJ K^-1mol^-1, T = 300 K 

ΔH = AU + ΔngRT 

= - 3270 + (- 1.5 × 8.314 × 10^-3 × 300) 

= -3270 - 3.7413 

ΔH = -3273.741kJ