Question

The heat liberated on complete combustion of 7.8 g of benzene is 327 kJ, at constant volume and 27 °C. The heat of combustion of benzene at constant pressure is (R = 8.3 JK−1 mol−1)

Answer 1

C6H6 + 15/2 O------> 6 CO2 + 3H2O

Heat liberated on complete combustion of 7.8 g or benzene = 327 kJ

∴Heat liberated on complete combustion of 78 g (1mol) of benzene = 327 kJ  

Δn = 6-7 ½ = -1.5  

 R = 8.3 × 10 kJ mole K  

 T = 300 K

ΔH = ΔE + ΔngRT;    

   = -327kJ + (-1.5) (8.314 × 10 ) (300) kJ mole-1                  

-327 -3.7413 = 330.7413 KJ  

So the answer is 330.7413

Answer 2

Explanation:

• the of combantion at constant pressure is △H and the heat of combantion at constant volume is△E