• # question_answer The enthalpy of combustion of ${{C}_{6}}{{H}_{6}}$is 3250 kJ when 0.39 g of ${{C}_{6}}{{H}_{6}}$is burnt in excess of oxygen in an open vessel, the amount of heat evolved is A)  8.32 kJ                       B)  12.34 kJC)  16.25 kJ                     D)  24.74 kJ

Combustion of benzene can be represented as follows: $\underset{78}{\mathop{{{C}_{6}}{{H}_{6}}}}\,+{{O}_{2}}\to 6C{{O}_{2}}+{{H}_{2}}O+3250\,kJ$ 70 g of${{C}_{6}}{{H}_{5}}$produce 3250 kJ heat. 1 g of will produce $\frac{3250}{78}\,kJ$heat. 39 g will produce $=\frac{3250}{78}\times 0.39\,kJ$ = 16.256 kJ heat is liberated. Note: Enthalpy of combustion is the amount of heat liberated when one mole of a substance is burnt in excess of air. Hence, the correct option is [c].