The heatof combustion of benzene in a bomb calorimeter ( i.e., constant volume ) was found to be 3263.9 kJ mol^(-1) at 25^(@)C. Calculate the heatof combusion of benzene at constant pressure.

The heatof combustion of benzene in a bomb calorimeter ( i.e., constan

1.	The heatof combustion of benzene in a bomb calorimeter ( i.e., constant volume ) was found to be 3263.9 kJ mol^(-1) at 25^(@)C. Calculate the heatof combusion of benzene at constant pressure.
Answer» Solution :The reaction is `C_(6)H_(6) (l) +7(1)/(2)O_(2)(G) rarr 76CO_(2)(g) + 3H_(2)O(l)` In this reaction, `O_(2)` is the only gaseous reactant and `CO_(2)` is the only gaseous product. `:. Delta N_(g)= n_(p) - n_(r) = 6-7(1)/(2) = -1(1)/(2)= - (3)/(2)` Also, we are given`Delta U ( or q_(V))= - 3263.9 kJmol^(-1)` `T= 25^(@)C = 298 K` `R = 8.314 J K^(-1)mol^(-1) = (8.314)/(1000) KJ K^(-1) mol^(-1)` `Delta H ( or q_(p))= Delta U + Delta n_(g) RT = - 3263.9- 3.7 kJ mol^(-1) + (-(3)/(2)mol) ((8.314)/(1000) kJ K^(-1) mol^(-1)) ( 298K)` `= - 3263.9 - 3.7 kJ mol^(-1) = - 3267.6 kJ mol^(-1)`