The standard heat of formation listed for gaseous  $N{H}_3$  is – 11.02 kcal/mol at 298 k. Given that at 298 k, the constant pressure heat capacities of gaseous  $N_2\text{ , }{H}_2$  and $N{H}_3$  are respectively 6.96, 6.89, 8.38 cal/mol. $\Delta H_{773K}$  for the reactions,  $\frac{1}{2}{N}_2\left(g\right)+\frac{3}{2}{H}_2\left(g\right)\to N{H}_3\left(g\right)$