The specific heats of iodine vapor and solid are 0.031 and 0.055 cal/g respectively. If heat of iodine is 24 cal/g at 200°C, then its value of 250°C is

Solid I₂ is converted in I₁ vapor

$\begin{array}{l}{\mathrm{I}}_2\left(s\right)={\mathrm{I}}_2\left(\mathrm{g}\right)\mathrm{\Delta }H=24\mathrm{cal}/\mathrm{g}\text{ at }{200}^{\circ }\mathrm{C}\\ \mathrm{\Delta }{C}_p=\left(CP{)}_2\right(\mathrm{g})=\left(C_p\right){\mathrm{I}}_2(\mathrm{s})=0.031-0.055=-0.24\text{ cal }{\mathrm{g}}^{-1}\end{array}$

From Kirchhoff's equation

$\begin{array}{l}\mathrm{\Delta }{H}_{{250}^{\circ }\mathrm{C}}-\mathrm{\Delta }{H}_{{200}^{\circ }\mathrm{C}}=\mathrm{\Delta }{C}_p\left(T_{{250}^{\circ }\mathrm{C}}-T_{{200}^{\circ }\mathrm{C}}\right)\\ \mathrm{\Delta }{H}_{{250}^{\circ }\mathrm{C}}=24-0.024(523-473)\\ =24-1.2=22.8{\mathrm{calg}}^{-1}\end{array}$