Chemical reactions are invariable associated with the transfer of enery either in the form of heat or light. In the laboratory, heat energy I physical and chemical processes are measured with an instrument called caloriemter. Heat change in the process is calcualted as:
`q-msDeltaT," "s=`specific heat
`=cDeltaT," "c=` Heat capacity.
Heat of reaction at constant pressure is measured using bomb calorimeter.
`q_(V)=DeltaU=` Internal energy change
heat of reaction at constant pressure is measrued using simple or water calorimeter.
`q_(P)=DeltaH`
`q_(P)=q_(V)+PDeltaV`
`DeltaH=DeltaU+DeltanRT`
The amount of energy released during a chemical change depends on the physical state of reactants and products, te conditions of pressure, temperatrue and volume at which the reaction is carried out. the variation of heat of reaction with temperature and pressure is given by kirchhoff's equation:
`(DeltaH_(2)-DeltaH_(1))/(T_(2)-T_(1))=DeltaC_(P)," "(DeltaU_(2)-DeltaU_(1))/(T_(2)-T_(1))=DeltaC_(V)`.
Q. The specific heats of `I_(2)` in vapour and solid states are 0.031 and 0.055 cal/g respectively. The heat of sublimation of iodine at `200^(@)C` is 6.096 kcal `mol^(-1)`. the heat of sublimation of iodine at `250^(@)C` will be:

Options

A. 3.8 kcal `mol^(-1)`
B. 4.8 kcal `mol^(-1)`
C. `2.28` kcal `mol^(-1)`
D. 5.8 kcal `mol^(-1)`

Answer

D

Explanation

`I_(1)(s)hArrI_(2)(g)`
`DeltaC_(P)=(0.031-0.055)xx10^(-3)xx254`
`(DeltaH_(2)-DeltaH_(1))/(T_(2)-T_1)=DeltaC_(P)`
`(DeltaH_(2)-6.096)/(50)=(0.031-0.055)xx10^(-3)xx254`
`DeltaH_(2)=5.79` kcal `mol^(-1)`.