Chemical reactions are invariably assocated with the transfer of energy either in the form of heat or light. In the laboratory, heat changes in physical and chemical processes are measured with an instrument called calorimeter. Heat change in the process is calculated as: q= ms DeltaT, s= specific heat = c Delta T, c= heat capacity Heat of reaction at constant volume is measured using bomb calorimeter. qv= Delta U= internal energy change. Heat of reaction at constant pressure is measured using simple or water calorimeter. q_(p) = Delta H, q_(p) = q_(v) + P Delta V, DeltaH = DeltaU + Delta nRT The amount of energy released during a chemical change depnds on the physical state of reactants and products, the condition of pressure,temperature and volume at which the reaction is carried out. The variation of heat of reaction with temperature and pressure is givenby Kirchhoff's equation: (DeltaH_(2)- DeltaH_(1))/(TT_(2)-T_(1)) = DeltaC_(P) (At constant pressure), (DeltaU_(2)- DeltaU_(1))/(TT_(2)-T_(1)) = DeltaC_(V) (At constant volume) DeltaC_(P) for a reaction is given by 0.2T cal/deg. Its enthalpy of reaction at 10K is -14.2 kcal. Its enthalpy of reaction at 100K in kcal will be