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 enthalpy of fusion of ice is 6.02 kJ mol^(-1). The heat capacity of water is 4.18Jg^(-1).^(@)C^(-1). What is the smallest number of ice cubes at 0^(@)C, each containing one mole of water, that are needed to cool 500 g of liquid water from 20^(C) to 0^(@)C?