16.If temperature is kept constant during the reaction, the process is said to be�.

17.The heat of formation is the change in enthalpy accompanying the formation of a substance from its elements at 298 K and 1 atmospheric pressure. Since the enthalpies of elements are taken to be zero, the heat of formation of the compound may be

18.Heat of fusion of a molecular solid is

19.Evaporation of water is a spontaneous process although it is

20.On heating a liquid at its boiling point