Change in enthalpy of substance x is 300 j gm at its boiling point 300k then molar entropy change for Brainly.in Untitled Document THE ENTHALPY OF A SYSTEM Enthalpy (H) is the total heat content of a system, defined as its internal energy (E) plus the product of its pressure (P) and volume (V) (H = The difference between `Delta`H and `Delta`U at constant volume is equal to Calculated and Experimental Enthalpies vap H and vap H exp of Download Table What is `Delta U` when `2.0` mole of liquid water vaporises at `100^(@)C`? The heat of vaporisation `(Delta H_("vap".))` of water at `100^(@)C` is `40.66 KJmol^( 1)`.