Standard Enthalpy of Formation, \(\Delta H_{\rm f}^\circ \) The difference between `Delta`H and `Delta`U at constant volume is equal to Calculate the enthalpy change for the process CCl4(g) gives C(g) plus 4 Cl(g) and calculate bond enthalpy of C Cl in CCl4(g). Standard enthalpy of vapourisation `Delta_("vap")H^( )` for water at `100^@C` is `40.66 kJ mol^( 1)`. The internal energy of vapourisation of water at `100^@C` (in kJ `mol^( 1)`) is (Assume water vapour to behave like Finding Delta H using ln P vs 1 T (Hvap Lab)