Define and explain enthalpy of phase transformation.

Explanation

Enthalpy of phase transformation : The heat change involved in the change of phase (or) physical state of one mole of compound at atmosphere pressure.
(a) Standard molar enthalpy of fusion `(triangle_("fus")H^(0))` : The enthalpy change that accompanies melting of one mole of a soild substance in standard state is called Standard molar enthalpy of fusion.
`Eg : H_(2)O_(s) to H_(2)O(l) " "trianglef_("fus")H^0="6.00 KJ mol"(-1)`
(b) Standard molar enthalpy of vapourisation `(triangle_("vap")H^(0))` Amount of heat required to vapourise 1 mole of a liquid at constant temperature and under standard pressure (1 bar) is called its standard molar enthalpy of vapourisation `(triangle_("vap")H^(0))`
`Eg : H_(2)O_(l) to H_(2)O(g) " "trianglef_("vap")H^0= "40.79 KJ mol"(-1)`
c) Standard enthalpy of sublimation `triangle_("sub")H^0` : It is the change in the enthalpy when are mole of a solid substance sublimes at a constant temperature under standard pressure.
`Eg, underset("Dry ice")(CO_(2(s)) overset(195K)to underset("vapour")(CO_(2)) triangle_("sub") (H^0)="25.2KJ mol"^(-1)`