Explain enthalpy changes during phase transformations.

(N/A) Standard enthalpy of fusion $(\Delta_{fus} H)$: The enthalpy change that accompanies the melting of one mole of a solid substance in its standard state is called the standard enthalpy of fusion. Melting is an endothermic process,so $\Delta_{fus} H$ is always positive.
$H_2O_{(s)} \rightarrow H_2O_{(l)}$; $\Delta_{fus} H = 6.00 \ kJ \ mol^{-1}$
Standard enthalpy of vaporization $(\Delta_{vap} H)$: The amount of heat required to vaporize one mole of a liquid at a constant temperature and under standard pressure $(1 \ bar)$ is called its standard enthalpy of vaporization.
$H_2O_{(l)} \rightarrow H_2O_{(g)}$; $\Delta_{vap} H = +40.79 \ kJ \ mol^{-1}$
Standard enthalpy of sublimation $(\Delta_{sub} H)$: The change in enthalpy when one mole of a solid substance sublimes directly into its vapour at a constant temperature and under standard pressure $(1 \ bar)$.
$CO_{2_{(s)}} \rightarrow CO_{2_{(g)}}$; $\Delta_{sub} H^o = 25.2 \ kJ \ mol^{-1}$
The magnitude of these enthalpy changes depends on the strength of the intermolecular interactions in the substance.

Substance	$T_f / K$	$\Delta_{fus} H / (kJ \ mol^{-1})$	$T_b / K$	$\Delta_{vap} H / (kJ \ mol^{-1})$
$N_2$	$63.15$	$0.72$	$77.35$	$5.59$
$NH_3$	$195.40$	$5.65$	$239.73$	$23.35$
$HCl$	$159.0$	$1.992$	$188.0$	$16.15$
$CO$	$68.0$	$6.836$	$82.0$	$6.04$
$CH_3COCH_3$	$177.8$	$5.72$	$329.4$	$29.1$
$CCl_4$	$250.16$	$2.5$	$349.69$	$30.0$
$H_2O$	$273.15$	$6.01$	$373.15$	$40.79$
$NaCl$	$1081.0$	$28.8$	$1665.0$	$170.0$
$C_6H_6$	$278.65$	$9.83$	$353.25$	$30.8$