What is the formula for DeltaH_"fus"?

Aug 12, 2016

Enthalpy of fusion (or really, enthalpy of phase transitions) is a constant-pressure heat flow. So you can work it out just from knowing that and the units.

The molar enthalpy of (common) phase transitions (that is, in $\text{kJ/mol}$) would be:

\mathbf(DeltabarH_"trs" = q_p/(n_"substance"))

where:

• $q$ is the heat flow through the system at constant pressure and the same temperature.
• ${n}_{\text{substance}}$ is the $\setminus m a t h b f \left(\text{mol}\right)$s of the substance at hand that is transitioning to a new phase.

If you were looking at water freezing/melting, then $\Delta {\overline{H}}_{\text{fus" ~~ "6.02 kJ/mol}}$. That means if you had $\text{1 mol}$ of water, then you would have

$\textcolor{b l u e}{{q}_{p}} = {n}_{\text{substance" xx DeltabarH_"fus}}$

$= \left(\text{1 mol")("6.02 kJ/mol}\right)$

$=$ $\textcolor{b l u e}{\text{6.02 kJ}}$ of heat absorbed to melt it, or released when freezing it.