# How is DeltaH_(fusion) used to calculate the mass of solid that 1kJ of energy will melt?

Aug 27, 2017

With no need of a formula. Is $\Delta {\overline{H}}_{\text{fus}}$ positive or negative for melting?

Given the enthalpy of fusion, simple unit conversion gives:

${\overbrace{\text{kJ"/"mol")^(DeltabarH_"tr") xx overbrace("mol"/"g" xx "g")^(m_"solid"//M_"solid") = overbrace("kJ}}}^{q}$

where $\Delta {\overline{H}}_{\text{tr}}$ is the molar enthalpy of phase transition in $\text{kJ/mol}$, $q$ is heat flow in $\text{kJ}$, $m$ is mass in $\text{g}$, and $M$ is molar mass in $\text{g/mol}$.

Thus:

"g" = overbrace(cancel"kJ")^(q) xx overbrace(cancel"mol"/cancel"kJ")^(DeltabarH_"fus"^(-1)) xx overbrace("g"/cancel"mol")^(M_"solid"^(-1))

And yet, this still refers to a real equation that we could have invoked only at constant pressure:

$q = n \Delta {\overline{H}}_{\text{tr}}$

where $n$ is the mols of substance and $\Delta {\overline{H}}_{\text{tr}}$ is its molar enthalpy of phase transition.