# What amount of heat is required to melt "300 g" of ice at its freezing point if the enthalpy of fusion is "6.02 kJ/mol"?

Sep 27, 2016

For a phase transition, we assume a constant temperature (and also, pressure). So, the heat flow $q$ into a substance is equal to the enthalpy change $\Delta H$.

$\boldsymbol{{q}_{P}}$

$= \boldsymbol{m \Delta H}$, if $\Delta H$ is in $\text{J/g}$, or
$= n \Delta H = \boldsymbol{\frac{m}{{M}_{m}} \Delta H}$, if $\Delta H$ is in $\text{J/mol}$,

where:

• $m$ is the mass of the ice in $\text{g}$.
• $n$ is the $\boldsymbol{\text{mol}}$s of the ice.
• ${M}_{m}$ is the molar mass of the ice in $\text{g/mol}$.
• $\Delta H$ is the enthalpy of fusion, which is about $\text{6.02 kJ/mol}$ for ice at ${0}^{\circ} \text{C}$ and $\text{1 atm}$.

So, simply solve for the heat flow required to melt $\text{300 g}$ of ice:

$\textcolor{b l u e}{{q}_{P}} = \left(300 \cancel{\text{g" xx cancel"1 mol"/(18.015 cancel"g"))("6.02 kJ"/cancel"mol}}\right)$

$=$ $\textcolor{b l u e}{\text{100. kJ}}$