# How much heat is needed to melt 1.25 kg of water at its melting point?

Jun 29, 2017

Use the delta H fusion equation.

#### Explanation:

For this particular problem, we are not dealing with a temperature change, rather, we are dealing with a scenario in which we are melting ice. Hence, we need to use the delta H fusion equation:

$q = m \cdot \Delta H f u s$

You need to look up the $\Delta H f u s$ value in your textbook. This is also known as the molar heat of fusion. The value I obtained is $6.01$ kJ/mol, but your value may be different based on your textbook.

With this in mind, plug in the values, remembering that $m$ is mass (in g) so you need to convert 1.25 kg to g, and kJ/mol must be converted to kJ/g using the molar mass of water ($18.02 \frac{g}{\text{mol}}$).

$q = m \cdot \Delta H f u s$
q = ((1.25 " kg")((1000 " g")/(1 " kg"))) * (((6.01 " kJ")/(1 " mol"))((1 " mol")/(18.02 " g")))

$418.9 \text{ kJ}$
$419 \text{ kJ}$.