Question

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

Answer 1

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* DeltaHfus`

You need to look up the `Delta Hfus` 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 g/"mol"`).

`q = m * DeltaHfus`
`q = ((1.25 " kg")((1000 " g")/(1 " kg"))) * (((6.01 " kJ")/(1 " mol"))((1 " mol")/(18.02 " g")))`

Now, type this in your calculator, and you will get your answer in kJ.

`418.9 " kJ"`

With significant figures, you will get:

`419 " kJ"`.

I hope that helps!