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

1 Answer
Jun 29, 2017


Use the delta H fusion equation.


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!