How much heat energy, in kilojoules, is required to convert 76.0 g of ice at −18.0 ∘c to water at 25.0 ∘c ?

We should split the problem into three parts.

1) Amount of heat necessary to bring the ice from  to . This is given by:

where  is the mass,  is the variation of temperature, and  is the specific heat of ice. Calculating, we get


2) When the ice is at , the heat added at this point does not change the temperature of the ice, because it is used to fuse it into water. The amount of heat needed to cause the complete fusion of ice is

where  is the latent heat of fusion of ice. So,


3) Now the ice is transformed into water. We have to bring it to , so the variation of temperature is . The amount of heat needed to bring the water at this temperature is

where  is the specific heat of water. Therefore,


4) So, the total heat needed for the entire process is: