Let's suppose we have to consider the case of searching for thermal equilibrium between bodies in different physical states.  This would be the case, for example, of a block of ice in a container of hot water.  

In phenomena like this we have to consider that the heat lost or gained does not have to be used only in varying the temperature, but that there may be a total or partial change of state of one of the bodies involved. 

The law of the conservation of energy will still be valid, but in the use of the energy gained or lost by each body we must count that used in the change of state. 

In the visual we are going to study we will use ice and water in variable quantities and with variable temperatures.  After carrying out the activities suggested we should be able to predict the equilibrium temperature and the volume of water and ice left when equilibrium is reached.  We should note that the time taken to reach equilibrium depends on many external factors, so that the time taken to reach equilibrium in the visual is not necessarily the time taken in real life.