So, what happens when we mix hot stuff and cold stuff and place them in an environment where they can only exchange energy with each other and not with the outside world?  We know energy will flow as heat from the hotter material to the colder material until they reach the same final temperature.  For both substances, there are typically two kinds of processes which each material may undergo.  As energy is transferred from one substance to another, the temperature of the substance may change.  This is known as a specific heat process.  However, if the temperature of the substance remains the same as it takes in or releases energy as heat, but the phase of the substance changes, this is known as a latent heat process.  Keeping track of the energy transfers that occur when ice and water are combined in a thermos will let us determine the final state of the system.