To understand specific heat and latent heat and how they are related to temperature versus time graphs.

energy can be added to a system either by doing work w on it or by adding heat q to it. energy transfer by work requires a force to act through some distance. energy transfer in the form of heat occurs between objects that are at different temperatures, with energy spontaneously traveling from the higher-temperature object to the lower-temperature one. when energy is added to an isolated system in the form of heat, either the temperature t of the system will increase or the system will undergo a phase change at a fixed temperature.

the specific heat c of a sample characterizes the rate at which it changes temperature per unit mass when it receives energy in the form of heat. the relationship between the energy input in the form of heat q and the resulting temperature change ? t is

q=mc? t,

where m is the mass of the sample and c is its specific heat, which depends on its phase. for this problem, assume that specific heat values are a constant for all temperatures within a given phase, which is a good approximation.

the latent heat l of a sample characterizes how much energy is required per unit mass to force the system to undergo a phase change at a fixed temperature. the amount of energy input in the form of heat q required to completely change the phase of a sample with mass m is

q=ml.

phase changes between solid and liquid phases are characterized by a latent heat of fusion lf. phase changes between liquid and gas phases are characterized by a latent heat of vaporization lv.

in general, every phase (solid, liquid, or gas) has its own specific heat value and every phase change has its own latent heat value.

if the cooling power remains constant, what will be the temperature of the system tb after it has been in the freezer for exactly 1 hour? this temperature is off scale on the figure.