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When heat is applied to a system, two changes can occur: 1) the temperature could increase or 2) a phase change could occur. The amount of heat required to warm a substance 1 ^{\circ} C or 1 K is known as the heat capacity. Heat capacity is an extrinsic property, meaning that it depends on the amount. The specific heat (or specific heat capacity), C_s is the amount of heat required to warm 1 g of a substance 1 ^{\circ} C or 1 K. The molar heat capacity, C_m is the amount of heat necessary to warm 1 mol of a substance 1 ^{\circ} C or 1 K.

Heating curves are a graph showing the temperature of a substance plotted against the amount of energy it has absorbed. Cooling curves, on the other hand, show the temperature versus the amount of energy lost. On the plot, you should be able to easily find melting and boiling points as well as identify the state present at a given temperature. To learn more about these plots, please view the video below:

As is demonstrated in the video above, when substances undergo a phase change the temperature of the substance is constant. The reason for this is that all of the energy going into (or out of) the substance is breaking (or forming) intermolecular forces rather than increasing the average kinetic energy (temperature) of the molecules. This demonstration video illustrates this effect with a beaker of melting ice and boiling water. Once the thermometer reaches the temperature of the substance, you can see that it does not change for the duration of the melting/boiling. (Note: to do errors in measurement or differences in ambient pressure, the observed melting and boiling temperatures of water in the demonstration are off slightly from their standard values.)