We often think of temperature and heat as the same thing. While they both involve molecular motion, they are not in fact interchangeable. Thermal energy, or heat, depends on more than just the temperature. In the image above of a river running across the surface of a glacier, the liquid water and the ice have the same temperature, and yet they are in different states. In this chapter, we will uncover the realities of thermal energy, heat, temperature, and changes in states of matter.
The calculation of heat change is not as simple as measuring the temperature of an object. Different objects have different specific heats, meaning they change temperature at different rates. Temperature and heat, though closely related, are not the same. While temperature is a measurement of the average kinetic energy of the molecules, heat is the total kinetic energy. Calculations of changes in heat over phase changes depend not only on the specific heat, but also on the heat of fusion and the heat of vaporization.