Heat, q, is energy that is transferred between two objects as thermal motion. For example, if we bring together two blocks of copper, a hot one at 500 K and a cold one at 200 K, heat will flow out of the hot copper block and into the cold one until the two come to the same temperature.

The hot copper block loses energy, and its value of q will be negative. The cold copper block gains energy, and its value of q will be positive. Conservation of energy dictates that the amount of heat lost by the hot block is equal to the amount of heat gained by the cold one.

Note that q represents a change or redistribution of energy and is not, itself, a property of a static system. Students often confuse heat and temperature because they have everyday meanings that are not quite the same or as precisely defined as thermodynamics would have it. It is, therefore, very important to emphasize to students that heat is energy transferred in the form of thermal energy and temperature is a measure of one kind of energy - the kinetic energy a system has because of the translational motion of its atoms and molecules. However, temperature changes are very often used to determine q. If the volume is not changing, you can use the heat capacity of a material to measure the change in heat with temperature

q_v = C_vΔT

We will discuss the use of heat capacities to determine q later.

NASA, through its Jet Propulsion Laboratory, has an extensive set of web pages designed for teachers to help with these concepts through Project Genesis. Their heat module includes standards for grades 5-8 and 9-12 curricula, student activities and texts, and teachers guides. To go to the Genesis heat module click here. Clicking the Genesis banner below gets you into some additional activities, including the opportunity to view some material in Spanish.