"A thermodynamic property of a substance or its response to temperature changes is the coefficient of thermal expansion. The expansion relates the change in temperature to the change in a material's linear dimensions. This coefficient is the fractional change in length per degree of temperature change. When a substance has a temperature change, the energy stored in the intermolecular bonds
. between the atoms of the substance also changes. For example, when stored energy increases, so does the length of the molecular bonds. The result is usually that solids will normally expand in response to being heated and contract when cooled. http://en.wikipedia.org/wiki/Coefficient_of_thermal_expansion"
