heat capacity?

Question

why does water have such a high specific heat capacity ?

thanks

Answer 1

Specific heat capacity is the amount of heat to raise a unit *mass* one temperature unit. But what really matters at the molecular level is the *molar* heat capacity. So water may look like it has a high *specific* heat capacity, but that is partly an artifact of its relatively low molecular weight compared to other things that are liquid at similar conditions. If you were looking at molar heat capacities, there would not be as much difference. An illustration of this would be D2O (heavy water, with the mass-2 deuterium isotope of hydrogen), which has about the same amount of hydrogen bonding as H2O (actually slightly more) and about the same molar heat capacity, but because of the higher molecular weight D2O would have a lower specific heat capacity by a ratio of 18:20.

Hope that helps.

Answer 2

Because water is such a highly associated liquid. Heat is motion of molecules. It takes a lot of heat to raise the temperature of water molecules (get them moving faster), because they "stick" to one another. There are partial (+) charges on the H's, which are attracted to the partial (-) charges on the O's.

By the way, heat capacity is the amount of heat (cal, BTU) needed to raise a certain amount of water (lb, g) by a certain temperature (F, C). Specific heat is the ratio of the heat capacity of a substance to the heat capacity of water. Because the heat capacity of water in the metric system is 1.0, the ratio in the metric system happens to equal the heat capacity. Specific heat and heat capacity are not the same.