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Chemical Bonding

Why does water have a high and specific heat capacity?


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April 03, 2015 10:03AM

First, we need to know a little bit about water. Water is a polar molecule because oxygen bears partial negative charge and hydrogen bears partial positive charge. This results in extensive hydrogen bonding in water molecules between slightly negative oxygens and slightly positive hydrogens. Second, we need to remember that temperature is another way of saying the average kinetic energy of particles - the higher the temperature, the faster they move, in the case of gases and liquids, or vibrate, in the case of solids. Third, heat capacity is the ability of matter to absorb thermal energy. One calorie is defined as the amount required to heat a gram of water one degree Centigrade. That same calorie will heat a gram of gold 33 degrees.

Water's specific heat is defined as 1. The specific heat of gold is therefore .03. Water has a high specific heat because there are quite a few ways water can store heat. 1. Moving along three axes 2. Rotating the "V" shaped molecule in three different directions 3. Hydrogen atoms vibrating back and forth like a tuning fork 4. Hydrogen atoms vibrating up and down along their H-O axis.

Finally, the heat of fusion of water is 80 calories per gram, and the heat of vaporization for water is 540 calories. So ice can absorb 80 times as much heat while melting as the same mass of water. Water absorbs 540 times as much heat while turning into water vapor as the same mass of water absorbs. Both phase changes occur at constant temperature, 0 Centigrade and 100 Centigrade respectively. Look up phase change graph for water to see the interesting line.