Heat capacity is the amount of energy it takes to cause a subtance's temperature to increase. Heat capacity has units of energy/(mass*temperature), which shows that heat capacity describes how much energy it takes to raise a particular mass of a substance by a certain unit of temperature. The most common units are J/(goC), or Joules/(gram*degree Celsius). Heat capacity is constant for a substance at a constant temperature, and is usually reported for substances at 25oC. Water has an unusually high heat capacity--4.18 J/(goC). This means that to change the temperature of water requires a relatively high amount of energy.