Thermal Physics

States of Matter

How do you use specific heat capacity information?

Specific heat capacity is the energy per kilogram per change in temperature. So, to find the amount of energy needed to heat something you need to know the material, its mass, and the change in temperature desired. For example, if you wanted to increase the temperature of 2 liters (2 kilograms) of water from room temperature (20°C) to the boiling point (100°C) you need to multiply the specific heat capacity of water (4,186 J/kg°C) by 2 kg and by 80°C to obtain 669,760 J, or about 670 kJ.

Suppose that the water is placed in an aluminum pan with a mass of 300 g (0.3 kg). How much extra energy is needed to heat the pan? The answer is found by multiplying the specific heat capacity of aluminum (897 J/kg°C) by the mass (0.3 kg) and by the temperature change (80°C) to obtain 144,000 J or 144 kJ. So the total energy needed to heat both the water and the pan is 814 kJ. Note how much more energy is needed to heat the water than the pan. Look through the list of specific heat capacities on page 125 to find other metals from which you could make a pan that would need less energy to heat it.

The high specific heat capacity of water makes it a good material to use, for example, in cooling an automobile engine by circulating the water through the engine where the water is heated and then through the radiator where flowing air can cool the water.


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