Specific heat capacity and calculating heat energy

When substances are heated, they gain heat energy. The atoms and molecules of substances gain kinetic energy and their speed increases. The average kinetic energy of these particles is proportional to the temperature of the substance. When a substance is heated, causing its temperature to rise, this is because the average value of the kinetic energy of the atoms or molecules has increased.

When an object is heated or cooled, its temperature change, \Delta T, depends on the mass of the object and the material it is made from.

For example, when the same amount of heat energy is added to a 1 kg mass and a 2 kg mass of aluminium, the change in temperature of each mass is different.

Also, if 1 kg of copper and 1 kg aluminium have the same amount of heat energy added to them, the change in temperature for each metal is different.

The change in temperature also depends on a property of the material called its specific heat capacity.

The specific heat capacity, c, is the heat energy that is needed to raise the temperature of 1kg of the substance, by 1 ^{\circ} C. Specific heat capacity is measured in joules per kilogram degree-celsius ( J kg^{-1^{\circ}}C^{-1}).

The heat energy E_{h} which has to be supplied to a substance of mass m and specific heat capacity c to raise its temperature by \Delta T is given by the following relationship.

{E_h} = cm\Delta T

  • {E_h} is measured in joules ( J)
  • m is measured in kilograms ( kg)
  • \Delta T is measured in degrees celsius ( ^{\circ}C)
  • c is measured in joules J kg^{-1^{\circ}}C^{-1}

The same relationship can be used to calculate the heat that is given out by a substance as it cools.

You are expected to be able to use this relationship in calculating the heat gained, or the heat lost by a substance.