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The thermal capacity of an object is the amount of heat required to change the temperature of the object by a certain amount. This is measured in joules per Kelvin (J/K). Heating it and dividing the heat energy used by its temperature change can determine the thermal capacity of a block of copper.

Temperature and heat are not the same thing:

• temperature is a measure of how hot something is
• heat is a measure of the thermal energy contained in an object

Temperature is measured in °C, and heat is measured in J. When heat energy is transferred to an object, its temperature increase depends upon the:

• mass of the object
• substance the object is made from
• amount of energy transferred to the object

For a particular object, the more heat energy transferred to it, the greater its temperature increase.

Specific heat capacity

The specific heat capacity of a substance is the amount of energy needed to change the temperature of 1 kg of the substance by 1°C. Different substances have different specific heat capacities.

Heat capacities of different substances

• Water – 4181 J/kg°C
• Oxygen – 418 J/kg°C
• Lead – 128 J/kg°C

Notice that water has a particularly high specific heat capacity. This makes water useful for storing heat energy, and for transporting it around the home using central heating pipes.

Calculating specific heat capacity

Here is the equation relating energy to specific heat capacity.

• Q is the energy transferred in joules, J
• m is the mass of the substances in kg
• c is the specific heat capacity in J/kg°C
• Δθ (‘theta’) is the temperature change in degrees Celsius, °C

For example, how much energy must be transferred to raise the temperature of 2 kg of water from 20°C to 30°C?

E = m × c × θ (θ = 30 – 20 = 10°C)

E = 2 × 4181 × 10 = 83,620 J or 83.62 kJ