Why is specific heat important?

Specific heat is defined as the amount of thermal energy required to raise the temperature of a unit mass of a substance by one degree of temperature. It is important because it determines the amount of energy that needs to be added or removed to heat up or cool down a substance or an object.

The IB Physics data booklet formula involving specific heat is

$\hspace{2em}$ $Q = mc\Delta T$

Where

$\hspace{2em}$ $Q$ is the heat required in J
$\hspace{2em}$ $m$ is the mass of the sample in kg
$\hspace{2em}$ $c$ is the specific heat capacity of the substance
$\hspace{2em}$ $\Delta T$ is the change in temperature in k.

This formula can be rearranged to solve for specific heat capacity to get

$\hspace{2em}$ $c = \dfrac{Q}{m\Delta T}$

We can see from the formula that the units on $c$ will be J kg$^{-1}\ ^o$C$^{-1}$.

Substances with high values of specific heat require more energy for a given change in temperature than substances with a lower value for specific heat. Water is an example of a substance with a high specific heat, with $c$ equal to 4186 J kg$^{-1}\ ^o$C$^{-1}$. This relatively high value means that a significant amount of energy is required to raise water to its boiling point. It also means that a lot of energy is released when water cools down again. Some older heating systems in houses circulate hot water to deliver heat to the rooms. Water’s high carrying capacity for thermal energy makes it ideal for this use.

Another example of where water’s high specific heat plays an important role is in weather. Although the land may heat up and cool down relatively quickly as the air temperature changes, bodies of water will take much more time for their temperature to change. In summer, the water will stay cooler than the air and help moderate extreme heat. Similarly, in winter bodies of water can help moderate very cold air temperatures.

Because of our understanding of specific heat, we can calculate the heat capacity of objects. This is the amount of energy required to raise an object's temperature by one degree kelvin. Once this is known, we can predict the rate at which objects will change temperature and the amount of heat energy involved. Understanding specific heat is extremely valuable for designing systems where heat transfer is fundamental to their operation.