How do you calculate specific latent heat?

To calculate specific latent heat, divide the energy change by the mass of the substance.

Specific latent heat is a measure of the energy required to change the state of a unit mass of a substance without changing its temperature. There are two types of specific latent heat: latent heat of fusion (for melting/freezing) and latent heat of vaporisation (for boiling/condensing).

The formula to calculate specific latent heat (L) is:
\[ L = \frac{Q}{m} \]
where \( Q \) is the energy change in joules (J) and \( m \) is the mass of the substance in kilograms (kg).

For example, if you want to find the specific latent heat of fusion for ice, you would measure the amount of energy required to melt a certain mass of ice into water at 0°C. Suppose you supplied 334,000 joules of energy to melt 1 kilogram of ice. Using the formula, the specific latent heat of fusion would be:
\[ L = \frac{334,000 \text{ J}}{1 \text{ kg}} = 334,000 \text{ J/kg} \]

Similarly, to find the specific latent heat of vaporisation, you would measure the energy required to turn a certain mass of liquid into gas at its boiling point. If 2,260,000 joules of energy are needed to vaporise 1 kilogram of water at 100°C, the specific latent heat of vaporisation would be:
\[ L = \frac{2,260,000 \text{ J}}{1 \text{ kg}} = 2,260,000 \text{ J/kg} \]

Understanding specific latent heat is crucial in many practical applications, such as designing heating and cooling systems, and in natural processes like the water cycle. It helps us to analyse how much energy is needed for phase changes, which is essential for efficient energy use and management.