Specific Heat Capacity & Latent Heat

Understanding Heat Energy

Heat energy is a form of energy that is transferred between systems or objects with different temperatures. It flows from the hotter object to the cooler one until thermal equilibrium is reached.

Specific Heat Capacity

The specific heat capacity of a substance is the amount of heat required to change the temperature of 1 kg of the substance by 1°C (or 1 K). It is denoted by the symbol c and is measured in joules per kilogram per degree Celsius (J/kg°C).

The formula for calculating the heat energy ( $Q$) required to change the temperature of a mass ( $m$) of a substance is:

$$Q = mc\Delta T$$

• $Q$ = heat energy (Joules)
• $m$ = mass (kg)
• $c$ = specific heat capacity (J/kg°C)
• $\Delta T$ = change in temperature (°C)

Example

Calculate the heat energy required to raise the temperature of 2 kg of water from 20°C to 100°C. (Specific heat capacity of water = 4200 J/kg°C)

Latent Heat

Latent heat is the heat absorbed or released by a substance during a change of state (e.g., melting, boiling) without changing its temperature. It is measured in joules per kilogram (J/kg).

There are two types of latent heat:

• Latent heat of fusion: Heat required to change a solid into a liquid at its melting point.
• Latent heat of vaporization: Heat required to change a liquid into a gas at its boiling point.

The formula for latent heat ( $Q$) is:

$$Q = mL$$

• $Q$ = heat energy (Joules)
• $m$ = mass (kg)
• $L$ = specific latent heat (J/kg)

Example

Calculate the heat energy required to melt 3 kg of ice at 0°C. (Specific latent heat of fusion of ice = 334,000 J/kg)