Class 9 > Unit # 09:Thermal Properties of Matter > Latent heat of Fusion & Latent Heat of Vaporization

Talha's Physics Academy

Latent Heat of Fusion and Latent Heat of Vaporization

Q.5 Define Latent Heat of Fusion and Latent Heat of Vaporization. Explain experiments to determine them.

1. Latent Heat of Fusion

"The heat absorbed by a unit mass of a solid at its melting point in order to convert the solid into a liquid without any change in temperature is called the latent heat of fusion."

$H_f = \frac{Q_f}{m}$

2. Latent Heat of Vaporization

"The heat absorbed by a unit mass of a liquid at its boiling point in order to convert the liquid into vapor without any change in temperature is called the latent heat of vaporization."

$H_v = \frac{Q_v}{m}$

1. Determination of Latent Heat of Fusion of Ice

Experimental Procedure:

• Take a container and place it on a stand over a burner. Put small pieces of ice into the container.
• Suspend a thermometer in the container to measure temperature changes, and use a stopwatch to record accurate time intervals at different stages.
• Turn on the burner. The ice absorbs heat and starts melting, but the temperature remains constant at $0^\circ\text{C}$ until all the ice melts completely.
• Note the time duration ($t_1$ to $t_2$) taken by the ice to melt completely into water at $0^\circ\text{C}$.
• Continue supplying heat to the resulting water at $0^\circ\text{C}$. Its temperature will steadily rise until it reaches its boiling point at $100^\circ\text{C}$.
• Using the temperature-time graph, the latent heat of fusion of ice is calculated from the horizontal phase-change plateau.

Fig: Experimental Setup.

Fig: Temperature-Time graph showing thermal plateaus during fusion (ice to water) and vaporization (water to steam).

2. Determination of Latent Heat of Vaporization of Water

Experimental Procedure:

• This experiment is a continuation of the previous setup once the water reaches its boiling point ($100^\circ\text{C}$).
• Continue supplying heat at a steady rate to the boiling water until all the liquid completely converts into steam.
• Record the total time duration during which the water changes entirely into steam at its boiling point.
• Using the temperature-time graph, calculate the latent heat of vaporization corresponding to the flat vaporization plateau.

© 2026 Talha's Physics Academy. All rights reserved.