Experiment Overview

This experiment determines the specific latent heat of fusion of ice by supplying thermal energy electrically and observing the temperature change with time. During the phase change from solid to liquid, the supplied energy causes no temperature rise.

What This Experiment Demonstrates

• Energy absorption during a phase change
• Existence of latent heat
• Use of temperature–time graphs to analyze thermal processes

Apparatus Required

• Calorimeter with lid and insulation
• Crushed ice at \(0^\circ\text{C}\)
• Immersion heater
• Power supply
• Ammeter and voltmeter
• Stopwatch
• Thermometer or temperature probe
• Balance
• Stirrer

Theory

When heat is supplied to a substance undergoing a change of state, the temperature of the substance remains constant even though energy continues to be absorbed. This energy is known as latent heat.

The energy required to change the state of a mass \( m \) of a substance without changing its temperature is given by:

\[Q = mL\]

where \( L \) is the specific latent heat of fusion.

In this experiment, thermal energy is supplied electrically by an immersion heater. The electrical energy supplied is:

\[E = VIt\]

During the melting of ice at \(0^\circ\text{C}\), all the supplied energy is used to break intermolecular bonds, so:

\[VIt = mL\]

The latent heat of fusion can therefore be determined from the energy supplied during the constant-temperature region of the temperature–time graph.

Method

1. Measure the mass of the empty calorimeter.
2. Add crushed ice and measure the total mass to determine the mass of ice used.
3. Insert the immersion heater, thermometer, and stirrer into the calorimeter.
4. Ensure the ice is initially at \(0^\circ\text{C}\).
5. Switch on the power supply and start the stopwatch.
6. Record the voltage and current supplied to the heater.
7. Stir continuously and record the temperature at regular time intervals.
8. Continue heating until all the ice has melted and the temperature begins to rise.

Observations

A temperature–time graph shows an initial constant-temperature region at \(0^\circ\text{C}\) while the ice melts, followed by a rise in temperature once all the ice has turned into water.

Calculations

• Plot a graph of temperature against time.
• Identify the time interval \( t \) during which the temperature remains constant.
• Calculate the electrical energy supplied during this interval using \( E = VIt \).
• Determine the mass of ice melted.
• Calculate the latent heat of fusion using \( L = \dfrac{E}{m} \).

For guidance on plotting graphs and identifying gradients and plateaus, visit our Graph Guide.

Result

The temperature remains constant during the melting of ice despite continuous energy input. The specific latent heat of fusion of ice is determined from the energy supplied during this phase change.

Video Demonstration

Video courtesy of ibPhysicsHelp (YouTube). Video used for educational purposes under YouTube’s embedding policy.