Specific Latent Heat

Overview

This lesson brings together particle ideas and temperature-time data. The key point is that during a change of state, energy is still being transferred even though the temperature stays constant for a while.

What You Need to Know

• During melting or freezing, the temperature can stay constant even while energy is being transferred.
• This happens because the energy is being used to change the arrangement of the particles rather than increasing their kinetic energy.
• A cooling curve shows how temperature changes with time as a substance cools.
• A flat section on a cooling curve often shows a change of state.
• Stearic acid is useful for this practical because its cooling curve can show the phase change clearly.

How to Work Through It

1. Start by revisiting melting and freezing in terms of particles and energy.
2. Collect temperature readings for stearic acid as it cools.
3. Plot or interpret the cooling curve and identify the section where the temperature stays nearly constant.
4. Explain that flat section using the particle model and the idea of latent heat.

Check Your Understanding

• Why can temperature stay constant during a change of state?
• What does a flat section on a cooling curve show?
• Why is it still true that energy is being transferred during the flat section?
• How does the particle arrangement change as stearic acid freezes?

Common Mistakes

• Thinking no energy transfer is happening when the temperature stays constant.
• Treating a cooling curve as a shape to memorise without explaining the particle changes.
• Forgetting that the flat section is linked to a change of state, not just a pause in the experiment.
• Mixing up cooling with freezing. A substance can cool without changing state until it reaches the right temperature.

Next Steps

• Use the worksheet to practise linking the graph to the physical process.
• Keep the ideas of temperature, energy, and particle arrangement connected as you revise the topic.