AQA GCSE HIGHER PHYSICS - Latent Heat and Changes of State

AQA GCSE Higher Physics: Latent Heat and Changes of State

Introduction

This tutorial explores the concept of latent heat and its role in changes of state. We will discuss how energy is involved in melting, freezing, boiling, and condensation, and how to calculate the energy required for these processes.

What is Latent Heat?

Latent heat is the energy absorbed or released during a change of state at a constant temperature. This energy is used to break or form bonds between molecules, rather than increasing the temperature.

Types of Latent Heat

• Specific Latent Heat of Fusion (Lf): The amount of heat energy required to change 1 kg of a substance from a solid to a liquid at its melting point.
• Specific Latent Heat of Vaporization (Lv): The amount of heat energy required to change 1 kg of a substance from a liquid to a gas at its boiling point.

The Formula

The energy (Q) required for a change of state can be calculated using the following formula:

Q = m * L

where:

• Q is the energy transferred (in joules, J)
• m is the mass of the substance (in kilograms, kg)
• L is the specific latent heat (in joules per kilogram, J/kg)

Examples of Latent Heat in Action

• Melting Ice: When ice melts, it absorbs energy from its surroundings to break the bonds holding the water molecules in a rigid structure. This energy is the latent heat of fusion.
• Boiling Water: When water boils, it absorbs energy to overcome the attractive forces between the molecules, allowing them to escape into the gaseous state. This energy is the latent heat of vaporization.
• Freezing Water: When water freezes, it releases energy as the molecules form bonds and become more tightly packed in a solid structure. This released energy is the latent heat of fusion.
• Condensation: When water vapor condenses, it releases energy as the water molecules come closer together and form bonds. This released energy is the latent heat of vaporization.

Applications of Latent Heat

• Refrigeration: Refrigerators use the absorption of latent heat during the evaporation of a refrigerant to cool the interior of the refrigerator.
• Heating Systems: Central heating systems use the release of latent heat during condensation to warm homes.
• Cooking: Using latent heat during boiling allows us to cook food efficiently.

Conclusion

Understanding latent heat is crucial for comprehending the energy changes involved in changes of state. It allows us to calculate the energy required for these processes and understand how they are applied in various technological advancements.