Specific Heat & Latent Heat (Edexcel GCSE Physics: Combined Science)

Specific Heat Capacity

• If the temperature of the system increases, the increase in temperature of this system depends on:
  • The mass of the substance heated
  • The type of material
  • The energy input to the system

• The specific heat capacity of a substance is defined as:

The amount of energy required to raise the temperature of 1 kg of the substance by 1 °C

• Different substances have different specific heat capacities
  • If a substance has a low specific heat capacity, it heats up and cools down quickly (ie. it takes less energy to change its temperature)
  • If a substance has a high specific heat capacity, it heats up and cools down slowly (ie. it takes more energy to change its temperature)

Low v high specific heat capacity

• Specific heat capacity is mainly used for liquids and solids
• The specific heat capacity of different substances determines how useful they would be for a specific purpose eg. choosing the best material for kitchen appliances
  • Good electrical conductors, such as copper and lead, are excellent conductors of heat due to their low specific heat capacity
  • On the other hand, water has a very high specific heat capacity, making it ideal for heating homes as the water remains hot in a radiator for a long time

• The specific heat capacity of some substances are given in the table below as examples:

Table of values of specific heat capacity for various substances

Specific Latent Heat

• Energy is required to change the state of a substance
  • This energy is known as latent heat

• The specific latent heat is defined as:

The amount of thermal energy required to change the state of 1 kg of a substance with no change in temperature

• There are two types of specific latent heat:
  • Specific latent heat of fusion (solid to liquid and vice versa)
  • Specific latent heat of vaporisation (liquid to gas and vice versa)

• Latent heat is represented by the symbol L with units joules per kilogram (J/kg)

 The changes of state with heat supplied against temperature

• The specific latent heat of fusion is defined as:

The thermal energy required to convert 1 kg of solid to liquid with no change in temperature

• This is used when melting a solid or freezing a liquid
• When a solid substance is melted, its temperature stays constant until all of the substance has melted
• The latent heat of fusion is the energy needed to break the bonds between the molecules

• The specific latent heat of vaporisation is defined as:

The thermal energy required to convert 1 kg of liquid to gas with no change in temperature

• This is used when vaporising a liquid or condensing a gas
• When a liquid substance is heated, at its boiling point, the substance boils and turns into vapour
• The latent heat of vaporisation is the energy needed by the particles to break away from their neighbouring particles in the liquid

• Specific heat capacity and specific latent heat are slightly different
  • Specific heat capacity is used for a change in temperature in the same state
  • Specific latent heat is used for a change in state but no change in temperature

Difference between specific latent heat and specific heat capacity