Specific Heat & Latent Heat
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
Examiner Tip
The specific latent heat of fusion and vaporisation value of all substances will be provided for you in the exam question, so you do not need to memorise the value of any.However, make sure to include 'with no change in temperature' in your definition of specific latent heat to be awarded full marks.Use these reminders to help you remember which type of latent heat is being referred to:
- Latent heat of fusion = imagine ‘fusing’ the liquid molecules together to become a solid
- Latent heat of vaporisation = “water vapour” is steam, so imagine vaporising the liquid molecules into a gas