Internal Energy (AQA GCSE Physics)

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Internal Energy

  • Internal energy is defined as:

The total energy stored inside a system by the particles that make up the system due to their motion and positions

  • The molecules within a substance have energy in their:
    • Kinetic store (due to their random motion / vibration)
    • Potential store (due to their position relative to each other)

  • Together, these stores form the total energy that makes up the internal energy of the system

Gas molecules in a box_2, downloadable AS & A Level Physics revision notes

Molecules in a substance have kinetic energy since they are in motion and potential energy from their position relative to each other

Heating

  • Heating a system changes a substance's internal energy by increasing the kinetic energy of its particles
    • The temperature of the material, therefore, is related to the average kinetic energy of the molecules

  • The higher the temperature, the higher the kinetic energy of the molecules and vice versa
    • This means they move around faster

  • This increase in kinetic energy (and therefore internal energy) can:
    • Cause the temperature of the system to increase
    • Or, produce a change of state (solid to liquid or liquid to gas)

16-1-change-in-internal-energy-new

As the container is heated up, the gas molecules move faster with higher kinetic energy and therefore higher internal energy

Change of State

  • When a substance reaches a certain temperature, energy will stop being transferred to the kinetic store of the molecules and energy will be transferred to their potential store instead
  • This energy goes into overcoming the intermolecular forces of attraction between the molecules, causing them to move further apart from one another and leading to a change of state
    • For example, liquid to gas

  • When a substance changes its state:
    • The potential energy of the molecules increases, allowing them to overcome the intermolecular forces of attraction 
    • The kinetic energy remains the same, meaning that the temperature will remain the same, even though the substance is still being heated

Changing state, IGCSE & GCSE Chemistry revision notes

An increase in internal energy from heating can cause a change of state

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Ashika

Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.