GCSE Combined Science (AQA)

622 videos | 38 hours

Calculating Energy to Change State

Please subscribe to watch this video.

This, and all other videos, are included in our premium subscriptions.

Premium accounts get access to all videos.

Particle model of matter Internal energy and energy transfers

Calculating Energy to Change State

3:04 Heating to Change State
Spec 4.3.2.3
Previous Specific Latent Heat Next Heating Graphs
  • Energy change for a change in state depends on mass and specific latent heat.
  • Specific latent heat is the energy required to change the state of 1 kg of a substance without a temperature change.
  • Thermal energy needed for change = mass x specific latent heat (E = M x L).
  • Energy is measured in joules, mass in kilograms, and specific latent heat in joules per kilogram.
  • Example: Heat supplied to 5 kg of water at boiling point; 2.7 megajoules of heat supplied, 3.8 kg of water remains.
  • Calculate specific heat of vaporization of water.
  • Convert 2.7 megajoules to 2,700,000 joules.
  • Determine mass of water boiled: 5 kg - 3.8 kg = 1.2 kg.
  • Rearrange equation to make specific latent heat the subject: specific latent heat = thermal energy / mass.
  • Substitute values: specific latent heat = 2,700,000 joules / 1.2 kg = 2,250,000 joules per kilogram.
  • Answer can also be expressed as 2.25 megajoules per kilogram or 2.25 x 10^6 joules per kilogram.

Please subscribe to access these revision notes.

This, and all other video notes, are included in our premium subscriptions.

Premium accounts get access to all videos and revision notes.