The energy involved in change of state
4 marks · NormalA student heats a sample of solid wax in a beaker and records the temperature every minute as it melts and becomes a liquid.
Describe what happens to the temperature of the wax just as it is melting, even though heating continues.
Explain why the temperature behaves this way during melting.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) The temperature of the wax stays constant during melting, even though it is still being heated.
(b) The energy supplied while melting does not increase the temperature, but is used to break the bonds between the solid particles so the wax can change state from solid to liquid.
Common mistakes: Saying temperature rises during melting; Not mentioning latent heat or breaking forces between particles
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States temperature remains constant during melting
B2 (a) · 1 mark · Notes that this occurs even while heating continues
M1 (b) · 1 mark · Mentions that energy is used to change state/break bonds, not increase temperature
B3 (b) · 1 mark · Describes correctly it's a change from solid to liquid
Worked solution
a) The temperature of the wax does not rise while it is melting, even though it is being heated. It remains constant until all the wax has melted.
b) This is because the energy supplied by heating at this time goes into breaking the forces (or bonds) holding the particles in the solid together, not into raising the temperature. This energy is called latent heat.