Change of State
4 marks · EasyA student investigates how heating a solid wax block causes it to change state.
Describe how the arrangement and movement of particles change as the wax is heated from a solid to a liquid.
Explain why the temperature of the wax stays constant for a short time during melting, even though energy is still being supplied.
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) In solid wax, particles are tightly packed in a regular pattern and vibrate in fixed positions. As the wax is heated and melts, the particles gain energy, move faster, break away from their fixed positions, and are able to move freely but remain close together.
(b) The temperature stays constant during melting because the energy supplied is used to break the forces between particles, allowing them to change state rather than increasing their speed (temperature).
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States that particles are tightly packed/vibrate in fixed positions in a solid.
B2 (a) · 1 mark · Describes that in liquid, particles move more freely (no fixed positions) but are still close together.
B1 (b) · 1 mark · Explains temperature stays constant because energy is used to break bonds (forces) between particles.
B2 (b) · 1 mark · Mentions this allows a change of state instead of raising temperature.
Worked solution
a) In a solid, the wax particles are tightly packed in a fixed, regular arrangement and vibrate about their positions. When heated to melting point, the particles gain enough energy to break free from their fixed positions and can move around each other, describing a liquid's arrangement.
b) During melting, the temperature remains constant because the energy supplied is used to overcome the forces between particles, not to increase their speed (which is temperature). Thus, energy goes into breaking bonds, not raising temperature.