Question bank › IGCSE Physics › Solids, liquids and gases

Particles, change of state and specific heat capacity (P)

Answer on paper first, then reveal the mark scheme one mark at a time.

1Grade 1–3Triple only4 marks

Describe the differences between the particles in a solid and the particles in a gas.

Your answer should refer to the arrangement and the motion of the particles. [4]

solid: particles closely packed / touching / in a regular pattern (lattice)(1)
gas: particles far apart / widely spaced / randomly arranged; allow comparative answers (e.g. 'gas particles are much further apart')(1)
solid: particles vibrate about fixed positions; reject 'do not move' / 'stay still'(1)
gas: particles move randomly / in all directions / at high speed / move freely (from place to place); allow comparative answers (e.g. 'gas particles move much faster'); reject 'gas particles vibrate' alone(1)
Answer: Solid: close, regular, vibrate about fixed positions. Gas: far apart, random, move quickly in all directions.
Examiner tip: Saying solid particles 'don't move' loses the mark; they vibrate about fixed positions.

2Grade 4–5Triple only4 marks

A solid is heated at a steady rate. The graph shows how its temperature changes with time.

(a) Use the graph to state the melting point of the substance. [1]

(b) State the physical state of the substance at 4 minutes. [1]

(a) 40 °C(1)
(b) mixture of solid and liquid / melting / changing from solid to liquid; do not accept 'solid' or 'liquid' alone(1)
(c) (thermal) energy is used to overcome / break the forces (bonds) between particles; accept 'energy is used to change the state' / 'energy increases the potential energy of the particles'(1)
(c) so the (average) kinetic energy of the particles does not increase / particles do not speed up; ignore 'energy is lost'(1)
Answer: (a) 40 °C (b) solid and liquid (c) energy breaks bonds between particles, kinetic energy unchanged
Examiner tip: Students lose the second mark in (c) if they don't link temperature to the kinetic energy of the particles.

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