Describe the motion of molecules in a gas, according to the kinetic theory of gases.

Mark scheme

Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.

1. [B1] random/haphazard
2. [B1] constant velocity or speed in a straight line between collisions
3. [B1] or distribution of speeds/different directions
4. [M1] (small) specks of light/bright specks/pollen grains/dust particles/smoke particles
5. [A1] moving haphazardly/randomly/jerky/in a zigzag fashion
6. [C1] pV = 1/3 Nm<c²>
7. [C1] 1.05 × 10⁵ × 0.0240 = 1/3 × 4.00 × 10⁻³ × <c²>
8. [C1] <c²> = 1.89 × 10⁶
9. [(C1)] or 1/2 m<c²> = (3/2) kT
10. [(C1)] 0.5 × (4.00 × 10⁻³/6.02 × 10²³) × <c²> = 1.5 × 1.38 × 10⁻²³ × 300
11. [(C1)] <c²> = 1.87 x 10⁶
12. [(C1)] or nRT = 1/3 Nm<c²>
13. [(C1)] 1.00 × 8.31 × 300 = 1/3 x 4.00 × 10⁻³ × <c²>
14. [(C1)] <c²> = 1.87 x 10⁶
15. [A1] c_r.m.s. = 1.37 × 10³ m s⁻¹
16. [C1] <c²> ∝ T
17. [C1] <c²> at 177 °C = 1.89 × 10⁶ × (450 / 300)
18. [A1] c_r.m.s. at 177 °C = 1.68 × 10³ m s⁻¹