Edexcel IGCSE Physics (d) Ideal gas molecules Question Bank

idea that (large number of) molecules moving randomly;

idea of equal rate of collisions in each direction;

allow atoms or particles for 'molecules'

can be acquired from diagram by showing arrows of different lengths (by eye) or different directions (by eye)

condone idea of equal number in each direction

Marking points:
- evaluation of new volume
- substitution into $p_{1}V_{1}=p_{2}V_{2}$
- rearrangement
- evaluation of new pressure

Example:
$$V_{2}=130\times\frac{5.0}{8.4}=77\ \mathrm{cm^{3}}$$$$100\times130=p_{2}\times77$$$$p_{2}=\frac{100\times130}{77}$$$$p_{2}=170\ \mathrm{kPa}$$

Accept:
- $V_{2}=77.38\ldots\ \mathrm{cm^{3}}$
- any value that rounds to $170\ \mathrm{kPa}$
- ECF different yet incorrect volume

Marking guidance:
- Deduct 1 mark for a power-of-ten error.

For either graph:
- as temperature increases, pressure / speed increases

For graph 1:
- relationship is linear

For graph 2:
- relationship is non-linear
- gradient of curve decreases

Ignore:
- positive correlation

Accept:
- proportional only if there is a clear link to temperature being measured in kelvin

Any two from:
- this temperature is absolute zero
- pressure / speed / kinetic energy of gas particles would be 0 at this temperature
- it is impossible to have a temperature lower than this

Accept:
- negative pressure / speed / kinetic energy is impossible