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GCSE Questions: Kinetic Theory - Gases

Q6. Professor Snape demonstrated the relationship between the pressure in a gas and the volume of the gas. The diagram below shows the equipment used.

This is the method used.

1. Record the initial volume of gas in the syringe and the pressure reading before any weights are attached.

2. Attach a 2.0 N weight to the syringe.

3. Record the volume of the gas and the reading on the pressure gauge.

4. Repeat steps 2 and 3 until a weight of 12.0 N is attached to the syringe.

(a) What was the range of force used?

0.0 N - 12.0 N

[1 mark]

(b) Give one control variable in the investigation.

Mass of gas (in the syringe) or temperature (of the gas)

[1 mark]

(c) When the volume of gas in the syringe was 45 cm3, the pressure gauge showed a value of 60 kPa.

Calculate the pressure in the gas when the volume of gas in the syringe was 40 cm3. Give the answer to the correct number of significant figures for the data you have been given.

P1V1 = P2V2= constant value

P1 x 40 = 60 x 45

P1 = 60 x 45/40

P1 = 67.5 kPa

Figures in the question are given to 2sf so the answer should be written:

P1 = 68 kPa

[5 marks]

(d) When the volume of gas in the syringe increased, the pressure on the inside walls of the syringe decreased. Explain why.

There is more time between collisions of particles and the walls of the syringe when the volume increases so there are less frequent collisions between the particles and the walls of the syringe causing a lower average force on the walls of the syringe. As pressure is the total force per unit area the pressure will therefore decrease.

[3 marks]

[10 Marks TOTAL]