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GCSE Questions: Kinetic Theory - Gases

Q1. A student investigated how the pressure exerted by a gas varied with the volume of the gas.

A pump was used to compress the gas in a tube. As the volume of the gas decreases, the pressure of the gas increases. The student used the pump to increase the pressure on the trapped mass of gas.

Here is the equipment the student used:

(a) The student only recorded one set of results.

Give two reasons why taking repeat readings could provide more accurate data.

If you repeat your readings you can identify anomalies. This reduces the effect of random errors. If your repeat reading differs widely you can repeat again and find which of the two initial readings was most reliable. You can then average the ones that are close to each other.

(A maximum of 2 marks was awarded)

Just saying 'it reduces human error' was insufficient to get you a mark.

[2 marks]

(b) The diagram shows the position of the student's eye when taking volume measurements.

Explain what type of error would be caused if the student's eye was not in line with the level of the liquid in the tube.

By 'what type of error' they mean they want you to say whether it is 'random' or 'systematic'. This parallax error could cause either a random or systematic one!

It gives rise to a random error if eye position (relative to the liquid) would not be the same each time a reading was taken - sometimes below the meniscus, sometimes above it.

It gives rise to a systematic error only if the student always viewed liquid level from the same amount above meniscus (or below)... or read the point where the edge of the meniscus touched the tube not the bottom of the meniscus.

[2 marks]

(c) If the gas is compressed too quickly the temperature of the gas increases.

Explain how the temperature increase would affect the pressure exerted by the gas.

A temperature increase would increase the pressure in the tube, even if the volume was constant, because a higher temperature would mean the gas molecules had a higher average kinetic energy - their higher speed would mean an increase in bombardment on the glass tube wall.

[2 marks]

(d) One of the student's results is given below:

pressure = 1.6 × 105 Pa

volume = 9.0 cm3

Calculate the volume of the gas when the pressure was 1.8 × 105 Pa.

Assume the temperature of the gas was constant.

P1V1 = P2V2

1.6 × 105 x 9.0 = 1.8 × 105 x V2

V2 = (1.6 × 105 x 9.0)/(1.8 × 105)

V2 = (1.6 × 9.0)/1.8 = 8.0 cm3

[3 marks]

(e) The photo shows a person using a bicycle pump to inflate a tyre.

The internal energy of the air increases as the tyre is inflated.

Explain why.

Work is done on the air in the tyrewhen the pump is used , this energy is transferred to the air particles and so the temperature (and/or kinetic energy) of the air increases.

[2 marks]

[11 Marks TOTAL]