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GCSE Questions: Kinetic Theory - Gases

Q2. Claire investigated the cooling effect of evaporation.

She used the equipment shown in the diagram to measure how the temperature of three different liquids changed as they evaporated.

 

(a) The temperature and volume of each liquid was the same at the start of the investigation.

State one further control variable in this investigation.

Liquid surface area or shape of the beaker

OR

Duration of experiment

[1 mark]

(b) Give two advantages of using dataloggers and temperature probes compared to using a thermometer as shown below.

[2 marks]

Any two from:

takes readings automatically (do not say it makes it easier for you!)

takes readings more frequently

reduces instrument reading error

higher resolution

don't need to remove probe to take reading

more accurate

 

(c) Claire's results are plotted on the graph below:

(i) Calculate the average rate of temperature decrease of liquid C between 0 and 100 seconds.

See graph

ΔT = 20oC - 13oC

ΔT = 7oC

time = 100 s

Rate of temperature decrease = 7oC/100s

= 0.07 oC/s

[3 marks]

(ii) Give one conclusion that can be made about the rate of temperature decrease of all three liquids from her results.

The rate of temperature change decreases as the experiment proceeds.

[1 mark]

(iii) Which liquid had the lowest rate of evaporation? Give a reason for your answer.

Liquid A - it has the lowest temperature drop over 200 seconds.

[1 mark]

(iv) Gabriel did the same investigation but using a smaller volume of liquid than Claire. All other variables were kept the same.

What effect would this have on the results of Gabriel's investigation?

There would be a larger temperature change per second - as the mass of liquid is lower but the rate of evaporation would be the same

[1 mark]

(d) Explain how the evaporation of a liquid causes the temperature of the remaining liquid to decrease.

Temperature of a liquid is a measure of the average kinetic energy of the particles in it.Particles with higher than average kinetic energy leave the surface of the liquid during evaporations, which reduces the average kinetic energy of the remaining particles.

[3 marks]

[12 Marks TOTAL]