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Date May 2021 Marks available 2 Reference code 21M.2.SL.TZ2.2
Level Standard level Paper Paper 2 Time zone 2
Command term Deduce Question number 2 Adapted from N/A

Question

The graph shows the variation with temperature T of the pressure P of a fixed mass of helium gas trapped in a container with a fixed volume of 1.0 × 10−3 m3.

Deduce whether helium behaves as an ideal gas over the temperature range 250 K to 500 K.

[2]
a.

Helium has a molar mass of 4.0 g. Calculate the mass of gas in the container.

[2]
b.

A second container, of the same volume as the original container, contains twice as many helium atoms. The graph of the variation of P with T is determined for the gas in the second container.

Predict how the graph for the second container will differ from the graph for the first container.

[2]
c.

Markscheme

«He behaves as ideal gas if» pT «at constant V» 

uses two points to show that pT 


MP1
can also be described as pT=k OR pT=nRV

 

a.

100×103×10-3250×8.31=«0.048mol» ✓

«0.048×4=» 0.19«g» ✓


Allow any correct data point to be used.

Allow ECF from MP1

b.

recognizes that pressure will double

graph will be steeper OR gradient will be larger

graph will still go through the origin 


MP1
can be expressed as e.g.“pnORnRVwill double”.

Accept pv=2nRT for MP1.

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Core » Topic 3: Thermal physics » 3.2 – Modelling a gas
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