DP Physics (first assessment 2025)

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Question 22M.2.SL.TZ2.2

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Date May 2022 Marks available [Maximum mark: 6] Reference code 22M.2.SL.TZ2.2
Level SL Paper 2 Time zone TZ2
Command term Calculate, Discuss Question number 2 Adapted from N/A
2.
[Maximum mark: 6]
22M.2.SL.TZ2.2

A fixed mass of an ideal gas is contained in a cylinder closed with a frictionless piston. The volume of the gas is 2.5 × 10−3 m3 when the temperature of the gas is 37 °C and the pressure of the gas is 4.0 × 105 Pa.

Energy is now supplied to the gas and the piston moves to allow the gas to expand. The temperature is held constant.

(a)

Calculate the number of gas particles in the cylinder.

[2]

Markscheme

Correct conversion of T «T = 310 K» seen ✓

« use of = N=pVkT to get » 2.3 × 1023 ✓

 

Allow ECF from MP1 i.e., T in Celsius (Result is 2.7 x 1024)

Allow use of n, R and NA

Examiners report

a) This was well answered with the majority converting to K. Quite a few found the number of moles but did not then convert to molecules.

bi) Well answered. It was pleasing to see how many recognised the need to state that the mass/number of molecules stayed the same as well as stating that the volume increased. At SL this recognition was less common so only 1 mark was often awarded.

bii) This was less successfully answered. A surprising number of candidates said that the internal energy of an ideal gas increases during an isothermal expansion. Many recognised that constant temp meant constant KE but then went on to state that the PE must increase and so the internal energy would increase.

(b.i)

Discuss, for this process, the changes that occur in the density of the gas.

[2]

Markscheme

density decreases ✓

volume is increased AND mass/number of particles remains constant ✓

(b.ii)

Discuss, for this process, the changes that occur in the internal energy of the gas.

[2]

Markscheme

internal energy is constant ✓


internal energy depends on kinetic energy/temperature «only»

OR

since temperature/kinetic energy is constant ✓

 

Do not award MP2 for stating that “temperature is constant” unless linked to the correct conclusion, as that is mentioned in the stem.

Award MP2 for stating that kinetic energy remains constant.

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