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Date May 2015 Marks available 2 Reference code 15M.2.HL.TZ1.4
Level Higher level Paper Paper 2 Time zone Time zone 1
Command term Calculate, Estimate, Explain, and Identify Question number 4 Adapted from N/A

Question

This question is about an ideal gas cycle.

The P–V diagram shows a cycle ABCDA for a fixed mass of an ideal gas.

Estimate the total work done in the cycle.

[3]
a.

The change AB is isothermal and occurs at a temperature of 420K. Calculate the number of moles of gas.

[3]
b.

Identify and explain the change, if any, in the entropy of the gas when it has completed one cycle.

[2]
c.

Markscheme

use of area under the curve;

each (1 cm × 1 cm) square has energy of 250 J or each small square has energy of 10 J;

estimate (14 to 16 × 250) = 3500 to 4000 J;

a.

clear use of value on AB; (must see correct values)

use of PV = nRT;

0.56 to 0.60 mol;

b.
entropy unchanged;
gas returned to original state;
c.

Examiners report

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

Syllabus sections

Option B: Engineering physics » Option B: Engineering physics (Core topics) » B.2 – Thermodynamics
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