Syllabus Edition

First teaching 2020

Last exams 2024

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The First Law of Thermodynamics (CIE A Level Physics)

Exam Questions

34 mins4 questions
1a
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1 mark

A fixed mass of an ideal gas has a pressure and a volume V

The gas undergoes a cycle of changes, A to B to C, as shown in Fig. 1.1

16-1-1a-m-thermodynamics-cycle-of-change-sq-cie-a-level

Table 1.1 shows data for pand for points A, B and C. 

Table 1.1

  / 105 Pa / 10−3 m3 / K
A     680
B 1.6 4.4 451
C     698

State the change in internal energy Δfor one complete cycle, ABCA.

 
ΔU ...................................................................

1b
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2 marks

Calculate the number of particles in the gas.

1c
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2 marks

Complete Table 1.1 by filling in the missing pressures and volumes at A, B and C.

1d
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5 marks
(i)
The first law of thermodynamics of a system can be represented by the equation:
  
increment U space equals space q space plus space W
 
State, with reference to the system, what is meant by increment Uq and W
 
 [3]
 
(ii)
Explain how the first law of thermodynamics applies to the change C to A.
 
[2]

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2a
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2 marks

Define the work done by a gas.

 

2b
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2 marks

A mass of water with negligible volume is vapourised into water vapour of volume 0.82 m3 at a temperature of 100 °C and atmospheric pressure 1.0 × 105 Pa. The thermal energy supplied to the water is 9.5 × 10J. 

Calculate the magnitude of the work done by the water in expanding against the atmosphere when it vapourises. 
 
work done ............................................. J 
2c
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2 marks

Determine the increase in internal energy of the water when it vapourises at 100 °C. Explain your reasoning.

 
increase in internal energy = ....................................... J 

2d
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3 marks

Suggest, with a reason, how the specific latent heat of vapourisation of water at a pressure greater than atmospheric pressure compares with its value at atmospheric pressure.

 

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3a
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2 marks

State the first law of thermodynamics and include any relevant units.

3b
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2 marks

A fixed mass of water is in a beaker at atmospheric pressure. The initial temperature of the water is 0 °C. The water is supplied with thermal energy q, so that its temperature increases to 10 °C. There is no net change in the volume of the water. 

Determine the work done and the increase in internal energy of the water by completing Table 1.1, considering the first law of thermodynamics.

Table 1.1

Work done on water thermal energy supplied to water increase in internal energy of water
 

q

 

3c
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2 marks

The water from part (b) is now heated so it's temperature increases by a further 10 °C to a final temperature of 20 °C. This process causes the volume of the water to increase so that work is done.

Assume that the change in internal energy is the same as in part (b). 

Determine the work done, thermal energy supplied and the increase in internal energy of the water by completing Table 1.2, considering the first law of thermodynamics.

Table 1.2

Work done on water thermal energy supplied to water increase in internal energy of water
   

 

 

3d
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2 marks

Explain how the average specific heat capacity of the water, in parts (b) and (c), between 10 °C and 20 °C compares with its average value between 0 °C and 10 °C.

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4a
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1 mark

Define internal energy.

4b
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6 marks

State and explain, in molecular terms, whether the internal energy of the following increases, decreases or does not change.
 

(i)
A lump of copper as it is cooled.

[3]

(ii)
Some water as it evaporates at a constant temperature.
[3]

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