IB Questionbank

User interface language: English | Español

Date	May 2018	Marks available	2	Reference code	18M.3.SL.TZ2.7
Level	Standard level	Paper	Paper 3	Time zone	2
Command term	Sketch	Question number	7	Adapted from	N/A

Question

A cylinder is fitted with a piston. A fixed mass of an ideal gas fills the space above the piston.

M18/4/PHYSI/SP3/ENG/TZ2/07._01

The gas expands isobarically. The following data are available.

$\begin{array}{*{20}{l}} {{\text{Amount of gas}}}&{ = 243{\text{ mol}}} \\ {{\text{Initial volume of gas}}}&{ = 47.1{\text{ }}{{\text{m}}^3}} \\ {{\text{Initial temperature of gas}}}&{ = -12.0{\text{ °C}}} \\ {{\text{Final temperature of gas}}}&{ = + 19.0{\text{ °C}}} \\ {{\text{Initial pressure of gas}}}&{ = 11.2{\text{ kPa}}} \end{array}$

The gas returns to its original state by an adiabatic compression followed by cooling at constant volume.

Show that the final volume of the gas is about 53 m³.

[2]

Calculate, in J, the work done by the gas during this expansion.

[2]

Determine the thermal energy which enters the gas during this expansion.

[3]

Sketch, on the pV diagram, the complete cycle of changes for the gas, labelling the changes clearly. The expansion shown in (a) and (b) is drawn for you.

[2]

d.i.

Outline the change in entropy of the gas during the cooling at constant volume.

[1]

d.ii.

There are various equivalent versions of the second law of thermodynamics. Outline the benefit gained by having alternative forms of a law.

[1]

Markscheme

ALTERNATIVE 1

«Using $\frac{{{V_1}}}{{{T_1}}} = \frac{{{V_2}}}{{{T_2}}}$ »

V₂ = $\frac{{47.1 \times (273 + 19)}}{{(273 - 12)}}$

V₂ = 52.7 «m³»

ALTERNATIVE 2

«Using PV = nRT»

V = $\frac{{243 \times 8.31 \times (273 + 19)}}{{11.2 \times {{10}^3}}}$

V = 52.6 «m³»

[2 marks]

W «= PΔV» = 11.2 × 10³ × (52.7 – 47.1)

W = 62.7 × 10³ «J»

Accept 66.1 × 10³ J if 53 used

Accept 61.6 × 10³ J if 52.6 used

[2 marks]

ΔU «= $\frac{3}{2}$ nRΔT» = 1.5 × 243 × 8.31 × (19 – (–12)) = 9.39 × 10⁴

Q «= ΔU + W» = 9.39 × 10⁴ + 6.27 × 10⁴

Q = 1.57 × 10⁵ «J»

Accept 1.60 × 10⁵ if 66.1 × 10³ J used

Accept 1.55 × 10⁵ if 61.6 × 10³ J used

[3 marks]

concave curve from RHS of present line to point above LHS of present line

vertical line from previous curve to the beginning

M18/4/PHYSI/SP3/ENG/TZ2/07.d.i/M

[2 marks]

d.i.

energy is removed from the gas and so entropy decreases

temperature decreases «at constant volume (less disorder)» so entropy decreases

OWTTE

[1 mark]

d.ii.

different paradigms/ways of thinking/modelling/views

allows testing in different ways

laws can be applied different situations

OWTTE

[1 mark]

Examiners report

[N/A]

d.i.

[N/A]

d.ii.

[N/A]

Syllabus sections

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

Show 52 related questions

17N.3.SL.TZ0.8b: Using the axes, sketch the three-step cycle.
18M.3.SL.TZ1.7c.i:
Explain, without any calculation, why the pressure after this change would belower if the process was isothermal.
16N.3.SL.TZ0.10c:
The nuclear power plant works at 71.0% of the Carnot efficiency. The power produced is 1.33 GW. Calculate how much waste thermal energy is released per hour.
17M.3.SL.TZ2.7a.i:
Justify why the thermal energy supplied during the expansion AB is 416 J.
17N.3.SL.TZ0.8c:
The initial temperature of the gas is 290 K. Calculate the temperature of the gas at the start of the adiabatic expansion.
17M.3.SL.TZ2.7a.iii:
Show that the thermal energy removed from the gas for the change BC is approximately 330 J.
16N.3.SL.TZ0.10a:
Calculate the Carnot efficiency of the nuclear power plant.
17N.3.SL.TZ0.10c:
The final image of the Moon is observed through the eyepiece. The focal length of the eyepiece is 5.0 cm. Calculate the magnification of the telescope.
18M.3.SL.TZ1.7a:
Show that the pressure at B is about 5 × 10⁵ Pa.
17M.3.SL.TZ1.6a:
State what is meant by an adiabatic process.
17M.3.SL.TZ1.6b:
Identify the two isothermal processes.
19M.3.SL.TZ2.10bi:
Calculate the change in internal energy of the gas for the process A→B.
18N.3.SL.TZ0.7c.ii:
State, without calculation, during which change (A → B, B → C or C → A) the entropy of the gas decreases.
18N.3.SL.TZ0.7c.i:
The work done by the gas from A → B is 288 J. Calculate the efficiency of the cycle.
18N.3.SL.TZ0.7a.ii:
Show that at C the temperature is 254 K.
18M.3.SL.TZ2.7a:
Show that the final volume of the gas is about 53 m³.
18N.3.SL.TZ0.7a.i:
Show that at C the pressure is 1.00 × 10⁶Pa.
18M.3.SL.TZ2.7c:
Determine the thermal energy which enters the gas during this expansion.
16N.3.SL.TZ0.10b:
Explain, with a reason, why a real nuclear power plant operating between the stated temperatures cannot reach the efficiency calculated in (a).
16N.3.SL.TZ0.10d: Discuss the production of waste heat by the power plant with reference to the first law and...
17M.3.SL.TZ1.6e:
State a reason why a Carnot cycle is of little use for a practical heat engine.
19N.3.SL.TZ0.6b(iii): state and explain whether the second law of thermodynamics is violated.
18M.3.SL.TZ1.7b.ii:
For the process BC, calculate, in J, the change in the internal energy of the gas.
19N.3.SL.TZ0.6b(i):
determine the thermal energy removed from the system.
18M.3.SL.TZ1.7b.i:
For the process BC, calculate, in J, the work done by the gas.
18M.3.SL.TZ1.7c.ii:
Determine, without any calculation, whether the net work done by the engine during one full cycle would increase or decrease.
18M.3.SL.TZ2.7d.ii:
Outline the change in entropy of the gas during the cooling at constant volume.
18N.3.SL.TZ0.7b:
Show that the thermal energy transferred from the gas during the change B → C is 238 J.
19N.3.SL.TZ0.6a(ii):
Calculate the ratio $\frac{V_{A}}{V_{C}}$ .
17M.3.SL.TZ1.6c.ii:
The volume at B is 2.30 × 10^–3 $\,$ m³. Determine the pressure at B.
17N.3.SL.TZ0.8d:
Using your sketched graph in (b), identify the feature that shows that net work is done by the gas in this three-step cycle.
18M.3.SL.TZ2.7e:
There are various equivalent versions of the second law of thermodynamics. Outline the benefit gained by having alternative forms of a law.
18M.3.SL.TZ1.7d:
Outline why an efficiency calculation is important for an engineer designing a heat engine.
18M.3.SL.TZ2.7b:
Calculate, in J, the work done by the gas during this expansion.
18M.3.SL.TZ1.7b.iii:
For the process BC, calculate, in J, the thermal energy transferred to the gas.
17M.3.SL.TZ2.7a.ii:
Show that the temperature of the gas at C is 386 K.
20N.3.SL.TZ0.9b(i):
Calculate the pressure following this process.
20N.3.SL.TZ0.9a(i):
Calculate the work done during the compression.
20N.3.SL.TZ0.9a(ii):
Calculate the work done during the increase in pressure.
20N.3.SL.TZ0.9b(ii): Outline how an approximate adiabatic change can be achieved.
17M.3.SL.TZ1.6d.ii:
The volume at C is 2.90 × 10^–3 $\,$ m³. Calculate the temperature at C.
17N.3.SL.TZ0.8a:
Show that the volume of the gas at the end of the adiabatic expansion is approximately 5.3 x 10^–3 m³.
19N.3.SL.TZ0.6b(ii):
explain why the entropy of the gas decreases.
17M.3.SL.TZ1.6d.i:
Show that ${P_B}V_B^{\frac{5}{3}} = nR{T_C}V_C^{\frac{2}{3}}$
19N.3.SL.TZ0.6a(i):
Show that the pressure at B is about 130 kPa.
19M.3.SL.TZ2.10bii: Calculate the temperature at A if the temperature at B is −40°C.
19M.3.SL.TZ2.10c: Determine, using the first law of thermodynamics, the total thermal energy transferred to the...
19M.3.SL.TZ2.10d: Suggest why this cycle is not a suitable model for a working heat pump.
17M.3.SL.TZ2.7a.iv:
Determine the efficiency of the heat engine.
17M.3.SL.TZ1.6c.i:
Determine the temperature of the gas at A.
17M.3.SL.TZ2.7b:
State and explain at which point in the cycle ABCA the entropy of the gas is the largest.
19M.3.SL.TZ2.10a:
Show that the work done on the gas for the isothermal process C→A is approximately 440 J.

Hide related questions

Option B: Engineering physics » Option B: Engineering physics (Core topics)

Option B: Engineering physics

Question

Markscheme

Examiners report

Syllabus sections

View options