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Date November 2020 Marks available 1 Reference code 20N.2.SL.TZ0.3
Level Standard level Paper Paper 2 Time zone 0 - no time zone
Command term Calculate Question number 3 Adapted from N/A

Question

A sample of vegetable oil, initially in the liquid state, is placed in a freezer that transfers thermal energy from the sample at a constant rate. The graph shows how temperature T of the sample varies with time t.

The following data are available.

Mass of the sample =0.32kg
Specific latent heat of fusion of the oil =130kJkg-1
Rate of thermal energy transfer =15W

Calculate the thermal energy transferred from the sample during the first 30 minutes.

[1]
a(i).

Estimate the specific heat capacity of the oil in its liquid phase. State an appropriate unit for your answer.

[2]
a(ii).

The sample begins to freeze during the thermal energy transfer. Explain, in terms of the molecular model of matter, why the temperature of the sample remains constant during freezing.

[3]
b.

Calculate the mass of the oil that remains unfrozen after 60 minutes.

[2]
c.

Markscheme

«15×30×60»=27000«J» ✓

 

a(i).

27×103=0.32×c×290-250 OR 2100 ✓

Jkg-1K-1 OR Jkg-10C-1 ✓


Allow any appropriate unit that is
 energymass×termperature

a(ii).

«intermolecular» bonds are formed during freezing


bond-forming process releases energy
OR
«intermolecular» PE decreases «and the difference is transferred as heat»


«average random» KE of the molecules does not decrease/change


temperature is related to «average» KE of the molecules «hence unchanged»

 

To award MP3 or MP4 molecules/particles/atoms must be mentioned.

b.

mass of frozen oil «=27×103130×103»=0.21«kg» 

unfrozen mass «=0.32-0.21»=0.11«kg» 

c.

Examiners report

[N/A]
a(i).
[N/A]
a(ii).
[N/A]
b.
[N/A]
c.

Syllabus sections

Core » Topic 3: Thermal physics » 3.1 – Thermal concepts
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