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 =0.32 kg
Specific latent heat of fusion of the oil =130 kJ kg-1
Rate of thermal energy transfer =15 W
Calculate the thermal energy transferred from the sample during the first 30 minutes.
Estimate the specific heat capacity of the oil in its liquid phase. State an appropriate unit for your answer.
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.
Calculate the mass of the oil that remains unfrozen after 60 minutes.
Markscheme
«15×30×60»=27000 «J» ✓
27×103=0.32×c×(290-250) OR 2100 ✓
J kg-1 K-1 OR J kg-1 0C-1 ✓
Allow any appropriate unit that is energymass×termperature
«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.
mass of frozen oil «=27×103130×103»=0.21 «kg» ✓
unfrozen mass «=0.32-0.21»=0.11 «kg» ✓