| Date | May 2011 | Marks available | 3 | Reference code | 11M.2.SL.TZ2.3 |
| Level | Standard level | Paper | Paper 2 | Time zone | Time zone 2 |
| Command term | Distinguish | Question number | 3 | Adapted from | N/A |
Question
This question is about internal energy and thermal energy (heat).
Distinguish between internal energy and thermal energy.
Describe, with reference to the energy of the molecules, the difference in internal energy of a piece of iron and the internal energy of an ideal gas.
A piece of iron is placed in a kiln until it reaches the temperature θ of the kiln. The iron is then quickly transferred to water held in a thermally insulated container. The water is stirred until it reaches a steady temperature. The following data are available.
Thermal capacity of the piece of iron = 60JK–1
Thermal capacity of the water = 2.0×103JK–1
Initial temperature of the water = 16°C
Final temperature of the water = 45°C
The thermal capacity of the container and insulation is negligible.
Markscheme
internal energy is the total kinetic and potential energy of the molecules of a body;
thermal energy is a (net) amount of energy transferred between two bodies;
at different temperatures;
the internal energy of the iron is equal to the total KE plus PE of the molecules; the molecules of an ideal gas have only KE so internal energy is the total KE of the molecules;
(i) 60×[θ−45];
(ii) (2.0×103×29)=5.8×104J;(iii) 60×[θ−45]=5.8×104;
θ=1000°C; (allow 1010°C to 3 sig fig)
