O-LevelPhysicsThermal Physics5054/22 · May/June 2016 · Q46 Marks
A beaker is filled with water and placed on a hot-plate to boil, as shown in Fig. 4.1. The hot-plate is on top of a balance, which measures the mass of water in the beaker. The liquid boils for a long time. There are bubbles within the boiling water.
- (a)State what is inside each bubble.[1]
- (b)Calculate the specific latent heat of vaporisation of water.[3]
- (c)Explain, using ideas about molecules, how evaporation causes cooling.[2]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2016). The mark or mark type is shown in brackets.
- [1] steam or (water) vapour or water in gaseous form
- [1] (E =) mL numerical or algebraic or 52000-6000 or 46000 (J) seen
- [1] (52000-6000)/20 or 46000/20
- [1] 2300 J/g or 2.3 × 10³ J/kg
- [1] fast moving/energetic molecules escape/evaporate/break bonds/become gas
- [1] leaving slow(er) molecules/less energetic molecules or reducing average (kinetic) energy (of molecules or liquid)
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