A student makes a diagram of the molecules in a liquid, as shown in Fig. 10.1. The beaker shown in Fig. 10.2 contains pure water at a temperature of 80°C. A thermometer, initially at room temperature, is placed in the air just above the water. The reading on the thermometer starts to increase slowly. The heater placed underneath the beaker has a power of 200W. The mass of water in the beaker is initially 100g. The water in the beaker is heated for a time of 120s. During this time, the temperature of the water in the beaker rises from 80°C to 100°C and then the water boils. At the end of this time, the mass of water in the beaker is 95 g. The specific heat capacity of water is 4.2J/(g°C). The specific latent heat of vaporisation of water is 2250J/g. Calculate the thermal energy (heat) [Figure 10.1] [Figure 10.2]

1. (a)Suggest two ways in which the student's diagram does not show the positions and motion of the molecules accurately.[2]
2. (b)(i)Describe what happens during evaporation.[1]
3. (b)(ii)Explain why evaporation has a cooling effect on the liquid.[2]
4. (c)(i)Explain how convection in the air causes the reading on the thermometer to increase.[1]
5. (c)(ii)A heater is placed underneath the beaker and the water boils vigorously to produce steam. The thermometer reading increases quickly. Explain how the water in the gas state gives thermal energy (heat) to the thermometer.[2]
6. (c)(iii) 1.produced by the heater in 120s,[2]
7. (c)(iii) 2.used to warm the water from 80°C to 100°C,[2]
8. (c)(iii) 3.used to reduce the mass of water in the beaker,[2]
9. (c)(iii) 4.produced by the heater that is not transferred to the water.[1]

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