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(a) State two differences between boiling and evaporation. (2 marks)
(b) State three ways in which loss of heat by conduction is minimized in a vacuum flask. (3 marks)
c) In a certain experiment,50g of dry steam at `100^0C` was directed into some crushed ice at `0^0C`.(Latent heat of vaporization of water is `2.26 times 10^6` J/kg, latent heat of fusion for ice is `3.34 times 10^5`J/Kg and
specific heat capacity of water is `4.2 x 10^3` J/Kg) (i) Quantity of heat lost by steam to change to water at `100^oC`. (2 marks) (ii) Quantity of heat lost by water to cool to `0^oC`.(2 marks) (iii) Mass of ice melted at `0^oC`.(2 marks) (KCSE 2018 paper 1 question 14.)

Answer Text:
1. Boiling
Takes place at fixed temperature.
Takes place throughout the liquid.
It is lowered by decreasing the atmospheric pressure.

2. Evaporation:
Takes place at all temperatures.
Takes place on the surface of the liquid.
It is increased by decreasing the atmospheric pressure.

b).-Having a double wall.
-Having a cork made of an insulator.
-Having a vacuum between the double walls.
c).i) `Q =ML_V = 50/1000 X 2.26 X 10^6 =113000J`
ii) `Q= MCϴ = (50)/(1000) X 4200 X 100 = 21000J.`
iii).Heat lost by steam = Heat gained by the melting ice.\
`ML_V + MCϴ = ML_f`
113000 + 21000 = M X 334000
134000 =334000M
M= 0.4012Kg.