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Calorimetry
Rishi is surprised when he sees water boiling at 115o C in a container. Give reasons as to why water can boil at the above temperature.
Water might have some impurities (e.g., salt dissolved in it. Because the boiling point of liquid (Water) increases by the addition of impurities in it.
i) Name a gas caused by the Greenhouse effect.
ii) Which property of water makes it an effective coolant?
i) Carbon-di-oxide
ii) High specific heat capacity.
i) Water in lakes and ponds do not freeze at once in cold countries. Give a reason in support for your answer.
ii) What is the principle of calorimetry?
iii) Name the law on which the principle is based.
iv) State the effect of an increase of impurities on the melting point of ice.
i) The specific latent heat of fusion of ice is sufficiently high (336 J g-1 ) so as to freeze water, a large quantity of heat has to be withdrawn, hence it freezes slowly.
ii) Heat energy lost by the hot body is equal to the heat energy gained by the cold body. This is called the principle of calorimetry. For this, hot and the cold body should be kept in close contact and there is no exchange of heat from the surroundings.
iii) Law of conservation of energy.
iv) The melting of ice decreases by increasing of impurities in it.
A refrigerator converts 100 g of water at 20o C to ice at -10o C in 35 minutes. Calculate the average rate of heat extraction in terms of watts.
Given: Specific heat capacity of ice = 2.1 J g-10o C-1
Specific heat capacity of water = 4.2 J g-10o C-1
Specific Latent Heat of Fusion of ice = 336 J g-1
Mass of water = 100 g = 0.1 kg
Temperature of water = 20o C
Amount of heat extracted to convert water from 20o C to 0o C is, 
= 0.1 x 4200 x (20-0)
= 8400 J
Amount of heat extracted to convert water at 0 degree C to zero degree ice is,
Amount of heat extracted to convert ice at 0o C to ice at -10o C is,
Total heat (Q) = Q1 + Q2+ Q3
= 8400+ 33600+ 2100
= 44100 J
Therefore,
Q = Pt
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