Physics
How much heat energy is released when 500 g of water at 80° C cools down to 0° C and then completely freezes? [specific heat capacity of water = 4.2 J g-1 K-1, specific latent heat of fusion of ice = 336 J g-1].
Answer
Given,
Mass (m) = 500 g
Specific heat capacity of water (c) = 4.2 J g-1 K-1
Specific latent heat of fusion of ice (L) = 336 J g-1
(i) Heat energy released when water lowers it's temperature from 80° C to 0° C
= m x c x change in temperature
Substituting the values in the formula we get,
Q1 = 500 x 4.2 x (80 - 0)
= 500 x 4.2 x 80
= 168 x 103 J
(ii) Heat energy released when water at 0° C changes into ice at 0° C = m x L
Substituting the values in the formula we get,
Q2 = 500 x 336
= 168 x 103 J
From relation,
Q = Q1 + Q2
= 168 x 103 J + 168 x 103 J
= 336 x 103 J
Total heat released = 336 x 103 J
Related Questions
Explain the following —
(a) The surroundings become pleasantly warm when water in a lake starts freezing in cold countries.
(b) The heat supplied to a substance during it's change of state, does not cause any rise in it's temperature.
20 g of ice at 0° C absorbs 10,920 J of heat energy to melt and change to water at 50° C. Calculate the specific latent heat of fusion of ice. Specific heat capacity of water is 4200 J kg-1 K-1.
A molten metal of mass 150 g is kept at it's melting point 800° C. When it is allowed to freeze at the same temperature, it gives out 75,000 J of heat energy.
(a) What is the specific latent heat of the metal?
(b) If the specific heat capacity of metal is 200 J kg-1 K-1, how much additional heat energy will the metal give out in cooling to - 50° C?
A solid metal of mass 150 g melts at it's melting point of 800° C by providing heat at the rate of 100 W. The time taken for it to completely melt at the same temperature is 4 min. What is the specific latent heat of fusion of the metal?