The diagram below shows a cooling curve for a substance X:
(a) State the temperature at which the substance condenses.
(b) Mention the temperature range in which the substance is in its liquid state.
(c) State True or False: The amount of heat released when a substance is cooled by 10°C in its liquid state is greater than the heat released when it is cooled by the same amount in its solid state.
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(a) Substance condenses at 150 °C.
(b) 150 °C to 60 °C.
(c) True.
Reason — The amount of heat released when a substance is cooled depends on :
Q = mcΔT
Where:
- Q = heat released
- m = mass of the substance
- c = specific heat capacity
- ΔT = change in temperature
Now, for the same mass and same temperature drop (10°C), the specific heat capacity (c) of a liquid is usually greater than that of its solid form.
So,
Qliquid > Qsolid
Hence, more heat is released when cooling a substance by 10°C in its liquid state than in its solid state, due to higher specific heat capacity.