Question

The diagram below shows a cooling curve for a substance X:

(a) State the temperatures 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.

Answer 1

(a) Substance condenses at 150 °C.

(b) 150 °C to 60 °C.

(c) This statement is true.

Explanation:

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, `"Q"_"liquid" > "Q"_"solid"`

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.