The specific latent heat of vapourization of lead is 8.7 × 10^5 {Jkg}₁. This means that 8.7 × 10^5 {J} of thermal energy is required to change

Correct Answer is : 1 kg of molten lead to vapour at constant temperature and pressure.

1 kg of solid lead to vapour at constant temperature and pressure.

1 kg of molten lead to vapour for every degree rise in temperature.

Correct Answer is : 1 kg of molten lead to vapour at constant temperature and pressure.

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WAEC Physics 2023 Paper

Question : 30

Total: 50

8.7 \times 10^5 \mathrm{Jkg}_1

8.7 \times 10^5 \mathrm{J}

of thermal energy is required to change

Solution:

Concept:

Specific latent heat of vaporisation is the energy needed to change

1 \, \text{kg}

of a liquid into vapour without changing its temperature.

Explanation:

For lead, the value is

8.7 \times 10^5 \, \text{J kg}^{-1}

This means

8.7 \times 10^5 \, \text{J}

of thermal energy is required to convert exactly

1 \, \text{kg}

of molten (liquid) lead into vapour.

The change happens at constant temperature and pressure, so no temperature rise is involved.

Therefore, option B correctly matches this definition.

Answer:

1 \, \text{kg}

of molten lead to vapour at constant temperature and pressure.

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