Question

Steam of 100°C causes more severe burns than boiling water, because :

• A. Kinetic energy of steam is lesser than water
• B. Steam has latent heat of vaporization
• C. Steam has water vapour in it
• D. All the above

Answer 1

The correct option is B

Steam has latent heat of vaporization

Correct Answer: Option (B) Steam has a latent heat of vaporization.

The explanation of the correct answer:

1. Latent heat of vapourisation: The amount of heat energy required to change a unit mass of water into vapour at the boiling point of water under atmospheric pressure without any change in the temperature.
2. Boiling point: The temperature, at which a liquid boils and changes rapidly into a gas at atmospheric pressure, is called the boiling point of the liquid.
3. The boiling point of water is 100°C.
4. The value of latent heat of vapourisation of water is $22.6x{10}^{5}J/kg.$
5. Therefore, 1 kg of steam at 100°C has $22.6x{10}^{5}J/kg.$ more energy than 1 kg of water at the same temperature.

The explanation for the wrong answer:

1. Option(A) -Kinetic energy of steam is lesser than water: As steam possesses latent heat of vaporization, it has more kinetic energy than water.
2. Option(C)-Steam has water vapour in it: Steam contains water vapour, but it does not affect the rate of burning.

Steam of 100°C causes more severe burns than boiling water, because Option (B) Steam has a latent heat of vaporization.