Question

Alka was making tea in a kettle. Suddenly she felt intense heat from the puff of steam gushing out of the spout of the kettle. She wondered whether the temperature of the steam was higher than that of the water boiling in the kettle. Explain.

Answer 1

• The temperature of the steam is same as that of water boiling inside the kettle.
• But the steam carries more heat, as it contains latent heat of vaporization. That is a lot of heat.
• When the steam touches the body, it condenses, then the latent heat of vaporization touches the body.
• The boiling point of water is 100°C. The temperature of boiling water does not rise instead of continuous supply of heat, as the extra heat is supplied to the water is used to turn water into steam.
• Hence, steam has a lot of latent heat which can cause severe burn.
• Latent heat of vaporization for a liquid is defined as the quantity of heat required in Joules to convert 1 Kilogram of liquid into vapor without any change in temperature.
• Latent heat of vaporization of a liquid is 22.5 × 10⁵ J/kg.

That’s why Alka felt intense heat from the puff of steam gushing out of the spout of the kettle.