Q. 194.9( 12 Votes )
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. Comment.
Particles in steam, that is, water vapour at 373 K (1000 C) have more energy than water at the same temperature. This is because particles in steam have absorbed extra energy in the form of latent heat of vaporisation*. When steam tends to cool down, first steam condenses to water on skin and then water tends to cool down to the temperature of the skin. This is the reason why Alka felt intense heat from the puff of steam.
* Latent heat of vaporisation: When a liquid is changed into vapour phase, then the energy absorbed in this process is called the latent heat of Vapourisation. The heat of vaporization of water is about 2,260 kJ/kg.
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