the latent heat of vaporisation of steam is more than that of boiling water. explain why?
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It is a fact that steam causes more severe burns than does hot, or boiling water.
To understand why that is, consider these two things...
1) When you add heat energy to water its temperature progressively rises until the boiling point is reached. At this point heat energy continues to be added, but without a concurrent rise in temperature, which results in steam having a higher energy content than heated water. (By an amount that can be considerable, depending on the conditions).
2) When water evaporates from a liquid to a vapour (a “phase change”) energy is absorbed from its surroundings and there is a cooling effect (the latent heat of vapourization) as anyone who has gone swimming on a windy day has experienced. When water then condenses from its vapour form back into its liquid form (again, a “phase change”) the latent energy that was taken up during evaporation is now released, and heat is produced.
When steam comes into contact with skin the burn is more severe than with water at the same temperature because the steam has more heat energy content to begin with (1 above) and also because that heat energy is suddenly released when the hot steam condenses on the colder skin (2 above).
Once the steam has condensed and released its heat onto, and burned the skin, the resulting water is still at a high temperature and continues to burn the skin just as hot water would.
To understand why that is, consider these two things...
1) When you add heat energy to water its temperature progressively rises until the boiling point is reached. At this point heat energy continues to be added, but without a concurrent rise in temperature, which results in steam having a higher energy content than heated water. (By an amount that can be considerable, depending on the conditions).
2) When water evaporates from a liquid to a vapour (a “phase change”) energy is absorbed from its surroundings and there is a cooling effect (the latent heat of vapourization) as anyone who has gone swimming on a windy day has experienced. When water then condenses from its vapour form back into its liquid form (again, a “phase change”) the latent energy that was taken up during evaporation is now released, and heat is produced.
When steam comes into contact with skin the burn is more severe than with water at the same temperature because the steam has more heat energy content to begin with (1 above) and also because that heat energy is suddenly released when the hot steam condenses on the colder skin (2 above).
Once the steam has condensed and released its heat onto, and burned the skin, the resulting water is still at a high temperature and continues to burn the skin just as hot water would.
Answered by
25
The latent heat of vaporisation of steam is more than that of boiling water because when the water converts into vapours,it gains extra energy in the form of latent heat of vaporisation.
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