As a demonstration of the sheer magnitude of the latent heat of vaporization, La

Question

As a demonstration of the sheer magnitude of the latent heat of vaporization, Last year I showed a demonstration of how long it takes water to rise to the boil from room temperature compared to the time it takes the same amount of water to be converted to steam. In doing so, I got a nasty burn on my finger from the steam. Why do burns from steam lead to a worse burn than from boiling water? To see this, consider the following: When steam condenses on your skin, it drops in temperature from 100 ºC to 40ºC in a very short amount of time. How much heat is removed from 0.001 kg of steam at 100ºC in bringing it down to 40ºC? Compare this to the amount of heat removed from the same amount of boiling water at 100ºC reducing to 40ºC. FYI, 0.001 kg of water is ~20 drops.

Explanation / Answer

When water is cooled from 100 to 40 degree it will release

H= 1 * 4.2 * (100-40) = 252 J

When heat is released from steam we get

H = Hlatent + H cooling = 334 + 252 J = 586 J

Hence the burn is severe in Steam burn.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.