Vapor/Gas Compression

[Molly McAndrew 1 1H]

In Dr. Lavelle's example regarding the difference between burns that occur from water in liquid form or as vapor, he mentioned the vapor "compressing" quickly when hitting the arm of someone. It releases more kJ/mol than when water hits the arm of someone, which explains why the burn is worse. However, I wanted to clarify if this is true for all gases. Does this "compression" always take place?

[Mia Hansen 2I]

I think that this would apply to all gases since they have to go through a phase change before becoming a liquid. This transfers more heat on your skin than a liquid would.

[Noa Popko 3I]

I remember from my physics class that compression of gases from pressure is mostly from a thermal contribution, so yes I would assume this applies to all gases in thermochemistry.

[Ivy Nguyen 3I]

Hi! Yes I would assume so because of the phase change that transfers a great amount of heat. I think that "compression" he referred to is that consolidation of molecules as liquid is much more compact than free roaming vapor.

[Andrew Nguyen 1E]

Hi,

In this case, when steam hits a person's arm, it condenses from a gaseous vapor into liquid water. That phase change releases a lot of energy (as seen by water's phase diagram, about 40kJ). Additional energy would be released onto the arm as the hot water cools to reach body temperature. If the person were to have been splashed with boiling water instead, they would not feel the 40kJ of energy from the phase change as the water is already liquid, only the lesser amount of energy released as the water cools.

[Brandon Padilla 2L]

Yes, the same principle should apply for all gases as the same compression phase change processes occur no matter the gas.

[305561744]

So I might just be stupid but I've touched steam many times before, which means the water must be at or over 100C, whereas if I stuck my hand in near boiling water, I'd get burned pretty badly, even though the water is technically cooler. How does this work? Sorry for the random question.