Gas Expansion  [ENDORSED]

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Thu Uyen Tran 1B
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Joined: Fri Sep 29, 2017 7:05 am

Gas Expansion

Postby Thu Uyen Tran 1B » Sun Jan 28, 2018 1:27 am

Can someone explain to me why even though deltaU=0, a gas can still expand?

Nora Sharp 1C
Posts: 53
Joined: Sat Jul 22, 2017 3:00 am

Re: Gas Expansion

Postby Nora Sharp 1C » Sun Jan 28, 2018 1:35 am

A gas can still expand without internal energy changing because deltaS, the maximum number of positional states (entropy) of a system, is going up. If we assume that the gas is expanding into a vacuum at constant temperature (deltaU is zero), its expansion is still favored because deltaS is positive. This is in line with the second law of thermodynamics: the total entropy of an isolated system will increase.

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Re: Gas Expansion

Postby miznaakbar » Sun Jan 28, 2018 1:51 pm

A gas would want to reach its maximum entropy because doing so maximizes the number of positions/states it can occupy. Thus, even without any change in heat, work, or internal energy, the gas will spontaneously expand (volume increase) because it is the most favorable possible state. Hope this helps.

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Re: Gas Expansion  [ENDORSED]

Postby 204932558 » Sat Feb 03, 2018 10:13 am

DeltaU = deltaQ + work. When the gas expands, it does work to the surrounding. But that loss of internal energy can be made up by the heat flowing into the system. So overall, U can stay unchanged.

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