Reaction Constant P

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Cynthia Ulloa
Posts: 52
Joined: Fri Feb 23, 2018 3:02 am

Reaction Constant P

Postby Cynthia Ulloa » Sat Feb 02, 2019 6:33 pm

Can someone briefly re-explain what would happen to our internal energy when our P is constant and the moles of a gas change versus when our P is constant and solids and liquids are involved? I more or less understand what the Professor said at Friday's lecture, but I just want clarification.

Jonas Talandis
Posts: 60
Joined: Fri Sep 28, 2018 12:16 am

Re: Reaction Constant P

Postby Jonas Talandis » Sat Feb 02, 2019 7:09 pm

I think it's a similar concept of not including solids or liquids in equilibrium expressions. The gas is the only phase that is able to affect volumetric change. But idk lol

Matthew Mar 1J
Posts: 61
Joined: Fri Sep 28, 2018 12:15 am
Been upvoted: 1 time

Re: Reaction Constant P

Postby Matthew Mar 1J » Sat Feb 02, 2019 9:10 pm

The formula for internal energy is U = q+w, but when pressure is constant w = -P/\V, which gives us /\U = q - P/\V.
If there's a gas involved, we can use the ideal gas law PV = nRT to get /\U = q - /\nRT, where /\n is the change in moles. According to this equation, when moles increase, internal pressure will decrease for a system with gas under constant pressure.
Solids and liquids have a set volume so there won't be any /\V.

Margaret Akey
Posts: 80
Joined: Fri Sep 28, 2018 12:18 am

Re: Reaction Constant P

Postby Margaret Akey » Sat Feb 02, 2019 10:53 pm

the biggest difference is that in solids and liquids there is no volume change!!

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