K expression

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Donna Nguyen 2L
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Joined: Sat Aug 24, 2019 12:17 am

K expression

Postby Donna Nguyen 2L » Thu Jan 09, 2020 12:37 am

Why are solids and liquids not included in the K expression?

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Joined: Sat Aug 17, 2019 12:17 am

Re: K expression

Postby Diana_Diep2I » Thu Jan 09, 2020 12:55 am

There technically isn't a concentration for a solid b/c it doesn't make sense. We're measuring the change in concentration of compounds in K. As for pure liquids, the concentration isn't changed much. The change is negligible it's practically 0. So if we put something like the concentration of water on both sides of the reaction, it's going to appear in the numerator and denominator in the expression and it would be cancelled out anyways.

Brooke Yasuda 2J
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Re: K expression

Postby Brooke Yasuda 2J » Thu Jan 09, 2020 10:23 am

so liquids that act as solvents can be involved in a reaction, such as dissolving an ionic compound. However, because the liquid such as water is the solvent, there are so many more water molecules per molecule of the ionic compound, that there is water on both sides of the equilibrium constant equation and would cancel out.

Bryce Barbee
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Re: K expression

Postby Bryce Barbee » Thu Jan 09, 2020 11:13 am

When looking at it in a pressure sense, I saw something that was explaining it by talking about how the pressure of a gas can be changed and measured better than the pressure of solids and liquids.

Can someone please explain to me how to ask a question on Chem Community. I cannot figure it out. Thanks

Joanne Lee 1J
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Re: K expression

Postby Joanne Lee 1J » Thu Jan 09, 2020 1:08 pm

Solids and liquids are not counted in the equilibrium constant because the concentration does not change in between the products or reactants.

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Re: K expression

Postby vanessas0123 » Thu Jan 09, 2020 3:15 pm

Solids and liquids don't have concentrations nor partial pressures.

Jada Brown 2H
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Joined: Sat Aug 17, 2019 12:15 am

Re: K expression

Postby Jada Brown 2H » Thu Jan 09, 2020 3:21 pm

Solids are not included because you can't have a concentration of a solid. Liquids aren't included because they often act as a solvent whose concentration changes so minimally that it isn't worth noting.

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