Solvents absence in equilibrium constant eq

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Felicia Wei 1B
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Joined: Wed Nov 18, 2020 12:28 am

Solvents absence in equilibrium constant eq

Postby Felicia Wei 1B » Wed Jan 06, 2021 11:50 am

In the lecture, this was covered but I'm not fully sure about the explanation as to why solvents aren't written in the equilibrium constant equation. Is it that the solvent is in excess and therefore in both the products and reactants so they cancel out? Is there anything else I need to know?

Stuti Pradhan 2J
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Re: Solvents absence in equilibrium constant eq

Postby Stuti Pradhan 2J » Wed Jan 06, 2021 12:00 pm

Solvents aren't written in the equilibrium constant equations because there tends to be such an excess of solvent, that even if there was a small change, it is insignificant. For example, if there are 1 million bees and 10 more are added, we still say there are about 1 million bees because the change is so minor. This excess of solvent would therefore end up on both sides and cancel in the equilibrium constant equation.

For liquids other than water, they are typically very dilute and can essentially be considered to be water, so they are not included either.

Hope this helps!

Isabella Chou 1A
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Re: Solvents absence in equilibrium constant eq

Postby Isabella Chou 1A » Wed Jan 06, 2021 12:30 pm

To add on, when writing the Kc expression, even if you included the concentration of solvent as a product in the numerator and the concentration of solvent as a reactant in the denominator, these concentrations would be so similar in value that they would end up canceling (dividing them would give a number very close to 1), so the change in solvent concentration is considered insignificant.

Vanshika Bhushan 1A
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Re: Solvents absence in equilibrium constant eq

Postby Vanshika Bhushan 1A » Wed Jan 06, 2021 2:51 pm

Pure solids or liquids are excluded from the equilibrium expression because their effective concentrations stay constant throughout the reaction.


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