Solids and Liquids [ENDORSED]

[McKenna_4A]

Why exactly aren't solids and liquids included in equilibrium expressions?

[Fiona Latifi 1A]

Solids and liquids are considered pure substances. Therefore they have an activity value of 1. So in equilibrium expressions, we do not include them because their value would just be 1.

[Wendy 1E]

It does not make sense for solids to have a concentration since the units for concentration are mol/L. For liquids, the change in concentration is insignificant because the change is very small.

[Rebecca Remple 1C]

I agree with Fiona and McKenna! However, I am still confused on the matter of liquids being pure substancews. Can someone clarify how a liquid is different from an aqueous solution and give examples of each? From what I understand, aqueous solutions have a solute and solvent, and liquids do not. Can someone explain this a little more? Thank you!

-Rebecca

[KHowe_1D]

They aren't calculated in equilibrium expressions because they are considered pure substances which don't affect the equilibrium concentration.

[Donavin Collins 1F]

Since solids and liquids are considered pure substances, they wouldn't affect the equilibrium concentration.

[Kayla Maldonado 1C]

I agree with Fiona and McKenna! However, I am still confused on the matter of liquids being pure substancews. Can someone clarify how a liquid is different from an aqueous solution and give examples of each? From what I understand, aqueous solutions have a solute and solvent, and liquids do not. Can someone explain this a little more? Thank you!

-Rebecca

Liquidity is a state of matter where it can flow, takes the shape of its container, and has surface tension. Aqueous is a solution where water is the solvent. “Aqueous” means “similar to,” “related to,” or “dissolved in water.”

[805394719]

Solids and liquids are excluded from the equilibrium constant expression because their concentration equals their density divided by their molar mass. Since the density of a pure solid or liquid is constant regardless of how much solid or liquid is present, their concentrations stay constant throughout the reaction. Because their concentration does not change, they are not included in the equilibrium expression.

[Rebecca Remple 1C]

I agree with Fiona and McKenna! However, I am still confused on the matter of liquids being pure substancews. Can someone clarify how a liquid is different from an aqueous solution and give examples of each? From what I understand, aqueous solutions have a solute and solvent, and liquids do not. Can someone explain this a little more? Thank you!

-Rebecca

Liquidity is a state of matter where it can flow, takes the shape of its container, and has surface tension. Aqueous is a solution where water is the solvent. “Aqueous” means “similar to,” “related to,” or “dissolved in water.”

Hi Kayla,

Thank you so much for your explanation! It helps a lot :) Good luck on the test and have a great weekend!

-Rebecca

[Sanjana Borle 2K]

Also for solids and liquids, pressure does not affect them, in other words they can't be compressed further, whereas gases can.

[Matthew Tsai 2H]

Regardless of conditions, solids and liquids will be pure substances with a concentration of 1, so for calculating the equilibrium constant of a reaction, they would have no effect.