# A2 equilibrium constant question

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#1
for homogeneous reaction if all the substances in the reaction is eg solid do we use all of them in finding the Ka

and for heterogeneous reaction, if all is liquid and 1 solid do we leave out the solid, or if all was gas do we leave out liquid?
and if so why do we leave out solid and liquid ?
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1 month ago
#2
I quote from the internet source: "For substances that are liquids or solids, the standard state is just the concentration of the substance within the liquid or solid. Because the molar concentrations of pure liquids and solids normally do not vary greatly with temperature, the ratio of the molarity to the standard state for substances that are liquids or solids always has a value of 1." The number of "1" is called activity and this term usually appeared in physical and analytical chemistry.
https://chem.libretexts.org/Bookshel...ms_of_Pressure
It gives some examples to demonstrate the exclusion cases.
Why do we write the activity of solids and pure liquids in equilibrium constants at standard conditions as 1?
https://socratic.org/questions/59fb1d0b7c014970f4c719e6
The concept of activity is not in A level and just for interest.
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1 month ago
#3
Ka is for acids. Acids are AQUEOUS SOLUTIONS. If you are looking for an example with a liquid then I am sure your teacher did Kw with you, the Kw expression contains a liquid (water). Its concentration is CONSTANT and is incorporated into the equilibrium constant. Homogeneous means all in the same state, so if 1 substance is a solid then they all are. Equilibrium constants are used for solutions and gases. The concentration of solids DO NOT change during a reaction (the only way I can think of to measure concentration of a solid is density/Mr), you may use a solid up in a reaction but its concentration remains constant and so will be included in any equilibrium constant.

Look on google, I would to see what you find, but as far as I know equilibrium constants are for gases and solutions
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