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### Reaction Quotient

Posted: Thu Jan 10, 2019 12:21 pm
Only Kp is measured in terms of partial pressure, always? when it comes to a reaction that is homogeneous (gas), but both Kc and even Qc are always measured in terms of concentration?

### Re: Reaction Quotient

Posted: Thu Jan 10, 2019 12:27 pm
When you have a reaction that consists of only gasses, you use their partial pressures in the equation that we learned to find the Kp value. When the reaction consists of compounds in a non gas state (for instance aqueous) you would plug in the concentrations of the products and reactants into the same equation to now find the Kc value (omitting solids and liquids). The p and c just denote what is being used to find the equilibrium constant (partial pressure or concentration).

### Re: Reaction Quotient

Posted: Thu Jan 10, 2019 1:00 pm
I agree that the p or c denotes what unit is being used and that liquids and solids must be omitted, but I believe you can use partial pressure or concentration for gases. Using the ideal gas law, we can convert partial pressure to concentration by calculating concentration=P over R times T since this is an equivalent value it can be used to calculate Kc and Qc even if you were given partial pressures. This is to the best of my knowledge according to what has been taught in class.

### Re: Reaction Quotient

Posted: Fri Jan 11, 2019 3:27 pm
You use Kp or Kc based on the other information they give you, but gases can be found using either method.

### Re: Reaction Quotient

Posted: Fri Jan 11, 2019 3:34 pm
The problem should specify whether or not you have to use Kp or Kc by either telling you, or having units that demonstrate that you should use one or the other. You shouldn't have to guess.

### Re: Reaction Quotient

Posted: Fri Jan 11, 2019 4:44 pm
Yes...