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It says on outline 1 that we have to know when to differentiate between using partial pressure and concentration for the equilibrium constant. How do we know which one to use when there are only gases but they don't give any other information like concentration or partial pressure?
If it doesn't give a hint in the problem whether it is concentration (would give molarities) or partial pressure (atm or bar), you can use either as the ratio represents the same thing: products over reactants.
Usually in the problem will you be given molarity or moles and this will hint that you need to use concentration (Kc) but if the problem gives you atm or barr then you will use the partial pressure (Kp). However, the question should be clear about which one you should be using from the given information.
When they tell you to use partial pressures, you have to use the given information and plug into PV=nRT to find bars/atmospheres. When it's partial concentration, then you would just find moles over liters.
I believe in a problem it has to give you some sort of information that leads towards either using partial pressure or concentration. If it doesnt exactly specify Kc or P of something, but then gives you the moles of one of the final products, then you know that Kc should probably be used.
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