K and Q rules

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Alyssa Wilson 2A
Posts: 65
Joined: Fri Sep 28, 2018 12:18 am

K and Q rules

Would it be best if we memorized the rules of when k is large, small, Q>k, Q<k, and Q=k rather than just going through the process of what occurred in the reaction?

Rachana Jayaraman 1H
Posts: 61
Joined: Fri Sep 28, 2018 12:26 am

Re: K and Q rules

Yes, those rules are important to know. The first two will help you answer if the reaction is product or reactant favored, and the last three will help you answer/determine which direction the reaction will proceed. It would be hard to answer these sort of questions without the rules.

whitney_2C
Posts: 74
Joined: Fri Sep 28, 2018 12:28 am

Re: K and Q rules

I definitely think that memorizing those rules is the best way to go because it's hard to know which reaction is being favored without them if you are given concentrations/partial pressures for both products and reactants in a problem. The way that I remember them is actually the opposite of how Lavelle teaches them, I find it easier to remember it as when K > Q, K < Q, and K = Q because if you order it this way then your <, > signs point to the direction that the reaction is going. If this confuses you then just stick to Lavelle's way but I found it easier to remember.

WilliamNguyen_4L
Posts: 65
Joined: Fri Sep 28, 2018 12:28 am

Re: K and Q rules

You can memorize the rules but I think it is also good to understand why the rules are the way they are. If you think of K and Q as ratios and know that Q will be moving towards being equal to K then it's not necessary to memorize the rules. If Q is smaller than K its because the denominator (reactants) is bigger and the numerator (products) is smaller so then the reaction would favor the products in order to increase the value of Q to match K. If Q is bigger than K it's because the denominator is smaller and the numerator is bigger so the reaction would favor the reactants to decrease the value of Q.