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K vs. Q

Posted: Sat Jan 19, 2019 8:08 am
by hazelyang2E
Could someone please explain to me the difference between K and Q, the reaction quotient? I'm just a little confused on the differences between the two as they are essentially calculated in the same way. Thank you!

Re: K vs. Q

Posted: Sat Jan 19, 2019 9:50 am
by klarratt2
Both K and Q have the same equation ([products]/[reactants]).

K is the equilibrium constant. You use the equilibrium concentrations of the products and reactants to find it.

Q is the reaction quotient. For Q, the reaction is not at equilibrium. You use Q to compare the current reaction to the reaction when it is at equilibrium. By doing this, you can tell whether the concentration of reactants or products is greater and in which direction the reaction will proceed.

For example, if Q>K, it means that at that moment, there is a greater concentration of products than reactants (compared to when the reaction is at equilibrium). This means that the reaction will proceed to the left to make more reactants.

On the other hand, if Q<K, there is a greater concentration of reactants than products, which means the reaction will proceed to the right to make more products.

Re: K vs. Q

Posted: Sat Jan 19, 2019 10:36 am
by Sean Reyes 1J
K is the equilibrium constant, meaning to calculate it, you must use equilibrium concentrations/partial pressures.
Q is the reaction quotient and is calculated the same way as K, except using non-equilibrium concentrations/partial pressures.
In comparing the two values (K and Q), you can find which direction a reaction will proceed in. For example, if K>Q, then the reaction will favor the creation of products and will thus favor the forward reaction.
Hope this helps !

Re: K vs. Q

Posted: Sun Jan 20, 2019 2:51 pm
by Simmi Diwanji 2B
Q is very similar to K in that they are calculated the same way, but Q calculates the ratio of products/reactants at any given time, usually at initial concentrations or partial pressures. It is used to compare a reaction to its equilibrium constant K to see what side the reaction favors.

Re: K vs. Q

Posted: Sun Jan 20, 2019 5:08 pm
by 904914909
K is the equilibrium constant, the proportion of products to reactants when the reaction is at equilibrium. Q is the reaction quotient and it show the proportion of products to reactants when the reaction is not at equilibrium.

Re: K vs. Q

Posted: Sun Jan 20, 2019 5:12 pm
by Cienna Henry 1J
It is also important to note that Q can be equal to K. In this case, the reaction is at equilibrium.