CHEMISTRY COMMUNITY

Does anyone have any mnemonics to remember the Q and K relationship better?

Hello! I remember it as Q standing for quotient and K standing for constant. You calculate them in the same way, but Q is for anytime in the reaction and K is only for when it is at equilibrium. I hope this helps!

Hello! I remember it as Q standing for quotient and K standing for constant. You calculate them in the same way, but Q is for anytime in the reaction and K is only for when it is at equilibrium. I hope this helps!

A cool one that I heard about before was that when we think of K and Q in alphabetical order and put an arrow in between, the arrow will point to the direction that the reaction is taking place at.

It is also pretty helpful to think that the inequality sign will be open to the side that the reaction favors. So a less-than sign would signify a favoring of the products side of the equilibrium because the sign opens up to the right side. (and vis-versa) =)

Q is the reaction ratio at any point while K is at equilibrium and I think the easiest way is to compare Q and see if it's smaller or larger than K rather than memorizing it.

In AP Chem we had a funny way of remembering that's still stuck with me. So when comparing Q and K we would say that the way the mouth is open shows the direction Q needs to favor in order to reach equal. For example, if Q < K then the forward reaction must be favored in order to reach equilibrium. I know it's silly but it works for me, hope it helps!

Q stands for quotient and K stands for constant. To remember which direction the reaction shifts to, it is helpful to always put the letters in alphabetical order, so K always goes before Q. Think of the greater and less than signs as arrowheads, and depending on the sign (either < or >), you follow the arrowhead and it indicates which direction the reaction shifts to. For example, if K > Q, then the reaction shifts to the right and favors the products. and if K < Q, then the reaction shifts to the left and favors the reactants.

Jessica Luong 3K wrote:Does anyone have any mnemonics to remember the Q and K relationship better?

Hi,
Here is a really nice one I learned in one of the workshop sessions:
When you write it in terms of K first, then the sign points to the direction the reaction proceeds -
if K>Q, reaction proceeds towards the products/favors the forward reaction.
if K<Q, reaction proceeds towards the reactants/favors the reverse reaction.

Hope this was helpful!

Another helpful way to remember Q and K is to plot Q and K on the number line. If Q is ever to the right of K (greater than K), draw an arrow pointing from Q to K. Remember that Q will always want to go to K. An arrow pointing from right to left would mean that the reactants are favored. Likewise, if Q is ever to the left of K (less than K), the arrow will now be pointing from left to right. This would mean that the products are favored.

I don't have a mnemonic for this, but for questions that ask me to compare Q and K, I just think of Q as the "product" and K as the "reactant." If Q (product) is smaller than K (reactant), that means I need more product to achieve equilibrium (to be equal to K), so now I know that forward reaction is favored. I am definitely unsure if this is the right way to approach this, but that's how I made it make sense in my head without having to memorize their relationship since now, I have it logic-based.

In terms of comparing Q and K, I use that if Q<K, I think of it as K moved left to get to Q, following the arrow of the sign, so to go back, it needs to go right, so the reaction favors the products and vice versa.

Rather than trying to memorize it, you should just remember that K is a constant and so Q represents the state of the reaction in relation to that constant. The reaction will always "want" to be in equilibrium and so it will favor either products or reactants in order to achieve the K ratio.
So K<Q than the reaction will favor the reactants.
K>Q the reaction will favor the products or go in the forward reaction.

Since Q and K are calculated the same way, if Q is less than K, this means that DURING the reaction there are more reactants than products because (a greater denominator for reactants means a smaller number). Therefore, in order for the system to reach/return to equilibrium, the greater number of reactants must form products. This means that the forward rxn (R--> P) will be favored and the system will proceed to products and vice versa if q>k.

A mnemonic device wouldn't be too necessary here. Just remember Q is the reaction Quotient for chemical equations that are not at equilibrium and K for the equilibrium K(c)onstant.

I always think of it in terms of playing cards order; the King card is typically higher than the Queen card, so Q<K (where K is greater than Q) goes to the right because that is the "right" order typically seen in card games. (vice versa when Q>K)

I just think of K as a baseline, and everything else that is not K is Q. If Q is bigger than K, it will favor reactants, and if Q is less than K, it will favor products.

Nishka Vipul 1J wrote:

Jessica Luong 3K wrote:Does anyone have any mnemonics to remember the Q and K relationship better?

Hi,
Here is a really nice one I learned in one of the workshop sessions:
When you write it in terms of K first, then the sign points to the direction the reaction proceeds -
if K>Q, reaction proceeds towards the products/favors the forward reaction.
if K<Q, reaction proceeds towards the reactants/favors the reverse reaction.

Hope this was helpful!

This mnemonic was super helpful, thank you

If Q is less than K the reaction is favored to the products and to the right. There are more reactants in this scenario. If Q is greater than K, the reaction is favored to the left and reactant side. There are more products in this scenario.

Q is the [P]/[R] when the reaction is not in equilibrium. When Q<K, it means P is not big enough, so the reaction is now favoring the forward reaction, meaning more P is produced now. When Q = K, the reaction is in equilibrium. When Q>K, it means P is too big, so now the reaction is favoring the reverse reaction, meaning more R is produced now.

When K>Q, the forward reaction is favored. When K<Q, the reverse reaction is favored.
And remember, Q is the value we get when the equation is not at equilibrium, while K is the value we get when we are at equilibrium.

Hello! to simplify things I usually just remember them as one since basically the calculations are the same. but the only difference to remember is that K is for when the reaction is at equilibrium and Q is anything beside that.

Q is anytime and K is at equilibrium. If you can't remember how these 2 influence which way the reaction leans towards, write k before q (alphabetical order) and them put the </> and based on your values, this symbol will tell you which way it leans. An easy trick!