Difference between K and Q

[Shanzey]

What is the difference between the equilibrium constant K and the reaction quotient Q? Does K remain constant, while Q is subject to change?

[Elena Bell 1C]

K is the ratio of products to reactants only when the reaction is at equilibrium. Q is the ratio of products to reactants when the reaction is NOT at equilibrium.

[Chem_Mod]

K is an equilibrium constant which is constant for a given temperature. The above answer is mostly correct, just one technicality: it should be noted Q can be measured at any point in the reaction, including at equilibrium, which is when Q=K.

[TimVintsDis4L]

In addition to what everyone else has said regarding Q being used at any point in the equation, it can alos help us solve problems as to which way the reaction is heading.
If Q < K, pre equilibrium, then reaction will proceed forward
( too much reactant , or not enough product) Greater Denominator
If Q = K, at equilibrium
If Q > K, after equilibrium, the reverse reaction will proceed
(too little reactant, too much product) Greater Numerator

[Shail Avasthi 2C]

K is the ratio of the concentrations of the products and reactants when the reaction is at equilibrium. Q is the ratio of the concentrations of the products and reactants at any point in the reaction. Comparing K to Q will tell you which way the reaction will proceed.

[Nicholas_Gladkov_2J]

What is the difference between the equilibrium constant K and the reaction quotient Q? Does K remain constant, while Q is subject to change?

k is the EQUILIBRIUM CONSTANT. Q is just like k (in the sense that you solve for it exactly like k), however it is for when an the concentrations are NOT IN EQUILIBRIUM. Q can change and can be thought of as anything, however k is a constant, but is temperature dependent (one k for every temperature).

[EthanPham_1G]

K is the equilibrium constant for a reaction, a known, experimentally determined value. Q is the reaction quotient which determines the ratio between products and reactants in a reaction. Q can be solved for when the reaction is not in equilibrium. K can only be solved when the reaction is in equilibrium.