Define reaction quotient (Q).

The reaction quotient, often denoted as "Q," is a measure of the relative concentrations of reactants and products in a chemical reaction at a specific point in time. It is used to determine whether a reaction is at equilibrium or if it is proceeding in the forward or reverse direction. The reaction quotient is similar to the equilibrium constant (K), but it is calculated using concentrations of reactants and products that may not necessarily correspond to the equilibrium state.

The general formula for calculating the reaction quotient (Q) for a chemical reaction is:

=
[
]
[
]
[
]
[
]
Q=
[A]
a
[B]
b

[C]
c
[D]
d

​


Where:

[
]
,
[
]
,
[
]
,
[
]
[A],[B],[C],[D] are the concentrations of the reactants A, B, and the products C, D, respectively.
,
,
,
a,b,c,d are the coefficients of the balanced chemical equation for the respective reactants and products.
Comparing the value of Q to the equilibrium constant (K) helps determine the direction in which the reaction is proceeding:

If
=
Q=K, the reaction is at equilibrium.
If
<
QIf
>
Q>K, the reaction tends to proceed in the reverse direction (towards reactants).
It's important to note that the reaction quotient Q is calculated using concentrations at any point during the reaction, not just at equilibrium. This means that Q can provide information about the reaction's progress and whether it's moving towards equilibrium.