If the composition of the reaction mixture at 400 k is [brcl] = 0.00415 m, [br2] = 0.00366 m, and [cl2] = 0.000672 m, what is the reaction quotient, q?

Q is unlike K value it describes the reaction that is not at equilibrium.

by considering this reaction:

aA + bB⇄ cC

and our reaction is:

Br2 + Cl2 ⇄ 2 BrCl

According to Q low:

Q = concentration of products/concentration of reactants

but this equation in the gaseous or aqueous states only.

∴ Q = [BrCl]^2 / [Br2] [Cl2]

and we have [Br2] = 0.00366 m [Cl2] = 0.000672 m [BrCl] = 0.00415 m

by substitution:

= [0.00415]^2 / ([0.00366] * [0.000672])

∴ Q = 7