# Equilibrium constant

#### carrera901

Hey all

I have trouble understanding something about the Equilibrium constant.

If you have this chemical equilibrium:

pA + qB $$\Leftrightarrow$$ rC + sD

You can define the equilibrium constant with

[C]r [D]s
______ = K
[A]p q

I don't understand why you multiply the concentrations, can anyone explain?

I'm very sorry if this is a very dumb question and sorry for my english

And no idea why the arrow goes up

#### Borek

Mentor
Use LaTeX

$$K = \frac {[A]^p^q} {[C]^r[D]^s}$$

Are you asking why it is defined this way? Because it was defined this way

Are you asking why it works? That's a much better question. As a first approximation you may assume that's because to react molecules have to collide and amount of collisions is directly proportional to the concentration.

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