# What is the Concept of Equilibrium?

Concept of Equilibrium

A chemical reaction can operate in the forward direction, which we would draw like this: A moving towards B. Now, a chemical reaction can also move in the backward (or reverse) direction, which we would draw like this: B going into A, because the arrow here demonstrates in which direction the reaction is moving.

We see the reaction moving in two different directions. Now each direction has a rate law. The rate law for the forward direction looks like this, and the rate law for the backward direction looks like this. Now in a closed system, the two reactions which we’ve written up here will reach equilibrium, which is a state where opposing chemical reactions are balanced.

At that point we would draw the chemical reaction like this. This has a double-headed arrow showing that the reaction is moving in both directions, so when this happens the two rates are now equal. Now that the two rates (or the two rate laws) are equal, we can rearrange this right here to yield a constant called the equilibrium constant, which we write like this.

This right here stands for equilibrium constant, we could also just write this as a capital K. Then we rearranged this equation right here to be like this, with B being over A. This is the equation to find the equilibrium constant.

Now the equilibrium condition can be reached from either direction, so when we get to equilibrium, know that it could have happened going from either direction. Again, a chemical reaction can move in both ways, and both directions have a rate law, but when you reach equilibrium they’re now moving in both directions and the rate laws are equal. This equation right here can be rearranged to find the equilibrium constant.