Le Chatelier's Principle explains what happens when a balanced system experiences a change.

When a system is stable and something changes—like the amount of stuff in it, the heat, or the pressure—the system will react to try and regain balance. This idea is important when we talk about something called the equilibrium constant, or $K$.

Let’s break it down:

1. Changes in Concentration

• If we add more of a reactant (the starting materials), the balance shifts to create more products.

• If we take away some of the reactants, the balance moves back toward the reactants.

For example, in a reaction like:
$aA + bB \rightleftharpoons cC + dD$
The equation we use for the balance is:
$K = \frac{[C]^c[D]^d}{[A]^a[B]^b}$

2. Changes in Temperature

• For reactions that release heat (called exothermic), raising the temperature lowers $K$.

• For reactions that absorb heat (called endothermic), raising the temperature raises $K$.

For example, in the reaction that creates carbon dioxide ($CO_2$), the value of $K$ usually goes down by about 10% when the temperature rises by 10°C.

3. Changes in Pressure

• If we increase pressure, the balance shifts to the side with fewer gas molecules. This affects how much reactant and product there is, but the value of $K$ only changes if the temperature also changes.

In short, Le Chatelier's Principle helps us understand how reactions can adjust to changes in concentration, temperature, or pressure to maintain balance.