Equilibrium Constant Calc
What is Chemical Equilibrium?
In many chemical reactions, the process doesn't just go one way (Reactants turning into Products). Often, it is reversible.
The products can break back down into reactants. Equilibrium is the point where the rate of the forward reaction equals the rate of the backward reaction. It looks like the reaction has stopped, but on a molecular level, the exchange is still happening perfectly evenly.
The Law of Mass Action
To quantify this balance, chemists use the Equilibrium Constant ($K_c$). It is a ratio of Products over Reactants.
- [Square Brackets]: Indicate Concentration in Molarity (mol/L).
- Exponents: The concentration is raised to the power of its stoichiometric coefficient (the number in front of the molecule).
Interpreting Your $K$ Value
The value of $K$ tells you where the balance lies.
| K Value | Meaning | Dominant Side |
|---|---|---|
| K > 1 | Reaction goes forward strongly. | Mostly Products |
| K < 1 | Reaction barely starts. | Mostly Reactants |
| K ≈ 1 | Balanced reaction. | Equal mix |
Only Gases (g) and Aqueous solutions (aq) are included in the $K$ calculation.
Pure Solids (s) and Liquids (l) are ignored because their concentration (density) does not change.
Reaction Quotient ($Q$) vs. $K$
How do you know if a reaction has finished?
- $K$: The ratio at equilibrium (the finish line).
- $Q$: The ratio at any specific moment in time (current status).
If you calculate $Q$ and it is less than $K$, the reaction will continue moving forward (making more products). If $Q$ is greater than $K$, the reaction will move in reverse.
Le Chatelier’s Principle
If you disturb a system at equilibrium (by adding heat, pressure, or more chemicals), the system will shift to counteract the disturbance.
- Add Reactants: Equilibrium shifts Right (makes more Product).
- Add Product: Equilibrium shifts Left (makes more Reactant).
- Increase Pressure: Equilibrium shifts to the side with fewer gas molecules.