General Chemistry/Chemical Equilibria

Chemical equilibrium occurs when a reversible reaction is occurring backwards and forwards at the same time by the same amount. The ratio of products to reactants, or K is known as the equilibrium constant. For the reaction mA + nB → xC + yD, the equilibrium constant is

$K_{eq}=\frac{[C{]}^m[D{]}^n}{[A{]}^x[B{]}^y}$

Shifts in Equilibrium

Le Chatelier's principle, if you remember, states that a system will adapt to stress. In chemical equilibrium, it is the same. Look at the following examples:

• Pressure - increased pressure will push equilibrium towards the side with less moles of particles.
• Concentration of particles - increase in a particle will push equilibrium to the side that does not contain that particle.
• Temperature - An increase in temperature will push the reaction in a way that is endothermic.
• Addition of ions - If two solutes with the same ion are added to a solution, a compound will precipitate out of the solution. This is known as the common-ion effect.

Acids and Bases

Acids and bases have special ionization constants, which show how they react with water. The acid ionization constant, or K_a, is $\frac{[H_3{0}^{+}][A^{-}]}{[AH]}$, and the base ionization constant K_b is $\frac{[{\text{OH}}^{-}][\text{BH}]}{[\text{B}]}$.

Solubility

The solubility product K_sp of a substance AB is $\frac{[A^{+}][B^{-}]}{[AB]}$.