Equilibrium Cheat Sheet: Le Chatelier's Principle & K Manipulation

A set of vocabulary-style flashcards covering Le Chatelier's Principle, K manipulation rules, and the small-x approximation guidelines for General Chemistry.

Le Chatelier's Principle: Adding Reactant or Removing Product

Results in a shift toward the products (right); the value of $K$ remains unchanged.

Le Chatelier's Principle: Adding Product or Removing Reactant

Results in a shift toward the reactants (left); the value of $K$ remains unchanged.

Le Chatelier's Principle: Decreasing Volume (Increasing Pressure)

Results in a shift toward the side with fewer moles of gas; the value of $K$ remains unchanged.

Le Chatelier's Principle: Increasing Volume (Decreasing Pressure)

Results in a shift toward the side with more moles of gas; the value of $K$ remains unchanged.

Le Chatelier's Principle: Increasing Temperature

Results in a shift in the endothermic direction ($\text{heat} = \text{reactant}$) and changes the actual value of $K$.

Le Chatelier's Principle: Decreasing Temperature

Results in a shift in the exothermic direction ($\text{heat} = \text{product}$) and changes the actual value of $K$.

Le Chatelier's Principle: Adding a Catalyst

Results in no shift in equilibrium; the system only reaches equilibrium faster and there is no change to $K$.

Le Chatelier's Principle: Adding Inert Gas at Constant Volume

Results in no shift because partial pressures remain unchanged; the value of $K$ remains the same.

Temperature (Equilibrium Constant)

The only disruption that changes the actual value of $K$; all other disruptions only shift position along the same $K$.

Exothermic Reaction ($-\Delta H$)

A reaction where heat is considered a product, written on the right side of the equation.

Endothermic Reaction ($+\Delta H$)

A reaction where heat is considered a reactant, written on the left side of the equation.

K Manipulation: Reverse the Reaction

The new equilibrium constant is calculated as $K_{new} = \frac{1}{K_{original}}$.

K Manipulation: Multiply Coefficients by n

The new equilibrium constant is calculated as $K_{new} = (K_{original})^n$.

K Manipulation: Add Two Reactions Together

The overall equilibrium constant is the product of the individual constants: $K_{overall} = K_1 \times K_2$.

K Manipulation: Subtract One Reaction from Another

The overall equilibrium constant is the quotient of the individual constants: $K_{overall} = \frac{K_1}{K_2}$.

Small-x Approximation Pre-check

The approximation is likely safe if the ratio of $\frac{\text{initial concentration or pressure}}{K}$ is $\ge 1000$, or $\ge 500$ for a $1:1$ acid–base reaction.

Small-x Approximation Post-check

After solving, the approximation is confirmed if $x$ is $< 5\%$ of the value it was dropped from; otherwise, the full quadratic or cubic must be solved.