What is chemical equilibrium?
A dynamic state where the forward and reverse reactions occur at the same rate, and the concentrations of reactants and products remain constant.
What does it mean that equilibrium is “dynamic”?
Reactions continue in both directions, but overall concentrations don’t change.
What is the equilibrium constant (K)?
A ratio of product concentrations to reactant concentrations at equilibrium, each raised to their coefficients.
What does a large K (>1) indicate?
Products are favored at equilibrium.
What does a small K (<1) indicate?
Reactants are favored at equilibrium.
What is Le Châtelier’s Principle?
When a stress is applied to a system at equilibrium, the system shifts to counteract the stress.
Which states appear in K expressions?
Only gases (g) and aqueous (aq). Solids and liquids are excluded.
What is the reaction quotient (Q)?
A ratio calculated using initial concentrations to predict which direction the reaction will shift to reach equilibrium.
If Q < K, which direction does the reaction shift?
Forward (toward products).
If Q > K, which direction does the reaction shift?
Reverse (toward reactants).
What happens to equilibrium if concentration of a reactant is increased?
Shifts right to use up added reactant.
What happens to equilibrium if temperature is increased in an exothermic reaction?
Shifts left (to absorb heat).
What effect does a catalyst have on equilibrium?
Speeds up reaching equilibrium but does NOT shift equilibrium or change K.
How does increasing pressure affect a gas equilibrium?
Shifts to the side with fewer moles of gas.
Write the K expression for: 2A(g) + B(aq) ⇌ 3C(g)
𝐾 = [C]³ / ([A]² [B])
A reaction has K = 5.0. If Q is calculated to be 9.0, what happens?
Q > K, so the reaction shifts left (toward reactants).
At equilibrium, [N₂] = 0.40 M, [H₂] = 0.60 M, and [NH₃] = 0.20 M. For: N₂ + 3H₂ ⇌ 2NH₃ Calculate K.
𝐾 = [NH₃]² / ([N₂] [H₂]³) = (0.20)² / (0.40)(0.60)³
A + B ⇌ C Initially: [A] = 1.0 M, [B] = 1.0 M, [C] = 0 M At equilibrium: [C] = 0.40 M Calculate K.
A and B each decrease by 0.40 → [A] = [B] = 0.60 𝐾 = (0.40) / ((0.60)(0.60))
For a reaction with a very small K (e.g., 1×10⁻⁷), what can you assume during ICE calculations?
The change in reactant concentration (x) is negligible.
True or false? Changing temperature changes the value of K.
True. Temperature is the only factor that changes K.
What is heterogeneous equilibrium
Reactants and products exist in two or more phases (solid, liquid, gas, aqueous.)
What is homogenous equilibrium
All reactants and products are in the same phase, most commonly gas or liquid
