For the reaction N₂ + 3H₂ ⇌ 2NH₃ at equilibrium, you suddenly increase the concentration of H₂. What happens to Q and the direction of shift?
AQ increases above K, so the reaction shifts in reverse (toward reactants)
BQ decreases below K, so the reaction shifts forward (toward products)
CK increases to match the new conditions, so there is no shift
DQ equals K still, because equilibrium is self-correcting
Adding a reactant makes Q smaller than K (more reactants relative to products compared to the equilibrium ratio). The system shifts forward to restore Q = K. K itself is unaffected — only temperature changes K.
Question 2 True / False
A reaction at equilibrium has K = 0.001, meaning the reactants are strongly favored. If you add more product, the system will shift forward (toward more product) to maintain equilibrium.
TTrue
FFalse
Answer: False
Adding product increases Q above K, so the system shifts in reverse (toward reactants) to reduce Q back to K. When Q > K the system always shifts backward. The small value of K (0.001) already tells you reactants predominate; adding more product makes the imbalance worse and the reverse shift corrects it.
Question 3 Short Answer
A student claims 'a reaction is at equilibrium when the concentrations of reactants and products are equal.' What is wrong with this statement?
Think about your answer, then reveal below.
Model answer: Equilibrium means the forward and reverse reaction rates are equal, not that concentrations are equal. The equilibrium concentrations are determined by K, which can be very large (products dominate) or very small (reactants dominate).
This is the most common equilibrium misconception. K = [products]/[reactants] can take any positive value. Only when K = 1 are the equilibrium concentrations roughly equal. The defining feature of equilibrium is equal rates, not equal amounts.