Le Chatelier's Principle Quiz
Questions: 16 · 10 minutes
1. For 2NO₂(g) ⇌ N₂O₄(g), the container is expanded at constant temperature. In which direction does the equilibrium shift?
Toward N₂O₄, because expansion favors larger molecules
Toward N₂O₄, because its concentration falls more slowly
Toward NO₂, the side with more moles of gas
There is no shift because expansion affects both gases equally
2. For a reaction at a fixed temperature, the reaction quotient Q is less than the equilibrium constant K. What must occur as equilibrium is approached?
The value of K decreases until it equals Q.
The reaction proceeds in reverse overall, forming more reactants.
The reaction proceeds forward overall, forming more products.
No net change occurs because Q and K describe unrelated quantities.
3. Which change can alter the value of the equilibrium constant, K, for a particular reaction?
Adding more reactant
Changing the container volume
Adding a catalyst
Changing the temperature
4. Consider N₂O₄(g) ⇌ 2NO₂(g). At constant temperature, the container volume is decreased. Which response is expected?
The equilibrium shifts right because the NO₂ concentration initially rises.
The equilibrium constant decreases, favoring N₂O₄.
The equilibrium shifts left, toward the side with fewer moles of gas.
There is no shift because both sides contain only gases.
5. The forward reaction in A(g) ⇌ B(g) releases heat. What happens when the temperature is increased?
The equilibrium shifts toward whichever side has fewer gas molecules.
The equilibrium shifts toward B because particles collide more often.
There is no shift, but both reaction rates become zero.
The equilibrium shifts toward A, favoring the endothermic reverse direction.
6. An inert gas is added to a gaseous equilibrium in a rigid container at constant temperature. What is the usual result?
There is no equilibrium shift because the reacting gases' partial pressures do not change.
The equilibrium shifts toward the side with fewer gas molecules.
The equilibrium shifts toward products because total pressure rises.
The equilibrium constant falls because the inert gas dilutes the mixture.
7. For N₂(g) + O₂(g) ⇌ 2NO(g), what is the effect of decreasing the volume at constant temperature?
The equilibrium shifts right because products have a larger coefficient.
The equilibrium constant increases because pressure increases.
The equilibrium shifts left because reactant gases are compressed first.
There is no pressure-driven shift because both sides have the same total moles of gas.
8. Which statement best describes Le Chatelier's principle?
At equilibrium, reactant and product concentrations must be equal.
A system at equilibrium responds to a disturbance by shifting in a direction that partially opposes it.
Every reversible reaction eventually converts all reactants into products.
An equilibrium always shifts toward the side with fewer chemical species.
9. For C(s) + CO₂(g) ⇌ 2CO(g), extra solid carbon is added while carbon is already present. What is the expected effect at constant temperature and volume?
There is no shift because increasing the amount of a pure solid does not change its activity.
The equilibrium shifts left because adding solid raises the pressure.
The equilibrium shifts right because carbon is a reactant.
The equilibrium constant increases in proportion to the carbon added.
10. For A(aq) + B(aq) ⇌ C(aq), some C is removed from an equilibrium mixture. How does the system respond?
It shifts left to replace A and B.
It does not shift because removing material cannot affect equilibrium.
Its equilibrium constant decreases.
It shifts right to replace some of the removed C.
11. The forward direction of X ⇌ Y is endothermic. How will cooling the equilibrium mixture affect its composition?
It shifts toward Y because cooling favors heat absorption.
It shifts toward X because the exothermic reverse direction is favored.
It shifts toward the side with fewer particles, regardless of enthalpy.
It does not shift because temperature affects rate only.
12. What does a catalyst do when added to a system already at equilibrium?
It speeds up both forward and reverse reactions without changing the equilibrium composition.
It increases the equilibrium constant by stabilizing the products.
It shifts equilibrium toward the side with the lower activation energy.
It temporarily stops the reverse reaction so products can accumulate.
13. For the equilibrium A(g) + B(g) ⇌ C(g), what happens when more A is added at constant temperature and volume?
The equilibrium shifts right, consuming some of the added A and forming more C.
The equilibrium shifts left, producing additional A and B.
The equilibrium constant increases, so more C is formed.
The forward and reverse reactions stop until A is removed.
14. For CaCO₃(s) ⇌ CaO(s) + CO₂(g), some CaO is removed while both pure solids remain present. At constant temperature, what happens to the equilibrium CO₂ pressure?
It rises because the system produces more CaO and CO₂.
It remains unchanged because the amounts of pure solids do not enter the equilibrium expression.
It becomes zero because the product side has been disturbed.
It falls in direct proportion to the amount of CaO removed.
15. For PCl₅(g) ⇌ PCl₃(g) + Cl₂(g), the pressure is lowered by increasing the container volume at constant temperature. Which outcome is expected?
The equilibrium shifts left because all gas concentrations decrease.
The equilibrium shifts right, toward the side with more moles of gas.
There is no shift because the equilibrium constant is unchanged.
The forward and reverse reactions both stop at the lower pressure.
16. In the Haber equilibrium N₂(g) + 3H₂(g) ⇌ 2NH₃(g), ammonia is continuously removed at constant temperature. What effect does this have?
The equilibrium shifts left to increase nitrogen and hydrogen concentrations.
The equilibrium constant increases as ammonia leaves.
The equilibrium shifts right, helping replace the removed ammonia.
The forward reaction stops because one product is missing.