Chemistry Test Chemical Equilibrium 2 — Questions and Answers
Question 1: The reaction quotient Q is used primarily to:
- Calculate the activation energy of a reaction
- Determine the rate constant at a given temperature
- Predict the direction a reaction will shift to reach equilibrium (Correct answer)
- Measure the enthalpy change of a reaction
Correct answer: Predict the direction a reaction will shift to reach equilibrium
Comparing Q to Kc tells you whether the system needs to shift toward products (Q < Kc), toward reactants (Q > Kc), or is already at equilibrium (Q = Kc).
Question 2: If Q > Kc for a reaction, which direction will the reaction shift to reach equilibrium?
- To the right, producing more products
- To the left, producing more reactants (Correct answer)
- The system is already at equilibrium
- The reaction will stop
Correct answer: To the left, producing more reactants
When Q > Kc, there are too many products relative to equilibrium, so the reaction shifts left (reverse direction) to reduce product concentrations.
Question 3: According to Le Chatelier's Principle, increasing the pressure on the equilibrium N₂(g) + 3H₂(g) ⇌ 2NH₃(g) will:
- Shift equilibrium to the left toward N₂ and H₂
- Shift equilibrium to the right toward NH₃ (Correct answer)
- Have no effect because Kc doesn't change
- Decrease the temperature of the system
Correct answer: Shift equilibrium to the right toward NH₃
Increasing pressure favors the side with fewer moles of gas; the left has 4 moles (1+3) and the right has 2 moles, so equilibrium shifts right toward NH₃.
Question 4: For the exothermic reaction: N₂(g) + 3H₂(g) ⇌ 2NH₃(g) + heat, increasing the temperature will:
- Increase Kc and shift equilibrium toward products
- Decrease Kc and shift equilibrium toward reactants (Correct answer)
- Increase Kc but not shift the equilibrium
- Have no effect on Kc
Correct answer: Decrease Kc and shift equilibrium toward reactants
For an exothermic reaction, heat is a product; adding heat (increasing temperature) shifts the equilibrium left toward reactants, decreasing Kc.
Question 5: Adding an inert (noble) gas at constant volume to a gaseous equilibrium system will:
- Shift the equilibrium toward the side with more moles of gas
- Shift the equilibrium toward the side with fewer moles of gas
- Not affect the equilibrium position (Correct answer)
- Always increase Kp
Correct answer: Not affect the equilibrium position
At constant volume, adding an inert gas increases total pressure but does not change the partial pressures or concentrations of the reactants or products, so equilibrium is unaffected.
Question 6: For the endothermic dissolution: KNO₃(s) ⇌ K⁺(aq) + NO₃⁻(aq), what happens to the solubility of KNO₃ as temperature increases?
- Solubility decreases because more energy disrupts the solution
- Solubility remains unchanged since Ksp is constant
- Solubility increases because the endothermic process is favored by heat (Correct answer)
- Solubility first increases then decreases
Correct answer: Solubility increases because the endothermic process is favored by heat
For an endothermic dissolution, heat acts as a reactant; increasing temperature shifts equilibrium right, increasing solubility and Ksp.
Question 7: Which change to the system PCl₅(g) ⇌ PCl₃(g) + Cl₂(g) will NOT shift the equilibrium position?
- Adding more PCl₅(g)
- Removing Cl₂(g)
- Adding a platinum catalyst (Correct answer)
- Decreasing the volume of the container
Correct answer: Adding a platinum catalyst
A catalyst speeds up both the forward and reverse reactions equally, allowing equilibrium to be reached faster without changing the equilibrium position or Kc.
Chemistry Test Chemical Equilibrium 2
The reaction quotient Q is used primarily to: