CART Equilibrium and Reaction Rates 1 — Questions and Answers
Question 1: At chemical equilibrium, which of the following is true?
- The reaction has stopped completely
- The concentrations of reactants and products are equal
- The forward and reverse reaction rates are equal (Correct answer)
- All reactants have been consumed
Correct answer: The forward and reverse reaction rates are equal
At equilibrium, the forward and reverse reactions occur at the same rate, so concentrations remain constant but are not necessarily equal.
Question 2: For the reaction: N₂(g) + 3H₂(g) ⇌ 2NH₃(g), the equilibrium constant expression Kc is:
- [NH₃]² / ([N₂][H₂]³) (Correct answer)
- [N₂][H₂]³ / [NH₃]²
- [NH₃] / ([N₂][H₂])
- [NH₃]² / [H₂]³
Correct answer: [NH₃]² / ([N₂][H₂]³)
Kc = [products]^coefficients / [reactants]^coefficients = [NH₃]² / ([N₂][H₂]³).
Question 3: If Kc >> 1 for a reaction, the equilibrium mixture contains mostly:
- Reactants
- Products (Correct answer)
- Equal amounts of both
- Only catalysts
Correct answer: Products
A large Kc value means the equilibrium lies far to the right, favoring product formation.
Question 4: According to Le Chatelier's Principle, increasing the pressure on a gas-phase equilibrium will shift the reaction toward:
- The side with more moles of gas
- The side with fewer moles of gas (Correct answer)
- The endothermic side
- The exothermic side
Correct answer: The side with fewer moles of gas
Le Chatelier's Principle states that increased pressure shifts the equilibrium toward the side with fewer moles of gas to relieve the stress.
Question 5: Adding a catalyst to a reaction at equilibrium will:
- Shift the equilibrium toward products
- Shift the equilibrium toward reactants
- Increase the value of Kc
- Not change the equilibrium position but speed up reaching it (Correct answer)
Correct answer: Not change the equilibrium position but speed up reaching it
A catalyst lowers activation energy for both forward and reverse reactions equally, allowing equilibrium to be reached faster without changing Kc or position.
Question 6: Which factor does NOT affect the value of the equilibrium constant Kc?
- Temperature
- Concentration of reactants (Correct answer)
- Pressure (for some reactions)
- Nature of the reaction
Correct answer: Concentration of reactants
Kc depends only on temperature; changing concentrations shifts the position of equilibrium but does not change the value of Kc.
CART Equilibrium and Reaction Rates 1
At chemical equilibrium, which of the following is true?