AP Chemistry: Kinetics & Chemical Equilibrium 3 — Questions and Answers
Question 1: For the equilibrium N2(g) + 3H2(g) ⇌ 2NH3(g), what is the correct expression for Kc?
- [NH3]^2 / ([N2][H2]^3) (Correct answer)
- [N2][H2]^3 / [NH3]^2
- [NH3] / ([N2][H2])
- 2[NH3] / ([N2] + 3[H2])
Correct answer: [NH3]^2 / ([N2][H2]^3)
Kc places products over reactants, each raised to its stoichiometric coefficient.
Question 2: If Q < K for a reaction, the system will
- shift toward reactants
- shift toward products (Correct answer)
- already be at equilibrium
- stop reacting
Correct answer: shift toward products
When Q < K, the reaction proceeds forward to form more products until Q = K.
Question 3: For an exothermic reaction at equilibrium, increasing temperature will
- shift toward products and increase K
- shift toward reactants and decrease K (Correct answer)
- shift toward products and decrease K
- have no effect on K
Correct answer: shift toward reactants and decrease K
Adding heat to an exothermic reaction shifts equilibrium toward reactants, lowering K.
Question 4: Decreasing the volume of a gaseous equilibrium system shifts the reaction toward
- the side with more moles of gas
- the side with fewer moles of gas (Correct answer)
- neither side
- the side with heavier molecules
Correct answer: the side with fewer moles of gas
Increasing pressure by reducing volume shifts equilibrium toward fewer gas moles.
Question 5: Which change does NOT alter the value of the equilibrium constant K?
- Changing temperature
- Adding a catalyst (Correct answer)
- Changing the reaction itself
- Reversing the reaction
Correct answer: Adding a catalyst
Only temperature changes K; a catalyst speeds equilibrium but leaves K unchanged.
Question 6: For a reaction with a very large K (K >> 1), the equilibrium mixture contains
- mostly reactants
- mostly products (Correct answer)
- equal reactants and products
- no products
Correct answer: mostly products
A large K means products dominate at equilibrium.
Question 7: Adding an inert gas at constant volume to a gaseous equilibrium will
- shift toward products
- shift toward reactants
- not shift the equilibrium (Correct answer)
- double the value of K
Correct answer: not shift the equilibrium
At constant volume an inert gas does not change partial pressures or concentrations, so no shift occurs.
AP Chemistry: Kinetics & Chemical Equilibrium 3
For the equilibrium N2(g) + 3H2(g) ⇌ 2NH3(g), what is the correct expression for Kc?