Reaction Quotient (Q) Examples: Real-World Applications

🧪 Quick Study Guide

• ⚖️ The reaction quotient ($Q$) predicts the direction a reversible reaction will shift to reach equilibrium.
• 📝 $Q$ uses the same formula as the equilibrium constant ($K$), but concentrations are not necessarily at equilibrium.
• ➗ For the reaction $aA + bB \rightleftharpoons cC + dD$, the reaction quotient is: $Q = \frac{[C]^c[D]^d}{[A]^a[B]^b}$
• 📈 If $Q < K$, the reaction will proceed forward (more products).
• 📉 If $Q > K$, the reaction will proceed in reverse (more reactants).
• 🎯 If $Q = K$, the reaction is at equilibrium.
• 🌡️ Temperature affects both $Q$ and $K$.

Practice Quiz

1. Which of the following statements is true regarding the reaction quotient, Q?
   1. A) Q is always equal to K at equilibrium.
   2. B) Q can only be calculated at equilibrium.
   3. C) Q predicts the direction a reaction will shift to reach equilibrium.
   4. D) Q is independent of temperature.
2. For the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$, what is the correct expression for Q?
   1. A) $Q = \frac{[N_2][H_2]}{[NH_3]}$
   2. B) $Q = \frac{[NH_3]^2}{[N_2][H_2]^3}$
   3. C) $Q = \frac{[N_2][H_2]^3}{[NH_3]^2}$
   4. D) $Q = \frac{[NH_3]}{[N_2][H_2]}$
3. If Q > K for a reversible reaction, which direction will the reaction shift?
   1. A) Forward (towards products)
   2. B) Reverse (towards reactants)
   3. C) No shift (at equilibrium)
   4. D) Impossible to determine
4. In the Haber-Bosch process ($N_2 + 3H_2 \rightleftharpoons 2NH_3$), if the current concentrations result in Q < K, what should be done to maximize $NH_3$ production?
   1. A) Increase the temperature
   2. B) Decrease the pressure
   3. C) Add more $N_2$ and $H_2$
   4. D) Remove $NH_3$
5. Consider the reaction: $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$. At a certain point, $[SO_2] = 0.5 M$, $[O_2] = 0.2 M$, and $[SO_3] = 0.4 M$. What is the value of Q?
   1. A) 0.8
   2. B) 1.6
   3. C) 3.2
   4. D) 6.4
6. For the esterification reaction: $CH_3COOH + CH_3OH \rightleftharpoons CH_3COOCH_3 + H_2O$. If you start with 1M of each reactant and no products, what happens to Q initially?
   1. A) Q = 1
   2. B) Q > 1
   3. C) Q = 0
   4. D) Q < 0
7. A reaction has a K value of 10. If the current concentrations give a Q value of 5, how will the reaction proceed to reach equilibrium?
   1. A) The reaction is already at equilibrium.
   2. B) The reaction will proceed in the reverse direction.
   3. C) The reaction will proceed in the forward direction.
   4. D) The reaction will stop completely.