AP Chemistry Questions on Linking Rate Constants and Equilibrium

📚 Quick Study Guide

• ⚛️ The equilibrium constant, $K$, represents the ratio of products to reactants at equilibrium.
• ⏱️ The rate constant, $k$, describes the speed of a chemical reaction.
• ➡️ For a reversible reaction: $aA + bB \rightleftharpoons cC + dD$
• ⚖️ The equilibrium constant is related to the forward ($k_f$) and reverse ($k_r$) rate constants: $K = \frac{k_f}{k_r}$
• 🌡️ Temperature affects both rate constants and the equilibrium constant.
• 💡 A large $K$ indicates that the products are favored at equilibrium.
• 📈 A large $k_f$ indicates that the forward reaction is fast.

🧪 Practice Quiz

1. Question 1: For the reaction $N_2O_4(g) \rightleftharpoons 2NO_2(g)$, if the forward rate constant is $k_f = 5 \times 10^{-3} s^{-1}$ and the reverse rate constant is $k_r = 2 \times 10^{-3} s^{-1}$, what is the equilibrium constant $K$?
1. 0.4
2. 2.5
3. 10
4. 0.1
2. Question 2: Given the reaction $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$ with an equilibrium constant $K = 4.0$, and a forward rate constant $k_f = 0.08 M^{-2}s^{-1}$, what is the reverse rate constant $k_r$?
1. 0.02 $M^{-2}s^{-1}$
2. 0.32 $M^{-2}s^{-1}$
3. 0.5 $M^{-2}s^{-1}$
4. 0.16 $M^{-2}s^{-1}$
3. Question 3: If increasing the temperature increases both the forward and reverse rate constants, but the equilibrium constant decreases, what can be concluded?
1. The forward reaction is endothermic.
2. The reverse reaction is exothermic.
3. Both reactions are endothermic.
4. Both reactions are exothermic.
4. Question 4: For a reaction where $K = 1$, what can be said about the forward and reverse rate constants?
1. $k_f > k_r$
2. $k_f < k_r$
3. $k_f = k_r$
4. $k_f = 0$
5. Question 5: Consider the reaction $A + B \rightleftharpoons C$. If adding a catalyst increases the rate of both the forward and reverse reactions equally, what happens to the equilibrium constant?
1. Increases
2. Decreases
3. Remains the same
4. Becomes zero
6. Question 6: The equilibrium constant for a reaction is $K = 100$. If the reverse rate constant is $k_r = 0.01 s^{-1}$, what is the forward rate constant, $k_f$?
1. 0.0001 $s^{-1}$
2. 1 $s^{-1}$
3. 100 $s^{-1}$
4. 0.1 $s^{-1}$
7. Question 7: For the elementary step $A \rightleftharpoons B$, the forward activation energy is lower than the reverse activation energy. What does this imply about the equilibrium constant $K$?
1. K > 1
2. K < 1
3. K = 1
4. Cannot be determined