Magnitude of the Equilibrium Constant - AP Chemistry

1. What will happen to $K_c$ if the equation coefficients are doubled?

   $K_c$ is squared. When coefficients are multiplied by $n$, $K$ is raised to the $n$th power.

2. For $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$, write the $K_c$ expression.

   $K_c = \frac{[SO_3]^2}{[SO_2]^2[O_2]}$. Products over reactants, raised to stoichiometric coefficients.

3. What happens to $K_c$ if the equation is reversed?

   $K_c$ becomes $1/K_c$. Reversing the equation inverts the equilibrium constant.

4. State how $K_c$ is affected by a change in concentration.

   $K_c$ is unaffected. Equilibrium constant is independent of concentration changes.

5. For the reaction $A \rightleftharpoons B$, if $K_c = 1$, what does this indicate?

   The concentrations of products and reactants are equal. $K_c = 1$ means equal concentrations of A and B at equilibrium.

6. What is the effect on $K_c$ if the temperature increases for an endothermic reaction?

   $K_c$ increases. Higher temperature favors endothermic direction (products).

7. What is true about the equilibrium constant when a reaction reaches equilibrium?

   The rate of the forward and reverse reactions are equal. At equilibrium, the equilibrium constant value remains constant.

8. What is the effect on $K_c$ if the temperature decreases for an endothermic reaction?

   $K_c$ decreases. Lower temperature shifts endothermic equilibrium toward reactants.

9. Predict how $K_c$ will shift if pressure is increased for $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$.

   $K_c$ does not change. Equilibrium constant depends only on temperature, not pressure.

10. If $K_c = 1000$ for a reaction, is it product or reactant favored?

    Product favored. $K > 1$ indicates products are favored at equilibrium.

11. What does a large $K_c$ value indicate about the position of equilibrium?

    The equilibrium favors products. Large $K$ means products are more abundant at equilibrium.

12. If $K_p = 5$ and $K_c = 5$ for a reaction, what is $\triangle n$?

    $\triangle n = 0$. When $K_p = K_c$, the change in gas moles is zero.

13. Determine the $K_c$ expression for $C(s) + CO_2(g) \rightleftharpoons 2CO(g)$.

    $K_c = [CO]^2 / [CO_2]$. Solids are omitted from equilibrium expressions.

14. State how $K_c$ is affected by a change in concentration.

    $K_c$ is unaffected. Equilibrium constant is independent of concentration changes.

15. For the reaction $2A(g) \rightleftharpoons B(g) + C(g)$, write the $K_p$ expression.

    $K_p = \frac{P_B P_C}{P_A^2}$. Partial pressures of products over reactants, raised to coefficients.

16. State the relationship between $K_c$ and the rate constants $k_f$ and $k_r$ for a reaction.

    $K_c = \frac{k_f}{k_r}$. Ratio of forward to reverse rate constants equals equilibrium constant.

17. What is the equilibrium constant $K_c$ for the reverse reaction if the forward reaction has $K_c = 10$?

    $K_c = 0.1$. Reverse reaction constant equals $1/K_{forward}$.

18. What is the $K_c$ expression for the reaction $2H_2(g) + O_2(g) \rightleftharpoons 2H_2O(g)$?

    $K_c = \frac{[H_2O]^2}{[H_2]^2[O_2]}$. Products over reactants, each raised to stoichiometric coefficients.

19. Determine the $K_c$ expression for $CH_4(g) + 2O_2(g) \rightleftharpoons CO_2(g) + 2H_2O(g)$.

    $K_c = \frac{[CO_2][H_2O]^2}{[CH_4][O_2]^2}$. Products over reactants, each raised to their stoichiometric coefficients.

20. What does a small $K_c$ value indicate about the position of equilibrium?

    The equilibrium favors reactants. Small $K$ means reactants are more abundant at equilibrium.

21. If the equilibrium constant $K$ for a reaction is $0.01$, what does this suggest?

    The reaction is reactant-favored. $K < 1$ means reactants predominate at equilibrium.

22. What is the effect on $K_p$ if the temperature increases for an exothermic reaction?

    $K_p$ decreases. Le Chatelier's principle: heat shifts equilibrium toward reactants.

23. What is the equilibrium expression for $K_c$ for the reaction $2SO_3(g) \rightleftharpoons 2SO_2(g) + O_2(g)$?

    $K_c = \frac{[SO_2]^2[O_2]}{[SO_3]^2}$. Products over reactants, raised to stoichiometric coefficients.

24. What is the effect on $K_c$ if the temperature increases for an endothermic reaction?

    $K_c$ increases. Higher temperature favors endothermic direction (products).

25. Determine the $K_c$ expression for $C(s) + CO_2(g) \rightleftharpoons 2CO(g)$.

    $K_c = [CO]^2 / [CO_2]$. Solids are omitted from equilibrium expressions.

26. What is the expression for the equilibrium constant $K_c$ for the reaction $aA + bB \rightleftharpoons cC + dD$?

    $K_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}$. Products raised to coefficients over reactants raised to coefficients.

27. For the reaction $2A(g) \rightleftharpoons B(g) + C(g)$, write the $K_p$ expression.

    $K_p = \frac{P_B P_C}{P_A^2}$. Partial pressures of products over reactants, raised to coefficients.

28. How does $K_c$ change if a catalyst is added to a reaction?

    $K_c$ remains unchanged. Catalysts affect reaction rate but not equilibrium position.

29. Define the equilibrium constant $K$ in terms of partial pressures.

    $K_p = \frac{(P_C)^c(P_D)^d}{(P_A)^a(P_B)^b}$ for gases. Equilibrium constant using partial pressures for gaseous species only.

30. State how $K_c$ is affected by a change in concentration.

    $K_c$ is unaffected. Equilibrium constant is independent of concentration changes.

31. How does changing volume affect $K_c$?

    $K_c$ is unaffected. Volume changes affect concentrations but not $K_c$ value.

32. What is true about $K_c$ if a reaction is at equilibrium?

    The value of $K_c$ is constant. At equilibrium, $K_c$ has a fixed value at constant temperature.

33. For the reaction $A \rightleftharpoons B$, if $K_c = 1$, what does this indicate?

    The concentrations of products and reactants are equal. $K_c = 1$ means equal concentrations of A and B at equilibrium.

34. Identify the equilibrium constant expression $K_p$ for the reaction $aA(g) + bB(g) \rightleftharpoons cC(g) + dD(g)$.

    $K_p = \frac{(P_C)^c(P_D)^d}{(P_A)^a(P_B)^b}$. Uses partial pressures instead of concentrations in the expression.

35. Calculate $K_p$ from $K_c = 50$ for $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$ at 300 K.

    $K_p = 50$. $\Delta n = 0$, so $K_p = K_c$.

36. What is the $K_c$ expression for $CO(g) + 2H_2(g) \rightleftharpoons CH_3OH(g)$?

    $K_c = \frac{[CH_3OH]}{[CO][H_2]^2}$. Products over reactants, each raised to stoichiometric coefficients.

37. Determine the $K_c$ expression for $2NO_2(g) \rightleftharpoons N_2O_4(g)$.

    $K_c = \frac{[N_2O_4]}{[NO_2]^2}$. Products over reactants, with each raised to stoichiometric coefficients.

38. What is the $K_c$ expression for $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$?

    $K_c = \frac{[HI]^2}{[H_2][I_2]}$. Products over reactants, each raised to stoichiometric coefficients.

39. For $2NO(g) + O_2(g) \rightleftharpoons 2NO_2(g)$, provide the $K_c$ expression.

    $K_c = \frac{[NO_2]^2}{[NO]^2[O_2]}$. Products over reactants, raised to stoichiometric coefficients.

40. Determine the $K_c$ expression for $C(s) + CO_2(g) \rightleftharpoons 2CO(g)$.

    $K_c = [CO]^2 / [CO_2]$. Solids are omitted from equilibrium expressions.

41. For $N_2(g) + O_2(g) \rightleftharpoons 2NO(g)$, write the $K_c$ expression.

    $K_c = \frac{[NO]^2}{[N_2][O_2]}$. Products over reactants, raised to stoichiometric coefficients.

42. What is true about the equilibrium constant when a reaction reaches equilibrium?

    The rate of the forward and reverse reactions are equal. At equilibrium, the equilibrium constant value remains constant.

43. What is the expression for $K_c$ for the decomposition of $H_2O(g)$ into $H_2(g)$ and $O_2(g)$?

    $K_c = \frac{[H_2]^2[O_2]}{[H_2O]^2}$. Decomposition: $2H_2O(g) \rightleftharpoons 2H_2(g) + O_2(g)$.

44. What is the relationship between $K_p$ and $K_c$?

    $K_p = K_c(RT)^{\Delta n}$. $\Delta n$ is the change in moles of gas in the reaction.

45. What is the $K_c$ expression for $CO(g) + 2H_2(g) \rightleftharpoons CH_3OH(g)$?

    $K_c = \frac{[CH_3OH]}{[CO][H_2]^2}$. Products over reactants, each raised to stoichiometric coefficients.

46. For the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$, write the $K_c$ expression.

    $K_c = \frac{[NH_3]^2}{[N_2][H_2]^3}$. Products over reactants, each raised to their stoichiometric coefficients.

47. What does a large $K_c$ value indicate about the position of equilibrium?

    The equilibrium favors products. Large $K$ means products are more abundant at equilibrium.

48. For the reaction $A \rightleftharpoons B$, if $K_c = 1$, what does this indicate?

    The concentrations of products and reactants are equal. $K_c = 1$ means equal concentrations of A and B at equilibrium.

49. For the equilibrium $PCl_5(g) \rightleftharpoons PCl_3(g) + Cl_2(g)$, write the $K_c$ expression.

    $K_c = \frac{[PCl_3][Cl_2]}{[PCl_5]}$. Products over reactants, raised to stoichiometric coefficients.

50. What is true about the equilibrium constant when a reaction reaches equilibrium?

    The rate of the forward and reverse reactions are equal. At equilibrium, the equilibrium constant value remains constant.

51. For $N_2(g) + O_2(g) \rightleftharpoons 2NO(g)$, write the $K_c$ expression.

    $K_c = \frac{[NO]^2}{[N_2][O_2]}$. Products over reactants, raised to stoichiometric coefficients.

52. What is the expression for the equilibrium constant $K_c$ for the reaction $aA + bB \rightleftharpoons cC + dD$?

    $K_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}$. Products raised to coefficients over reactants raised to coefficients.

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