Representations of Equilibrium - AP Chemistry

1. What is the relationship between $K_p$ and $K_c$ for a gas-phase reaction?

   $K_p = K_c(RT)^{\Delta n}$, where $\Delta n$ is the change in moles of gas. Accounts for the pressure difference when converting between concentration and pressure equilibrium constants.

2. Identify the condition when $Q = K_c$ in a chemical reaction.

   The system is at equilibrium. When the reaction quotient equals the equilibrium constant, rates are balanced.

3. Identify the principle that explains the effect of concentration changes on equilibrium.

   Le Chatelier's Principle. States that systems respond to stress by shifting to counteract the disturbance.

4. What is the unit of $K_c$ for the reaction $N_2 + 3H_2 \rightleftharpoons 2NH_3$?

   $M^{-2}$. Units are $\frac{M^2}{M \cdot M^3} = M^{-2}$ based on the concentration terms.

5. What happens to equilibrium when an inert gas is added at constant volume?

   No change in equilibrium position. At constant volume, adding inert gas doesn't change partial pressures of reactants.

6. What is the effect of decreasing volume on the equilibrium of a reaction with gases?

   Equilibrium shifts toward the side with fewer moles of gas. System reduces stress by shifting to the side that occupies less volume.

7. State the effect of removing heat from an endothermic reaction.

   Shifts equilibrium to the left (toward reactants). Heat is treated as a reactant in endothermic reactions, so removing heat shifts left.

8. What does a $K_{eq} = 1$ indicate about a reaction?

   Neither reactants nor products are favored. Equal concentrations of reactants and products at equilibrium when $K_{eq} = 1$.

9. What is the effect of adding more $H_2O$ to a gaseous equilibrium system?

   No effect if $H_2O$ is not a reactant or product in gaseous form. Liquid water doesn't affect gas-phase equilibria unless it participates as a gas.

10. What is the effect of adding more $N_2$ to the equilibrium $N_2 + 3H_2 \rightleftharpoons 2NH_3$?

    Equilibrium shifts right, producing more $NH_3$. Adding reactants increases their concentration, driving the reaction forward.

11. What is the general effect of pressure increase on a gaseous equilibrium?

    Shifts towards the side with fewer moles of gas. System responds to pressure increase by reducing the total number of gas molecules.

12. State the effect of temperature increase on an exothermic reaction's equilibrium position.

    Shifts the equilibrium to the left (toward reactants). Heat is treated as a product in exothermic reactions, so adding heat shifts left.

13. What is $Q$ for the reaction $2A \rightleftharpoons B + C$ if $[A]=2$, $[B]=1$, $[C]=3$?

    $Q = \frac{[B][C]}{[A]^2} = \frac{1 \times 3}{2^2} = 0.75$. Using $Q = \frac{[B][C]}{[A]^2}$ with the given concentrations.

14. Identify the factor that does not affect the value of $K_c$ for a reaction.

    Pressure changes do not affect $K_c$.. Only temperature changes affect $K_c$; pressure and concentration changes don't.

15. What is the $K_c$ expression for $H_2 + I_2 \rightleftharpoons 2HI$?

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

16. How does the addition of a common ion affect the solubility of a salt?

    Solubility decreases due to the common ion effect. Increased concentration of a common ion shifts equilibrium toward the undissolved solid.

17. How do you determine the direction of the shift if $Q > K_c$?

    The reaction shifts left towards reactants. When $Q > K_c$, there are too many products relative to equilibrium.

18. What is the expression for $K_{sp}$ of $CaF_2$?

    $K_{sp} = [Ca^{2+}][F^-]^2$. Products of ion concentrations raised to their stoichiometric coefficients for the dissolution.

19. What is the Le Chatelier's response to the removal of a product from the equilibrium mixture?

    Equilibrium shifts right to produce more product. Removing products decreases $Q$, making the forward reaction more favorable.

20. What is the relationship between $K_p$ and $K_c$ for a gas-phase reaction?

    $K_p = K_c(RT)^{\Delta n}$, where $\Delta n$ is the change in moles of gas. Accounts for the pressure difference when converting between concentration and pressure equilibrium constants.

21. What is the significance of $K_{eq} > 1$ for a chemical reaction?

    Products are favored at equilibrium. Large equilibrium constants mean the forward reaction is thermodynamically favorable.

22. What does a very small $K_c$ value indicate about a reaction?

    The reaction favors reactants at equilibrium. Small $K_c$ values mean the equilibrium position lies far to the left.

23. What is the effect of decreasing volume on the equilibrium of a reaction with gases?

    Equilibrium shifts toward the side with fewer moles of gas. System reduces stress by shifting to the side that occupies less volume.

24. What is the effect on equilibrium when a solid reactant is added?

    No effect on the equilibrium position. Solid concentrations don't appear in equilibrium expressions and don't affect position.

25. How does $K_{eq}$ relate to the spontaneity of a reaction?

    $K_{eq} > 1$ indicates a spontaneous reaction. Large equilibrium constants indicate thermodynamically favorable forward reactions.

26. What is the result of tripling the volume of a gaseous equilibrium system?

    Shifts towards the side with more moles of gas. Increasing volume decreases pressure, favoring the side with more gas molecules.

27. Identify the effect of pressure decrease on equilibrium with equal moles of gas on both sides.

    No change in equilibrium position. When $\Delta n = 0$, pressure changes don't affect equilibrium position.

28. What is the expression for $K_{sp}$ of $CaF_2$?

    $K_{sp} = [Ca^{2+}][F^-]^2$. Products of ion concentrations raised to their stoichiometric coefficients for the dissolution.

29. What does a $K_{eq} = 1$ indicate about a reaction?

    Neither reactants nor products are favored. Equal concentrations of reactants and products at equilibrium when $K_{eq} = 1$.

30. How does the addition of a non-reactive gas affect the equilibrium position?

    No effect on the equilibrium position. Inert gases don't participate in the reaction and don't change partial pressures.

31. Describe how a catalyst affects the position of equilibrium.

    A catalyst does not affect the position of equilibrium. Catalysts only speed up the rate of reaching equilibrium but don't change the final position.

32. In which direction will equilibrium shift when $K_c < Q$?

    Shifts left, towards reactants. When $Q > K_c$, there are excess products, so the reaction proceeds backward.

33. What is the relationship between $K_p$ and $K_c$ for a gas-phase reaction?

    $K_p = K_c(RT)^{\Delta n}$, where $\Delta n$ is the change in moles of gas. Accounts for the pressure difference when converting between concentration and pressure equilibrium constants.

34. How does the addition of a non-reactive gas affect the equilibrium position?

    No effect on the equilibrium position. Inert gases don't participate in the reaction and don't change partial pressures.

35. How does the addition of a common ion affect the solubility of a salt?

    Solubility decreases due to the common ion effect. Increased concentration of a common ion shifts equilibrium toward the undissolved solid.

36. What happens to $K_c$ when the temperature is changed?

    $K_c$ changes with temperature. Temperature is the only factor that changes the equilibrium constant value.

37. What is the result of doubling the concentration of reactants at equilibrium?

    Equilibrium shifts right, producing more products. Increasing reactant concentration makes the forward reaction more favorable.

38. Identify the factor that does not affect the value of $K_c$ for a reaction.

    Pressure changes do not affect $K_c$.. Only temperature changes affect $K_c$; pressure and concentration changes don't.

39. What is the relationship between $K_{sp}$ and solubility?

    Higher $K_{sp}$ indicates greater solubility. Larger $K_{sp}$ values correspond to more soluble compounds at equilibrium.

40. What is the Le Chatelier's response to the removal of a product from the equilibrium mixture?

    Equilibrium shifts right to produce more product. Removing products decreases $Q$, making the forward reaction more favorable.

41. What happens to $K_c$ when the temperature is changed?

    $K_c$ changes with temperature. Temperature is the only factor that changes the equilibrium constant value.

42. What is the Le Chatelier's response to the removal of a product from the equilibrium mixture?

    Equilibrium shifts right to produce more product. Removing products decreases $Q$, making the forward reaction more favorable.

43. What is the effect of decreasing volume on the equilibrium of a reaction with gases?

    Equilibrium shifts toward the side with fewer moles of gas. System reduces stress by shifting to the side that occupies less volume.

44. What is the expression for $K_{sp}$ of $CaF_2$?

    $K_{sp} = [Ca^{2+}][F^-]^2$. Products of ion concentrations raised to their stoichiometric coefficients for the dissolution.

45. Identify the condition when $Q = K_c$ in a chemical reaction.

    The system is at equilibrium. When the reaction quotient equals the equilibrium constant, rates are balanced.

46. How does the addition of a common ion affect the solubility of a salt?

    Solubility decreases due to the common ion effect. Increased concentration of a common ion shifts equilibrium toward the undissolved solid.

47. What happens to $K_c$ when the temperature is changed?

    $K_c$ changes with temperature. Temperature is the only factor that changes the equilibrium constant value.

48. State the effect of removing heat from an endothermic reaction.

    Shifts equilibrium to the left (toward reactants). Heat is treated as a reactant in endothermic reactions, so removing heat shifts left.

49. What is the result of doubling the concentration of reactants at equilibrium?

    Equilibrium shifts right, producing more products. Increasing reactant concentration makes the forward reaction more favorable.

50. What is the unit of $K_c$ for the reaction $N_2 + 3H_2 \rightleftharpoons 2NH_3$?

    $M^{-2}$. Units are $\frac{M^2}{M \cdot M^3} = M^{-2}$ based on the concentration terms.

51. What is the relationship between $K_{sp}$ and solubility?

    Higher $K_{sp}$ indicates greater solubility. Larger $K_{sp}$ values correspond to more soluble compounds at equilibrium.

52. Identify the condition when $Q = K_c$ in a chemical reaction.

    The system is at equilibrium. When the reaction quotient equals the equilibrium constant, rates are balanced.

53. Identify the factor that does not affect the value of $K_c$ for a reaction.

    Pressure changes do not affect $K_c$.. Only temperature changes affect $K_c$; pressure and concentration changes don't.

54. What is the effect of increasing the temperature on $K_c$ for an exothermic reaction?

    $K_c$ decreases. For exothermic reactions, higher temperature makes products less stable, decreasing $K_c$.

55. What does a very small $K_c$ value indicate about a reaction?

    The reaction favors reactants at equilibrium. Small $K_c$ values mean the equilibrium position lies far to the left.

56. What is the effect of diluting a solution at equilibrium?

    Shifts towards the side with more moles of dissolved species. Dilution favors the side that produces more particles to maintain equilibrium.

57. What is the effect of adding more $N_2$ to the equilibrium $N_2 + 3H_2 \rightleftharpoons 2NH_3$?

    Equilibrium shifts right, producing more $NH_3$. Adding reactants increases their concentration, driving the reaction forward.

58. What is the unit of $K_c$ for the reaction $N_2 + 3H_2 \rightleftharpoons 2NH_3$?

    $M^{-2}$. Units are $\frac{M^2}{M \cdot M^3} = M^{-2}$ based on the concentration terms.

59. What is the effect of diluting a solution at equilibrium?

    Shifts towards the side with more moles of dissolved species. Dilution favors the side that produces more particles to maintain equilibrium.

60. What is the effect of diluting a solution at equilibrium?

    Shifts towards the side with more moles of dissolved species. Dilution favors the side that produces more particles to maintain equilibrium.

61. State the effect of removing heat from an endothermic reaction.

    Shifts equilibrium to the left (toward reactants). Heat is treated as a reactant in endothermic reactions, so removing heat shifts left.

62. How does the addition of a non-reactive gas affect the equilibrium position?

    No effect on the equilibrium position. Inert gases don't participate in the reaction and don't change partial pressures.

63. What is the result of doubling the concentration of reactants at equilibrium?

    Equilibrium shifts right, producing more products. Increasing reactant concentration makes the forward reaction more favorable.

64. What does a very small $K_c$ value indicate about a reaction?

    The reaction favors reactants at equilibrium. Small $K_c$ values mean the equilibrium position lies far to the left.

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