Direction of Reversible Reactions - AP Chemistry

1. What happens if a catalyst is added to a reaction at equilibrium?

   No effect on the equilibrium position. Equilibrium position remains unchanged with catalyst addition.

2. What is the reaction quotient, $Q$, used for?

   To predict the direction of a reaction's shift to reach equilibrium. Compares current concentrations to equilibrium to determine reaction direction.

3. What is the effect of adding a pure liquid to a reaction at equilibrium?

   No effect on the equilibrium position. Pure liquids have constant activity and don't appear in $K_c$.

4. What happens to equilibrium if the volume of a gaseous system is decreased?

   Shifts toward the side with fewer moles of gas. Higher pressure favors the side with fewer gas molecules.

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

   $K_p = K_c(RT)^{\Delta n}$. Standard relationship connecting concentration and pressure equilibrium constants.

6. How do you convert $K_c$ to $K_p$?

   $K_p = K_c(RT)^{\Delta n}$. Conversion formula where $R$ is gas constant and $T$ is temperature.

7. How does an increase in temperature affect $K_c$ for an endothermic reaction?

   $K_c$ increases. Higher temperature favors the endothermic direction.

8. What is the partial pressure equilibrium constant, $K_p$?

   Equilibrium constant in terms of partial pressures. Uses partial pressures instead of molar concentrations.

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

   $K_c$ decreases. Higher temperature shifts equilibrium away from the exothermic direction.

10. What effect does increasing pressure have on a gaseous reaction with fewer moles on the right?

    Shifts equilibrium to the right. System minimizes pressure by favoring the side with fewer gas molecules.

11. What effect does decreasing pressure have on a gaseous reaction with more moles on the right?

    Shifts equilibrium to the right. System reduces pressure by favoring the side with more gas molecules.

12. How does adding a catalyst affect the position of equilibrium?

    It does not affect the position of equilibrium. Catalyst speeds both forward and reverse reactions equally.

13. What will happen if a product is removed from a reversible reaction?

    The equilibrium will shift to the right. System responds by producing more of the removed product.

14. What does it mean if $K_c$ is much greater than 1?

    The equilibrium favors products. Large $K_c$ indicates products are thermodynamically favored.

15. What does the double arrow in a chemical equation signify?

    The reaction is reversible. Double arrows indicate the reaction can proceed in both directions.

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

    $K_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}$. Products raised to stoichiometric powers divided by reactants raised to powers.

17. What is the effect of a catalyst on the rate of reaching equilibrium?

    Increases the rate but does not change the position. Catalyst accelerates approach to equilibrium without changing final position.

18. What does it mean if $K_c$ is much less than 1?

    The equilibrium favors reactants. Small $K_c$ indicates reactants are thermodynamically favored.

19. State Le Chatelier's principle.

    An equilibrium will shift to oppose changes in concentration, temperature, or pressure. System adjusts to counteract any imposed change or stress.

20. What is the unit for the equilibrium constant, $K_c$?

    Unitless. Concentration units cancel out in the equilibrium expression.

21. Identify the effect of increasing temperature on an endothermic reaction.

    Shifts equilibrium to the right. Heat is a reactant, so adding heat favors product formation.

22. Identify the effect of removing a reactant from a reversible reaction.

    The equilibrium will shift to the left. System responds by consuming more products to replace removed reactant.

23. What does $\Delta n$ represent in the $K_c$ to $K_p$ conversion?

    Change in moles of gas: (moles of gaseous products) - (moles of gaseous reactants). Difference in moles of gaseous species between products and reactants.

24. What type of reaction is $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$?

    A reversible reaction. Double arrows indicate the reaction proceeds in both directions.

25. What is the definition of dynamic equilibrium?

    Rates of forward and reverse reactions are equal. Forward and reverse reactions occur at the same rate continuously.

26. How does a decrease in temperature affect $K_c$ for an exothermic reaction?

    $K_c$ increases. Lower temperature favors the exothermic direction.

27. What is the effect of adding a pure solid to a reaction at equilibrium?

    No effect on the equilibrium position. Pure solids have constant activity and don't appear in $K_c$.

28. What is the effect of adding more reactant to a system at equilibrium?

    Shifts equilibrium to the right. System consumes added reactant by forming more products.

29. What does it mean if $Q > K_c$ for a reaction?

    The reaction will shift to the left. More reactants need to form to reach equilibrium.

30. What is the effect of adding an inert gas at constant volume?

    No effect on the equilibrium position. Inert gas doesn't change partial pressures of reactants or products.

31. How does a change in concentration affect the value of $K_c$?

    It does not change the value of $K_c$. $K_c$ depends only on temperature, not concentration changes.

32. What happens to equilibrium when the concentration of a product is increased?

    Shifts equilibrium to the left. System consumes excess product by favoring the reverse reaction.

33. What is the effect of compressing a gaseous equilibrium system?

    Shifts toward the side with fewer moles of gas. Compression increases pressure, favoring the side with fewer gas moles.

34. What does it mean if $Q = K_c$ for a reaction?

    The reaction is at equilibrium. Forward and reverse reaction rates are equal, no net change.

35. What is the primary factor affecting the magnitude of $K_c$?

    Temperature. Only temperature changes affect the equilibrium constant value.

36. Identify the effect of decreasing temperature on an exothermic reaction.

    Shifts equilibrium to the right. Heat is a product, so removing heat favors product formation.

37. What does it mean if $Q < K_c$ for a reaction?

    The reaction will shift to the right. More products need to form to reach equilibrium.

38. How does decreasing the volume of a gaseous system affect equilibrium?

    Shifts toward the side with fewer moles of gas. Reduced volume increases pressure, favoring fewer gas molecules.

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