Introduction to Equilibrium - AP Chemistry

1. What does it mean if $Q = K$ for a reaction?

   The reaction is at equilibrium. Current reaction quotient equals equilibrium constant; no net change occurs.

2. How do you calculate $K_c$ for a reversed reaction?

   $K_c$ for reversed reaction is $\frac{1}{K_c}$ of the forward reaction. Reversing a reaction inverts its equilibrium constant value.

3. What is the effect of temperature change on $K$?

   $K$ changes; depends on reaction's endothermic or exothermic nature. Temperature is the only factor that changes the equilibrium constant value.

4. What is the effect of a pure solid or liquid on $K$?

   No effect; not included in $K$ expressions. Pure phases have constant activity and don't appear in expressions.

5. What is the significance of $K$ being temperature-dependent?

   Equilibrium position changes with temperature. Different temperatures give different $K$ values for the same reaction.

6. What is the role of coefficients in equilibrium expressions?

   They become exponents for concentration terms in $K$ expressions. Stoichiometric coefficients become powers in the equilibrium constant expression.

7. Identify the effect of increasing temperature on an endothermic reaction at equilibrium.

   Shifts towards the product side. Higher temperature favors the endothermic direction (forward reaction).

8. What does a $K_c$ value less than 1 indicate?

   Reactants are favored at equilibrium. Smaller $K$ means equilibrium lies toward the reactant side.

9. How does the addition of an inert gas affect equilibrium?

   No effect on the position of equilibrium. Inert gases don't participate in the reaction or affect concentrations.

10. What is the unit for the equilibrium constant $K_c$?

    Unitless; derived from concentration terms. Concentration units cancel out in the ratio of products to reactants.

11. What is the effect of adding a catalyst to a reaction mixture?

    Increases rate without affecting equilibrium position. Catalyst speeds both directions equally, reaching equilibrium faster.

12. Define homogeneous equilibrium.

    Equilibrium where all reactants and products are in the same phase. All species exist in one phase (all gas, liquid, or aqueous).

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

    $K_p = K_c(RT)^{\Delta n}$, where $\Delta n$ is moles of gas change. Converts between concentration and pressure equilibrium constants.

14. How does a catalyst affect the position of equilibrium?

    A catalyst does not affect the position of equilibrium. Catalysts speed up both forward and reverse reactions equally.

15. What does a high $K$ value suggest about the reaction?

    Significant formation of products at equilibrium. Large $K$ indicates equilibrium strongly favors product formation.

16. What is the reaction quotient $Q$?

    The ratio of product and reactant concentrations at any point in time. Same form as $K$ but uses current concentrations, not equilibrium values.

17. Identify the effect of decreasing pressure on the position of equilibrium.

    Shifts towards the side with more moles of gas. Lower pressure favors the side with more gas molecules to increase volume.

18. What does a low $K$ value suggest about the reaction?

    Significant formation of reactants at equilibrium. Small $K$ indicates equilibrium strongly favors reactant formation.

19. What happens when $Q = K$ during a reaction process?

    The system is at equilibrium. No driving force exists for net reaction in either direction.

20. Define heterogeneous equilibrium.

    Equilibrium with reactants and products in different phases. Species exist in multiple phases (solid, liquid, gas, aqueous combinations).

21. What is the definition of chemical equilibrium?

    The state where the rates of forward and reverse reactions are equal. Forward and reverse reaction rates balance, maintaining constant concentrations.

22. Identify the effect of adding a reactant on the position of equilibrium.

    Shifts towards the product side. System shifts to consume the added reactant by forming more products.

23. What is the general form of the equilibrium constant expression?

    $K = \frac{\text{[products]}}{\text{[reactants]}}$. Products in numerator, reactants in denominator, each raised to their coefficients.

24. State 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 their coefficients divided by reactants raised to their coefficients.

25. Compare $Q$ and $K$ to predict the direction of a reaction shift.

    If $Q < K$, shifts right; if $Q > K$, shifts left. Compares current state to equilibrium to predict reaction direction.

26. Identify the effect of adding a product on the position of equilibrium.

    Shifts towards the reactant side. System shifts to consume the added product by forming more reactants.

27. What is the unit for the equilibrium constant $K_p$?

    Unitless; derived from partial pressure terms. Pressure units cancel out in the ratio of products to reactants.

28. What type of reactions have equilibrium constants?

    Reversible reactions. Irreversible reactions proceed to completion; only reversible ones reach equilibrium.

29. How is the reaction direction affected by $Q$?

    Determines if the reaction shifts left or right to reach equilibrium. Comparison of $Q$ and $K$ predicts which direction favors equilibrium.

30. What happens to $K$ when a reaction is multiplied by a factor?

    $K$ is raised to the power of that factor. Multiplying equation by $n$ raises the equilibrium constant to power $n$.

31. Identify the effect of decreasing temperature on an exothermic reaction at equilibrium.

    Shifts towards the product side. Lower temperature favors the exothermic direction (forward reaction).

32. What does the equilibrium constant $K$ indicate about a reaction?

    The ratio of product concentrations to reactant concentrations at equilibrium. Higher $K$ means more products; lower $K$ means more reactants at equilibrium.

33. What does a $K_c$ value greater than 1 indicate?

    Products are favored at equilibrium. Larger $K$ means equilibrium lies toward the product side.

34. What is the significance of a dynamic equilibrium?

    Reactants and products form at the same rate. Concentrations remain constant while reactions continue in both directions.

35. What is the effect of changing concentration on the equilibrium constant?

    No effect; $K$ is constant at a given temperature. Only temperature affects $K$; concentration changes shift position only.

36. What factors affect the value of $K$?

    Temperature; not concentration or pressure. Pressure and concentration changes shift position but don't change $K$.

37. Identify the effect of increasing pressure on the position of equilibrium in a gaseous reaction.

    Shifts towards the side with fewer moles of gas. Pressure increase favors the side with less gas molecules to reduce volume.

38. State the expression for the equilibrium constant $K_p$ for the reaction $aA + bB \rightleftharpoons cC + dD$.

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

39. What is the definition of Le Chatelier's Principle?

    Systems at equilibrium react to disturbances by shifting to counteract the change. Equilibrium shifts to oppose external changes and restore balance.

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