Equilibrium Review Sheet Answers

**Equilibrium Review Worksheet** **Name** Answer Key **Date** Per 1. Give three factors that would speed up the rate of the reaction given below, and EXPLAIN how those factors alter the rate.   2Mg(s) + O₂(g) → 2MgO(s) a. **Catalyst:** speeds up rate of reaction but does not change Keq b. **Stir it!** - creates more collisions between particles c. **Crush/increase surface area:** more S.A. means more reactive sites 2. Using a concentration vs time graph, describe the rate of an equilibrium reaction over time. [Image of a concentration vs time graph showing equilibrium] Reaction rates are variable at first but when they remain constant, equilibrium is reached. The concentrations of substances can change. 3. Describe what you could do if you wanted to shift the equilibrium of the following reaction towards products. (At least 4 things!) 2A(g) + B(g) ⇌ 2C(g) + 3D(g) + heat a. **increase [reactant]** b. **remove heat** c. **remove product** d. **increase pressure (gases will move to the side w/ fewer moles)** 4. Write the equilibrium constant expression for the following reaction: 2A ⇌ 2C + 3D K = [C]^2[D]^3 / [A]^2 5. You have 25.0 grams of sodium hydroxide and you dissolve it in 457 mL of water. What is its concentration? 25.0 g NaOH * (1 mol NaOH / 40.0 g NaOH) / 0.457 L = 1.37 M NaOH 6. Using the equations and equilibrium constant equation from #4 calculate the equilibrium constant if the [A] = 0.1077 mol/L, [C] = 0.0004104 mol/L, [D] = 0.0004104 mol/L. Are products or reactants favored at equilibrium? Keq = (0.0004104)²(0.0004104)³ / (0.1077)² = 1.004 × 10⁻¹⁵ Reactants favored 7. Write the chemical equilibrium expression for the following equations. Then use the given equilibrium constant to determine if the forward or reverse reaction is favored.   a. N₂O₄(g) ⇌ 2NO₂(g) K = 0.1 K = [NO₂]² / [N₂O₄] Reverse favored b. H₂(g) + I₂(g) ⇌ 2HI(g) K = 2 × 10⁻³ K = [HI]² / [H₂][I₂] Reactant favored c. NH₄OH ⇌ NH₄⁺ + OH⁻ K = 1.8 × 10⁻⁵ K = [NH₄⁺][OH⁻] / [NH₄OH] Reactant favored 8. Consider the following equilibrium equation: CH₃OH(g) + 101 kJ ⇌ CO(g) + 2H₂(g) a. Increasing the concentration of CO will shift the rxn toward reactants. b. Increasing the pressure of the system will shift the rxn toward reactants. c. Increasing the volume of the container for the reaction will shift the rxn toward products. **Continued from the previous response:** **d. Placing the reaction vessel in a water bath to remove heat from the reaction will** Shift toward reactants **e. Adding a catalyst will** Speed up reaction but not affect equilibrium **f. Removing the hydrogen gas through a secondary reaction will** Shift toward products **9. Will raising the temperature of an equilibrium system favor exothermic reactions, endothermic reactions, or all reactions? Explain!** ↑ heat to endothermic rxns produces more products. ↑ heat to exothermic rxns produces more reactants **10. How do you know a reaction has reached equilibrium? Discuss the rates of the forward and reverse reactions as well as the concentration of reactants and products in your answer.**   Equilibrium is reached when the forward and reverse reactions are equal. The concentrations of reactants and products are not the same, but experience no net change. **11. Use this reaction for each of the following: 2NO₂(g) + O₂(g) → 2NO₃(g)** a. Write the expression for the equilibrium constant. Keq = [NO₃]² / [NO₂]²[O₂] b. If gas concentrations are as follows: 2.10 M NO₂, 1.75 M O₂, and 1.00 M NO₃, calculate Keq. Keq = (1.00)² / (2.10)²(1.75) = 0.130 c. Using Keq from part b, are the reactants or the products favored? Reactants are favored (less than 1) d. Using Keq from part   b, calculate the equilibrium concentration of NO₂ if [O₂] = 4.3 x 10⁻⁶ M and [NO₃] = 0.180 M. 0.130 = (0.180)² / (x)²(4.3 x 10⁻⁶) x = 3.2 x 10⁻⁹ M e. A reaction mixture contains [NO₂] = 1.20 M, [O₂] = 0.85 M, and [NO₃] = 3.00 M. Calculate the reaction quotient (Q) and predict which direction the reaction will shift to reach equilibrium. Q = (3.00)² / (1.20)²(0.85) = 7.35 Shifts to reactants (left) **12. Use the following acidity constants to help answer the questions below:** Ka(HC₂H₃O₂) = 1.8 x 10⁻⁵ Ka(HCN) = 4.9 x 10⁻¹⁰ Ka(HCOOH) = 1.7 x 10⁻⁴ Which of the three acids is the weakest? HCN (smallest Ka) **13. Consider the reaction: CH₃NH₂(aq) + H₂O(l) ⇌ CH₃NH₃⁺(aq) + OH⁻(aq) where Kb = 4.4 x 10⁻⁴. To a solution formed from the addition of 2.0 mol CH₃NH₂ to 1.0 L of H₂O is added 1.0 mol of KOH (assume no volume change on addition of solutes). What is the concentration of CH₃NH₂ at equilibrium?** A) 3.2 x 10⁻² M B) 2.2 x 10⁻⁴ M C) 2.0 x 10⁻³ M D) 8.8 x 10⁻⁴ M E) None of these [CH₃NH₃⁺] = 8.8 x 10⁻⁴ M **14. When CaF₂ dissolves, it dissociates like this: CaF₂(s) ⇌ Ca²⁺(aq) + 2F⁻(aq) and the Ksp of CaF₂ is 3.92 x 10⁻¹¹. What is the Ksp expression?** Ksp = [Ca²⁺][F⁻]² **15. Calculate the equilibrium concentration of N₂O₅ in the reaction: 2N₂O₅(soln) ⇌ 4NO₂(g) + O₂(g) where Keq @ 45°C is 2800 and the equilibrium concentration of O₂ is 1.0 M.** 2800 = (4)²(1) / [N₂O₅]² [N₂O₅] = 0.30 M