Module 4 - Equilibrium 2023 with complete solution

When a system is at dynamic equilibrium, ______ a) no reactions are occurring b) a reaction is occurring in only 1 direction c) the rates of the forward and reverse reactions are equal d) all of the reactants have been converted to products c) the rates of the forward and reverse reactions are equal Construct the expression for Kc for the following reaction 3NO (g) = N2O (g) + NO2 (g) Kc = [N2O][NO3]/[NO]^3 Construct the expression for Kc for the following reaction 4HCl (aq) + O2 (g) = 2H2O (l) + 2Cl2 (g) Kc = [Cl2]^2/[O2][HCl]^4 Which of the following is the correct expression for the concentration based equilibrium constant for the reaction: N2 (g) + 3Br2 (g) = 2NBr3 (g) a) Kc = [N2][Br2]^3/[NBr3]^2 b) Kc = [N2][Br2]^3[NBr3]^2 c) Kc = [NBr3]^2/[N2][Br2]^3 d) Kc = [N2][Br2]/[NBr3] Kc = [NBr3]^2/[N2][Br2]^3 A sealed reaction flask contains a mixture of 0.100 M CH3OH, 0.152 M CO, and 0.250 M H2 at constant temperature. Given the following reaction, CO (g) + 2H2 (g) = CH3OH (g) and Kc = 10.5. Select the answer that best describes the state of equilibrium in the flask. a) The contents of the flask are not at equilibrium, the reaction will shift left. b) The contents of the flask are at equilibrium an no shift will occur c) The contents of the flask are not at equilibrium, the reaction will shift right. d) The flask will form more reactants and the amount of products will stay constant e) The flask will form more products and the amount of reactants will stay constant. b) The contents of the flask are at equilibrium an no shift will occur Qc = [0.100]/[0.152][0.250]^2 = 10.5 If the equilibrium constant of a given reaction is 8.76, what is the equilibrium constant of its reverse reaction? 1/8.76 = 0.114 Consider the reaction: Mg(OH)2 (s) = Mg^2+ (aq) + 2OH^- (aq). At equilibrium, a 1.0 L reaction vessel contains 5.3 mol of Mg(OH)2, and concentrations of 0.0080 M and 0.010 M of Mg^2+ and OH^- respectively. What is Kc for this equilibrium? Kc = [Mg^2+][OH^-]^2 Kc = [0.0080 M][0.010 M]^2 Kc = 8 x 10^-7 At equilibrium, a 1.0 L reaction vessel contains 2.3 mol of Mg(OH)2 and 0.170 mol of OH^-. What is the equilibrium concentration of Mg^2+ based on the reaction: Mg(OH)2 (s) = Mg^2+ (aq) + 2OH^- (aq) Kc = 1.80 x 10^-11 Kc = [Mg^2+][OH^-]^2 1.80 x 10^-11 = (0.170)^2[Mg^2+] [Mg^2+] = 6.228 x 10^-10 For the reaction below, Q = 600. What must happen for the reaction to reach equilibrium? a) Reaction needs to shift forwards b) Reaction needs to shift backwards c) The reaction is already at equilibrium; no shift occurs d) Not enough information is provided a) Reaction needs to shift forwards Consider the equilibrium system described by the chemical reaction below. For this reaction, Kc = 2.4 x 10^-3 at particular temperature. If the equilibrium concentrations of H2O and H2 are 0.11 M and 0.019 M respectively, determine the concentration of O2 at equilibrium. 2H2O (aq) = 2H2 (g) + O2 (g) 2.4 x 10^-3 = [0.019]^2[x]/[0.11]^2 x = 0.08 Consider the following reaction - 2SO2 (g) + O2 (g) = 2SO3 (g) If you decrease the volume of the reaction chamber, you would observe ___ a) an increase in SO2 b) an increase in O2 c) an increase in SO3 d) both (a) and (b) e) none of the above c) an increase in SO3 For the reaction Mg(OH)2 (s) = Mg^2+ + 2OH^- (aq), adding Mg(OH)2 will: a) have no effect b) increase the concentration of the hydroxide ions c) decrease the concentration of the magnesium d) change the value of the equilibrium constant a) have no effect Which of the following changes would cause the reaction below to shift in the forward direction to reestablish equilibrium? 2NBr3 (g) = N2 (g) + 3Br2 (g) a) adding a catalyst b) adding Ar (g) c) increasing the total volume of the container d) adding N2 c) increasing the total volume of the container What does it mean to describe a reaction as "reversible"? The reaction can occur forwards as well as backwards If a reaction is reversible, when can it be said to have reached equilibrium? If a system is in equilibrium, no further changes in reactant and product concentration occur. the reaction continues, but at equal rates. If the concentrations of products and reactants are equal, is the system at equilibrium? No, it could be, but this doesn't necessarily mean it's at equilibrium. Equilibrium systems have constant reactant and product concentrations, but the concentrations themselves don't need to all be equal. Explain why an equilibrium between Br (l) and Br2 (g) would not be established if the container were not a closed vessel The system would not be closed - the vapor would escape until all the liquid disappeared. More liquid would evaporate than would condense back into a liquid. Benzene is one of the compounds used as octane enhances is unleaded gasoline. It is manufactured by the catalytic conversion of acetylene to benzene 3C2H2 (g) = C6H6 (g). What value of Kc would make this reaction the most useful commercially? 0.01, 1, or 10? Kc = [C6H6]/[C2H2]^3 A value of 10 means that C6H6 dominates C2H2 For a titration to be effective, the reaction must be rapid and the yield must be 100%. Is Kc 1, 1, or =1 for a titration? K1 Calculate the reaction quotient and determine the direction in which each system will proceed a) 2NH3 (g) = N2 (g) + 3H2 (g) Kc = 17 0.20 M, 1.00 M, 1.00 M respectively b) 2NH3 (g) = N2 (g) + 3H2 (g) Kp = 6.8 x 10^4 3 atm, 2.0 atm, 1.0 atm respectively a) Qc = [N2][H2]^3/[NH3]^2 = [1.00 M][1.00 M]^3/[0.20 M]^2 = 25 Qc Kc, shift left b) Qc = [2.0 atm][1.0 atm]^3/[3.0 atm]^3 = 0.2 Qc Kc, shift rig