Leader: Deborah Course: CHEM 178 Instructor: Bonaccorsi/Vela Date: 2/6/18 + H 2 CHF 3. a. Express the rate law in terms of m, n, and k.

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1 EXAM I REVIEW KEY Leader: Deborah Course: CHEM 178 Instructor: Bonaccorsi/Vela Date: 2/6/18 1. Given the following reaction: CF 4 + H 2 CHF 3 + HF a. Express the rate law in terms of m, n, and k. Rate = k[cf 4 ] m [H 2 ] n b. Use the following data to solve for m and n: [CF 4 ] initial (M) [H 2 ] initial (M) Rate (M/s) m = 1, n = 1 c. Solve for the rate constant k. k = (45 M/s) / ([0.10 M] * [0.10 M]) = 4500 M -1 s How does a catalyst increase the rate of a reaction? a. Increasing reactant concentration b. Increasing temperature c. Decreasing temperature d. Increasing activation energy of a reaction e. Decreasing activation energy of a reaction

2 3. Consider the following reaction: 3 H 2 (g) + N 2 (g) 2 NH 3 (g) ( H = kj) a. What happens when excess ammonia is added to the system? Reaction shifts to the left b. What happens when nitrogen is removed from the system? Reaction shifts to the left c. What happens when the pressure of the system is increased? Reaction shifts to the right d. What happens when the temperature of the system is increased? Reaction shifts to the left 4. Given the two reactions: H 2 S HS - + H + K 1 = 9.43 x 10-8 and HS - S 2- + H + K 2 = 1.16 x What is the equilibrium constant K for the following reaction? S H + H 2 S K = [1 / (9.43 x 10-8 )] * [1 / (1.16 x )] = 9.14 x At a point in time, the rate of consumption of HO 2(g) in the reaction 2 HO 2 (g) H 2 O 2 (g) + O 2 (g) is M/s. a. What is the rate of production of O 2 at this time? 4.35 x 10-2 M/s b. What is the rate of change of H 2 O 2 at this time? 4.35 x 10-2 M/s 6. Given the following reaction at 120 C Cu (s) + 2 Ag + (aq) Cu 2+ (aq) + 2 Ag (s) K c = 2.34 x 10-5 a. Find the equilibrium-constant value for 5 Cu (s) + 10 Ag + (aq) 5 Cu 2+ (aq) + 10 Ag (s) K c = 7.02 x b. Which species is favored at this temperature? Cu (s) and Ag + (aq) (reactants)

3 7. Draw the reaction profile of an endothermic reaction, labeling each part. 8. Consider the following equilibrium reaction: NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) If the initial concentrations of NH 3, NH 4 +, and OH - are 0.02 M, 0.05 M, and 0.6 M respectively, what is the equilibrium constant K C for this reaction? K C = ([NH 4 + ][OH - ]) / [NH 3 ] = ([0.05 M][0.6 M]) / [0.02 M] = The equilibrium constant (K C ) for the reaction N 2 O 4 (g) 2NO 2 (g) is 4.63 x 10-3 at 25 C. What is the value of K P for this reaction at this temperature? K P = K C (RT) Δn = (4.63 x 10-3 )[( L*atm/mol*K)( K)] 2-1 = Complete the table given the following reaction: A (s) + 3 B (aq) AB 3 (g) K c = 8.20 [B] [AB 3 ] Q c Process Occurring (in terms of species being consumed or produced) M 1.50 M 6.94 AB 3 formed M M 9.00 A and B formed 1.20 M 14.2 M ~8.20 Equilibrium

4 11.For the reaction, F 2 (g) + 2 ClO 2 (g) 2 FClO 2 (g) the rate law is - [F 2 ] / t = k[f 2 ] 3. If the rate of formation of FClO 2(g) is M/s when the concentration of F 2(g) is 0.68 M, what is the rate constant s value? k = 3.7 x 10-3 M -2 s For the reaction H ICl I HCl (Rate = k[h 2 ][ICl]), a two-step mechanism is proposed. Complete this mechanism and write down the rate law for each elementary step. Elementary step Rate Law (1) H 2 + ICl HI + HCl Rate(1) = k 1 [H 2 ][ICl] (2) HI + ICl I 2 + HCl Rate(2) = k 2 [H 2 ][ICl] 2 a. Which is the rate-determining step and what is its molecularity? step 1; bimolecular b. Are there any intermediates or catalysts? If yes, identify them. Intermediate: HI; no catalysts 13.For the reaction A + B 2C, it is determined that doubling the amount of A causes the reaction rate to double, while doubling the amount of B causes the reaction rate to quadruple. Propose a rate law for this reaction. Rate = k[a][b] 2 14.For the reaction 2 SO 2 + O 2 2 SO 3, the following mechanism has been proposed: Step 1: 2 NO + O 2 2 NO 2 slow Step 2: 2 NO SO 2 2 NO + 2 SO 3 fast What is the rate law for the reaction? Rate = k[no] 2 [O 2 ] (slow initial step) 15.Fill in the table with the appropriate rate constant units for each reaction order: Reaction Order Rate Constant Units Zeroth M s -1 First s -1 Second M -1 s The half-life of a radioisotope is found to be 4.55 minutes. If the decay follows first-order kinetics, what percentage of isotope will remain after 2.50 hours? 1.16 x %

17. PH 3 is known to decompose in a second-order process that has a rate constant of 2.87 x 10 4 M -1 s 1. If [PH 3 ] = 0.93 M at the start of a reaction, how long will it take until [PH 3 ] = 0.

5 17. PH 3 is known to decompose in a second-order process that has a rate constant of 2.87 x 10 4 M -1 s 1. If [PH 3 ] = 0.93 M at the start of a reaction, how long will it take until [PH 3 ] = M (in hours)? 95.7 hours 18. Write the rate law expression for this reaction based on these experimental results. Rate = k [C 4 H 8 ] 19.A mixture of 1.0 mole CO 2 and 1.0 mole CO are contained in a 1 L vessel. Later 2.0 moles of water vapor is then introduced into the vessel. The following reversible reactions takes place CO (g) + H 2 O (g) CO 2 (g) + H 2 (g) K = 0.64 How many moles of the different molecules will be present after equilibrium is obtained?

20.3.00 moles of N 2 gas and 1.00 mole of H 2 gas are combined in a 1 L reaction vessel.

6 moles of N 2 gas and 1.00 mole of H 2 gas are combined in a 1 L reaction vessel. At equilibrium, moles of H 2 remain. What are the resulting concentrations? N 2 (g) + 3 H 2 (g) 2 NH 3 (g)

FINAL EXAM REVIEW KEY

FINAL EXAM REVIEW KEY Leaders: Deborah Course: CHEM 178 Instructor: Date: 1. What is the rate-determining step and why is it important? The slowest step of the elementary steps; looks the most like the