Midterm 2 Practice Test 1

Chem. 1B Midterm 2Version AFirst letterof last nameName__________________________________________Student Number _________________________________All work must be shown on the exam for partial credit. Points will be taken off forincorrect or no units. Calculators are allowed. Cell phones may not be used forcalculators. On fundamental and short answer problems you must show your work inorder to receive credit for the problem. If your cell phone goes off during the examyou will have your exam removed from you.Fundamentals(of 36 possible)Problem 1(of 16 possible)Problem 2(of 18 possible)Multiple Choice(of 30 possible)Midterm Total(of 100 possible)1

Fundamental QuestionsEach of these fundamental chemistry questions is worth 6 points. You must show workto get credit. Little to no partial credit will be rewarded. Make sure to include thecorrect units on your answers.1) 6 pts Consider this reaction:2CH3OH(g) +3O2(g) 2CO2(g) + 4H2O(l)At a certain temperature it obeys this rate law.Rate= 3.30 Lmol∙s [CH3OH]2Suppose a vessel contains CH3OH at a concentration of 1.20 M. Calculatethe concentration of CH3OH in the vessel 0.920 seconds later. You mayassume no other reaction is important.2) 6 pts The rate constant of the reaction O(g) + N2(g) NO(g) + N(g) is9.7×10 10 LkJat 800.˚C. The activation energy of the reaction is 315 mol∙s molDetermine the rate constant at 700.˚C.3) 6 pts A voltaic cell, at 25˚C, represented by the following cell diagram hasEcell =1.45 V. What must be [Ag + ] in the cell?Zn(s)|Zn 2+ (1.00M)||Ag + (x M)|Ag(s)2

4) 6 pts If the rate law was determined to be0.9 3rate k[ A] [ B]And the following data was collected[A]o (M) [B]o (M) Initial Rate( molLs2.5 0.75 6.0What is k? Remember to include units.)5) 6 pts Draw the following galvanic cell:Pb(s) + Cl2(g) Pb 2+ (aq) + 2Cl - (aq)Calculate E˚, show the direction of electron flow and the direction of ionmigration through the salt bridge, and identify the cathode and anode.6) 6 pts How much time is required to electroplate 1.50 g of silver from a silvernitrate solution by using a current of 13.6 mA?3

Short Answer QuestionsEach of the following short answer questions are worth the noted points. Partial creditwill be given. You must show your work to get credit. Make sure include proper unitson your answer.1) 16 pts Consider the cell described below:Al|Al 3+ (1.00 M)||Pb 2+ (1.00 M)|PbCalculate the cell potential after the reaction has operated long enough forthe [Al 3+ ] to have change by 0.60 M . (Assume T=25˚C)4

2a) 10 pts In the gas phase, production of phosgene from chlorine and carbon monoxide isassumed to proceed by the following mechanism:k 1Cl 2 ⇌ 2Clk −1k 2Cl + CO ⇌ COClk −2COCl + Cl 2 k 3→ COCl 2+ Cl Slow2Cl k 4→Cl 2FastWrite the rate law for this reaction.Fast equilibriumFast equilibrium2b) 8 pts Is this rate law consistent with the following experimental data.Expt. [CO]˳ (M) [Cl 2] ˳ (M) Rate ( mol L∙s1 1.00 2.00 5.662 2.00 2.00 11.313 2.00 2.10 12.78You must show what the rate law is for this data in order to get credit.5

Multiple Choice QuestionsEach of the following multiple choice questions are worth 5 points.Your answers need to be filled in on the Scantron provided.Note: Your Scantrons will not be returned to you, therefore, foryour records, you may want to mark your answers on this sheet.On the Scantron you need to fill in your perm number, test version,and name. Failure to do any of these things will result in theloss of 1 point. Your perm number is placed and bubbled in underthe “ID number”. Do not skip boxes or put in a hyphen. Inaddition, leave bubbles blank under any unused boxes. Theversion number (A) is bubbled in under the “test form.”Use the following to answer question 1:You make a galvanic cell with a copper electrode in a solution of copper nitrate and asilver electrode in a solution of silver nitrate.Cu 2+ + 2e – Cu E° = 0.34 VAg + + e – Ag E° = 0.80 V1. If you could increase the concentration of Ag + , which of the following would be trueabout the cell potential?A) It would remain constant.B) This cannot be determined.C) It would decrease.D) It would increase.2. A galvanic cell is constructed with copper electrodes and Cu 2+ in each compartment. Inone compartment, [Cu 2+ ] = 3.4 10 –3 M, and in the other compartment, [Cu 2+ ] = 1.4 M.Calculate the potential for this cell at 25°C. The standard reduction potential for Cu 2+ is+0.34 V.A) 0.077 VB) 0.42 VC) –0.077 VD) –0.42 VE) none of these3. In which of the following cases can E° be equal to zero?I. In any cell at equilibriumII. In a concentration cellIII. E° can never be equal to zero.A) IIIB) I onlyC) I and IID) II only6

4. When the equation for the following reaction in basic solution is balanced, what is thesum of the coefficients?MnO4 – (aq) + CN – (aq) MnO2(s) + CNO – (aq)A) 20B) 13C) 8D) 10E) none of theseUse the following to answer questions 5-6:For the reaction A products, select the reaction order(s) that best fit(s) theobservations.5. A plot of [A] 2 vs. t gives a straight line.A) second order in AB) zero order in AC) first order in AD) all of theseE) none of these6. The half-life decreases over time.A) second order in AB) zero order in AC) first order in AD) all of theseE) none of these7