Study Guides (234,578)
Canada (113,214)
Chemistry (189)
CHEM 110 (24)
Midterm

Chem 120- Midterm 2 - 2011.pdf
Chem 120- Midterm 2 - 2011.pdf

16 Pages
300 Views
Unlock Document

School
McGill University
Department
Chemistry
Course
CHEM 110
Professor
Sebastien Breau
Semester
Fall

Description
FACULTY OF SCIENCE MID-TERM EXAMINATION2 MARCH 18, 2011. 6:30 TO 8:30 PM CHEMISTRY 120 GENERAL CHEMISTRY Examiners: Prof. B. Siwick Name:_________________________ Prof. A. Mittermaier Dr. A. Fenster Associate Examiner: A. Fenster INSTRUCTIONS 1. Enter your student number and name on the computer scorecard provided, by filling in the appropriate circles. Check that your scorecard has the correct version number filled in (version 1). If not, fill that in. One mark will be awarded for correctly recording your student number on the scantron card. Double check that this has been done properly! 2. This examination comprises 30 questions but will be marked out of 31 (see point 1 above). All questions are of equal value. 3. Transfer all answers to the scantron computer scorecard provided. 4. ONLY the SHARP EL510RB calculator may be used in the Midterm. Translation dictionariesare also permitted. NO notes or texts are allowed. 5. The Examination Security Monitor Program detects pairs of students with unusually similar answer patterns on multiple-choice exams. Data generated by this program can be used as admissible evidence, either to initiate or corroborate an investigation or a charge of cheating under Section 16 of the Code of Student Conduct and Disciplinary Procedures. Page 1 of 16 1. The heat of fusion for water is 6.01 kJ/mol and for ethyl alcohol is 5.01 kJ/mol. The amount of heat that would melt 25.0 grams of water would melt how many grams of ethyl alcohol (C H OH) ? 2 5 a) 8.2 g b) 53.3 g c) 76.7 g d) 32.0 g e) 11.7 g 2. Which compound is most likely to be soluble in both water and benzene? a) propyl alcohol 3 7H OH) b) hexane (6 14) c) calcium chloride (Ca2l ) d) naphthalene (10 8) e) toluene (7 8 ) 3. The equilibrium constants for the chemical reaction: N 2g) + O2(g) ↔ 2NO (g) are Kp = 1.1 × 103 and 3.6 × 103 at 2,200 K and 2,500 K respectively. Which one of the following statements is true? a) Higher total pressure shifts the equilibrium to the left. b) The partial pressure of NO(g) is less at 2,200 K than at 2,500 K. c) The total pressure at 2,200 K is the same as at 2,500 K. d) The reaction is exothermic; i.e. ΔH° < 0. e) K is less than K by (RT). p c 4. For the reaction2 H (g)2+ I (g) ↔ 2 HI(gc, K = 92.0. When equilibrium concentrations of HI and I are [HI] = 0.115 M and [I ] = 0.250 M, the equilibrium 2 2 concentration of [2 ] is: a) 0.135 M -4 b) 5.75 × 10 M c) 1.74 × 10 M d) 9.56 M -3 e) 5.00 × 10 M Page 2 of 16 5. A total of 0.12 g of a compound is dissolved in 10.0 g benzene. The resulting solution freezes at 4.62 °C. Pure benzene freezes at 5.48 °C and has a freezing point depression constant of K = 4.90 °C/m. What is the molecular mass of the compound, assuming it is f not an electrolyte? a) 68 g mol-1 -1 b) 106 g mol c) 570 g mol-1 -1 d) 11 g mol e) 57 g mol-1 2 2 6. For the formation of NO2, Kc= [NO ]2/([NO] [O ]).2At equilibrium in a 2.50 L container, there are 3.00 mol NO, 4.00 mol O2 and 22.0 mol NO .2The value of K cs: a) 3.75 b) 13.4 c) 33.6 d) 5.38 e) 0.0116 7. A reaction is always spontaneous if: i) ΔG is a negative value ii) both enthalpy and entropy increase iii) ΔH is negative and ΔS is positive iv) both enthalpy and entropy decrease v) ΔH is positive and ΔS is negative a) i and iii b) cannot be determined without temperature c) i and ii d) iii and iv e) ii and v 8. Henry’s Law constants for aqueous solutions at 25 °C are 8.20 × 10 molal/mmHg for N 2nd 1.62 × 10 -6molal/mmHg for O . 2etermine the solubility of nitrogen in water under an atmospheric pressure of 760 mmHg, assuming that air is 80% N 2nd 20% O , 2 by mole. a) 4.99 × 10-4m b) 1.23 × 10-3m c) 6.23 × 10-4m -4 d) 1.25 × 10 m e) 5.16 × 10-3m Page 3 of 16 9. The element oxygen was prepared by Joseph Priestley in 1774 by heating mercury(II) oxide. HgO(s) ↔ Hg(l) + ½O (g2 ΔH° = 90.84 kJ Use the data given below to estimate the temperature at which this reaction will become spontaneous under standard state conditions. S°(Hg) = 76.02 J/K⋅mol S°(O2) = 205.0 J/K⋅mol S°(HgO) = 70.29 J/K⋅mol a) 840 K b) 108 K c) 620 K d) 430 K e) 775 K 10. Commercial perchloric acid is 70.0% by mass, HClO (aq), and has a density of 1.67 4 g/mL. Calculate the molarity of perchloric acid in the solution, assuming the molecular weight of HClO i4 100.5 g/mol. a) 23.7 M b) 1.17 M c) 16.5 M d) 0.12 M e) 11.6 M 11. The following reaction is exothermic: 2N 2(g) → 2N (g2 + O (g)2 This means the reaction a) will be spontaneous only at low temperatures. b) is not spontaneous at any temperature. c) will be spontaneous only at high temperatures. d) will be spontaneous at all temperatures. e) none of the above 12. If ΔG is positive for a certain reaction at a given T and P, then: a) the reaction is endothermic b) the reaction is spontaneous at high temperatures. c) one would need to know the Kelvin temperature to determine spontaneity. d) the reverse of the reaction is spontaneous. e) the system is in equilibrium. Page 4 of 16 13. For Cl2O(g) + 3/2 O2(g) → 2 ClO 2 ΔH° = 126 kJ/mol and ΔS° = -74.9 J/mol-K at 377 °C. What is Keq a) 2.66 b) 6.12 × 107 c) 9.17 × 1015 d) 4.27 × 1022 14 e) 1.07 × 10 14. Consider the following reaction: C(s) + H2O(g) ↔CO(g) + H (g2 At equilibrium at a certain temperature, [H O(g)] = 0.12 M, and [CO(g)] = [H (g)] = 1.2 2 2 M. If suddenly these concentrations are increased by 0.50 M, which of the following is true? a) more H2O(g) will be formed b) Kc= 4.66 c) Since Kcdoes not change, nothing happens. d) more products are formed e) All the additional H O(g) is consumed 2 15. Given the following: I) N O(g) + 1/2 O (g) ↔ 2NO(g) K = 1.7 × 10 -13 2 2 c II) N2(g) + O2(g) ↔ 2NO(g) K c 4.1 × 10 -31 Find the value of the equilibrium constant for the following equilibrium reaction: N 2g) + 1/2 O2(g) ↔N O2g) a) 7.0 × 1044 -9 b) 1.6 × 10 c) 2.4 × 1018 -22 d) 2.6 × 10 e) 4.2 × 107 3 16. Calculate the temperature at whicheq for a reaction is 1.04 × 10 if ΔH° = -83.2 kJ/mol and ΔS° = -246 J/mol ∙ K. a) 307 K b) 274 K c) 0.274 K d) cannot be determined without ΔG° e) 0.307 K Page 5 of 16 17. The vapor pressures of pure hexane and pure heptane at 25 °C are 151.4 mmHg and 45.62 mmHg respectively. An ideal solution contains 0.700 mol fraction hexane and 0.300 mol fraction heptane. What is the composition of the vapor in equilibrium with this solution at 25 °C? a) 70.0% hexane, 30.0% heptane b) 88.6% hexane, 11.4 % heptane c) 23.2% hexane, 76.8% heptane d) 76.8% hexane, 23.2% heptane e) 11.4% hexane, 88.6% heptane 18. Consider the following reaction at equilibrium: 2SO 2g) + O (2) ↔ 2SO (g)3ΔH° = -196.6 kJ/mol The equilibrium is displaced to the left if: a)
More Less

Related notes for CHEM 110

Log In


OR

Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.

Submit