Jan 18, 2012 ... Write your name also on the second part of this exam – on pages 5 and 8. 4.
Complete ... [internal energy, heat, entropy, work, enthalpy, Gibbs.
CHEMISTRY 122 Dr. Dolson
EXAM I
100 POINTS January 18, 2012
INSTRUCTIONS 1. 2. 3. 4. 5.
Write and mark your name and UID# on the blue scantron sheet. Mark your answers for questions 1-15 on the blue scantron sheet. Write your name also on the second part of this exam – on pages 5 and 8. Complete the calculations for questions 16-18 and show all work clearly. You may use a simple (nongraphing/nonprogrammable) scientific calculator. You may not share calculators or refer to notes or other references. 6. When finished, submit Part II of your exam (pages 5-8) and your scantron sheet for grading at the lecture table and show your picture ID.
Some potentially useful equations and relationships 1 cal = 4.184 J
1 L atm = 101.3 J
Ek = ½ m v 2
qp = ∆H
q = C ∆T
∆E = ∆H - P ∆V
qv = ∆E
∆G = ∆H - T ∆S
w = - P ∆V
C(J/°C) = (specific heat) x (mass) = (Cm ) x (moles) ∆H ≈ Σ D0 (all bonds broken) – Σ D0 (all bonds formed) PART I. Multiple Choice, 60 Points (4 pts/each) 1.
is a measure of the kinetic energy of molecular motion.
A. Entropy
B. Heat
C. Enthalpy
D. Temperature
2. Which of these is/are not state functions? [internal energy, heat, entropy, work, enthalpy, Gibbs energy] A. heat and work D. entropy and enthalpy 3. A. B. C. D.
B. Gibbs energy C. internal energy E. enthalpy and internal energy
The process of vaporization of a pure substance is
.
favored by enthalpy but disfavored by entropy disfavored by enthalpy and by entropy favored by enthalpy and by entropy disfavored by enthalpy but favored by entropy
4. The First Law of Thermodynamics states that the total internal energy of an isolated system is constant. A. TRUE
B. FALSE
5. Choose the correct value for ∆E for the case in which a system absorbs 500 J of heat from its surroundings while doing 1200 J of work on the surroundings. A. -1700 J 6. A. Entropy
B. +1700 J
C. -700 J
D. +700 J
E. -1200 J
is energy transferred between two objects as the result of a temperature difference. B. Heat
C. Enthalpy
D. Temperature Exam I - 1
Questions 7 - 11 are concerned with the dissociation reaction of the N2O4 molecule (a “dimer” of NO2 molecules held together by a weak N-N bond): N2O4 (g) → 2 NO2 (g), for which ∆H° = + 57 kJ , and ∆S° = + 176 J/K. 7. A. B. C. D.
The dissociation of N2O4 is
.
favored by enthalpy but disfavored by entropy disfavored by enthalpy and by entropy favored by enthalpy and by entropy disfavored by enthalpy but favored by entropy
8. The reaction is A. spontaneous at all temperatures C. spontaneous only for T325 K
B. 28.5 kJ of heat is evolved D. 88 J of heat is absorbed
Which of the following is true for this reaction at constant pressure ?
A. work is done by the system on the surroundings C. work is done on the system by the surroundings 11.
by the system.
This dissociation reaction is
A. endothermic
B. no work is done
.
B. exothermic
12. What is the specific heat (c, in J/g·°C) of a substance if 72 J of heat are required to raise the temperature of 12 grams of this substance by 15 ºC? A. 0.60
B. 0.50
C. 0.40
D. 0.30
E. 0.20
Questions 13-15 are concerned with the estimation of ∆H°° for a reaction using bond dissociation energy values. The problem is presented in question 13. Students are to provide answers for this problem on the scantron sheet for questions 13-15 13. Given the following bond dissociation energies, DH-H = 436 kJ/mol, DCl-Cl = 243 kJ/mol and DH-Cl = 432 kJ/mol, estimate ∆H for the reaction, H2 (g) + Cl2 (g) → 2 HCl (g). A. ∆H° ≈ +247 kJ
B. ∆H° ≈ -185 kJ
C. ∆H° ≈ -247 kJ
D. ∆H° ≈ +185 kJ
14.
Choose an answer (same or different) for question 13 and report it here.
15.
Choose an answer (same or different) for question 13 and report it here. End of the multiple choice questions.
Exam I - 2
CHEMISTRY 122 Dr. Dolson
EXAM I
100 POINTS January 18, 2012
NAME INSTRUCTIONS 1. PRINT YOUR NAME LEGIBLY on the line above and on the back of page 8. 2. Work problems 16-18. Show all work. 3. You may use a simple (nongraphing/nonprogrammable) scientific calculator. You may not share calculators or refer to notes or other references. 4. When finished, submit Part II of your exam (pages 5-8) and your scantron sheet for grading at the lecture table and show your picture ID.
PART II. SOLUTIONS TO PROBLEMS, 45 POINTS SHOW ALL WORK CLEARLY (including set ups) FOR FULL CREDIT 16. (15 pts) Use the stated standard enthalpies of formation to determine the standard enthalpy change for the following balanced chemical equation. Show your work clearly. Write your answer in the space provided. C2H2 (g) + 3 N2O (g) → 2 CO (g) + H2O (g) + 3 N2 (g) ∆H°f (C2H2 (g)) = + 227 kJ/mole ∆H°f (N2O (g)) = +82 kJ/mole ∆H°f (CO (g)) = - 111 kJ/mole ∆H°f (H2O (g)) = - 242 kJ/mole
∆H°rxn =
Exam I - 5
kJ
17. (15 pts) When 0.0400 mole of calcium oxide, CaO, is added to 100.0 mL of water at 20.00 °C in a calorimeter, the temperature of the water increased to 27.83 °C. Assuming that the specific heat of the solution is 4.184 J/(g⋅°C) and that the calorimeter itself absorbs a negligible amount of heat, calculate ∆H (in kJ) for the reaction, CaO(s) + H2O(l) → Ca(OH)2(aq) Show your work clearly, and fill in the blank spaces below. Please limit your numerical answers to 3 significant digits. (A)
The experimental value of qcal =
kJ
(B)
∆H for the stated reaction in kJ is, ∆H =
kJ
Exam I - 6
18.
(15 pts) Use Hess’ law and the two reactions below to determine ∆H° for the stated reaction: NO (g) + O3 (g) → NO2 (g) + O2 (g)
Show your work clearly below and write your answer in the space provided: ∆H°rxn = (1) (2)
3 O2 (g) → 2 O3 (g) 2 NO (g) + O2 (g) → 2 NO2 (g)
kJ ∆H1° = + 286 kJ ∆H2° = - 114 kJ
Exam I - 7
