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FACULTY OF SCIENCE
MID-TERM EXAMINATION
CHEMISTRY 120
GENERAL CHEMISTRY
Examiners: Prof. B. Siwick Name:_________________________
Prof. A. Mittermaier
Prof. J. Schwarcz
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 4 ). If
not, fill that in.
2. This examination comprises 30 questions (14 pages including cover
page and 4 blank pages). All questions are of equal value.
3. Transfer answers to the scantron computer scorecard provided.
4. Both the scorecard and the examination paper will be collected
separately at the end of the examination period.
5. Simple Calculators are allowed, and translation dictionaries. NO
notes or texts are allowed.
6. 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.
NOTE TO INVIGILATORS: At the end of the exam, both scorecards and exam papers should be collected. Collect scorecards separately.
THESE DATA WILL BE PROVIDED ON THE MIDTERM
EXAMINATION
STP: 0°C and 1 atm 1 mol gas at STP: 22.4 L k = 1.38 x 10 –23^ J/K 0 K = – 273.15 °C e = 2.718 1 Pa = 1 N/m^2 g = 9.81 m/s 2 1 atm = 101.3 kPa = 760 Torr π = 3.14 1 bar = 100,000 Pa = 100 kPa R = 8.314 J/(mol K) 1 J = 1 kg m^2 /s 2 = 1 kPa L
= 0.08206 L atm /(mol K) 1 mol = 6.02 x 10 23 molecules
PV = nRT
2 2
2 2
1 1
1 1
n T
PV
nT
PV
RT
MP
d =
RT
MPV
m =
2
mu
V
N
P =
A
k
N
RT
e
M
RT
u rms
= P = hdg
Integrated Rate Laws: Arrhenius Equation:
Order 0: [A] = [A] 0 - k t
Ea / RT
k Ae
−
Order 1: [A] = [A] 0 e-^ k t
2
1 2 1
ln a
k E
k R T T
Order 2: 1/[A] = 1/[A] 0 + kt
The standard enthalpy of formation for CuSO 4 · 5H 2 O(s) is -2278.0 kJ/mole at 25°C. The chemical equation to which this value applies is: a) Cu(s) + S(s) + 5 H 2 O(g) + 2 O 2 (g) → CuSO 4 · 5H 2 O(s) b) Cu(s) + SO 4 (g) + 5 H 2 O(g) → CuSO 4 · 5H 2 O(s) c) Cu(s) + S(s) + 9/2 O 2 (g) + 5 H 2 (g) → CuSO 4 · 5H 2 O(s) d) 2Cu(s) + 2 SO 2 (g) + 5 H 2 O(g) → 2CuSO 4 · 5H 2 O(s) e) Cu(s) + S(s) + 5/9 O 2 (g) + 5 H 2 (g) → CuSO 4 · 5H 2 O(s)
Choose the INCORRECT statement. a) The heat capacity is the quantity of heat required to change the temperature of the system by one degree. b) The temperature of two gases is equal when the average kinetic energy per molecule is the same in each. c) Specific heat capacity is an extensive quantity. d) The law of conservation of energy can be written: qsystem + qsurroundings = 0. e) In general, the specific heat capacity of a substance in solid form is lower than that of the liquid form.
Calculate ΔH°f of octane, C 8 H 18 (l), given the enthalpy of combustion of octane to CO 2 (g) and H 2 O(l), -5471 kJ/mol, and the standard enthalpies of formation of CO 2 (g) and H 2 O(l), -393.5 kJ/mol and -285.8 kJ/mol, respectively. a) +4792 kJ/mol b) -4792 kJ/mol c) +249.2 kJ/mol d) -249.2 kJ/mol e) +589.1 kJ/mol
For the reaction H 2 (g) + 1/2 O 2 (g) → H 2 O(g) ΔH° = -241.8 kJ/mol, what quantity of heat, in kJ, evolved when a 72.0 g mixture containing equal parts of H 2 and O 2 (by mass) is burned? a) 1088 kJ b) 544 kJ c) 272 kJ d) 8630 kJ e) 4860 kJ
Which of the following is NOT a thermodynamic function of state: a) temperature b) enthalpy c) density d) heat e) volume
- For the reaction: 2N2O5(g) → 4NO2(g) + O2(g) at the time when N2O5 is being
consumed at a rate of - 1.2 × 10 - 4 M/s, what is the rate at which O2 is being formed? a) 2.4 × 10 - 4 M/s b) 3.0 × 10 - 5 M/s c) 1.2 × 10 - 4 M/s d) 4.8 × 10 - 4 M/s e) 6.0 × 10 - 5 M/s
Define "rate law". a) An equation derived using collision theory that describes how the rate of reaction depends on the concentration of reactants. b) A statement that describes how the rate of a reaction depends on the concentration of reactants derived from the balanced equation. c) An equation derived using collision theory that describes how the rate of reaction depends on temperature, orientation and number of collisions d) An experimentally determined equation that describes how the rate of reaction depends on temperature, orientation and number of collisions. e) An experimentally determined equation that describes how the rate of reaction depends on the concentration of reactants.
Data for the reaction A + B → C are given below. Find the rate constant for this system. Experiment [A], M [B], M Initial rate, M/s 1 0.030 0.060 2.5 × 10 -^5 2 0.030 0.020 2.5 × 10 -^5 3 0.060 0.060 10.0 × 10 -^5 a) 2.8 × 10 - 2 Ms-^1 b) 2.8 × 10 - 2 M2s-^1 c) 1.7 × 10 - 3 M-1s-^1 d) 2.8 × 10 - 2 M-1s-^1 e) 1.7 × 10 - 3 Ms-^1
In the first order, reaction A → products, [A] = 0.400 M initially and 0.250 M after 15.0 min, what will [A] be after 175 min? a) 2.31 × 10 - 1 M b) 3.70 × 10 - 2 M c) 1.04 × 10 - 3 M d) 6.024 × 10 - 3 M e) 1.67 × 10 - 3 M
250.0 g of hot coffee at 95.0 °C are placed in a 0.200 kg mug at 20.0 °C. The specific heat of the coffee is 4.00 J/g °C, while that of the mug is 0.80 J/g °C. Assuming no heat is lost to the surroundings, what is the final temperature of the system: mug + coffee? a) 84.7 °C b) 61.7 °C c) 76.0 °C d) 57.5 °C e) 117 °C
Some “beetles” defend themselves by spraying hot quinone, C 6 H 4 O 2 (l), at their enemies. Calculate ΔH° for the reaction: C 6 H 4 (OH) 2 (l) + H 2 O 2 (l) → C 6 H 4 O 2 (l) + 2H 2 O(l)
Given: C 6 H 4 (OH) 2 (l) → C 6 H 4 O 2 (l) + H 2 (g) ΔH°= +177.4 kJ, and the standard enthalpies of formation of H 2 O 2 (l) and H 2 O(l) are -187.4 and -285. kJ/mol, respectively.
a) +79.00 kJ b) -384.2 kJ c) -206.8 kJ d) -561.6 kJ e) 624.2 kJ
Enthalpy is defined as: a) the energy contained within a system b) the heat of combustion c) the work not limited to pressure volume work d) the sum of the kinetic and potential energies e) the sum of the internal energy and the pressure-volume product of a system.
For the reaction: 2N2O5(g) → 4NO2(g) + O2(g) the rate law is:
t
O
Δ [ 2 ]
= k [N2O5]
At 300 K, the half-life is 2.50 × 104 seconds and the activation energy is 103.3 kJ/mol O2. What is the rate constant at 310 K?
a) 7.29 × 10 - 8 s-^1 b) 1.05 × 10 - 4 s-^1 c) 7.29 × 10 - 6 s-^1 d) 2.78 × 10 - 5 s-^1 e) (^) 3.70 × 10 - 5 s- 1
- For the reaction C2H4Br2 + 3KI → C2H4 + 2KBr + KI3, initial rate data at 60 °C are
[C2H4Br2], M [KI], M Δ[KI3]/Δt (M/min) 0.500 1.80 0. 0.500 7.20 1. 1.500 1.80 0.
The rate law is:
a) rate = k [KI][C2H4Br2] b) rate = k [KI][C2H4Br2] c) rate = k [KI] d) rate = k [KI] e) rate = k [C2H4Br2]
For a second order reaction, what are the correct dimensions for the rate constant? a) 1 b) M-^1 · time c) M · time-^2 d) M-^1 · time-^1 e) M · time-^1
The first-order reaction A → Products has a half-life, t 1/2, of 55.0 min at 25 °C and
6.8 min at 100 °C. What is the activation energy for this reaction? a) - 25.8 kJ/mol b) - 38.8 kJ/mol c) 25.8 kJ/mol d) 38.8 kJ/mol e) 347 kJ/mol
- Why is rate = k [HgCl2] 2[C2O4^2 - ] not the rate law for the following reaction if the
reaction proceeds by the mechanism given? 2HgCl2 + C2O4^2 -^ → 2Cl-^ + 2CO2 + Hg2Cl2 (overall reaction) Mechanism: HgCl2 + C2O4^2 -^ ⇌ HgCl2C2O4^2 -^ (Fast) HgCl2C2O4^2 -^ + C2O4^2 -^ → Hg + 2C2O4Cl2-^ (Slow) Hg + HgCl2 → Hg2Cl2 (Fast) 2C2O4Cl2-^ → C2O4^2 -^ + 2Cl-^ + 2CO2 (Fast)
a) The steps do not add to the overall reaction b) The first step is not the slow step. c) The rate law does not agree with the overall reaction. d) The exponents of HgCl2 and C2O4^2 -^ are not equal. e) The rate law calculated from the slow step is not the rate law: rate = k [HgCl2]2[C2O4^2 - ].
Which of the following gases is less dense than air? (density of air = 1.3 g/L at STP) a) CO 2 b) NO 3 c) CH (^4) d) Cl (^2) e) Ar
Consider the following reaction:
N 2 (g) + 3 H 2 (g) → 2 NH 3 (g)
What volume of NH 3 (g) can be produced from 400.0 L of H 2 (g) if the gases are measured at 300 °C and 450 atm pressure? a) 267 L b) 600 L c) 400 L d) 800 L e) 133 L
- Nitroglycerine (C 3 H 5 N 3 O 9 ) decomposes according to the reaction:
4 C 3 H 5 N 3 O 9 (l) → 12 CO 2 (g) + 10 H 2 O (g) + 6 N 2 (g) + O 2 (g).
If 100g of nitroglycerine are detonated, what volume of gas is produced at STP? a) 9.87 L b) 162 L c) 71.5 L d) 39.5 L e) 286.0 L
- A 10 L container holds a mixture of 5 gases at 0ºC. The composition of the mixture is given below. What is the partial pressure of N 2?
N 2 (g) 10 g O 2 (g) 1 g H 2 (g) 20 g CO 2 (g) 7 g He (g) 3 g a) 608 torr b) 800 torr c) 1340 torr d) 932 torr e) 22 torr
