CHEM 1411 Practice Exam#2 (chapters 5-8))
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Part I. Multiple choice questions (2 points each)
Direction-Please bubble your correct answer in in the scantron.
1. How many moles of N2 gas occupy 11.2 liters volume a STP
condition?
A. 1.0 mol
B. 2.0 mol
C. 0.5 mol
D. cannot be determine
2. Which of the following is/are not characteristic of gases?
I. high density
II. formation of homogeneous mixtures
III. low intermolecular forces
A. I only
B. I and III
C. I, II, and III
D. II and III
3. An unknown gas "X" effuses four times faster than a sample of
SO2(g) through a porous container. Which of the following is the
unknown gas ?
A. H2
B. CH4
C. He
D. NO
4. What volume of air at 760 torr would have to be put into a car tire with a
volume of 15 L if the pressure in the car tire is to be 2.38 atm?
A. 6.3 L
B. 35.7 L
C. 0.05 L
D. 21.3 L
5. If 400 mL of a gas sample at 25˚C expands to 600 mL, the resulting
temperature of the gas is
A. 37.5˚C
B. 433.5˚C C. 174˚C
D. 447˚C
6. At STP, 48 g of O2 will occupy…
A. 67.2 L
B. 33.6 L
C. 22.4 L
D. 32 L
7. In which of the following states of matter there is almost no difference in
physical behavior between different compounds?
A. solid
B. liquid
C. gas
D. all of the above
8. In a combustion reaction…….
A. An element combine with other element to form a compound
B. A substance rapidly reacts with oxygen to produce heat and light
C. Carbon reacts with bromine to produce carbon tetrabromide
D. Non of the above
9. The standard enthalpy of formation (ΔH°f ) for any element in its
standard state is
A. 0
B. 100 kj mol−1
C. 10 kj mol−1
D. − 100 kj mol−1
10. How many kJ of heat must be removed from 1000. g of water (specific
heat 4.184 J /g.˚C) to lower the temperature from 18.0°C to 12.0°C?
A. 2.5x10-2 kJ
B. 1.4 kJ
C. 4.2 kJ
D. 25 kJ
11. From the following heats of reaction,
2C (graphite) + H2 (g)  C2H2 (g)
ΔH˚ = 227 kJ/mole
6C (graphite) + 3H2 (g)  C6H6 (l)
ΔH˚ = 49 kJ/mole
calculate the heat for the reaction
3C2H2 (g)  C6H6 (l)
a. 632 kJ/mole
b. -632 kJ/mole
c. -178 kJ/mole
d. 178 kJ/mole
12. The heat of combustion of fructose, C6H12O6, is -2812 kJ/mole. Using
f for fructose.
C6H12O6 (s) + 6 O2(g)
 6 CO2(g) + 6 H2O (l)
ΔH°f ( CO2 ) = -393.5 KJ/mole
A. -210.3 kJ
B. 210.3 kJ
ΔH°f (H2O) = - 285.83 KJ/mole
C. -1264 kJ
D. 1264 kJ
13. Consider the combustion reaction of ethane gas, C2H6(g):
C2H6(g) + 7/2O2(g)  2CO2(g) + 3H2O(g)
ΔH˚ = -1430 kJ
What is the enthalpy change for the reverse reaction if whole number
Coefficients are used?
A. +1430 kJ
B. -1430 kJ
C. -2860 kJ
D. +2860 kJ
14. Determine the value of ΔH˚ (in Kj) for the following reaction
2SO2 (g) + O2 ----------> 2SO3(g)
(ΔH˚f for SO2 = −297 kj and ΔH˚f for SO3 = −396 kj)
A. −198kJ
B. + 198 kj
C. −99 kj
D. +99 kj
15. Use the information shown for equations 1 and 2 to determine the value
of ΔH˚ (in Kj) for equation 3.
1. 2S (s) + 3O2 (g) --------> 2SO3 (g)
ΔH˚ = -790 Kj
2. S (s) + O2 (g) --------------> SO2 (g)
ΔH˚ = - 297 Kj
3. 2SO2 (g) + O2 ---------------> 2SO3 (g)
A. −196 kj
B. 493 kj
C. −493 kj
ΔH˚ = ?
D. 196 kj
16. Use the information shown for equations 1 and 2 to determine the value
of ΔH˚ (in Kj) for equation 3.
1. 2 NO ---------> N2 + O2
ΔH˚ = -180kJ
2. 2NO + O2 -----------> 2NO2
ΔH˚ = -112kJ
3. N2 + 2O2 -----------> 2NO2
ΔH˚ = ?
A. − 68 kj
B. 68 kj
C. 292 kj
D. −292 kj
17. 2CO (g) + O2 (g) ----> 2CO2 (g)
The value of heat exchange ΔH˚ for the above reaction is -482 Kj.
What is the amount of heat (kj) exchanged when 10 g of CO ( g)
Completely reacts?
A. −172.14 kj
B. 86.07 kj
C. −86.07 kj
D. non
18. If the value of heat exchange ΔH˚ of the following reaction is -240 kj and
the value of heat energy ( enthalpy) of C2H4 is 52 Kj. What is the value of
heat energy for C2H2?
C2H2 (g) + H2(g) → C2H4 (g)
A. 292 kj
B. −292 kj
C. −188 kj
D. 188 kj
19. Which one of the following acids is a weak electrolyte ?
A. HCl
B. HNO3
C. H2SO4
D. HSO4-
20. What is the frequency of radiation that has a wavelength of
0.589 pm?
A. 1.96 x 10-21 s-1
B. 5.09 s-1
C. 5.09 x 108 s-1 D. 5.09 x 1020 s-1
21. Statement, electrons fill the orbital singlet then double up is
called………….
A. Aufbau principle
B. Hund's rule
C. Puali's exclusion principle
D. none of these
22. For n = 4, what are the possible values of l?
A. 3, 2, 1
B. 4, 3, 2, 1
C.
3, 2, 1, 0
D. 4, 3, 2, 1, 0
23. What is the maximum number of electrons that can occupy the
subshell 3d?
A. 1
B. 3
C. 5
D. 10
24. Write the electron configuration for the atom Cu, using the
appropriate noble-gas inner core for abbreviation.
A. [Ar]4s23d10
B. [Ar]4s24d9 C. [Ar]4s13d10 D. [Kr]4s13d10
25. The maximum electron population in a shell, where n = 3 is
A. 3
B. 18
C. 12
D. 8
26. Arrange the orbitals 4s,4p,4d,and 4f in the order of increasing energy
A. 4s<4p<4d<4f
B. 4f<4d<4p<4s
C. 4p<4s<4f<d
d.non
27. What is the energy (in joules) of a photon with a wavelength of
5.00 x 104nm?
A. 3.98x10-30 J
B. 3.98 x10-21 J
C. 3.98 x 10-12 J
D. 3.98 J
28. Which set of elements is in order of increasing atomic size
A. C, N, O
B). Na, K, Rb
c). Br, Cl, F
D. Non
29. Which element from the following has the greatest electronegativity?
A. Si
B. Mg
C. P
d) S
30. Which one of the following has the largest radius ?
A. K+
B. Cl-
C. K
D. Na
31. Which of the following species has the highest ionization energy?
A. K
B. Na
C. F
D. O
32. The effective nuclear charge in a period
A. Increases from left to right
B. Decreases from left to right
C. does not change
D. first increases and then decreases
33. The atomic radius in the periodic table
A.
B.
C.
D.
Increases from top to bottom in a group
Decreases from left to right in a period
A&B
Non
34. Which of the following species are isoelectronic?
A. Co3+ and Ar
B. F- and Ne
C. Fe3+ and N3-
35. Which one of the following is a f-block element
A. Rb
B. Ru
C. Lu
Rn
D. No
Part II. Show all your work for complete credit (5 points each)
36. A certain substance strongly absorbs infrared light having a wavelength of
6.85 μm. What is the frequency of this light in hertz?
37. Which of the following atoms in their ground states are expected to be
paramagnetic: (a) Mn, (b) As, (c) S, (d) Sr, (e) Ar ?
38. Write electron configuration and core configuration for cromium and
determine the total number of unpaired electrons.
39. Using the following information and the fact that the average C-H bond
enthalpy is 414 kj/mol, estimate the standard enthalpy of formation of
methane (CH4)
C (s)  C(g) ∆H° = 716 kj/mol
2H2 (g)  4H(g) ∆H° = 872.8 kj/mol
40. 2.50 g CO2 gas occupies 5.6 liters at 700 torr.
a) Calculate the temperature of gas in 0C.
b) b) What is the density of CO2 gas at STP condition?
41. One thermochemical equation for the reaction of carbon monoxide with
oxygen is
3CO(g) + 3/2 O2(g) → 3CO2(g)
ΔH˚ = −849 kj
a. What is ΔH˚ for the formation of 1 mol of CO2 by this reaction?
b. Write the thermochemical equation for the reaction using 2 mol of CO
Bonus Question ( 10 points) – Solve one of the following problems: Please
show all your work.
1. Given the following thermochemical equations,
2Cu(s) + O2(g)  2CuO(s)
ΔH˚= -115 kj
Cu(s) + S(s)  CuS(s)
ΔH˚= -53.1 kj
S(s) + O2(g)  SO2(g)
ΔH˚= -297 kj
4CuS(s) + 2CuO(s)  3Cu2S(s) + SO2(g)
Calculate ΔH˚ (in kilojoules) for the reaction
Cus(s) + Cu(s)  C2S
ΔH˚= -13.1 kj
2. Assuming no change in temperature and pressure calculate the volume of
Oxygen in liters required for the combustion of 14.9 L of Butane (C4H10)
Practice Exam 2 Key.
Part 1. Multiple choice
1-C, 2-A, 3-C,
if rate of SO2 is r1, the rate of X, r2 would be 4r1
MSO2 = 64, Mx = ?
r1
Use
r2
=

(r1/4r1)2 = Mx/64
1/16 = Mx/64
Mx = 64/16=4
Since the molecular mass of X is 4, it is He.
4-B, 5-C, 6-B, 7-C, 8-B; 9-A, 10-D,
q = msΔt
m = 1000 g
s = 4.184 J/g.˚C
Δt = 18-12 = 6 ˚C
q = 1000 g x 4.184 J/g.˚C x 6˚C
25104 J
q = 25.104 KJ
11-B
2C (graphite) + H2 (g)  C2H2 (g)
ΔH = 227 kJ/mole
6C (graphite) + 3H2 (g)  C6H6 (l)
ΔH = 49 kJ/mole
M2
M1
calculate the heat for the reaction
3C2H2 (g)  C6H6 (l)
Entholpy of formation of C2H2 = 227 KJ/mole
Entholpy of formation of C6H6 = 49 KJ/mole
Hess’s Law:
ΔHReaction = (ΔHProducts) – (ΔH Reactants)
=(49) – (3 x 227)
=49-681
= - 632 KJ/mole
12-C
C6H12O6 (s) + 6 O2(g)
 6 CO2(g) + 6 H2O ; ΔH = - 2812 KJ/mole
ΔH°f ( CO2 ) = -393.5 KJ/mole Δ H°f (H2O) = - 285.83 KJ/mole
Hess’s Law:
ΔH˚Reaction = (ΔH˚Products) – (ΔH˚ Reactants)
-2812 = [(6 x -393.5) + (6 x – 285.83)] – [ (ΔHC6H12O6)+ (6 x 0)]
-2812 = [(-2361) + ( - 1714.98)] – [(ΔHC6H12O6) + 0]
-2812 = [ - 4075.98] – [(ΔHC6H12O6)]
-
ΔHC6H12O6 = -2812 + 4075.98
ΔHC6H12O6 = + 1263.98
ΔHC6H12O6 = - 1263.98 ≈ -1264
13-D
C2H6(g) + 7/2O2(g)  2CO2(g) + 3H2O(g)
Δ H = -1430 kJ
What is the enthalpy change for the reverse reaction if whole number
Coefficients are used?
Whole number equation:
(C2H6(g) + 7/2O2(g)  2CO2(g) + 3H2O(g)
2C2H6(g) + 7O2(g)  4CO2(g) + 6H2O(g)
Δ H = -1430 kJ) 2
Δ H = -2860 kJ
Reverse equation:
4CO2(g) + 6 H2O(g)  2C2H6(g)+ 7O2(g) ΔH = + 2860 KJ
14-A
2SO2 (g) + O2 ----------> 2SO3(g)
(ΔHf for SO2 = −297 kj and ΔHf for SO3 = −396 kj)
Hess’s Law:
ΔHReaction = (ΔHProducts) – (ΔH Reactants)
ΔH = [(2 x -396)] – [(2 x -297) + 0]
=[ -792] – [-594]
= - 792 + 594 = -198 KJ
15-A
1. 2S (s) + 3O2 (g) --------> 2SO3 (g) H = -790 Kj
2. S (s) + O2 (g) --------------> SO2 (g) H = - 297 Kj
3. 2SO2 (g) + O2 ---------------> 2SO3 (g) ΔH = ?
ΔHReaction = (ΔHProducts) – (ΔH Reactants)
= [-790] – [ (2 x -297) + 0]
= (- 790) – ( - 594)
= -790 + 594 = -196 KJ
16-B
1. ΔH˚Reaction = (ΔH˚Products) – (ΔH˚ Reactants)
-180kJ
= [0] – [2 NO]
2NO = +180kj
2. 2NO + O2 -----------> 2NO2
ΔH˚ = -112kJ
ΔH˚Reaction = (ΔH˚Products) – (ΔH˚ Reactants)
(2NO2) – (180) = -112
2NO2 -180 = -112
2NO2 = -112 + 180
2NO2 = 68
3. N2 + 2O2 -----------> 2NO2
ΔH˚ = ?
ΔH˚Reaction = (ΔH˚Products) – (ΔH˚ Reactants)
ΔH˚ = [68] – [0]
ΔH˚ = 68
Alternate Procedure: Rearrange the equations
N2 + O2  2NO, ΔH˚= 180
2NO + O2  2NO2, ΔH˚ = -112
--------------------------------------------------------N2 + O2  2NO2, ΔH˚ = (180 + (-112) = 68
17-C
2CO (g) + O2 (g) ----> 2CO2 (g) ΔH˚= -482 Kj.
2 x 28 g of CO produces -482 kj
10 g of CO …………?
10 x -482/56 = -86.07 kj
18-A
(ΔH˚Products) – (ΔH˚ Reactants)= ΔH˚Reaction
[52] – [C2H2 + 0] = - 240
52 – C2H2 = - 240
-C2H2 = -240-52
-C2H2 = -292
C2H2 = 292 kj
19. D
20-D
ν = C/λ
C= 3 x 108 ms-1
λ = 0.589 pm = 0. 589 x 10-12 m
ν = 3x108 ms-1/0.589 x 10-12 m
ν = 5.09 x 1020 s-1
21-B, 22-C, 23-D, 24-C, 25-B, 26-A,
27-B,
E = hν,
ν = C/λ
E= h C/λ
h= Planck’s constant = 6.63 x 10-34 J.s
C= speed of light = 3.00 x 108 m/s
λ = wavelength = 5.00 x 104 nm
1 nm = 1x10-9 m
E = 6.63x10-34 J.s X 3.00 x 108 m/s
5.00 x 104 x 1x10-9 m
E = 3.98 x10-21 J
28-B, 29-D, 30-B, 31-C, 32-A, 33-C, 34-B, 35-C
Part II
36.
ν = C/λ
C = 3.00 x 108 m s-1, λ = 6.85μm
(Hz = 1s-1; 1μm = 10-6 m)
ν = 3.00 x 108 ms-1/6.85 x 10-6 m = 4.37 x1013 s-1 =4.37x1013 Hz
37. a. paramagnetic, b. paramagnetic, c. paramagnetic,
d. not a paramagnetic, e. not a paramagnetic
38.
Cr (24)
Electronic configuration :1s22s22p63s23p64s23d4
Core configuration: [Ar] 3d44s2
Since half filled, or fully filled orbitals give grater stability, the core
configuration is [Ar] 3d54s1 and total unpaired electrons are 6
39. C + 2H2  CH4
H0 = total energy input – total energy released
= BE(reactants) – BE(products)
(716 + 872.8) – ( 4x 414) = - 67.2 kj/mol
40. use PV = nRT, n= 2.5/44= 0.0568 moles
a. T = 1106 k = 833 °C
b. D = MP/RT, where M= 44, P= 1 atm, R= 0.0821, T = 273 k
D = 1.96 g/L
41. a. for 1 mole of CO2 = -849/3 = -283 kj
b. 2CO + O2  2CO2 ΔH˚= -566 KJ
Bonus Questions:
1. Rearrange the equations as in Q. 16
2. Write the equation for combustion of butane and balance and then
calculate