Download CHM2045 Exam 2 Review Questions Fall 2015

CHM2045 Exam 2 Review Questions
Fall 2015
The steps to solving any chemistry problem
1) Read Question
2) Re-read Question
3) Write down everything you are given
4) Write down what you are trying to find
1) The overall reaction in the commercial heat pack can be represented as
4Fe(s) + 3O2(g) → 2Fe2O3(s) ∆H = – 1652 kJ
How much heat is released when 30.0 g Fe and 6.00 g O2 are reacted?
2) 21. The space shuttle orbiter utilizes the oxidation of methylhydrazine by dinitrogen tetroxide for
propulsion: 4N2H3CH3(l) + 5N2O4(l)  12H2O(g) + 9N2(g) + 4CO2(g)
∆Hf : N2H3CH3(l) = +54 kJ/mol; N2O4(l) = – 20 kJ/mol; H2O(g) = – 242 kJ/mol; CO2(g) = – 393.5 kJ/mol
Calculate the ∆Ho for this reaction.
3) Use the following information to find ΔH°f of gaseous HCl:
N2(g) + 3 H2(g) → 2 NH3(g)
ΔH°rxn = − 91.8 kJ
N2(g) + 4 H2(g) + Cl2(g) → 2 NH4Cl(s)
ΔH°rxn = − 628.8 kJ
NH3(g) + HCl(g) → NH4Cl(s)
ΔH°rxn = − 176.2 kJ
CHM2045 Exam 2 Review Questions
Fall 2015
4) Both Mg3N2 (100.9 g/mol) and Mg(OH)2 (58.3 g/mol) can be converted to MgO (40.3 g/mol) by
appropriate means. If a 2.00 g mixture of these two compounds is converted, and 1.89 g of MgO is
obtained, what is the approximate mass percent of Mg3N2 in the mixture?
5) A 2.50 mol sample of benzene (C6H6, 78.11 g/mol) was burned in a bomb calorimeter with a heat
capacity of 800 J/°C. The calorimeter contained 85g of water (4.18 J/g°C), and the temperature
increased by 10°C. What is the molar enthalpy of combustion of benzene in kJ/mol of benzene?
6) A certain light bulb consumes 200 J of energy per second. If a light bulb converts all of this energy to
500 nm light, how many photons are produced each second?
CHM2045 Exam 2 Review Questions
Fall 2015
7) Enormous numbers of microwave photons are needed to warm household samples. A bowl of soup
containing 400g of water is heated in a microwave oven from 20.0°C to 98.0°C using radiation with
wavelength 122 mm. Assuming that the specific heat capacity of the soup is the same as that of
water (4.184 J/g°C) and no heat loss to the bowl, which choice is closest to the number of photons
absorbed?
8)
Select the false statement :
(1) Photons of green light have greater energy than photons of red light
(2) Light emitted by an n = 4 to n = 2 transition will have greater energy than light from an
n = 3 to n = 1 transition
(3) The energy of a photon is directly related to its frequency and inversely related to its
wavelength
(4) There are only two subshells associated with the n = 2 shell of an atom
(5) In accordance with Hund's rule, a ground-state phosphorus atom contains three unpaired
electrons in its 3p subshell
9)
Which choice contains a possible set of quantum numbers (n, l, ml, ms) for the first electron
removed from a ground-state vanadium atom?
(1) 4, 0, 0, +½
(2) 4, 1, 0, –½
(3) 3, 2, 0, +½
(4) 3, 1, 1, +½
(5) 4, 2, 2, –½
CHM2045 Exam 2 Review Questions
Fall 2015
10) Select the false statement below :
(1) Fe has 2 outer electrons, 8 valence electrons, and 18 core electrons
(2) Fe2+ is more paramagnetic (has more unpaired electrons) than Fe3+
(3) Fe3+ is isoelectronic with Mn2+
(4) none of these ions (Fe2+, Fe3+, Mn2+) have any electrons in the 4s subshell
(5) Fe3+ is predicted to be a stronger potential oxidizing agent (can be reduced more) than Fe2+
11) Estimate the standard molar enthalpy of formation (ΔH°f) of ClNO, expressed as kJ per mol of ClNO
formed, using any of the following average bond enthalpy data that may apply : Cl—Cl, 243 kJ/mol ;
N—N, 160 kJ/mol ; N=N, 418 kJ/mol ; N≡N, 945 kJ/mol ; O—O, 204 kJ/mol ; O=O, 498 kJ/mol ; Cl—N,
200 kJ/mol ; N=O, 607 kJ/mol ; N—O, 201 kJ/mol.
12) Rank the following five ions in order of increasing ionic radius:
Rb+, In3+, Al3+, Sr2+, Ga3+
CHM2045 Exam 2 Review Questions
Fall 2015
13) Select the false statements below.
A) In any given atom, a l = 2 subshell can accommodate up to 5 electrons that have ms = –1/2
B) The n = 1 shell of any given atom can accommodate up to 2 electrons
C) The following set of quantum numbers is allowed: n = 4, l = 2, ml = −2, ms = +1/2
D) The n = 4 shell of any given atom has a total of 7 orbitals
E) In any given atom, a l = 1 subshell has 3 degenerate orbitals
F) n = principal energy level
G) l = angular momentum and therefore determines the speed of the orbital
H) The sublevel 3d would have n = 3 and l = 2
14) Which of the following transitions in a hydrogen atom would emit the longest wavelength photon?
(1) n = 1 to n = 2 (2) n = 3 to n = 2 (3) n = 5 to n = 1 (4) n = 2 to n = 8 (5) n = 6 to n = 5
15) Name the Period 3 element with the following successive ionization energies (in kJ/mol):
IE1
IE2
IE3
IE4
IE5
IE6
1012
1903
2910
4956
6278
22,230
16) Predict which of the following exhibits the longest bond length between the hydrogen atom and the
non-hydrogen atom.
(1) H2S
(2) HCl
(3) H2O
(4) HF
(5) HI
17) Why does sodium always occur as a monovalent cation (Na+) in compounds?
(1) Its electronegativity is too large
(2) Its 1st ionization energy is too large
(3) Its 2nd ionization energy is too large
(4) Its 1st electron affinity is too large
(5) Its 2nd electron affinity is too large
CHM2045 Exam 2 Review Questions
Fall 2015
18) Write out the following Lewis Structures
a) NO3b) SeCl4
c) ClF4+
d) NI3
e) C6H10 (There are two structures)
f) COCl2
19) Use the following information to calculate the lattice energy (ΔHlattice) per mole of potassium
fluoride.
K(s) + ½F2(g) → KF(s)
K(s) → K(g)
K(g) → K+(g) + e−
½F2(g) → F(g)
F(g) + e− → F−(g)
(1) −308 kJ/mol
ΔHreaction = −567 kJ
ΔHsublimation = +89 kJ
ΔHionization = IE1 of K = +419 kJ
ΔHbond-energy = ½BE of F2 = +79 kJ
ΔHelectron-affinity = EA1 of F = −328 kJ
(2) −826 kJ/mol
(3) −993 kJ/mol
(4) −1170 kJ/mol
(5) −662 kJ/mol
CHM2045 Exam 2 Review Questions
Fall 2015
20) How much energy is absorbed or released (identify which) when each of the following reactions
takes place? Use stoichiometric amounts in each case (e.g. 1.0 mol of CH4 and 2.0 mol of O2 for
problem #1)
1. CH4 (g) + 2 O2 (g)  CO2 (g) + 2 H2O (g)
2. 2 H2 (g) + O2 (g)  2 H2O (g)
The possible relevant bond energies are:
C—H 414 kJ/mol
O==O 502 kJ/mol
C==O 730 kJ/mol
O—H 464 kJ/mol
H—H 435 kJ/mol
Cl—Cl 243 kJ/mol
H—Cl 431 kJ/mol
C—Cl 331 kJ/mol
GOOD LUCK ON THE EXAM! 
-Broward Teaching Center