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Chemistry 210 • Exam 3 • Fall 2009
FREE RESPONSE:
Name:
Section:
Answer the following questions in the spaces provided. Show all work and express final answers with the
correct number of significant figures and units to receive full credit. If you use exponential notation for
your answer, you must use proper scientific notation.
Note: If a solution requires determination of a limiting reagent, you must in some way indicate you have
determined what the limiting reagent is.
1.
(4 points) Write a reaction for which the !Hrxn = !Hºformation for NH4Cl(s). Include states for all species.
2.
(8 points) Consider the reaction:
2 CO2(g)
"
2 CO(g) +
O2(g)
A) Calculate !H for the reaction above given the equations below with the enthalpies indicated:
2 CO(g)
"
2 C(s) + O2(g)
!H = 218 kJ
CO2(g)
"
C(s)
!H = 393 kJ
+ O2(g)
B) Draw an energy diagram that illustrates the relationships of the !H values for each of above reaction steps and the overall
reaction.
!H (kJ)
Reaction coordinate
3.
(12 points) A 3.00 g sample of ethanol (C2H5OH(l), Mm= 45.06 g/mol) is burned with excess oxygen inside a bomb calorimeter
(with a heat capacity you wish to determine) that holds 1.75 kg of water. The whole apparatus increases in temperature from
22.30 ºC to 27.65 ºC. Determine the heat capacity (Hc) of the calorimeter.
The combustion of ethanol is described by the equation:
C2H5OH(l)
4.
+
3 O2(g)
!
2 CO2(g)
!
2 N2H4(l)
+
3 H2O(g)
(8 points) Consider the reaction:
2 N2O(g)
+
4 H2O(g)
+
3 O2 (g)
If 6.25 g of dinitrogen monoxide is mixed with 8.00 g of water vapor, what quantity of heat is produced or consumed by the
resulting reaction?
5.
(8 points) To investigate the amount of heat absorbed by ammonium nitrate, 6.00 g NH4NO3 (Mm = 80.05 g/mol) is dissolved in
100.0 g of water at 24.5ºC in a container that absorbs a negligible amount of heat. The final temperature of the solution is 21.2°C.
The solution that results has a density of 1.02 g/mL a specific heat capacity of 4.21 J/g•C°.
Based on these data, determine the enthalpy of solution (enthalpy of dissolving) for ammonium nitrate (!H) in kJ/mol.
NH4NO3(s) ! NH4NO3(aq)
6.
(7 points) The energy required to remove the outermost electron from a mole of beryllium atoms is 899 kJ/mol. What is the
wavelength of a photon of EM radiation would have just enough energy to remove one electron from a single beryllium atom?
7.
(4 points) Sketch the shape of a single p-orbital:
8.
(9 points) Give the electron configuration for the following species. You may use noble gas abbreviations as appropriate.
K
Ag
Bi+5
Sketch the shape of a single d-orbital:
9.
(6 points) Draw the electron dot structure for the sulfate ion:
SO42–
You may draw one reasonable resonance structure.
What is the SHAPE of the sulfate ion? ___________________________________________
What is the O-S-O bond angle? __________________
10. (6 points) Draw all of the reasonable resonance structures for the nitrite ion:
What is the N-O bond order in the ion? ____________
What is the O-N-O bond angle? __________________
11. (6 points) Draw a reasonable Lewis structure for nitric acid:
What is the hybridization on the N? _____________
Assign formal charges to all of the atoms in the structure.
HNO3
NO2–
12. (6 points) Consider the molecule:
CH2F2 for which carbon is the single, central atom.
What is the SHAPE of the molecule?_________________________________________
Sketch the molecule.
a. Indicate partial positive and negative charges on atoms, if there are any.
b. If the overall molecule is polar, clearly show how you can determine its polarity in your sketch.
c. If not, briefly explain.
13. (18 points) Provide the information requested for the following covalent molecules.
A)
IF3
SHAPE = _________________________________
BOND ANGLE = ___________________
Is the molecule POLAR or NON-POLAR ?
(please circle which it is.)
B)
NCl3
SHAPE = _________________________________
BOND ANGLE = ___________________
Is the molecule POLAR or NON-POLAR ?
(please circle which it is.)
C)
AlBr3
SHAPE = _________________________________
BOND ANGLE = ___________________
Is the molecule POLAR or NON-POLAR ?
(please circle which it is.)
CHEM 210
•
Exam Reference Information
Notes on the Exam:
•
All quantum numbers should follow the conventions discussed in the course for the assignment of
orbital number & spin.
•
ELECTRON ARRANGEMENT refers to the shape that the hybrid orbitals, regardless of being bonds
or lone pairs.
•
SHAPE refers to the shape of just the atoms in the molecule.
•
All BOND ANGLES should be given to be as precise as possible.
General Equations and Information
D=
m
V
DH2O = 1.00 g/mL
kilo = k = 103
nano = n = 10-9
milli = m = 10-3
Avogadro’s Number = NA = 6.022 x 1023
Absolute Zero = !273.15 °C
Heat Constants & Equations
Cp,H20 = 4.184 J/g C
! qsystem = qsurroundings
q = mCp"T
! qlost = qgained
q = (heat capacity) "T
•
( Heat capacity may be abbreviated as Hc )
"Hreaction =
qreaction
moles reacting
qreaction
# coefficient
moles reacting
"H rxn = #(np"H f,products) ! #(nr"H f,reactants)
!
°
!
"Hreaction =
°
°
EM radiation and Hydrogen atom energy levels
c = $%
NA = 6.022 x 1023
E = h%
Ephoton = |"E|
c = 3.00 x 108 m/s
h = 6.626 x 10 34 J•s
!
Rhc = 2.18 x 10 18 J
!
°
Selected SHAPE Sketches
Electronegativities:
Periodic Table: