Hourly
Exam # 2 Dunnivant
Name
(PRINTED)
____________________________________
There
are 100 points. The exam will be
graded on a percentage basis.
The honor statement must be
signed in order for your exam to be graded.
Closed
book, closed Internet, closed notes, closed cell
phone, closed neighbor!
I
have neither given nor received aid on this exam.
Signature
________________________
NOTES: NEATNESS COUNTS AND POORLY DISPLAYED OR
PRESENTED WORK WILL BE DISCOUNTED!!!!!!!!!!!!!
-Show all work for partial
credit.
-CIRCLE FINAL ANSWERS in
math problems
-Significant figures and
units will be graded throughout the exam.
1. (5 pts) A series of
hydrocarbons, with increasing molecular weight, are placed in a reaction
chamber with excess O2 and combusted. Each hydrocarbon is combusted individually and the excess
energy from the reactions is measured.
The DGo of formation of each gas is shown in the table below.
Compound DGo of formation
Methane -50.5
Ethane -32.0
Propane -23.4
Butane -15.0
Arrange the gases in order of increasing energy
produced from each combustion reaction.
Hint: no calculations are
necessary, nor do you have the necessary information to make such a
calculation!
Lowest amount of energy
___________________
___________________
___________________
___________________
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Highest amount of energy
2. (5 pts) Which gas law
explains the bends that deep-sea divers can get from rising too fast from deep
in the water? Give the equation,
not necessarily the name of the law and explain (in the space below) how the
bends develop.
3. (5 pts) One (1.000) mole of
He is experimentally determined to occupy a volume of 22.4 L at 0oC
and 1 atm of pressure. Atmospheric oxygen (O2) has eight times the
molecular weight of He. What
volume will 1.000 mole of O2 occupy under the same conditions?
4. (10 pts) A steel container
with a volume of 0.350 L can withstand pressures up to 88.0 atm
before exploding. Find the mass of
He that can be stored in this container at 299oK.
5. (15 pts) Charles, of Charles
gas law, used to make H2 to fill his balloon and float across the
French countryside. To produce the
H2 he reacted Fe metal with HCl. If his balloon needed 20.0 cubic meters
to lift him, his wicker basket, one bottle of French wine, 100 g of Brie, and
one baguette, how much Fe and HCl (in grams) did he need to start with assuming a
complete reaction. (1.000 m3
= 1000. L). The reaction is
Fe(s) + HCl(aq)
FeCl3(s) + H2(g)
Also fill out a complete flow chart for your
reaction.
6. (5 pts) Explain the concept
of a state function in the space provided below.
7. (10 pts) Water has a
specific heat of 4.184 J/g-oK and glass
has a specific heat of 0.84 J/goK. If 100. J of energy is put into equal
masses of water and glass, and the energy is converted to heat, which one will
heat up to a higher temperature?
Show calculations to confirm your answer; you will need to make a simple
assumption.
8. (10 pts) In class we
calculated the energy needed to heat liquid water from one temperature to
another based on the specific heat of water. Water (H2O) has three phases, solid, liquid, and
vapor, and each phase change has a heat conversion unit associated with
it. For example, you have to add
heat to convert 1.0 g of ice at 0oC to liquid water at 0oC. The phase change needs energy because
some of the water-water bonds in ice need to be broken. The total amount of energy needed to
heat ice to water is the sum of the melting energy and the heating energy. Given this basis, how much energy is
needed to melt a 100. g piece of ice (at 0oC)
and then heat it to 50.0oC?
The specific heat of water is 4.18 J/g-oC
and the heat capacity of ice is 333 J/g.
9. (5 pts) Estimate the sign,
positive or negative, of DGo if DHo is positive and DSo is negative at a low
temperature.
10. (10 pts) You are studying a
reaction that produces 1000kJ free energy/mol of reactant.
a) Is the reaction endothermic
or exothermic? (Think carefully)
b) Would you expect the
reaction to go forward (proceed spontaneously)?
c) What limitations may be
present concerning the progress of the reaction? (What may limit or keep the
reaction from occurring.)
11. (10 pts) For each pair of
substances, choose the one that you expect to have the higher standard molar
entropy value at 25oC. Circle the correct answer.
a) PCl3(g) or PCl5(g)
b) CH4(g) or CF4(g)
c) C as a diamond or amorphous
C
d) Ar(g) or CO(g)
e) Br2(g) or Br2(l)
12. (15 pts) In our discussion
of lake biochemistry and terminal electron acceptors, we observed that for a
given food molecule (glucose), a range of energy can be obtained by microbes
depending on the terminal electron acceptor that the organisms have evolved to
use (i.e. the biochemical machinery they evolved with). With oxygen, the reaction produces
2863kJ/mol of glucose and the values go down to 420 kJ/mole when CO2
is used as the terminal electron acceptor. In each case one reagent (compound) is reduced and one is
oxidized. As I mentioned in class,
very weird biochemical reactions occur in guts of tubeworms present near
deep-sea ocean vents, but thermodynamic calculations must always be
followed. For the example below,
two halves of a redox reaction occur and are
controlled by enzymes in the organism; CO2 is transformed to glucose
at the same time sulfide goes to sulfate, as shown in the reaction below. The oxygen and carbon dioxide present
in the process come from the ocean surface.
H2O +
S-2 + O2 + CO2 C6H12O6 + SO42-
Balance the equation noting that all stoichiometric coefficients may not be whole numbers.
Which reactant is being reduced?
Which reactant is being oxidized?
Which reactant is the food source?
Which reactant is the terminal electron acceptor?
Calculate DGo for the reaction given the
following:
SUBSTANCE DGo (kJ/mol)
H2O -237.1
S-2 83.7
O2 Standard
State
CO2 -386.0
C6H12O6 -910.4
SO4-2 -744.6
What
do your results predict about the quality of life for these organisms?
(3
pts) Bonus: Who is your favorite
musician (of all time) and what is their best song?