Chemistry 114
First Hour Exam
Name:____________
(4 points)
Please show all work for partial credit
1. The Mariana Trench in the Pacific Ocean is 6.8 miles deep. At that bottom of the trench
the pressure is 1,086 bar. Convert that pressure to:
A. (4 points) Atmosphere
B. (4 points) Torr
C. (4 points) Pascal
2. (12 points) Last October, Felix Baugartner used a balloon to get to an altitude of 24
miles, then he jumped off and set a world record for a free fall parachute jump. (At one
point in his jump he actually exceeded the speed of sound.) If Felix had filled a balloon
with 2L of helium when he was on the ground where the temperature was 250C and the
pressure was 1 atm, how big would the balloon be when he was 24 miles above the earth,
where the temperature was 0oC and the pressure was .02 atm?
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3. I have a container with 5 liters of N2 gas that is at a pressure of 5 atm. I am going to
connect it with a second container that contains 1 liter of O2 gas that is also at a pressure
of 5 atm. When I open the valve that lets the two gases mix, what will be:
A. (3 points) The final total pressure in the system?
Since both containers are at 5 atm, the pressure will not change when you open the
valve between the containers!
B. (3 points) What will be the partial pressure of N2 in the system?
There is also a way you can do this with mole fraction and total pressure.
C. (3 points) What will be the partial pressure of O2 in the system?
4. Define the following terms:
Mole fraction (2 points)
÷=n1/(n1+n2.....)
Adiabatic (2 points)
No heat exchanged with the surroundings.
Extensive property (2 points)
A property that depends on the amount of material.
state function (2 points)
A quantity that depends only on the current state of the system, not on the
pathway that the system took to get to that state.
Exothermic (2 points)
Something that releases heat (gets warmer).
ÄHfo (2 points)
The energy that is gained or released when a compound is formed from its
elements.
Molar heat capacity (2 points)
The energy needed to change the temperature of 1 mole of material by 1oC or 1K
For 1 point, a constant volume calorimeter measures (Circle one) ÄH or ÄE?
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5. Energy
A. (6 points) How much work must be done on a system to decrease its volume
from 25.0 to 7.5 L by exerting a constant pressure of 7 atm? (Please express your answer
in Joules)
B. (6 points) If a system does 4.00 x102 joules of work on the surroundings and
accepts 5.00x102 joules of heat from the surroundings, what is the change in internal
energy of the system?
E=q+w
q=heat =+500J (since system accepted from surroundings)
w=work =-400J (Since system worked on the surroundings)
=500-400
=+100J
6. (12 points) Use the following bond energies to determine ÄHRXN
For the reaction: N2 + 3 H2 62NH3
Bond
Energy
(kJ/mole)
N-H
390
N=H
750
N-N
159
N=N
418
N/N
945
H-H
435
H=H
790
N2 is N/N; H2 is H-H; NH3 has 3 N-H bonds
For this system only we do Reactants - products
=945 +3(435) -6(390) (2 molecules x 3 bonds per NH3)
=-90kJ
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7. (12 points)The reaction H3O +(aq) + OH- (aq) 62H2O(l) has a ÄHRXN of -55.85 kJ/mol
If I react 0.1 mole of H3O +(aq) with 0.08 mole of OH-(aq) in 90 g of water that is at 240C,
what is the final temperature of the water after the reaction is complete (assume adiabatic
conditions)?
First, the limiting reactant is the .08 moles of OHThe heat of the reaction = -55.85 kJ/mole × .08 mole of limiting reactant
=-4.468 kJ or -4468.0J
The heat lost by the reaction = heat gained by water (adiabatic conditions)
So heat gained by water = +4468.0J
Heat = S.H.C ×mass water×ÄT
+4468=4.186J/K@g ×90g×(TF-TI)
4468/(4.186×90)=Tf-24
11.9= TF-24
11.9+24 = Tf = 35.9oC
8. (12 points) In each set of compounds, circle the compound that will have the....
Highest melting point?
NaCl CH4
Strong Charge-Charge interaction makes for a high melting point
Lowest viscosity
CH3CH2OH CH3CH3
CH3CH2OH makes hydrogen bonds that will give it strong interactions and high viscosity
Lowest freezing point
HF HBr
HF can hydrogen bond so it will have a stronger interaction and a higher freezing point
Highest vapor pressure
He(l) Xe(l)
Both have weak London forces, but Xe has more electrons so it has the stronger force;
with the stronger force, less molecules can go into the gas phase so it has a lower vapor
pressure
Highest surface tension
H2O H2S
H2O can make hydrogen bonds so it has the stronger intermolecular force and the
higher surface tension
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