Chemistry 114
First Hour Exam
Name:____________
(4 points)
Please show all work for partial credit
All problems are worth 12 points
1. Define the following terms:
Surface tension The energy needed to expand the surface of a liquid
Cohesive forces The forces within a liquid or solid that tend to hold it together.
Normal melting or freezing point The temperature at which the vapor pressure of a solid
and a liquid are in equilibrium, and the over pressure is 1 atm.
Delocalized covalent bond Also a metallic covalent bond. The type of bond found in metals
where the electron that holds the metal together is not constrained to a particular place,
so the electrons holding the metal together are free to move anywhere in the metal lattice.
Critical Pressure - The pressure required to compress a gas into a liquid when the liquid
is at its critical temperature.
Second order reaction A reaction where the order parameter is 2.
2. When I shine an X-ray with a wavelength of 1.54Å at a crystal, I get a reflection from the
crystal at 15.2o. What is the distance between atom layers in this crystal. (Assume that
n=1)
1
3. Below are 4 pairs of solids.
melting point and why.
For each pair circle the compound with the HIGHER
MgO and CO
Why?
CCl4 and CH3Cl
Why?
Ionic compound
Charge-Charge forces found in
Ionic compound are very strong
CH3Cl is polar which gives it a stronger
interactive force than the non-polar CCl4
CCl4 and CBr4
Why?
CH3NH2 and NH2CH2NH2
Why?
Both compounds are nonpolar
and held together by London forces
But London forces are proportional
To the number of electrons so CBr4
has more electrons and a stronger
London force
The NH2 in both compounds has a
potential to make strong hydrogen
bonds, but NH2CH2NH2 has 2 NH2's
so it can make twice as many hydrogen
bonds
4. I am going to make a solution by mixing 20 grams of NaOH with 80 grams of water
A. What is the weight or mass % of NaOH in this solution?
B. What is the mole fraction of NaOH in this solution
C. Assuming the solution has a volume of 95 mls, what is the molarity of NaOH in the
solution?
D. What is the colligative molality of the solution?
2
5. I am going to make a solution with 25 grams of methanol (CH3OH) and 50 grams of
ethanol (CH3CH2OH). What is the mole fraction of each liquid in this solution?
If the vapor pressure of methanol is 260 torr @ 40o C, and ethanol has a vapor pressure
of 150 torr at 40oC, what is the vapor pressure of this solution at 40oC?
What is the mole fraction of methanol in this vapor?
If the actual vapor pressure of the solution was HIGHER than your answer in part B, would
that be a positive or negative deviation from Raoult’s law, and what would that indicate
about the interactions between methanol and ethanol in solution?
When the vapor pressure is higher than predicted by Raoult’s law this is called a positive
deviation and it is associated with poor solvent-solute interactions.
6.You may have heard of the ‘Bends’ a painful, potentially fatal problem that occurs when
divers ascend too fast. It is caused by air bubbles forming in the bloodstream as a diver
comes up from the bottom and nitrogen dissolved in their blood forms bubbles in the
bloodstream.
A. If the Henry’s Law constant for N2 is 1500 atm/M, and we assume that at sea level the
pressure of N2 is 0.8 atm, what is the molar concentration of N2 in your blood.
B. If you dive to 66 feet, where the pressure on your body is 3 atm, what is the molar
concentration of N2 in your blood now?
C. If an average body contains 5.5 liters of blood, use the difference between your answers
for A and B to determine the volume of bubbles in your blood that could form as a diver
rises from 66 feet to the surface (Assume the temperature is 25oC) .
The Ä molarity = .002-.00053 or .00147M
.00147 moles/Liter X 5.5 liters = .0081 moles of N2 must escape from the blood
using good ol’ PV=nRT
V=nRT/P V = (.0081 molesA.08206 lAAtm/KAmol A298K)/1atm
=.198L or ~200 mLs of gas that needs to escape from the blood
3
7. I am investigating the reaction A + B 6C.
obtained the data shown in the table below:
[A](M)
[B] (M)
0.7
1
1
Using the method of initial rates I have
rate M/min
0.7
0.7
1.4
1.19
1.70
3.89
What are the order parameters for A and B in this reaction, and what is the rate
constant for this reaction?
8. I have a first order reaction with a rate constant of .2 min-1. If the initial concentration
of my reactant, Z is 1.5 M, how long will it take for the concentration of Z to reach .75M?
Two ways to do this.
1. If you notice that the second concentration is ½ of this first, you can do this with the
half-life for a first order reaction t1/2 = .693/k = .693/.2 min-1 = 3.465 minutes
2. If you don’t see that this is a half-life problem, then you must use the equation
ln[A]t = ln[A]0 -kt
ln(.75)=ln(1.5)-.2X
-.288=.405 -.2X
-.693=-.2X
.693=.2X
X=.693/.2
=3.465 min
4