Chemistry 112
Third Hour Exam
Name:____________
Please show all work for partial credit
1. (12 points) Determine the oxidation number of all elements in the following compounds:
Copper(II) chloride (CuCl2)
Cu= +2, Cl= -1
Na2SO4 Na= +1, O= -2,
0 = 2(+1) + S + 4(-2); S= 8-2 = +6
HOBr H= +1, O = -2,
0=+1 -2 + Br; Br 2-1 = +1
CrO42- O = -2
-2 = Cr + 4(-2); Cr = 8-2= +6
2A. (6 points) Balance the following redox reaction under neutral conditions:
Solid zinc and aqueous hydrochloric acid react to form zinc chloride and hydrogen gas
Zn(s) + 2HCl(aq) 6ZnCl2(aq) + H2(g)
2B (6 points) Balance the following redox reaction under basic conditions:
CN-(aq) + MnO4-(aq) 6CNO-(aq) + MnO2(s)
CN-6CNOMnO4-6MnO2
H2O + CN 6CNO
MnO4-6MnO2 + 2H2O
+
+
H2O + CN 6CNO + 2H
4H + MnO4-6MnO2 + 2H2O
H2O + CN-6CNO- + 2H+ + 2e3e- + 4H+ + MnO4-6MnO2 + 2H2O
x3
x2
3H2O +3CN-63CNO- + 6H+ + 6e6e- + 8H+ + 2MnO4-62MnO2 + 4H2O
3H2O +3CN-+ 6e- + 8H+ + 2MnO4-62MnO2 + 4H2O + 3CNO- + 6H+ + 6e3CN-+ 2H+ + 2MnO4-62MnO2 + 1H2O + 3CNO+ 2OH+ 2 OH3CN-+ 2H2O + 2MnO4-62MnO2 + 1H2O + 3CNO-+ 2 OH3CN-(aq) + H2O(l) + 2MnO4-(aq)62MnO2(s) + 3CNO-(aq)+ 2 OH-(aq)
2
3. (12 points)
A diamond anvil is used by chemists and physicists to obtain pressures in excess
of 360 GPa, roughly equivalent the pressure in the center of the earth. Express this
pressure in Torr, Atm, and Lbs/in2
Torr
Atm
Lbs/in2
4. (13 points) Assume you have 1 1.0 L container of He gas at STP. What will happen to
the specified properties of the gas under the following conditions.
Acceptable answers are: No Change (NC); Increase (8); Decrease (9); or cannot be
determined (NOT).
Volume is increased to 2 l
Average Kinetic E
average velocity
NC
NC
frequency of
collisions
Pressure
9
9
frequency of
collisions
Pressure
Temp is decreased to 200K
Average Kinetic E
9
Mole fraction of He
NC
9
9
Half the molecules of the He are removed
Non-ideality of Gas
NC or NOT
average velocity
NC
frequency of
collisions
9
Pressure
9
3
5.) I have 5 grams of water (Molar mass 18.016g) and 5 grams of methanol (Molar mass
32.04g) In a closed container with a volume of 200 ml. I am going to heat the container
to 200oC, so both liquids will be turned into gases.
A. (4 points) What is the mole fraction of water in the container?
Moles water = 5/18.016 = .278; moles methanol = 5/32.04 = .156
÷=moles water/total moles = .278/(.278+.156)
=.641
B. (4 points) What is the partial pressure of water in the container?
Pressure as if there was only water, using ideal gas; PV=nRT
P = nRT/V = .278(.08206)(200+273) / .2 liters
= 53.9 atm
C. (4 points) What is the total pressure in the container?
Pressure using total moles of gas for n; PV=nRT
P = nRT/V = (.278+ .156)(.08206)(200+273) / .2 liters
= 84.2 atm
6. (13 points) Under what conditions of temperature and pressure will a gas act in a nonideal manner? Why?
High pressure and moderate to low temperature. Under these conditions there are
lots of gas molecules packed into a given volume, so the volume of the individual gas
molecule becomes significant. Further, since the gas molecules are at a high
concentration they can interact with each other and this changes their apparent pressure.
To some degree these effects can be overcome at higher temperature where the higher
T gives the individual gas molecules more kinetic energy, and this tends to alleviate these
non-ideality effects
4
7. (12 points) What is the density of SF6 gas at STP
at STP 1 mole of gas occupies 22.42 l
SF6 has a molar mass of 32.07 + 6(19.00) = 146.02g
so density is 146.02g/22.42R = 6.52g/l
8. (13 points) Define the following terms
State Function
A function or property of a system that depends only on the current state of the system,
and not the path by which the state was achieved.
Internal Energy
Sum of the kinetic and potential energies of all the particles in a system.
ÄE=q+w
Potential Energy
The energy that is stored in the position or composition of a system.
Work
Force acting over a distance. Work of a gas expanding is w =-PÄV
Exothermic
A process that releases heat energy.
Thermodynamics
The study of energy flow.