GaAs is zinc-blende with a = 0.56 nm, ε = 12.8, me* = 0.067me, and mh* = 0.2me.

(a) What is the exciton binding energy and radius?
(b) How many unit cells are contained within the n = 1 orbital?
(c) What is the highest temperature at which ground-state excitons are still observable?

why did my prof chose to right the stoichiometry of the combustion reaction for propane like this:

1/20 C3H8(g) + 1/4 O2(g) --> 3/20 CO2(g) + 1/5 H2O(l)

why did he write it in fractions, and its not because O2 is a diatomic.

he told does we have to get used to writing equations in fraction.

Ethane is chlorinated in a continuous reactor: C2H6 +Cl2 → C2H5Cl + HCl Some of the product monochloroethane is further chlorinated in an undesired side reaction: C2H5Cl +Cl2 → C2H4Cl2 + HCl

a. Take a basis of 100 mol of C2H5Cl produced. Assume that the feed contains only ethane and chlorine and that all of the chlorine is consumed. How many degrees of freedom remain (use atomic balances)?

b. The reactor is designed to yield a 19% conversion of ethane and a selectivity of 8 mol C2H5Cl / mol C2H4Cl2 with a negligible amount of chlorine in the product gas. Calculate the feed ratio (mol Cl2/mol C2H6).

Calculate the fractional yield (mol C2H5Cl produced / mol Cl2 consumed)

I did part a i am just confused about part b

Let 4 moles of methanol (liquid) combust in 3 moles of gaseous oxygen to form gaseous carbon dioxide and water vapor. Suppose this occurs in a chamber of fixed volume and fixed temperature. If the original pressure is 1.0 atm, what is the final pressure in the chamber. Express your answer in atm. Enter only a numerical value, do not enter units. Assume liquids take up negligible volume.

Consider the titration of 20.0 mL of 0.0800 M C5H5N (a weak base; Kb = 1.70e-09) with 0.100 M HCl. Calculate the pH after the following volumes of titrant have been added:

(a) 0.0 mL pH =

(b) 4.0 mL pH =

(c) 8.0 mL pH =

(d) 12.0 mL pH =

(e) 16.0 mL pH =

(f) 22.4 mL pH =

Fe(NO3)₃. 9H₂O in 0.5M HNO₃ forms a colorless hexa-aquocomplex with the chemical formula {Fe(H2O)₆}³⁺ (aq).

This complex can then undergo an equilibrium reaction with potassium thiocynate (KSCN) to form a red complex with the chemical formula {Fe(H2O)5SCN}²⁺ (aq). In order to make this reaction occur, the two chemicals need to be mixed with 0.5M nitric acid. This equilibrium reaction is shown below:

{Fe(H₂O)₆}^₃₊ (aq) + SCN^-(aq) <--------> {Fe(H₂O)₅SCN}²⁺(aq) + H₂O (l)

a) When recording the absorbance values, what should be used as a blank slution and how show its data be treated?

b) K_eq is quoted to have a value of 250 at 20°C. When an initial potassium thiocynate concentration of 2x10^-4M was used, the red {Fe(H2O)₅SCN}²⁺ (aq) complex had an absorbance value of 0.5 . If the molar absorptivity coefficient of the red complex is 5400 cm-¹M^-1 and a 1 cm cuvette was used, calculate the equilibrium concentrations of [{Fe(H20)₆}³⁺(aq)]eq, [SCN^-]eq , [{Fe(H2O)₅SCN}²⁺_(aq)]_eq

c) Briefly describe the experiment you might conduct to determine if this reaction is endothermic or exothermic. What sort of results would lead you to conclude it was one or the other?

a) How many moles of Al₂(SO₄)₃ are required to make 45 mL of a 0.080 M Al₂(SO₄)₃ solution?
(Hint, molarity is moles per liter. You know the molarity. You are given the number of mL's, which can be converted to liters. Just set it up so the units cancel and you get "moles".)
_____________ moles Al₂(SO₄)₃

b) What is the molar mass of Al₂(SO₄)₃, to the nearest gram?
_____________ [grams/mole]

c) What mass of Al₂(SO₄)₃ is required to make 45 mL of a 0.080 M Al₂(SO₄)₃ solution?
(If you've got moles and molecular weight you can get to grams.)
______________ g Al₂(SO₄)₃

d) How many moles of aluminum ions are present in the solution?
(This is easy. You know how many moles of Al₂(SO₄)₃ there are from part a. Just think about how many aluminum ions there are per Al₂(SO₄)₃.)
______________ mol

Pure pools of benzo [a] pyren and p-xylene are found floating in the Groundwater. What concentrations do you expect to find dissolved in the water directly belo the pools (mg/L and mM)? What concentrations do you expect to find in the air above the pools? (mg/L and mM). Compare how two chemicals behave in the environment. Benzo a pyrene MW: 252.32 g/mol; Henry's law constnt= 2.4 x10^-6 atm m^3/mol; Vapor pressure= 5.6 x10^-9 mmHg; Solubility=0.0038 mg/L; Log Koc=5.60-6.29. For p-xylene MW=106.17 g/mol; Henrys constant=0.0063 atm m^3/mol;Vapor pressure=8.763mmHg ; Solubiity =200 mg/L ; Log Koc=2.31

3. Assume that a particle is confined to a box of length L, and that the system wave function is

ψ(x)=sqrt(2/L)*sin[(π*x)/(L)]
(1) Is this state an eigenfunction of the momentum operator? Show your work.
(2) Calculate the average value of the momentum <p> that would be obtained for a large number of measurements. Explain your result.
(3) Calculate the probability that the particle is found between 0.31 L and 0.35 L.

(a) Calculate the percent ionization of 0.00690 M hypochlorous acid (Ka = 3e-08). % ionization =

(b) Calculate the percent ionization of 0.00690 M hypochlorous acid in a solution containing 0.0300 M sodium hypochlorite. % ionization =

consider space group Fdd2

1) What is point symmetry of an atom located at (0,0,Z)

2) give d-glides coordinates of Fdd2

3) what is multiplicity at a general position on Fdd2

4) Give a possible maximal non-isomorphic subgroup of Fdd2 that would be considered a translationengleiche group. What is the crystal system of this subgroup?

Band Theory

(A) Give a brief description of the formation of electron bands in crystals including reference to the atomic structure of the constituent atoms.

(B) Explain the following

i.Sodium, which has 2 atoms in a bcc (conventional cubic) unit cell, is a metal

ii.Calcium, which has 4 atoms in a fcc (conventional cubic) unit cell, is a metal

iii.Diamond, which has 8 atoms in a fcc (conventional cubic unit cell with a basis, is an electrical insulator, whereas silicon and germanium, which have similar structures, are semiconductors.

(C) Why is diamond transparent?

consider space group Fdd2

1) What is point symmetry of an atom located at (0,0,Z)

2) give d-glides coordinates of Fdd2

3) what is multiplicity at a general position on Fdd2

4) Give a possible maximal non-isomorphic subgroup of Fdd2 that would be considered a translationengleiche group. What is the crystal system of this subgroup?

Temperature and Phase Changes In this exercise, you will make observations of the phase changes of water (H 2 O). You will measure temperature and create a heating curve to determine the melting point and boiling point of water. 1. Gather the 250-mL beaker, approximately 150 mL of crushed ice, a watch or timer, the thermometer, burner stand, burner fuel, and matches. Note: Large ice cubes may be crushed by placing them in a large plastic bag, placing the bag on a durable surface, and breaking the pieces apart with a hammer or other heavy object. 2. Fill the beaker to about the 150-mL line with crushed ice. 3. Place the thermometer in the center of the ice. Do not allow the thermometer to touch the sides or bottom of the beaker. 4. After holding the thermometer in the ice for about a minute, note the time and record temperature at 0 minutes in Data Table 2 of your Lab Report Assistant . Additionally, record your observations about the state of matter (solid, liquid, or gas) of the water in Data Table 2 . 5. Uncap the burner fuel, light the wick with a match or lighter, and place the fuel under the stand on a pie pan. Burner setup. Note that the flame is blue which is sometimes difficult to see. 6. Place the beaker on the burner stand. Keep holding the thermometer in the middle of the ice. 7. Start the timer and begin taking temperature and observation readings every minute, recording your findings in Data Table 2 . Note: It is important that you record both the temperature AND the state or states of matter present every minute throughout the experiment. 8. Gently stir the ice with the thermometer as it heats. www.HOLscience.com 13 ©Hands-On Labs, Inc. Experiment Liquids and Solids 9. Continue to stir the ice or water and record temperature and observations every minute until the water has boiled for 5 minutes . Do not allow the thermometer to rest on the glass of the beaker. 10. Extinguish the burner fuel by lightly placing its cap over the flame; do not tighten cap until the burner fuel container has fully cooled. 11. Thoroughly wash and rinse the equipment for future use. Questions: A. Using the temperature data recorded in Data Table 2 , create a heating curve. ● Plot time (minutes) on the x-axis (horizontal axis) and temperature (°C) on the y-axis (vertical axis). Connect the plotted points with a line. ● Label the heating curve to show each phase of matter (solid, solid + liquid, liquid, liquid + gas). ● Label the melting point and boiling point on the heating curve. Note: An example heating curve is given in Figure 6 of the Background B. Are there parts of the curve with positive slopes and parts that are flat (slope of zero)? What states of matter are present when the slope of the heating curve is positive and what states of matter are present when the slope is zero or close to zero? C. Describe the key characteristics for the three states of matter. D. Define the melting point. What was the observed melting point of water?

E. Define boiling point. What was the observed boiling point of water?

F. What happens to heat energy when it is not increasing the temperature of the substance in the beaker? Use your heating curve to explain your answer. G. Was temperature perfectly constant during your test while the water was melting and while it was boiling? Explain why or why not.

H. The published melting point of H 2 O is 0°C, and the published boiling point is 100°C. Why may you have found different values?

I. Use the following information to determine if the intermolecular forces of isopropyl alcohol are greater or weaker than the intermolecular forces of water. Explain your answer. The melting point of isopropyl alcohol (rubbing alcohol, C 3 H 8 O) is about -90 °C and the boiling point is about 82 °C