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11 Dec 2019

During biological treatment processes, microorganisms could use O2, CO2, or NO3 - as the terminal electron acceptors and harvest energy through cellular respiration. Depends on the terminal electron acceptors used, such reactions can be categorized into aerobic, anaerobic, and anoxic reactions as we discussed in class. NADH (nicotinamide adenine dinucleotide + hydrogen) is a crucial coenzyme that helps the cells to transport electrons so that energy can be harvested for microbial growth. Therefore, the free energy yield can be calculated using the overall stoichiometry of the redox reactions involving half reactions below,

NADH + H+ = NAD+ + 2H+ + 2e- ( ÎG0 = -62 kJ/mol)

Â¼ O2 + H+ + e- = Â½ H2O ( ÎG0 = -78.14 kJ/mol)

1/8 CO2 + H+ + e- = 1/8 CH4 + Â¼ H2O ( ÎG0 = 25.53 kJ/mol)

1/5 NO3 - + 6/5 H+ + e- = 1/10 N2 + 3/5 H2O ( ÎG0 = -72.20 kJ/mol)

Construct the overall stoichiometry for aerobic, anaerobic, and anoxic reactions and determine the energy yield for each. Discuss why the aerobic biochemical reactions are the widely used practice to remove BOD.

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1. A certain reaction has the following general form: aA â bB At a particular temperature and [A]0 = 4.00 Ã 10-3 M, concentration versus time data were collected for this reaction, and a plot of 1/[A] versus time result in a straight line with a slope value of +4.00 Ã 10-2 L/molÂ·s. a. Determine the differential rate law. b. Determine the integrated rate law. c. Determine the value of the reaction rate constant. d. Calculate the half-life, tÂ½, for this reaction. e. How much time is required for the concentration of A to decrease to 1.00 Ã 10-3 M ?

2. One mechanism for the destruction of ozone in the upper atmosphere is: O3(g) + NO(g) â NO2(g) + O2(g) Slow NO2(g) + O(g) â NO(g) + O2(g) Fast Overall reaction: O3(g) + O(g) â 2O2(g) a. Which species is a catalyst? b. Which species is an intermediate? c. Ea for the uncatalyzed reaction O3(g) + O(g) â 2O2(g) is 14.0 kJ. Ea for the same reaction when catalyzed is 11.9 kJ. What is the ratio of the rate constant for the catalyzed reaction to that for the uncatalyzed reaction at 25 ÂºC? Assume that the frequency factor A is the same for each reaction.

3. Draw a rough sketch of the energy profile for each of the following cases: a. ÎE = +5 kJ/mol, Ea = 30 kJ /mol b. ÎE = -10 kJ/mol, Ea = 30 kJ /mol

4. At a given temperature, K = 1.44 Ã 10-2 for the reaction: N2(g) + 3H2(g) â 2NH3(g) Calculate values of K for the following reactions at the given temperature. a. 4NH3(g) â 2N2(g) + 6H2(g) b. Â½N2(g) + Â³â2H2(g) â NH3(g)

5. What will happen to the concentration of SO3 in equilibrium with SO2 and O2 in the reaction: 2SO3(g) â 2SO2(g) + O2(g) (ÎHÂº = 197 kJ) in each of the following cases? a. O2(g) is added: b. The pressure is increased by decreasing the volume of the reaction container: c. Adding Ar(g) into the reaction container: d. The temperature is decreased: e. SO2(g) is removed:

6. K = 0.090 for the reaction H2O(g) + Cl2O(g) â 2HOCl(g) at 25 ÂºC. Calculate the equilibrium concentrations of all species when 1.0 mol pure HOCl is placed in a 1.0-L flask.

7. Fill in the missing particles in each nuclear equation: a. Am Np _______ 237 93 241 95 ï® ï« b. e 0 -1 237 _____ï® 93Np ï« c. Np _______ He 4 2 237 93 ï® ï« d. e 0 1 275 35Br ï®_______ï« ï« e. N _______ C H 1 1 14 6 14 7 ï« ï® ï«

8. A layer of peat beneath the glacial sediments of the last ice age has a 14C/12C ratio that is 22.8% of that found in living organisms. How long ago was this ice age? (The half-life of 14C is 5730 years).

Practice problems for exam 2 ______________

Useful Information:

h=6.626Ã10-34JÂ·s.; c=3.0Ã108 m/sec; E=hï® ; E= hc , ï¬ = h/mv; 1J = 1 kg-m2/s2 ï¬

mass of electron = 9.11 Ã 10-28 g, ïE= q + w ; 1 cal = 4.184 Joules Please Show all Work

1. Which of the following substances have standard heats of formation that are equal to zero by definition (circle your answers): H2(g), H(g), O3(g), H2O(s), H2O(l), Hg(l), Hg(s), Hg(g).

2. Limestone stalactites are formed in the reaction: Ca2+(aq) + HCO3-(aq) ï CaCO3(s) + CO2(g) +

H2O(l)
If one mole of CaCO3 is produced at 298 K under one atmosphere of pressure, the reaction performs 590 calories of expansion work, pushing back the atmosphere as CO2 is formed. At the same time, 9310 calories of heat are absorbed from the environment. What is ïE in Kcal/mole for CaCO3.

3. What is the minimum wavelength of light in AÌ (1 AÌ = 10-8 cm) needed to provide enough energy per quantum to rupture the chemical bond in hydrogen iodide (HI). The bond dissociation energy of HI is 71.4 Kcal/mole.

4. Sketch the shape and orientation of the following types of orbitals: s, px, dxy, dz2, dx2-y2

5. Give the values of (n) , (l) and (ml) for each orbital in the 4p subshell.

6. Write the complete electron configuration for the following: Ti 2+_____________________________________ Cr_______________________________________

N______________________________________

7. Calculate the standard enthalpy of formation ( ï Ho) for diamond from graphite [i.e. C (graphite) ï C (diamond)] given that:

C (graphite) + O2 ï CO2 (g) ( ï Ho = -393.5 KJ/mole) C (diamond)] + O2 ï CO2 (g) ( ï Ho = -395.4 KJ/mole)

If 1.0g of graphite is converted to diamond, what is the energy change? Is this an endothermic or exothermic reaction?

8. An 160 pound astronaut on his way to Mars is buzzing along at 10,000 miles per hour. (a) Express his weight in grams (one pound = 454 grams) so that you can calculate the astronautâs wavelength (1mile/hour = 44.7 cm/sec)

(b) Suppose the astronaut detects outside his spacecraft a proton (m=1.7 x 10-24 g) from a âsolar windâ moving at exactly the spacecraft velocity. What is the proton wavelength is in AÌ (1 AÌ = 10-8 cm.

9. What is the maximum number of electrons that can occupy each of the following subshells? a) 3d_________________ b) 1s____________________ c) 2p ____________________

10. Identify the element represented by the following electronic configuration.

a) [Ne] 3s2____________________

b) What is the electron configuration for the first excited state of this atom.______________

11. Determine the number of valence electrons for each element.
(a) Br___________ (b) Na _________ (c) Sn __________

12. 175 g of Fe at 15.0oC is mixed with 225 g of H2O at 95.0oC. What is the final temperature of the mixture? The specific heats of iron= 0.448 J/g oC and water = 4.184 J/g oC). (keep in mind the following: heat gained + heat lost = 0 and q=mass x heat capacity x ïT)

13. (5 pts) Calculate values of ÎHrxn for the following reactions: CS2(g) + 3O2(g) ï® CO2(g) + 2SO2(g)

The heat of formation for the following substances is given in kJ/mol:

CS2 CO2 SO2 117.4 -393.51 -296.83

14. (6 pts) Use the electron configuration of Li and Be and determine which element has the greatest second ionization energy. Defend your answer.

15. Mark beside each of the following processes either âexoâ or âendoâ according to whether you think the process will release heat or absorb heat.

a. Ca(g) ï Ca(g)+2 + 2e-
b. I(g)+1e-ï I(g)-1
c. Ca(g)+2 + S(g)-2 ï CaS(s) d. I2(g)ï 2I(g)

( ) ( ) ( ) ( )

16. (6 pts) In each of the following pairs, which of the two species is larger?
a) O-2 or Na+ b) Ti+4 or Ti+2 c) B or C d) N or N-3

17. Write down the Lewis dot structure for the following (a) N_______________ (b) Ne________________

18. THE BORN HABER CYCLE: I may have a problem on the Born Haber cycle. Please check my lecture notes to see how to set up the process and then calculate the lattice energy from the various thermodynamic quantities such as in the NaCl example below;

ï H ï¯ f NaCl = -411KJ

Na(s) ï® Na(g) ï H =108KJ
1â2 Cl2 ï® Cl(g) ï H = 122KJ Ionization Energy of Na ï H = 496 KJ Electron affinity of Cl ï H = -349KJ

1- The molar heat capacity of silver is 25.35 J/molâ âC. How much energy would it take to raise the temperature of 8.20 g of silver by 14.5 âC?

Express your answer with the appropriate units.

_____________

Part A

Calculate the enthalpy of the reaction

2NO(g)+O2(g)â2NO2(g)

given the following reactions and enthalpies of formation:

12N2(g)+O2(g)âNO2(g), ÎHâA=33.2 kJ

12N2(g)+12O2(g)âNO(g), ÎHâB=90.2 kJ

Express your answer with the appropriate units.

2- A total of 2.00 mol of a compound is allowed to react with water in a foam coffee cup and the reaction produces 196 g of solution. The reaction caused the temperature of the solution to rise from 21.00 to 24.70 âC. What is the enthalpy of this reaction? Assume that no heat is lost to the surroundings or to the coffee cup itself and that the specific heat of the solution is the same as that of pure water.

Enter your answer in kilojoules per mole of compound to three significant figures.

_________

3- A volume of 110. mL of H2O is initially at room temperature (22.00 âC). A chilled steel rod at 2.00 âCis placed in the water. If the final temperature of the system is 21.00 âC , what is the mass of the steel bar?

Use the following values:

specific heat of water = 4.18 J/(gâ âC)

specific heat of steel = 0.452 J/(gâ âC)

Express your answer to three significant figures and include the appropriate units.

Part B

The specific heat of water is 4.18 J/(gâ âC). Calculate the molar heat capacity of water.

Express your answer to three significant figures and include the appropriate units.

______-

4- What is the enthalpy for the following reaction?

overall: N2O4â2NO2

Express your answer numerically in kilojoules per mole.

____________

Part B

Calculate the enthalpy of the reaction

4B(s)+3O2(g)â2B2O3(s)

given the following pertinent information:

B2O3(s)+3H2O(g)â3O2(g)+B2H6(g), ÎHâA=+2035 kJ

2B(s)+3H2(g)âB2H6(g), ÎHâB=+36 kJ

H2(g)+12O2(g)âH2O(l), ÎHâC=â285 kJ

H2O(l)âH2O(g), ÎHâD=+44 kJ

Express your answer with the appropriate units.

_____________

5- What is the balanced chemical equation for the reaction used to calculate ÎHâf of MgCO3(s)?

If fractional coefficients are required, enter them as a fraction (i.e. 1/3). Indicate the physical states using the abbreviation (s), (l), or (g) for solid, liquid, or gas, respectively without indicating allotropes. Use (aq) for aqueous solution.

Express your answer as a chemical equation.

__________

6- Part A

Determine the enthalpy for this reaction:

Ca(OH)2(s)+CO2(g)âCaCO3(s)+H2O(l)

Express your answer in kilojoules per mole to one decimal place.

_______

Part B

Consider the reaction

Ca(OH)2(s)âCaO(s)+H2O(l)

with enthalpy of reaction

ÎHrxnâ=65.2kJ/mol

What is the enthalpy of formation of CaO(s)?

Express your answer in kilojoules per mole to one decimal place.

________

7- Part A

Write a balanced chemical equation depicting the formation of one mole of H2O2(g) from its elements in their standard states.

Express your answer as a chemical equation. Identify all of the phases in your answer.

_____

Part B

For H2O2(g), find the value of ÎHâf. (Use Appendix C)

Express your answer using five significant figures.

_____

PART C: Write a balanced chemical equation depicting the formation of one mole of CaCO3(s) from its elements in their standard states.

Express your answer as a chemical equation. Identify all of the phases in your answer.

_____

Part D

For CaCO3(s), find the value of ÎHâf. (Use Appendix C)

Express your answer using five significant figures.

_____

Part E

Write a balanced chemical equation depicting the formation of one mole of POCl3(l) from its elements in their standard states.

Express your answer as a chemical equation. Identify all of the phases in your answer.

____

Part F

For POCl3(l), find the value of ÎHâf. (Use Appendix C)

Express your answer using four significant figures.

_____

Part G

Write a balanced chemical equation depicting the formation of one mole of C2H5OH(l) from its elements in their standard states.

Express your answer as a chemical equation. Identify all of the phases in your answer.

_____

Part H

For C2H5OH(l), find the value of ÎHâf. (Use Appendix C)

Express your answer using four significant figures.

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