Search found 28 matches

Fri Mar 14, 2014 12:34 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 2013 final
Replies: 3
Views: 567

Re: 2013 final

Do we get these formulas from the sheet?
Also, so since we need to have n for the equation we have to take apart the equation in order to find the n?
Fri Mar 14, 2014 12:31 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Winter Final 2013 Q3C
Replies: 1
Views: 344

Winter Final 2013 Q3C

An environmental chemist is interested in measuring the concentration of Cr^3+(aq). At pH 2.0, with [Cr2O7^2-]=0.80M, [HClO2]=0.15, [HClO]=0.20M. The cell voltage is found to be 0.15V at 298K. Calculate the concentration of Cr^3+(aq). Why do we use logQ instead of lnQ for the Nerst equation? What is...
Thu Mar 13, 2014 11:58 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: pH of Buffers: Winter 2010 Final Q4B
Replies: 3
Views: 548

pH of Buffers: Winter 2010 Final Q4B

When a pH meter was standardized with a boric acid-borate buffer with a pH of 9.40, the cell emf was +0.060V. When the buffer was replaced with a solution of unknown hydronium ion concentration, the cell emf was +0.22V. What is the pH of the solution. I have a question. How do you start the process ...
Tue Feb 11, 2014 12:27 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: R or 3/2R (8.11)
Replies: 7
Views: 855

Re: R or 3/2R (8.11)

Yup. and you are assuming ideal behavior.
Tue Feb 11, 2014 12:26 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Winter 2013 Midterm Q8B
Replies: 1
Views: 327

Winter 2013 Midterm Q8B

The questions gives us a galvanic cell at 25C and we have to identify the two half-reactions and show a balanced equation. In the second part, we are given: concentration of the Ce4+ and Ce3+ ions are 0.015M and we need to find the concentration for Fe2+ when it powers a 2.20V green LED light. I use...
Tue Feb 11, 2014 12:13 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: R or 3/2R (8.11)
Replies: 7
Views: 855

Re: R or 3/2R (8.11)

For 4A. in the second change of entropy you use Cv because you assume constant volume when it is an ideal behavior for an ideal gas and there is change of temperature.
you use the Cp when it is an ideal gas at it is at constant pressure.
Tue Feb 11, 2014 12:11 pm
Forum: Balancing Redox Reactions
Topic: 2009 winter midterm question 7B (ii)
Replies: 3
Views: 599

Re: 2009 winter midterm question 7B (ii)

It is just a conductor that is normally use. I believe you can use others but it is more common to use Pt.
Tue Feb 11, 2014 12:10 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Midterm Winter 2012 Question 8
Replies: 2
Views: 354

Re: Midterm Winter 2012 Question 8

0.66V is given. If you look at the equation it says that the potential of the cell .....(cell diagram)...is +0.661V.
When you do the problem you get E(standard)=0.63V. Since that is two sig figs I believe thats why they used 0.66V. but the answer should be similar if you still use 0.661V.
Tue Feb 11, 2014 12:04 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Winter 2013 Midterm Q7-F constant
Replies: 1
Views: 329

Winter 2013 Midterm Q7-F constant

The question says to calculate K and change in free energy at 298 for the following redox reaction. There are two ways to solve it and I solved for change in free energy by using -nFE(cell). However, I use the constant F=96,4853C/mol because that is in the sheet, but in the solutions it shows F to b...
Tue Feb 11, 2014 12:02 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Reaction enthalpy 7.57
Replies: 1
Views: 819

Re: Reaction enthalpy 7.57

If the volume is fixed then work is 0. So change of internal energy is equal to q. However, if you look at the formula sheet, q does not equal change in enthalpy for when volume is constant. q (constant pressure) does equal change in enthalpy though.
Tue Feb 11, 2014 12:11 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: winter 2012 midterm Q1A
Replies: 4
Views: 555

Re: winter 2012 midterm Q1A

ok. That makes sense. Thank you!
Sun Feb 09, 2014 10:55 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: winter 2012 midterm Q1A
Replies: 4
Views: 555

Re: winter 2012 midterm Q1A

Oh ok. So we got to take into account the change of liquid to gas. For this we don't need to use the C(water) correct?
Thanks.
Fri Feb 07, 2014 12:12 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Winter 2007 midterm question 2
Replies: 2
Views: 527

Re: Winter 2007 midterm question 2

If i remember correctly, it is because for calorimeter q is different since the mass of the calorimeter is not taken into account. it is q(cal)=C(cal)delta T But we multiply it by the n of benzoic acid but since it is in grams we change it to moles. Because we need to take into account the substance...
Fri Feb 07, 2014 12:06 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: winter 2012 midterm Q1A
Replies: 4
Views: 555

winter 2012 midterm Q1A

1A. Researchers at Sandia National Laboratories have recently developed a ceramic material that can withstand extremely high temperatures without melting. A 7500 g brick of this material, initially at 2000K, is dropped into an insulated tub containing 16000g of liquid water at 298.15K. The brick is ...
Thu Jan 30, 2014 1:20 am
Forum: Student Social/Study Group
Topic: Study Groups!
Replies: 6
Views: 2042

Re: Study Groups!

Im interested for the future :)
Thu Jan 30, 2014 1:17 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 8.43 Standard Entropy of Vaporization
Replies: 2
Views: 430

Re: 8.43 Standard Entropy of Vaporization

Oh ok. So since it is already like that then we don't need it.
Thanks!
Wed Jan 29, 2014 9:21 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 8.43 Standard Entropy of Vaporization
Replies: 2
Views: 430

8.43 Standard Entropy of Vaporization

43. "Calculate the standard entropy of vaporization of water at 85C, given that its standard entropy at 100C is 109.0 J/(K*mol) and the molar heat capacities at constant pressure of liquid water and water vapor are 75.3 J/(K*mol) and 33.6 J/(K*mol), respectively in this range." I am workin...
Tue Jan 21, 2014 1:37 pm
Forum: Phase Changes & Related Calculations
Topic: How to calculate final temperature? (7.39)
Replies: 10
Views: 33832

Re: How to calculate final temperature? (7.39)

When we are finding H(fusion). We change 50g of ice cube to moles. Do we also change 6.01kJ/mol to J/mol?
Fri Jan 10, 2014 12:26 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: HW 7.19-Heat Capacity
Replies: 1
Views: 468

HW 7.19-Heat Capacity

On problem 7.19: A piece of copper of mass 20.0g at 100.0Cis placed in a vessel of negligible heat capacity but containing 50.7g of water at 22.0C. Calculate the final temperature of the water. Assume that there is no energy lost to the surroundings. I understand how to set up the problem to find Tf...
Fri Dec 06, 2013 8:20 pm
Forum: Naming
Topic: Fall2012 Final-5B
Replies: 3
Views: 544

Re: Fall2012 Final-5B

Awesome. Thanks!
Fri Dec 06, 2013 8:19 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Fall 2012 final 5C-reactants or products favored
Replies: 1
Views: 370

Fall 2012 final 5C-reactants or products favored

H2+I2<->2HI
Kc @25C is 4.23x10^-5
Reaction is endothermic.

If a small amount of I2 is added neither reactants or products favor. Is this because the amount is too small to make a difference?
Fri Dec 06, 2013 8:04 pm
Forum: Empirical & Molecular Formulas
Topic: F2009 Final Exam Question1C-Molecular Formula.
Replies: 4
Views: 507

Re: F2009 Final Exam Question1C-Molecular Formula.

Ok. Thanks!
Fri Dec 06, 2013 8:03 pm
Forum: Naming
Topic: Fall2012 Final-5B
Replies: 3
Views: 544

Fall2012 Final-5B

I have a question on how to write (oxalato) when doing it for the formula of coordination compounts. I have seen it as (ox) and also (C2O4). For sodium tris(oxalato)cobaltate(III). It is written as (C2O4)3. For my answer i wrote it as (ox)3. Is this also acceptable or should I write it as (C2O4)3. T...
Thu Dec 05, 2013 1:25 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Fall 2011 4e-Bond length
Replies: 2
Views: 275

Re: Fall 2011 4e-Bond length

I was thinking of that but was unsure.
Thanks!
Wed Dec 04, 2013 11:58 pm
Forum: Empirical & Molecular Formulas
Topic: F2009 Final Exam Question1C-Molecular Formula.
Replies: 4
Views: 507

Re: F2009 Final Exam Question1C-Molecular Formula.

Ok. So since it is two Hydrogens to one O we divide it by 2.
Thanks this makes sense now.
Wed Dec 04, 2013 11:46 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Fall 2011 4e-Bond length
Replies: 2
Views: 275

Fall 2011 4e-Bond length

I was doing question 4e from Fall 2011 Final. The question is: "Arrange them in order of decreasing bond length." The answer is longest bond F2^(2-) > F2^- < F2 < F2^+ For my answer I had gotten F2^(2-) > F2^- > F2 > F2^+ Since F2^(2-) has a Bond Order of 0. I am confused how we got to thi...
Tue Dec 03, 2013 1:28 am
Forum: Bond Lengths & Energies
Topic: F2008 Final Exam Question 3B-Orbitals(LUMO and HOMO)
Replies: 1
Views: 347

F2008 Final Exam Question 3B-Orbitals(LUMO and HOMO)

The question answer included labeling the HOMO and LUMO orbitals. I do not remember discussing them in class, but I was wondering if the HOMO orbital will always be pi*2py and the LUMO orbital o*2pz. Also, what are these orbitals, such as why are they called these and why are they important?

Thanks!
Tue Dec 03, 2013 1:23 am
Forum: Empirical & Molecular Formulas
Topic: F2009 Final Exam Question1C-Molecular Formula.
Replies: 4
Views: 507

F2009 Final Exam Question1C-Molecular Formula.

The question is: "An industrial by-product consists of C, H, O and Cl. When 0.100g of the compound was analyzed by combustion analysis, 0.0682g of CO2 and 0.0140g of H2O were produced. The mass percentage of Cl in the compound was found to be 55.0%. The molar mass of the compound is 64.47g*mol^...