## Search found 48 matches

Sun Mar 15, 2015 11:59 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: bug's practice final #2
Replies: 2
Views: 1374

### Re: bug's practice final #2

So for step d, do you have

delta S = 1(30) ln 358/373
delta S = 1000/373
delta S = 1(5) ln 393/373
delta S = 1(5) ln 373/393
delta S = 1(30)ln185/373

Or do I have too many steps there?
Sun Mar 15, 2015 11:12 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: bug's practice final #2
Replies: 2
Views: 1374

### bug's practice final #2

On Bug's practice final #2b, it asks to calculate delta H vaporization at 85 degrees celsius. Do we assume constant pressure? I don't know how else to calculate this. Also on 2d and 2e-g, do we use the formula -q/T for delta S vaporization? Is delta S different from delta S vaporization? I'm not sur...
Sun Mar 15, 2015 10:07 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Change in Entropy: Bug's Finals
Replies: 3
Views: 1051

### Re: Change in Entropy: Bug's Finals

Then how do we find the delta S surrounding?
Fri Mar 13, 2015 9:58 am
Forum: *Free Energy of Activation vs Activation Energy
Topic: Reaction profiles using E vs. delta G
Replies: 1
Views: 479

### Reaction profiles using E vs. delta G

For the final, I know we are supposed to use delta G on the y-axis instead of E, but do we use the reaction profile organic chemists use as described in the text where if there is more than one transition state, both have the delta G (with the dagger) as the distance from the peak of the transition ...
Fri Mar 06, 2015 9:07 am
Forum: *Alkanes
Topic: Drawing line structures
Replies: 3
Views: 632

### Re: Drawing line structures

Okay that makes sense for the numbering but when you are drawing the line structure does it matter if you start the numbering from the left side of the structure or the right?
Thu Mar 05, 2015 3:08 pm
Forum: *Alkanes
Topic: Drawing line structures
Replies: 3
Views: 632

### Drawing line structures

When drawing line structures, does it matter what order you put it? For instance, on exercise #2.19, the lowest numbering option is from right to left. However, I first drew the line structure going from left to right if that makes sense. Is my line structure correct even though the one in the solut...
Wed Mar 04, 2015 8:00 pm
Forum: *Cycloalkanes
Topic: Exercise 1.16 Numbering Carbons in Parent Chain
Replies: 6
Views: 1046

### Exercise 1.16 Numbering Carbons in Parent Chain

On #16, I thought if different and equivalent numbering was possible (1,2 and 2,1 in this case), you make the first-named substituent (which is isopropyl) have the lower number? Why do the solutions say 2-isopropyl and 1,1-dimethyl?
Wed Mar 04, 2015 7:32 pm
Forum: *Alkenes
Topic: Exercise 1.11 b Systematic Names of stuctures
Replies: 2
Views: 531

### Exercise 1.11 b Systematic Names of stuctures

I'm confused on #1.11b where it asks you to draw a line structure and give the systematic name for CH3(CH2)3 CHCHCH3. I thought the 3 CH2's in the parentheses would be substituents, but why are they included as part of the parent chain?
Sun Feb 22, 2015 3:29 pm
Forum: General Rate Laws
Topic: Negative rates of formation
Replies: 2
Views: 618

### Negative rates of formation

If the given rate of decomposition of a reactant is positive, is the rate of formation of a product also positive? Or is it negative since the rate of decomposition is negative?
Wed Feb 18, 2015 4:25 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Midterm 2015 Q4&5 part B
Replies: 2
Views: 637

### Midterm 2015 Q4&5 part B

For Q4&5 part B on the midterm, I thought you use 5/2 R since the volume changes and the pressure is constant. Why do they use 3/2 R in the solutions?
Mon Feb 16, 2015 2:21 pm
Forum: First Order Reactions
Topic: HW #14.35b
Replies: 3
Views: 751

### HW #14.35b

I'm confused on 35b, where the question asks to find the time it takes for the concentration of SO2Cl2 to decrease to 10% of its initial concentration. Why does the solutions manual just do ln10, and when I solved ln10/k like they did, I got 0.000819 minutes, not 819 minutes. Could someone help expl...
Mon Feb 09, 2015 9:41 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Order of species in cell diagram?
Replies: 3
Views: 665

### Re: Order of species in cell diagram?

I was looking at previous posts about this and I do not think the order matters if it was Ce4+ or Ce3+ as long as you have it on the correct side of the salt bridge.
Fri Feb 06, 2015 12:08 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Units & sig figs for calculating gibbs free energy
Replies: 1
Views: 1416

### Units & sig figs for calculating gibbs free energy

On the 2010 midterm #5A, I correctly solved for the standard gibbs free energy, but I was wondering about the units and significant figures. The values of the standard gibbs free energy of formations have 2 decimal places since we are subtracting the values. However, the answer given in the solution...
Tue Feb 03, 2015 10:33 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: HW #13.33b Ti+ Disproportionate in aqueous solution
Replies: 1
Views: 975

### HW #13.33b Ti+ Disproportionate in aqueous solution

For #13.33b, the question asks if Tl+ will be disproportionate in aqueous solution. I'm confused in the solutions manual how they knew that the equation of interest is 3Tl+ ---> 2 Tl + Tl3+ and why you use standard gibbs free energy values. Can anyone explain this problem?
Tue Feb 03, 2015 10:32 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Hw #35b Solving for Equilibrium Constant
Replies: 3
Views: 623

### Hw #35b Solving for Equilibrium Constant

The homework problem #35b was explained on the solutions manual. The question asks to find the equilibrium constant and I did the exact same thing as the correct solutions manual. I did ln K = 1(0.12) / 0.02569 but I got K=107, not K = 10^12. Is the correction to the solutions manual error wrong too?
Tue Feb 03, 2015 12:18 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: HW #13d and 15 Balancing Half Reactions and Cell Diagrams
Replies: 2
Views: 679

### HW #13d and 15 Balancing Half Reactions and Cell Diagrams

I'm confused on #13d and #15 on the chapter 13 textbook problems. The question asks to write the half-reactions, balanced equation, and cell diagram for each equation. On 13, why is the equation for the anode Au(s) ---> Au3+ + 3 e- and not Au+ ---> Au3+ + 2e-? On 15, I'm in general confused on how t...
Wed Jan 28, 2015 8:29 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs free energy of formation for atoms HW #107b
Replies: 1
Views: 415

### Gibbs free energy of formation for atoms HW #107b

On #107b, it says to plot the Gibbs free energy of formation of the atoms against the atomic number. However, in the solutions manual, it plots free energy of dissociation. Where do they get these values?
Sun Jan 25, 2015 9:19 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 7.57b homework problem
Replies: 1
Views: 576

### 7.57b homework problem

On #57b for Chapter 7 text problems, the problem asks you to find the internal energy change for a reaction of 1.40 g of carbon monoxide with excess water vapor producing carbon dioxide and hydrogen gas in a bomb calorimeter. How do you know qreaction = - q calorimeter? Is that true for all bomb cal...
Sat Jan 24, 2015 8:38 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Quiz 1 prep #1 Winter 2014 Question #11
Replies: 2
Views: 511

### Quiz 1 prep #1 Winter 2014 Question #11

For #11 on the winter 2014 quiz #1 preparation, the question asks to find the final volume for a system that has a two-step process. I get step 1, but on step 2 I'm confused why ∆U goes from -158 J from step 1 to 158 J on step 2. Is it because it says it returns to the original internal energy?
Wed Jan 21, 2015 5:42 pm
Forum: Calculating Work of Expansion
Topic: Quiz 1 preparation, winter 2013 #3
Replies: 5
Views: 882

### Re: Quiz 1 preparation, winter 2013 #3

Well I noticed the change in volume but why don't you use 5 atm for both or 2 atm for both? The pressures for both change too and they both start at 5 atm and end at 2 atm.
Wed Jan 21, 2015 3:56 pm
Forum: Calculating Work of Expansion
Topic: Quiz 1 preparation, winter 2013 #3
Replies: 5
Views: 882

### Quiz 1 preparation, winter 2013 #3

For #3 on the first quiz 1 preparation in the chem 14B workbook, I don't understand the calculations for the work for the 2 pathways. I understand that you use w = -P ∆V, but how do you know what values of P to use for each pathway? Why do you use 5 atm for pathway 1 and 2 atm for pathway 2?
Wed Jan 14, 2015 10:18 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: HW #115e
Replies: 2
Views: 502

### Re: HW #115e

Oh okay I forgot to write that balanced equation. Do you understand why it's less CO2 for methane and more CO2 for ethanol and octane?
Tue Jan 13, 2015 9:29 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: HW #115e
Replies: 2
Views: 502

### HW #115e

On 115e, the questions asks to calculate the quantity of heat per mole of CO2 produced for methane, ethanol, and octane. I got this quantity correct for methane and ethanol but when I tried doing -5471/2 moles CO2, I got a different answer than the solution manual. Are we not supposed to use 5471? A...
Tue Jan 13, 2015 9:27 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: HW #109b
Replies: 1
Views: 618

### HW #109b

On #109b, the question asks to calculate the expected enthalpy of formation of C60 from bond enthalpies, assuming the bonds to be isolated double and single bonds. I'm confused on the calculations of the solutions manual. Could anyone explain the process of solving this problem? I started doing 60(3...
Mon Jan 12, 2015 10:17 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: HW #53
Replies: 4
Views: 772

### HW #53

For homework problem #53, the question asks to find the final temperature of the solution and the solutions manual says that the enthalpy of reaction = -153.89 + 2(-167.16) - 2(-167.16). I'm confused where they got these numbers. I looked up the enthalpy of formation of zinc and HCl and these weren'...
Mon Jan 12, 2015 4:40 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: HW #7.45, pg. 282
Replies: 5
Views: 1045

### HW #7.45, pg. 282

For #45 on the homework, the question asks to estimate the mass of octane that would need to be burned to product enough heat to raise the temperature of the air in a 12x12x8 ft room from 40 degrees F to 78 degrees F using the normal composition of air to determine its density and assuming a pressur...
Fri Jan 09, 2015 11:01 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimeter calculations, example 7.4 in the text
Replies: 1
Views: 374

### Calorimeter calculations, example 7.4 in the text

On example 7.4 in the textbook (pg. 246), why do we not take the mass into account? I see that the equation for calorimetry calculations is q = Ccal * T, but why does the mass not matter?
Sun Dec 14, 2014 11:57 am
Forum: *Titrations & Titration Calculations
Topic: 12.39
Replies: 1
Views: 361

### 12.39

What indicator could you use for a titration of 0.20 M CH3COOH with 0.20 M NaOH? I'm confused on this problem why at S, volume of solution will have doubled so [CH3COO-] will be 0.10 M, which you put into the ICE Box. I get that you flip the equation and at S, [CH3COOH] = [CH3COO-] but why do you ha...
Sat Dec 13, 2014 12:56 am
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Video: Buffer problem
Replies: 1
Views: 501

### Video: Buffer problem

I did an example of a buffer problem here:

Sorry it's sideways and please reply if you have any questions or if I did something wrong!
Fri Dec 12, 2014 10:11 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: FINAL EXAM 2013 Q8
Replies: 2
Views: 493

### Re: FINAL EXAM 2013 Q8

The lactic acid will donate its proton so adding more lactic acid increases [H3O+] on the reactant side and according to Le Chatelier's, the reaction will shift to the right, so HbO2- decreases
Fri Dec 12, 2014 9:38 pm
Forum: *Titrations & Titration Calculations
Topic: Halfway to stoichiometric point
Replies: 1
Views: 1841

### Re: Halfway to stoichiometric point

To find the volume of NaOH added at the equivalence point, you take the volume and concentration of CH3COOH that's given in the problem and plug it into the formula M1V1 = M2V2. The value for M2 is the concentration of the titrant NaOH. So for #8 it would be .025(.10) = (.1)V2 and V2 = 25 mL. Then y...
Fri Dec 12, 2014 1:25 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Salt of Conjugate Base and Effects on pH
Replies: 1
Views: 502

### Re: Salt of Conjugate Base and Effects on pH

When you add a salt to the solution, it dissociates and the concentration of the conjugate base of the weak acid increases. This causes a pH increase because the salt contains an anion that makes the neutral solution basic. For example, when you add NaCH3COO to the weak acid CH3COOH, the solution ha...
Fri Dec 12, 2014 1:03 pm
Forum: *Titrations & Titration Calculations
Topic: pH at half-equivalence point
Replies: 2
Views: 8978

### Re: pH at half-equivalence point

pH =7 for strong acid/strong base titrations
Fri Dec 12, 2014 12:50 am
Forum: *Titrations & Titration Calculations
Topic: The buffer period on the titration curve of weakacid/ s.base
Replies: 1
Views: 516

### Re: The buffer period on the titration curve of weakacid/ s.

The value at that midpoint is the pKa of the weak acid. At that point, the concentration of your weak acid = concentration of the acid's conjugate base and so pKa = pH. For example, if you're adding NaOH to CH3COOH, the point C on that initial "groove" is where [CH3COOH] = [CH3COO-]. I thi...
Thu Dec 11, 2014 11:00 pm
Forum: Calculating the pH of Salt Solutions
Topic: Determining if AlCl3 is acidic or basic?
Replies: 1
Views: 1819

### Determining if AlCl3 is acidic or basic?

We did this example at the end of lecture one day but I'm still slightly confused on how you know AlCl3 is acidic and how you come up with the reaction Al(H2O)6 ^ 2+ + H2O ---> H3O+ + Al(H2O)5OH^2+. Same with the other example of Cu(NO3)2. Is it because Al and Cu are small highly charged cations? Ho...
Thu Dec 11, 2014 10:21 pm
Forum: *Indicators
Topic: Indicators as Weak Acids
Replies: 3
Views: 1000

### Re: Indicators as Weak Acids

I think it's because the release of the H+ from the weak acid results in a structural change. The course reader says it absorbs light differently. Therefore, you need the release of an H+ for the indicator to be effective and that's why they are weak acids.
Tue Dec 09, 2014 9:11 pm
Forum: *Titrations & Titration Calculations
Topic: HW 12.33f
Replies: 1
Views: 397

### HW 12.33f

For a titration of 25.0 mL of 0.10 M CH3COOH and 0.10 M NaOH, I calculated that it takes a volume of 25 mL to reach the stoichiometric point. I'm confused on where the solutions manual got 0.050 M NaCH3CO2 to use in the ice table for calculating the pH. Also, why does the equilibrium switch?
Mon Dec 01, 2014 2:39 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Tetrahedral vs. square planar
Replies: 2
Views: 1141

### Tetrahedral vs. square planar

If we are asked to draw a complex that forms 4 bonds, how do we know if it is a tetrahedral or square planar shape? Can anyone give ay examples?
Fri Nov 21, 2014 10:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook HW problem #47b
Replies: 1
Views: 347

### Textbook HW problem #47b

I calculated that 0.019 M was the initial amount of PCl5 and then the equilibrium concentration was 0.009 and this was correct with the solutions manual. Then, in part b of this problem, it asks what percentage of the PCl5 has decomposed at equilibrium and the solutions does 0.010/0.019 * 100. I tho...
Fri Nov 21, 2014 9:09 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook HW problem #1c
Replies: 1
Views: 351

### Textbook HW problem #1c

T or F - If one starts with a higher pressure of reactant, the equilibrium constant will be larger. I'm a little confused on what this statement means and the explanation in the solutions says "The value of the constant is not affected by the amounts of reactants or products added as long as th...
Sun Nov 09, 2014 2:21 pm
Forum: Hybridization
Topic: Fall 2011 Midterm 6C and fall 2012 midterm 6A
Replies: 3
Views: 574

### Fall 2011 Midterm 6C and fall 2012 midterm 6A

I'm confused by these two problems about the hybridization of each atom. I missed all of them except for the hybridization of the carbon atoms because it always forms 4 bonds. Can anybody explain the answers to these?
Sun Nov 09, 2014 11:48 am
Forum: Sigma & Pi Bonds
Topic: Finding bond order?
Replies: 1
Views: 553

### Finding bond order?

If a question asks you to find the bond order of some molecule, do you always have to draw out the diagram and write out the valence electron configuration first in order to see the bonding and nonbonding pairs or is there an easier/quicker way to do it? Sometimes the question asks for the bond orde...
Sat Oct 25, 2014 3:11 pm
Forum: Bond Lengths & Energies
Topic: pg. 87, #87
Replies: 1
Views: 481

### pg. 87, #87

I tried calculating the bond lengths in CF4, SiF4, and SnF4 using Figure 2.21 in the textbook and I know that they are all single bonds but why is F's covalent radius 72 pm and not 58? It says on the diagram 58, but in the solutions manual it says 72 pm. So for part a I got 77 + 58 = 135 pm but the ...
Thu Oct 16, 2014 6:35 pm
Forum: Quantum Numbers and The H-Atom
Topic: How To Calculate Number of Electrons in Orbitals
Replies: 3
Views: 698

### Re: How To Calculate Number of Electrons in Orbitals

Sorry messed up my numbering! c is 2 electrons and d is 14
Wed Oct 15, 2014 9:24 pm
Forum: Quantum Numbers and The H-Atom
Topic: How To Calculate Number of Electrons in Orbitals
Replies: 3
Views: 698

### Re: How To Calculate Number of Electrons in Orbitals

a. 6
b. 10
c. 14
Mon Oct 13, 2014 9:27 am
Forum: Empirical & Molecular Formulas
Topic: M 13
Replies: 1
Views: 403

### M 13

I solved this problem and got to the part where you divide by the smallest # of moles to get to the empirical formula ratios. I got 2.7 for C, 5.4 for H, 1.3 for N, and 1 for O. Why do you multiply them all by 3 to get 8, 16, 4, and 3 for the empirical formula?
Mon Oct 13, 2014 9:25 am
Forum: Molarity, Solutions, Dilutions
Topic: G 11 and 13b
Replies: 1
Views: 287

### G 11 and 13b

Both of these problems are similar in that it asks how a solution can be prepared. I'm confused on why you add 4 volumes of water to the starting solution and get the concentration desired to be 1/5 of the starting solution? Can anyone explain how to prepare these solutions?
Mon Oct 13, 2014 9:24 am
Forum: Molarity, Solutions, Dilutions
Topic: G 11 and 13b
Replies: 1
Views: 365

### G 11 and 13b

Both of these problems are similar in that it asks how a solution can be prepared. I'm confused on why you add 4 volumes of water to the starting solution and get the concentration desired to be 1/5 of the starting solution? Can anyone explain how to prepare these solutions?