Search found 314 matches

by ch1995
Sun Mar 16, 2014 12:26 pm
Forum: *Constitutional and Geometric Isomers (cis, Z and trans, E)
Topic: organic chem textbook p.17
Replies: 4
Views: 668

Re: organic chem textbook p.17

I think the E/Z refer to the carbons 3 and 7 (because these numbers are after the E and Z in the name). Looking at the one in the left, the methyl group attached to C3 is pointing up while the one on C7 is pointing down (E), and on the molecule on the right, both methyl groups (C3 and C7) are pointi...
by ch1995
Sun Mar 16, 2014 11:44 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: final 2012 1b
Replies: 8
Views: 1044

Re: final 2012 1b

If we aren't given any enthalpy values for the temp that we are looking for (398K in this case), then we heat/cool the reactants to a diff temp that we do know values for (so cool down to 298K in this case), and perform the rxn at that temp (w/ known value of deltaH). After that, we cool/heat the pr...
by ch1995
Sun Mar 16, 2014 11:36 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: final 2009 4e
Replies: 5
Views: 1010

Re: final 2009 4e

004253593 wrote:and you find ph by doing 10^-(concentration of H) right?

Not quite:
pH = -log[H+]
[H+] = 10^(-pH)
by ch1995
Sun Mar 16, 2014 11:32 am
Forum: *Cycloalkenes
Topic: cis- and trans- for cycloalkenes
Replies: 10
Views: 1936

Re: cis- and trans- for cycloalkenes

That makes sense, thank you :) (But I sure hope we won't see anything so complicated on the exam!)
by ch1995
Sun Mar 16, 2014 11:03 am
Forum: *Cycloalkenes
Topic: cis- and trans- for cycloalkenes
Replies: 10
Views: 1936

Re: cis- and trans- for cycloalkenes

Ah I see, thanks! :)
by ch1995
Sun Mar 16, 2014 10:21 am
Forum: *Cycloalkenes
Topic: cis- and trans- for cycloalkenes
Replies: 10
Views: 1936

Re: cis- and trans- for cycloalkenes

So would the "trans" in trans-4-methylcyclopent-2-enol be referring to C1 and C4 (with the methyl and alcohol groups attached to them), and not the carbons involved in the double bond (C2 and C3)? (2011 final Q7A) Since this diagram is drawn in 2-D, can we still assume that since the -OH g...
by ch1995
Sun Mar 16, 2014 10:14 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 2011 Q1C
Replies: 4
Views: 1095

Re: 2011 Q1C

For this problem, we use S = kb Ln W to solve for S (residual entropy).

W = (# of orientations per molecule)(# of molecules)
^Since NO has multiple orientations and BF3 only has 1, NO has a greater residual entropy
by ch1995
Sun Mar 16, 2014 12:46 am
Forum: *Cycloalkenes
Topic: Priority
Replies: 4
Views: 933

Re: Priority

Actually, the prefixes iso- and neo- count when we arrange them alphabetically, so "i" comes before "n" and isopropyl is given priority.
by ch1995
Sun Mar 16, 2014 12:31 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: Final 2011 4d
Replies: 6
Views: 813

Re: Final 2011 4d

Right, oops!! I guess the real answer is because it cancels out the variables:

If we plug in n=1, we get:
1 = 0 + 1
1 = 1

(Sorry for the mix-up!)
by ch1995
Sun Mar 16, 2014 12:12 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 2013 final Q4A
Replies: 1
Views: 376

Re: 2013 final Q4A

We would look at pg 114's formula sheet to find the half reactions: Fe => Fe2+ + 2e- 2H2O + O2 + 4e- => 4OH- Multiplying the oxidation half-reaction by two: 2Fe => 2Fe2+ + 4e- ........................[Multiplied by 2] 2H2O + O2 + 4e- => 4OH- Overall: 2Fe+2H2O+O2->2Fe(OH)2 The 4e- in the half reactio...
by ch1995
Sat Mar 15, 2014 11:53 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Final 2011 4d
Replies: 6
Views: 813

Re: Final 2011 4d

Sorry, I wasn't sure how to type the superscript using the equation function thing... but I fixed it, I meant for n-1 to be in the exponent :)
by ch1995
Sat Mar 15, 2014 11:46 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Final 2012 2C
Replies: 1
Views: 368

Re: Final 2012 2C

When the temperature is raised, the safe has not leaked yet. This means it is has a fixed, constant volume. Also, since the volume is fixed and the temperature is being raised, the pressure will change (is not constant), so we use Cv and not Cp.
by ch1995
Sat Mar 15, 2014 11:42 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Final 2011 4d
Replies: 6
Views: 813

Re: Final 2011 4d

If we plug in n=1 into , we get 0 in the denominator of the fraction.
by ch1995
Sat Mar 15, 2014 10:16 pm
Forum: General Rate Laws
Topic: Final 2009 5A
Replies: 2
Views: 682

Re: Final 2009 5A

I think that might be a typo since (8.11x10-5 / 4.42x10^-5) = 1.83 (without the squares). (Also, another typo is that they wrote 8.11x10^-3 instead of 8.11x10^-5)
by ch1995
Sat Mar 15, 2014 10:11 pm
Forum: *Alkanes and Substituted Alkanes (Staggered, Eclipsed, Gauche, Anti, Newman Projections)
Topic: 2012 8a
Replies: 4
Views: 839

Re: 2012 8a

We assign the least stable conformation with a dihedral angle of 0*. In this case, the least stable would be eclipsed with I and CH3 on top of each other (in other words, the 2 largest atom/group of atoms "on top of each other," thus creating the most tension and is least stable). The ques...
by ch1995
Sat Mar 15, 2014 9:58 pm
Forum: *Cyclohexanes (Chair, Boat, Geometric Isomers)
Topic: 2013 Q8C
Replies: 1
Views: 455

Re: 2013 Q8C

We see that the C-H bonds are all staggered, so it is in chair conformation. If it were not chair conformation (or is planar conformation), then the bonds would all be eclipsed (pg 112 of organic chem txtbook)
by ch1995
Sat Mar 15, 2014 9:52 pm
Forum: *Alkanes and Substituted Alkanes (Staggered, Eclipsed, Gauche, Anti, Newman Projections)
Topic: 2012 Q8A
Replies: 2
Views: 667

Re: 2012 Q8A

We are told that the dihedral angle is +120*. (We assign 0* to the least stable, eclipsed conformation, so +60* would result in a staggered conformation, then +120* would be eclipsed again; refer to pg 105 of organic chem textbook)
by ch1995
Sat Mar 15, 2014 9:47 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: final 2012 1b
Replies: 8
Views: 1044

Re: final 2012 1b

We want to calculate deltaH for the reaction @398K. In order to do that, we have to use any information we are given/know . For example, we don't have a table of deltaHf values for each of the species involved in the rxn for that specific temp (398K), nor do we know what the bond enthalpies are at t...
by ch1995
Sat Mar 15, 2014 9:28 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Why cell potential is not a state function
Replies: 3
Views: 877

Re: Why cell potential is not a state function

I think example 13.6 on pg 533 of the textbook could be an example of why Ecell is not a state fcn.
by ch1995
Sat Mar 15, 2014 8:34 pm
Forum: Phase Changes & Related Calculations
Topic: 2011 Final, 1B
Replies: 1
Views: 393

Re: 2011 Final, 1B

"Irreversibly" tells us to use w constant pressure = -P \Delta V instead of w variable pressure = -nRT ln(V2/V1), which is for reversible processes. We want to calculate the work done for this process . During the process, the original 1.00mol of methane undergoes the reaction: CH4(g) + 2O...
by ch1995
Sat Mar 15, 2014 8:29 pm
Forum: *Alkenes
Topic: 2009 final Q7D
Replies: 4
Views: 676

Re: 2009 final Q7D

If we compared CH2 vs CH3, then we would be comparing 3 atoms (C, H, H) against 4 atoms (C, H, H, H). Instead we need to compare them one at a time. Since they both have CH2 , that will be the first group we compare. Then moving on to the next set of atoms attached, we see that the CH2 group on the ...
by ch1995
Sat Mar 15, 2014 8:18 pm
Forum: Phase Changes & Related Calculations
Topic: Final 2011, question 1A
Replies: 2
Views: 445

Re: Final 2011, question 1A

The density of water is 1g/mL
by ch1995
Sat Mar 15, 2014 5:09 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 2012 Final Q1B
Replies: 1
Views: 351

Re: 2012 Final Q1B

It is actually divided by 4 and multiplied by 2:
(-224kJ/4.00mol) * (2.00mol)
^Divided by 4 to find deltaH per mole of NO, then multiplied by 2 because there are 2mols of NO per reaction (2NO + O2 => 2NO2) and we want to find deltaHrxn.
by ch1995
Sat Mar 15, 2014 4:52 pm
Forum: First Order Reactions
Topic: k calculation for decomposition and rate law determination
Replies: 4
Views: 1032

Re: k calculation for decomposition and rate law determinati

I got the same answer for k when I plugged in [R]o = 0.729M, [R] = 0.315M, and t=31.2s into Ln[R] = -kt + Ln[R]o. Do you know what the correct answer is supposed to be?
by ch1995
Sat Mar 15, 2014 4:29 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Winter Final 2010 Question 3A
Replies: 3
Views: 768

Re: Winter Final 2010 Question 3A

When S is positive, there is increasing disorder. But remember that Ssys does not determine spontaneity, but Suniverse = Ssys + Ssurr does. So if Suniverse > 0, then the rxn is spontaneous.
by ch1995
Sat Mar 15, 2014 4:17 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Winter 2009 4C
Replies: 2
Views: 524

Re: Winter 2009 4C

We can use either E = Eo - (0.05916V / n) * logQ or E = Eo - (RT/nF) LnQ in this problem and we should get the same answer (both are given in the formula sheet). However, in general, we can only use the first "log" version of the equation if the temperature is @298K (which in this problem,...
by ch1995
Sat Mar 15, 2014 3:31 pm
Forum: Phase Changes & Related Calculations
Topic: 2011 Final #1A
Replies: 4
Views: 675

Re: 2011 Final #1A

If the question asked us to find how much heat it took to convert the liquid water to water vapor at 100*C, then we would have to account for the phase change. But since it only asked how much heat it took to boil the water, we assume that the water remain in liquid phase as it boils (such as a kett...
by ch1995
Sat Mar 15, 2014 3:14 pm
Forum: Phase Changes & Related Calculations
Topic: 2011 Final #1A
Replies: 4
Views: 675

Re: 2011 Final #1A

By raising the temperature to 100*C, the water is already boiling (since BP = 100*C), so no additional heat is required.
by ch1995
Sat Mar 15, 2014 2:11 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: How do you calculate W?
Replies: 1
Views: 501

Re: How do you calculate W?

W = (# of orientations per molecule)(# of molecules)
So it would be W = 38
by ch1995
Sat Mar 15, 2014 11:13 am
Forum: *Ethers
Topic: 2011 Question 7D
Replies: 2
Views: 509

Re: 2011 Question 7D

...... C ...... | C - C - O - C ...... | ...... C ^ 2-methoxy-2-methyl propane Propane is the longest carbon chain, and the methoxy (-OCH3) and methyl (-CH3) groups are both attached to the second carbon. If it were 1- methoxy, it would probably look like this: ...... C - O - C ...... | C - C ........
by ch1995
Sat Mar 15, 2014 9:46 am
Forum: *Alkenes
Topic: double/triple bonds/functional groups priority
Replies: 4
Views: 18954

Re: double/triple bonds/functional groups priority

Akynes have priority over alkenes. For heteroatoms, any atom that is not carbon or hydrogen, the larger the atomic number, the higher the priority. Schematically: functional groups > triple bond > double bond > halogen > substituents ^ Does this mean we're supposed to number the carbons to give the...
by ch1995
Sat Mar 15, 2014 9:08 am
Forum: *Ethers
Topic: Naming Ethers pg. 70
Replies: 2
Views: 637

Re: Naming Ethers pg. 70

I think so. According to pg 70, the short chain (alkoxy group) should be treated as a regular substituent, so the double bond does have priority.
by ch1995
Sat Mar 15, 2014 8:17 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 14.69
Replies: 1
Views: 630

Re: 14.69

We use the formula k = Ae^(-Ea/RT): Original uncat rxn: kuncat = Ae^(-98kJmol-1/RT) The cat rxn: kcat = Ae^(-Ea/RT).......................................... [cat rxn has different Ea, but "all other factors being equal" to uncat rxn] If we write out the rate laws Rate = k[R]: Original unc...
by ch1995
Sat Mar 15, 2014 12:31 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Final 2010 Question 2
Replies: 2
Views: 609

Re: Final 2010 Question 2

Ssurr = -Ssys only applies for reversible, isothermal processes I think.
by ch1995
Sat Mar 15, 2014 12:23 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate law in 3 step mechanism
Replies: 5
Views: 3830

Re: Rate law in 3 step mechanism

Yes, but I think we need to define the variable k before using it (or state that k = K1K2k3) Also note that K1 and K2 are equilibrium constants (capitalized K). We can also write it in terms of the rate constant since K = (k/k'), with k being rate constant for the forward rxn and k' being rate const...
by ch1995
Fri Mar 14, 2014 11:35 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Quiz 2 8th question
Replies: 1
Views: 567

Re: Quiz 2 8th question

Lnk = -(Ea/RT) + LnA ^From this equation, we can see that if we plot Lnk and 1/T, we will get a straight line (because y = mx + b) Ln(k2/k1) = (Ea/R) [(1/T1) - (1/T2)] ^We use this equation to calculate the Ea using 37 Celsius and 60 Celsius values (k1 = 1.76h-1, T1 = 37.0*C, k2 = 60.7h-1, T2 = 60.0...
by ch1995
Fri Mar 14, 2014 11:17 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate law in 3 step mechanism
Replies: 5
Views: 3830

Re: Rate law in 3 step mechanism

Step 1: A+B <--> C (fast) K1 =\frac{[C]}{[A][B]} K1[A][B] = [C] Step 2: C <--> D (fast) K2 =\frac{[D]}{[C]} K2[C] = [D] Step 3: D --> E (slow) Rate3 = k3 [D] Overall: Rate = k3 [D] Rate = k3 (K2 [C] ) Rate = k3 K2 (K1 [A] [B]) After substituting/combining all constants into k, we should get Rate = k...
by ch1995
Fri Mar 14, 2014 11:01 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate law in 3 step mechanism
Replies: 5
Views: 3830

Re: Rate law in 3 step mechanism

Yep, the overall rate law is the same as the rate law for the slow step, but don't forget to substitute out the intermediates using the previous fast elementary steps.
by ch1995
Fri Mar 14, 2014 10:58 pm
Forum: Balancing Redox Reactions
Topic: Winter 2009 Final Question 4
Replies: 4
Views: 740

Re: Winter 2009 Final Question 4

Do you mean for part (c)? We were given that [HClO4] = 1.00M, so:
(1.00 mol HClO4 / 1L) (1 mol H+ / 1 mol HClO4) = 1.00M H+
by ch1995
Fri Mar 14, 2014 9:13 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: final 2009 4e
Replies: 5
Views: 1010

Re: final 2009 4e

Yep, the question asked for the pH, and pH is only affected by [H+] and not the conc of the other species (pH = -log[H+]).
by ch1995
Fri Mar 14, 2014 8:44 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation
Replies: 6
Views: 2286

Re: Nernst Equation

E = Eo - (0.05916V / n) * logQ is specifically for rxns at 298K (I don't know if the constant -0.05916V necessarily equals -RT/F, but the temp of 298K is included in the constant). On the other hand, the equation E = Eo - (RT/nF) LnQ includes the variable T, so we can still use that one if the tempe...
by ch1995
Fri Mar 14, 2014 8:11 pm
Forum: *Alcohols
Topic: 2.40 b c
Replies: 1
Views: 435

Re: 2.40

(b) When there are both a triple bond and functional group, the functional group has priority (lowest) number. (2 < 3, or 2-methylbut-3-yn- 2 -ol instead of 3-methylbut-1-yn- 3 -ol) (c) Again, the -OH (alcohol/functional group) has priority, so we start numbering from that (with the Carbon that -OH ...
by ch1995
Fri Mar 14, 2014 7:43 pm
Forum: General Science Questions
Topic: Definitions Please!
Replies: 3
Views: 1147

Re: Definitions Please!

#3 should be thermodynamic control (as opposed to kinetic control). Maybe #2 is deltaG (or deltaH)?
by ch1995
Fri Mar 14, 2014 7:35 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: final 2009 4e
Replies: 5
Views: 1010

Re: final 2009 4e

E = Eo - (0.05916V / n) logQ 0 = 0.19V - (0.05916V / 5) logQ ............................ [E = 0 at equilibrium, n = 5e- transferred, Eo = 0.19V] 0.19V = (0.05916V / 5) log(1000*[H+]^8) ..............[Plugging in all known conc] 16.3 = log1000 + log[H+]^8 ...................................[logA*B =...
by ch1995
Fri Mar 14, 2014 7:23 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 2009 Question 4E
Replies: 1
Views: 457

Re: 2009 Question 4E

I never thought of doing it that way, but I just tried and I got around the same answer (pH = -1.66), so I think that way might also work!
by ch1995
Fri Mar 14, 2014 7:11 pm
Forum: *Alkenes
Topic: final 2009 7b
Replies: 1
Views: 407

Re: final 2009 7b

It should be 9. No matter which way we start counting, the double bond starts at Carbon #9.
by ch1995
Fri Mar 14, 2014 6:47 pm
Forum: Balancing Redox Reactions
Topic: Winter 2009 Final Question 4
Replies: 4
Views: 740

Re: Winter 2009 Final Question 4

The question asks us to write the equation of the reaction that can occur. In other words, the reaction must be spontaneous, or Ecell > 0. (If Ecell < 0, then the rxn is not spontaneous and won't occur). If we make the top half reaction the cathode and bottom as the anode, then we get a positive Ece...
by ch1995
Fri Mar 14, 2014 5:11 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 2008 final 3 D
Replies: 2
Views: 416

Re: 2008 final 3 D

I think so. Since the question only mentions that the [Cu2+] is changed, we would assume that everything else remains at standard conditions (aqueous solutions at 1M, gas at 1 bar, etc.)
by ch1995
Fri Mar 14, 2014 5:06 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Boltzmann Distribution
Replies: 2
Views: 630

Re: Boltzmann Distribution

I think exp(-Ea/RT) means e^(-Ea/RT) (as seen here: http://chemwiki.ucdavis.edu/Physical_Ch ... ion_Theory)

If that's the case, then the fraction is greater as temperature increases.
by ch1995
Fri Mar 14, 2014 4:55 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Q in the Nernst Equation
Replies: 4
Views: 721

Re: Q in the Nernst Equation

LnQ = 15
Q = e^15

The number of sig figs in Q should be equal to the number of decimal places in the exponent. Since "15" has no decimal places, I guess we don't write any number in front of 10^6?
by ch1995
Fri Mar 14, 2014 11:41 am
Forum: *Organic Reaction Mechanisms in General
Topic: 2013 final Q5C
Replies: 1
Views: 476

Re: 2013 final Q5C

In this reaction, "N" from the reactant molecule on the left bonds to the "C" in the molecule on the right and the "-OH" group that was originally attached to the "C" leaves. Looking at the diagram of the reactant molecule on the right, this "C" is o...
by ch1995
Fri Mar 14, 2014 10:27 am
Forum: General Rate Laws
Topic: 2007 final question 4Bb
Replies: 1
Views: 302

Re: 2007 final question 4Bb

Because we are writing the rate laws for elementary steps, we don't need to worry about the intermediates. We only need to substitute out the intermediates when we write the rate law for an overall reaction.
by ch1995
Fri Mar 14, 2014 8:22 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 13.9
Replies: 1
Views: 883

Re: 13.9

(a) 2Ce4+(aq) + 3I-(aq) => 2Ce3+(aq) + I3-(aq) ........ Ecell o = +1.08V We would look at appendix 2B to find the half reactions for "Ce4+/Ce3+" and "I-/I3-": Ce4+ + e- => Ce3+ I3- + 2e- => 3I- Next, we have to add these 2 half-reactions together in a way that cancels out the e-....
by ch1995
Fri Mar 14, 2014 8:14 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 13.13c
Replies: 1
Views: 2753

Re: 13.13c

13.13 Write the half-reactions, the balanced equation for the cell reaction, and the cell diagram for each of the following skeletal equations: (c) Cl2(g) + H2(g) => HCl(aq) Since HCl is a strong acid, this equation can also be written as: Cl2(g) + H2(g) => H+(aq) + Cl-(aq) We look at Appendix 2B to...
by ch1995
Fri Mar 14, 2014 7:58 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: 617

Re: 2013 final

Yes, the formula sheet should provide us with the reduction half rxns. And it would definitely help if we write out the half-reactions in order to find n (since it would be hard to tell from the overall equation)
by ch1995
Fri Mar 14, 2014 7:55 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: 387

Re: Winter Final 2013 Q3C

We can use Ecell = Eocell - (0.05916V / n)logQ or Ecell = Eocell - (RT/nF)LnQ. (I used the second one and I got the same ans as the book)

pH = -log[H+] = 2
log[H+] = -2
[H+] = 0.01M
by ch1995
Thu Mar 13, 2014 11:32 pm
Forum: *Alkenes
Topic: 2009 final Q7D
Replies: 4
Views: 676

Re: 2009 final Q7D

First we locate the double bond, then look at the 2 Cs involved in the double bond separately. Looking at the C on top (with Ctop being one of the carbons involved in the double bond): HO \ / \ C top / .............. || If we fill in all the C's and H's: ........ H .... H ............ H ........ | ....
by ch1995
Thu Mar 13, 2014 11:15 pm
Forum: Calculating Work of Expansion
Topic: 2011 final Q1B
Replies: 1
Views: 380

Re: 2011 final Q1B

CH4(g) + 2O2(g) => 2H2O (l) + CO2(g)
1 + 2 = 3 .................0 + 1 = 1

^Reactants contains 3 moles of gas while product contain 1 mole.
delta(n) = moles of gas in products - moles of gas in reactants
delta(n) = 1.00mol - 3.00mol = -2.00mol
by ch1995
Thu Mar 13, 2014 5:51 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 2008 finalQ3D
Replies: 3
Views: 524

Re: 2008 finalQ3D

They give us the formula on pg 113 of the course reader: E = Eo - (0.05916V / n) * logQ
by ch1995
Thu Mar 13, 2014 5:48 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 2010 final 1b
Replies: 6
Views: 817

Re: 2010 final 1b

q = m C deltaT

^Butane gas C4H10, has a significantly larger molar mass than H2. So it should require more heat.
by ch1995
Thu Mar 13, 2014 5:46 pm
Forum: *Alkenes
Topic: 2007 final Q7(b)
Replies: 2
Views: 506

Re: 2007 final Q7(b)

Do you mean Q7(a)? For that molecule, we have to start naming from the bottom because that would give the double bond the lowest number. Remember that double bonds have priority over the regular substituents (methyl, chloro, etc.)
by ch1995
Thu Mar 13, 2014 3:30 pm
Forum: General Rate Laws
Topic: Reaction Rates
Replies: 2
Views: 518

Re: Reaction Rates

I agree:

Original rate:
rate0= k [H2] [Cl2]^2

If concentration of Cl2 is halved:
ratenew= k [H2] (1/2[Cl2])^2
ratenew= k [H2] 1/4 [Cl2]^2
ratenew= 1/4 (k [H2] [Cl2]^2)
ratenew= 1/4 (rate0)

Rate will be quartered when conc of Cl2 is halved
by ch1995
Wed Mar 12, 2014 8:58 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 2012 3
Replies: 9
Views: 1698

Re: 2012 3

The last question of the midterm Q8 (or #13.103 on hw) wants us to find the Ka value for HF given that: F2 + 2H+ + 2e- => 2HF ~~~ E = +3.03V F2 + 2e- => 2F- ~~~~~~~~E = +2.87V Since Ka is the equilibrium constant for HA => H+ + A-, then we know that we want the overall reaction to be in the form of ...
by ch1995
Wed Mar 12, 2014 8:37 pm
Forum: Calculating Work of Expansion
Topic: expansion
Replies: 1
Views: 443

Re: expansion

I think it would be: Vwater = 100g (1cm^3 / 1g) (1mL / 1cm^3) (1L / 1000mL) = 0.100L Vice = 100g (1cm^3 / 0.92g) (1mL / 1cm^3) (1L / 1000mL) = 0.109L w = -P * deltaV w = -1070 atm * (0.109L - 0.100L) w = -1070 atm * (0.009L) w = -9.30 L*atm * (101.325J / 1L * atm) w = -942J (I'm not sure about the s...
by ch1995
Wed Mar 12, 2014 12:41 am
Forum: *Alkenes
Topic: CH3(CH2)3CHCHCH3
Replies: 3
Views: 1778

Re: CH3(CH2)3CHCHCH3

We know that carbons can form 4 single bonds. ... | .... | ............. | .... | - C - C - etc. - C - C - ... | .... | ............. | .... | ^ As seen above, in a simple alkane like this, the 2 carbons at the end will be CH3 (it will be bonded to 1 C and 3 H = 4 bonds total). All the carbons in th...
by ch1995
Wed Mar 12, 2014 12:04 am
Forum: *Alkenes
Topic: Naming
Replies: 2
Views: 526

Re: Naming

I don't think that would be the most proper way of naming it. Since all 3 substituents are methyl groups in this case, be sure to group them all together and indicate the locations for these 3 groups: 3,4,4-trimethyl (tri- because there are 3 methyl groups, and list out each of the locations, even i...
by ch1995
Tue Mar 11, 2014 11:39 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Calculating Total Entropy
Replies: 1
Views: 791

Re: Calculating Total Entropy

(1) isothermal, reversible expansion DeltaS sys = n * R * Ln(V 2 /V 1 ) DeltaS surr = -DeltaS sys DeltaS tot = DeltaS sys + DeltaS surr = 0 [Isothermal: DeltaU sys = q sys + w sys = 0 q sys = -w q surr = -q sys = w = -nRTLn(V 2 /V 1 ) DeltaS surr = q surr / T DeltaS surr = -nRTLn(V 2 /V 1 ) / T Del...
by ch1995
Tue Mar 11, 2014 10:42 pm
Forum: *Amines
Topic: including (or not including) the 1
Replies: 6
Views: 958

Re: including (or not including) the 1

Oops! I guess we were all talking about cases where it is unambiguous that the substituent (or double/triple bond, etc.) are located on Carbon #1. But if there is ambiguity, we would definitely have to include the "1"
by ch1995
Tue Mar 11, 2014 9:19 pm
Forum: *Alkanes
Topic: CH3CH2CH(CH3)C(CH3)3
Replies: 3
Views: 2709

Re: CH3CH2CH(CH3)C(CH3)3

We see that no matter which way we count, the longest chain is 5 carbons long.
by ch1995
Tue Mar 11, 2014 8:39 pm
Forum: *Alkanes
Topic: CH3CH2CH(CH3)C(CH3)3
Replies: 3
Views: 2709

Re: CH3CH2CH(CH3)C(CH3)3

If we draw out the structure, we see that the longest continuous carbon chain is 5 carbons long, therefore it should not be named -heptane.
by ch1995
Tue Mar 11, 2014 8:35 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Winter Final 2010 Question 3A
Replies: 3
Views: 768

Re: Winter Final 2010 Question 3A

2CO(g) + O2(g) => 2CO2(g)
2+1=3 moles of gas => 2 moles of gas

^ There will be less "disorder" with less moles of gas. Therefore deltaSsys < 0
by ch1995
Tue Mar 11, 2014 7:01 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 8.45 - C value used for water
Replies: 2
Views: 542

Re: 8.45 - C value used for water

We can use 4.184J/oC*g or 75.29J/K*mol. Both should work as long as all the units are consistent.
by ch1995
Tue Mar 11, 2014 3:39 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Winter 2009 final 6A
Replies: 5
Views: 693

Re: Winter 2009 final 6A

For organic reactions, those with an activation energy below about 80kJ/mol can occur at room temperature (according to pg 154 of the organic chem txtbook). But I'm not sure if that applies to all other reactions...
by ch1995
Tue Mar 11, 2014 3:00 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Winter 2009 final 6A
Replies: 5
Views: 693

Re: Winter 2009 final 6A

For this problem, we do not need to know the exact value of Ea for each of the graphs, but just look at their Ea relative to each other. The activation energy of graphs (2) and (4) are clearly higher than that of (1) and (3), so those rxns are less likely to occur at room temp.
by ch1995
Tue Mar 11, 2014 1:03 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 2008 Final question 3D
Replies: 1
Views: 264

Re: 2008 Final question 3D

We would assume that they remain at standard conditions ([H+] = 1.00M, PH2 = 1.00bar)
by ch1995
Tue Mar 11, 2014 12:52 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: final 2008 3.
Replies: 7
Views: 835

Re: final 2008 3.

@704278444: I think the electrode would usually be a solid metal because it can transfer the e- (but there are some exceptions like liquid Mercury) @804338838: If we write both half-reactions as reduction rxns, we see that: Pb2+(aq) + 2e- => Pb(s) ~~~ E = -0.13V 2H+(aq) + 2e- => H2(g) ~~~ E = 0.0V S...
by ch1995
Tue Mar 11, 2014 11:34 am
Forum: Phase Changes & Related Calculations
Topic: 2010 final Q1B
Replies: 1
Views: 341

Re: 2010 final Q1B

Please see: https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=135&t=3690&p=8490&hilit=copper+water&sid=7075443220d621f1d6d9837a640b83a0#p8490"onclick="window.open(this.href);return false; For the 3rd subquestion, To vaporize 1 mole of water: q = (DeltaHvap)*(1mol) = 40.7kJ/mol * 1m...
by ch1995
Tue Mar 11, 2014 11:28 am
Forum: *Constitutional and Geometric Isomers (cis, Z and trans, E)
Topic: 2009 final Q6C
Replies: 3
Views: 648

Re: 2009 final Q6C

To determine cis/trans, we would look at the atoms by priority described on pg. 16 of the organic chem textbook. In the diagram of Q6C, we look at the carbons with non-hydrogen atoms attached. First, if we look at the Carbon at the top of the pentagon, there is an OH and H attached to it. From pg. 1...
by ch1995
Tue Mar 11, 2014 11:21 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 2010 final Q1A
Replies: 1
Views: 320

Re: 2010 final Q1A

q1 = n * Cp * DeltaT

The solution did not plug in 10*C, it used the change in temperature: DeltaT = 0*C - (-10*C) = 10*C (which is equal to a change of 10K)
by ch1995
Tue Mar 11, 2014 11:18 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 2009 final question 4C
Replies: 3
Views: 546

Re: 2009 final question 4C

Yes:

(1.00 mol HClO4 / 1L) (1 mol H+ / 1 mol HClO4) = 1.00mol H+

Since there's 1 mol of H+ per mol of HClO4, the concentration of H+ is also 1.00M
by ch1995
Tue Mar 11, 2014 12:20 am
Forum: *Cyclohexanes (Chair, Boat, Geometric Isomers)
Topic: Final Winter 2009, Question 7A
Replies: 1
Views: 480

Re: Final Winter 2009, Question 7A

Notice how the hydroxide group (-OH) is attached to a benzene ring. This benzene ring + -OH makes up the functional group phenol (see pg 56 of organic chem textbook).
by ch1995
Mon Mar 10, 2014 10:45 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Winter Final 2008 Question 1A
Replies: 3
Views: 520

Re: Winter Final 2008 Question 1A

Looking at page 114, we see that DeltaHf (H2O) = -285kJ/mol
by ch1995
Mon Mar 10, 2014 9:50 pm
Forum: *Electrophiles
Topic: Electrophilic Strength and Electron Affinity
Replies: 1
Views: 668

Re: Electrophilic Strength and Electron Affinity

I'm think they do parallel these patterns to a certain extent. For example, Cl- is a better nucleophile than F- because of its lower ionization energy (gives up e- more easily). But as we move down the column, I- is not necessarily an even better nucleophile than Cl- or Br- because Br- is too large ...
by ch1995
Mon Mar 10, 2014 9:26 pm
Forum: *Cycloalkenes
Topic: Where to start counting Winter 2013 final 6A
Replies: 6
Views: 3660

Re: Where to start counting Winter 2013 final 6A

1 ,5,5,6 tetramethylcyclohex-1-ene 2 ,3,4,4 tetramethylcyclo-hex-ene ^Comparing the #'s above, the first (lowest) numbers for each name are 1 and 2. Since 1<2, 1,5,5,6 tetramethylcyclohex-1-ene is the correct name. When we number the carbons, the double bond does determine where C1 is (C1 has to be...
by ch1995
Mon Mar 10, 2014 8:28 pm
Forum: *Alkanes
Topic: Functional Groups
Replies: 1
Views: 335

Re: Functional Groups

https://lavelle.chem.ucla.edu/wp-conten ... Groups.pdf
According to the syllabus, we need to know "alcohols, ethers, aldehydes, ketones, carboxylic acids, amines" (not phenol though)
by ch1995
Mon Mar 10, 2014 8:26 pm
Forum: *Constitutional and Geometric Isomers (cis, Z and trans, E)
Topic: Final 2011 Q7B
Replies: 3
Views: 696

Re: Final 2011 Q7B

Oh I see, thanks! :)
by ch1995
Mon Mar 10, 2014 6:49 pm
Forum: *Cycloalkanes
Topic: Listing all functional groups
Replies: 2
Views: 489

Re: Listing all functional groups

I think it's because the oxygen with the carbons bonded on either side is part of the ester functional group (as seen on page 78 of the course reader). We wouldn't name it again as an ether, just as we wouldn't name the -OH in a carboxyl group as alcohol.
by ch1995
Mon Mar 10, 2014 5:30 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Winter 2012 final 1B
Replies: 1
Views: 538

Re: Winter 2012 final 1B

We want to calculate deltaH for the rxn 2 NO + O2 => 2NO2 at 398K. What we know already from the first part of Q1B is that deltaH for this rxn at 298K is -112kJ: [Reactants @ 298 K] => [Products @ 298 K] .... deltaH = -112kJ But for this problem, we want to find deltaH for rxn [Reactants @398K] => [...
by ch1995
Mon Mar 10, 2014 3:37 pm
Forum: *Organic Reaction Mechanisms in General
Topic: Lewis structures ch.4
Replies: 1
Views: 498

Re: Lewis structures ch.4

We would calculate the formal charge of each atom: (7) SCN- In one of the resonance structure, S has 3 lone pairs and forms a single bond with C, which forms a triple bond with N, which has 1 lone pair of e-. Formal charge = (#Valence e-) - (#Lone Pair e- + 1/2*#Bonding Pair e-) For S, FC = (6) - (6...
by ch1995
Mon Mar 10, 2014 3:28 pm
Forum: *Alkenes
Topic: Winter 2009 7B
Replies: 3
Views: 703

Re: Winter 2009 7B

For this problem, I think the diagram (structure) is actually given, and we're told to name it.
by ch1995
Mon Mar 10, 2014 3:20 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Winter 2009 final 6A
Replies: 5
Views: 693

Re: Winter 2009 final 6A

Room temp is not considered a very high temperature for rxns to occur (we're not heating anything up). Therefore, rxns with high activation energies will less likely occur at room temp because not a lot of the reactant molecules will have enough energy to overcome the energy barrier.

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