Friday
August 1, 2014

Posts by DrBob222


Total # Posts: 43,229

(2-8) Chemistry - Science (Dr. Bob222)
work = 0 http://physics.bu.edu/~duffy/semester1/c27_process_expansion_sim.html

(2-8) Chemistry - Science (Dr. Bob222)
Copied from Wikipedia. "When no heat flows into or out of the gas because its container is at the same temperature, then there is no work done. Thus, work=0 which means external pressure on any moving surface is zero. This is called free expansion." So when the term ...

(2-8) Chemistry - Science (Dr. Bob222)
In the first question, D says that dE cannot change if T doesn't change and I was answering that it certainly can because pdV changes work and that changes dE and no T is necessarily involved. The point in the first one is that changing T changes q and changing T CAN chan...

(2-8) Chemistry - Science (Dr. Bob222)
dE = q + w q changes with T. w, though, is pdV and you can change w willy nilly which will always change dE but T is not necessarily involved in changing volume.

Chemistry
5.7 what? from what reaction? what conditions? I'll assume that is 5.7L H2O, then assume rxn is 2H2 + O2 ==> 2H2O and assume this is at STP. 5.7 L H2O x (1 mol O2/2 mols H2O) = 5.7 x 1/2 = ? L O2

Chemistry
Look up reduction potentials for Cd^2+ + 2e==> Cd and Co2^+ + 2e ==> Co. Look at which one of the two will give a positive voltage. That is the one that will proceed spontaneously.

Chemistry
I don't understand the question. Is that between Na and K? Any water involved?

chemistry
Instead of me guessing what you did why not show your work and let me find the error.

chem
Yes, and remember to substitute dHvap in J/mol, not kJ/mol. Also remember T must be in kelvin

oops---chemistry
The correct answer is d. As long as some carbon is present, adding or removing carbon will not affect the equilibrium.

chemistry
To avoid oxidation by oxygen.

science
I disagree. Think about it. A(l) + B(l) --> gas Say A has a mass of 2 g and B has a mass of 2 grams (and they are liquids), what does the gas weigh? And how did you weigh it?

chemistry
All are ok except 2. 2 is an ether.

Chemistry
First, determine the M of the HCl. That will be 25*0.2/20 = 0.25M Where is the equivalence point. That is at 25.0 mL, NaOH, of course. The questions divide the titration curve up nicely into a. at the beginning. b. before the eq point. c. at eq pt d. just after eq pt It's ...

Chemistry - Science (Dr. Bob222)
That's an interesting proposition but I don't think Le Chatelier's principle is quite the one to use here. However, if you look at it as an equilibrium (which it is), then H2O(l) --> H2O(g) So Kp = pH2O(g). When pH2O(g) has reached equilibrium with the liquid, t...

Chemistry
None of these is balanced. 5a. Mn^2+ + H2O2 ==> MnO2 + H2O b. unclear to me c. Mn^2+ + BiO3^- ==> MnO4^- + Bi^3+ 6. a & b. Fe^3+ + NH3 + H2O ==> Fe(OH)3(s) Cu + NH3(aq) ==> Cu(NH3)4]^2+(aq) c & d. Zn^2+ + NH3(aq) ==> Zn(NH3)4]^2+(aq) Al + NH3 + H2O ==> Al(OH)...

Chemistry
Convert oz to mass in grams. Then volume = mass/density

chemistry
I believe this must be to produce a ketone.

chemistry
coulombs = amperes x seconds. C = 2.3E-5 x 1200 d x (24 hr/d) x (60 m/hr) x(60 s/min) = ? 96,485 coulombs will produce (200.6/2)g Hg; therefore, g Hg = (200.6/2) x (?coulombs/96,485)

chemistry
I agree with your answer.

Organic Chemistry
Ask yourself, 79% of what = 135 or 0.79*x = 135, then 135/0.79 = x

(1-22)Chemistry - Science
However, following up on what Writeacher wrote, it is a huge help to us if you post what you think is the way to fo, post the process, explain what you don't understand, etc. That way we can focus on helping with the specific part of the problem that is causing concern rat...

(1-22)Chemistry - Science
.......C(s) + H2O(g) ⇌ CO(g) + H2(g) I.............1.00......0.......0 C..............-x.......x.......x E............1-x........x.......x Substitute the E line into Kp expressin and solve for x = pH2 = pCO pH2O = 1-x. The correct answer is D.

(1-17)Chemistry - Science
Isn't this done the same way except you know the reaction must shift to the left to reach equilibrium?

(1-16)Chemistry - Science
First you must determine which way the reaction will shift to reach equilibrium. Q = (SO3)(NO)/(NO2)(SO2) = (0.5*0.5/0.5*0.5) = 1. With K = 9 that means products are too small and reactants too large so the rxn must shift to the right to reach equilibrium. .....SO2(g) + NO2(g)...

(1-15) Chemistry - Science
Is this a comparison of KE to KE?

(1-13) Chemistry - Science
I think most of this covered in discussions of the "imperfect gas" and the van der Waals equation.

1-12. Chemistry - Science
D2 + E = product mols D2 = 3/22.4 = ? mols E = 3/22.4 = ? mols product = 1.5/22.4 However, when working with gases one can dispense with the 22.4 since that is a constant in all of the numbers; i.e., use L as if L = mols. I would think the formula of the product is D4E2. Try t...

(1-11) Chemistry - Science (Dr. Bob222)
Yes, the answer is C. Any liquid placed in a closed system will come to equilibrium with its vapor at a particular temperature. The vapor pressure then is say x. Adding more liquid will NOT make the liquid evaporate more which would, of course, increase the vapor. The vapor pr...

chemistry
https://answers.yahoo.com/question/index?qid=20100630090838AAcJFUB

To Ana
I saw you post 4-5 pages down about K for the disproportionation problem. I calculated K by RTlnK = nFEo

Chemistry
mols acid = grams/molar mass m acid = mols/kg solvent delta T = Kf*m Solve for T and add to normal freezing point of benzene to find the new f.p. Do the same for b.p. mols acid is same m acid is same delta T = Kb*m Add delta T to normal b.p. to find new b.p.

chemistry
Same as your post on benzoic acid/benzene EXCEPT delta T = i*Kf or Kb*m i = 2 for NaCl.

chemistry
a. 0.125M x 20/50 = ? b. 0.025 x 20/50 = ? c. mass = 0.1g/L x 0.010 L = ? Then mols = grams/molar mass d. mols I2 = M I2 x L I2 = ? e. I2 + 2S2O3^2- ==> 2I^- + S4O6^2- Therefore, delta mols I2 = 1/2 mols S2O3^2-

DR.bOBB
OK. Further down the list I note a bunch of question by deepa and they deal with biology. Yes, I skipped all of them. I am not a biologist. I am a chemist and most questions in biology are simply out of my field. I don't want to give any wrong answers. I do answer an occas...

DR.bOBB
I skipped a (meaning one) question yesterday because I wasn't sure of the answer. To answer your question, no I'm not skipping a massive number of questions that deal with chemistry. If you posted a question I don't remember it. Did you use chemistry as the subject...

chemistry
http://www.conserve-energy-future.com/Advantages_Disadvantages_HydrogenEnergy.php

CHEMISTRY HELP !!!! CHECK !!!
I didn't work it that way and I don't see anything wrong with the way you did it. I agree with the answer.

CHEMISTRY HELP ! Check Please!
I don't agree with a I agree with b although I'm not sure of "what a small fraction" is. .

chemistry
%alcohol = (weight alcohol/total weight)*100 = ?

chemistry
See your other post.

Chem
a. What's the original volume? P1V1 = P2V2 b. What's the original volume? (V1/T1) = (V2/T2) Remember T must be in kelvin

Chem
PV = nRT Watch the units

Chem
Use PV = nRT

Chem
PV = nRT

Chem
(P1V1/T1) = (P2V2/T2)

Chem
Intuitively you see that the pressure has decreased which means the volume must have increased; therefore, the volume of the old flask is v and the volume of the combined flasks is 32+v Since p1v1 = p2v2, then 389*v = 154(32+v) and solve for v.

Algebra ( benchmark)
do you mean, "and NO more than 3200"?

Science
No, the atomic number of Pb is 82 (that's number of protons in the nucleus). The atomic weight Pb is 207.2.

Science
Why not type in the 14 questions; preferably only one or two per post. And show your answers and why you answered that way.

no link--Science
And you will not be able to leave a link on this forum unless you are one of the tutors. And not all tutors have this privilege.

chemistry
Below are four stages: 1. heat needed to raise T ice @ 20C to zero C. 2. heat needed to melt ice at zero to liquid water at zero. 3. heat needed to raise T ice at zero C to final T. 4. heat lost by 20 degree water to final T. [mass ice @ 20 x specific heat solid ice x (Tfinal-...

Chemistry
I worked this just a few post below but the Ecell was 11 mv. Same process though. Ecell = Eo - (0059/2)log(0.1/x) and solve for x.

Chemistry 104
This has been posted numerous times today. See those answers.

Chemistry
Look at it this way. The dipoles from the H2O molecules attract the Na^+ and Cl^- and pull on them. That's the pull to disrupt the crystal lattice energy. And it isn't a one step here to disrupt the crystal lattice and then another step to form the hydrates. It's t...

Chemistry
One major correction. It is true that the intermolecular forces (the water molecules pulling at the lattice energy) but those are ion-dipole forces and not ionic. Charged yes but not ionic). The answer to your question is that youmust take into account the energy gained when t...

Chemistry 104
Ecell = Eocell - (0.0592/2)log(x)/(Zn^2+) 0.011 = 0 -(0.0592/2)log(0.1/x) Solve for x.

chemistry
heat to melt ice + heat to raise T of melted ice to Tfinal + heat lost by warm water = 0 [mass ice x heat fusion] + [mass melted ice x specific heat H2o x (Tfinal-Tinitial)] + [mass warm water x specific heat H2O x (Tfinal-Tinitial)] = 0 Substitute and solve. The only unknown ...

Chemistry 104
Instead of us guessing, why don't you show your work so we can find the error.

Chemistry
See your earlier post.

Chemistry
See your others posts. And please stop changing screen names. It won't help and in fact keeps us from helping as much as we might if you used the same name.

Chemistry
Eo is zero, right? :-) The SHE under standard condition is always 0.

Chemistry
I assume that's 3.8 atm. 2H^+ + 2e ==> H2 E = Eo - (0.0592/2)log[(pH2/(H^+)^2]

Chemistry
Ecell = Eocell - (0.0592/n)log[(Cr^2+)/(Ni^2+)] and you get Eocell by adding the OXIDATION for Cr to the REDUCTION of Ni^2+. I would do it here but the values in your text won't agree with the values in my OLD text.

Chemistry
Then you must be in the same room using the same computer so just talk to each other; you don't need to talk via computer.

Chemistry
Janu, Ladoo, et al. It helps us help you better if you use the same screen name. Look up the potentials, add the oxidation half to the reduction half to obtain Eocell. Then dG = -nFE

oops--Chemistry 104
Note that there are two mols of electrons and you must take that into account. A minor problem is that you will not plate out Ni(NO3)2 but Ni metal.

College Chemistry
Ptotal = pN2 + pAr

math lit ,geography,history,life science,LO
You need to provide some other information. What career choices do yo have? Which subjects are you taking? The first thing that come to my mind is that in grade 10 you aren't forced to make a career choice today; you still have a few years to think it over.

Chemistry
I don't understand your confusion. Silicon dioxide is SiO2. That's how you're supposed to write it.

Chemistry
SiO2 is THE formula for silicon dioxide. That's it. That's the only formula for silicon dioxide.

Chemistry
For some, such as silicon dioxide, the name tells you. Write the symbols. Si and O. The name says DI oxide so put 2 for O as a subscript and the formula is SiO2.

Chemistry
delta T = Kf*molality Substitute and solve for m m = mols/kg solvent Substitute and solve for mols. mols = grams/molar mass. You know grams and mols, solve for molar mass

Chemistry
q = mass H2O x specific heat H2O x (Tfinal-Tinitial)

Chemistry - Science (Dr. Bob222)
Thermodynamics is not my field. I would go with C but get a second opinion. I don't think A is right because for a diatomic gas Cp is 7/2R. B. B can't be right because at constant P there will be pdV work. C. The difference between Cv and Cp is 8.3 and that is about 28...

(12)Chemistry - Science (Dr. Bob222)
The problem here is in your assumptions. You KNOW the volume will change if the pressure is constant AND the temperature decreases from 165 to 65. Volume is proportional to T; therefore, volume decreases with decreasing T. dE = q + w You've made the assumption that w is ze...

(23.Chemistry - Science (Dr. Bob222)
Devron is right but I want to add a point or two. First, Ana is right. It PROBABLY isn't possible unless the reaction is carried out in under other than standard conditions; i.e., basic solution, complexing materials added to the basic mix, etc. Devron is right that none o...

(19) Chemistry - Science (Dr. Bob222)
RTlnK = nFEo

Chemistry
Calculate the molarity of the concentrated HCl. You made a typo and omitted the % after 37. M HCl = 1000mL x 1.20g/mL x 0.37 x (1 mol/36.5g) = about 12.2M Then mL1 x M1 = mL2 x M2 mL1 x 12.2M = 2850 mL x 0.500 Solve for mL 1 you need. Take mL you've calculated, add to a 50...

chemistry
mols = grams/molar mass

chemistry
I don't know and we can't find out. mols NaOH = M x L = approx 0.0042 IF the unknown acid is a monoprotic acid, then mols acid = mols base and mols acid = grams/molar mass You know mols acid and grams acid, calculate molar mass acid. However, the problem doesn't sa...

chemistry
See your other post under Harley.

chemistry
See your other posts. Just one is all ou need to see how to do these.

(11) Chemistry - Science (Dr. Bob222)
I'm sticking my neck out but go through this reasoning and see if you agree. reactants --> products k = P/R For k to be < 1, reactants must be favored. Just try A; if dH is - the reaction would be R ==> P + heat If we increase T the reaction will be shifted to the...

Chemistry - Science (Dr. Bob222)
A. dG has nothing to do with speed of a reaction. Carbon is the more stable form of diamond but all the girls getting diamond rings today need not worry about that ring crumbling tomorrow. :-). B. All reactions occur to some extent no matter how small. So this has an extremely...

science
I know very little about biology but that's what I think.

science
https://answers.yahoo.com/question/index?qid=20110503190756AADMkC7

CHEMISTRY HELP !!!!
OK. I told you how to do it. Do you need more assistance or do you have the right answer now?

CHEMISTRY HELP !!!!
What does either B or E mean? To me it means you don't know and you're guessing because they aren't close to each other. How many coulombs did you use. That's amperes x seconds = coulombs. Then you know that 27/3 = 9 g Al will be deposited for every 96,485 coul...

CHEMISTRY HELP !!!!
ok Now we can do something. Make the top numbers add up and the bottom numbers add up. on the left. top...1 + 235 = 236 bottom 0 + 92 = 92 which does nothing more than show that 236/92U is right. Now to the next part of the reaction. top: 236 = 137 + ? + (2*1) and solve for ?....

CHEMISTRY HELP !!!!
What's with the 1/2n? neutrons are 1/0n

CHEMISTRY HELP !!!!
Either you've made a typo or this is a screwed up question. 236/92 can't be Te. It MUST be U. And what is 2(1/2)n? neutrons are 1/0.

CHEMISTRY HELP !!!!
nope. And example for element X and I'll make up numbers. 24/12X ==>beta + Y 24/12 X ==> 0/-1 e + zYw and you want to know what z and w are. The upper numbers add up on both sides. The lower numbers add up on both sides. upper number first. 24 = 24 + ? so w must be 0...

Chemistry
22% w/w means 22 g solute Z in 100 g solution. mols in 22 g = 22/215.2 = ? Use density to convert 100 g to mL and convert to L. Then M = mols/L

Chemistry
mols K2SO4 = grams/molar mass Then M = mols/L solution.

Chemistry
The position of the metal and metal ion in the activity series.

chemistry
Probably none. Fe2O3 is not soluble. Sr3(PO4)2 is insoluble. No reaction.

chemistry
A. mols soln A = mol/dm3 x dm3 =? mols soln B = same thing. Bi. total mols HCl = mols of A + mols B Bii. NH3 + HCl ==> NH4Cl mols HCl you have. From the coefficients in the balanced equation, you know mols NH3 = mols HCl Then mols NH3 = mol/dm3 x dm3. You know mols and mol/...

chemistry
2Al(OH)3 + 3H2SO4 --> Al2(SO4)3 + 6H2O 1) How many mols Al(OH)3 do you want? That's M x L = 0.672 x 0.500 = approx 0.3 but you should be more accurate than that. mols Al(OH)3 = grams/molar mass. You know mols and molar mass; solve for grams. 2)How many mols H2SO4 did yo...

chemistry pls help me asap
3NaOH + H3PO4 ==> Na3PO4 + 3H2O mols NaOH = grams/molar mass = 4.0/40 = 0.1 mol. a) M NaOH = mols/dm3 = 0.1mol/0.1 dm3 = 1M b) From the equation, 3 mol NaOH = 1 mol H3PO4; therefore, 40 cc (0.04 dm3) of NaOH x 1 M = 0.04 mols NaOH. mols H3PO4 = 1/3 of that or 0.04/3 = about...

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