Saturday
April 18, 2015

Posts by DrBob222


Total # Posts: 48,372

chemistry
See your other post below.
January 31, 2015

Chem
k = 0.693/t1/2
January 31, 2015

chemistry
dHrxn = (n*dHf products) - (n*dHf reactants)
January 31, 2015

chemistry
Add equation 1 to the reverse of equation 2, then divide the final equation by 2. When reversing an equation change the sign of dH. When dividing an equation by 2 divide dH by 2. When adding equations add dH values for each.
January 31, 2015

chemistry
dHrxn = (n*dHf products) - (n*dHf products) dHrxn = -127 = (n*dHf .....etc) Substitute and solve for dHf CaC2 which is the only unknown in the equation.
January 31, 2015

chemistry
Thank you for showing your work. I don't see anything wrong with your set up or the numbers. Always check to see that you used the correct value from the tables. I suspect the problem is one of significant figures. I think the answer is -2512 kJ. -1.574E3 - 0.4836E3 = -2....
January 31, 2015

To Morgan---Chemistry
If you had shown your work instead of answers we could have seen at a glance what the problem was. As it is you must check your work against mine below. I recognize this as one of the answers I gave you a couple of days ago. You have made errors in q1, q2 and q2*. I didn't...
January 31, 2015

chemistry
Use the HH equation, then convert pH to H^+.
January 31, 2015

chemistry
millimols HCOOH = mL x M = approx 65 but you need to do all of these calculations more accurately. mmols HCOONa = base pH = pKa + log (base)/(acid) Substitute and solve for (base) in millimols. Change to mols, then g = mols x molar mass. You know mols and molar mass
January 31, 2015

chemistry
You have doubled the reaction; wouldn't the new enthalpy change be just twice as much.
January 31, 2015

Chemistry
What's the /\H = 90?
January 31, 2015

Chemistry
mL x N x mew = grams 1000 x 1.5N x (molar mass/1000) = grams if it's 100%. It is only 96.5%; therefore, Then grams/0.965
January 31, 2015

chemistry
q = mass x specific heat x delta T
January 31, 2015

chemistry
q = mass x specific heat H2O x (Tfinal-Tinitial) I would use mass = 17,000 and calculate q in J, then convert to kJ.
January 31, 2015

Science
I agree.
January 30, 2015

chemistry
mols = 4.18E16/5.02E23 = ? Then molar mass = g/mols = ? That "funny" unit you posted must be microgram or 5E-6g.
January 30, 2015

chemistry
1 light year is 9.46 x 10^15 m which converts to 9.46 x 10^12 km. So 4.3 light years is 4.3 x that.
January 30, 2015

chemistry
I don't see a question here. Also check to see that you have entered all of the data.
January 30, 2015

Science
How much pollution. How much energy value. Cost Can it be renewed. Ease/cost of waste disposal.
January 30, 2015

To Kekmaster
You are loading up the board with useless comments. You can quit now; if you continue I will ban you from posting on this board again.
January 30, 2015

biochemistry
..NH2CH2COOH + NaOH =>NH2CH2CONa + H2O I...0.2.........0..........0 add............0.1............. C...-0.1.......-0.1........+0.1 E....0.1.........0.........0.1 pH = pKa glycine + log (base)/(acid) base = salt = 0.1 acid = glycine = 0.1 pH = pKa + log 0.1/0.1 0.1/0.1 = 1 ...
January 30, 2015

chemistry
I am not familiar with your equation. I would use the Clausius-Clapeyron equation (and please note the correct spelling of celsius). ln(p2/p1) = dHvap/R(1/T1-1/T2) If you let p1 = 92.7 and T1 = 50C+273; then solve for p2 = ? when T2 = 25+273
January 30, 2015

Chemistry
dG = -RTlnK, then convert dG in J to kJ.
January 30, 2015

Chemistry
Is that H or dH? Is that S or dS. Are you sure that is -75 kJ/mol for S? Usually they are measured in J/mol. Is there a T listed?
January 30, 2015

Chemistry
A reaction is favored thermodynamically when delta G < 0.
January 29, 2015

Chemistry
How would you like us to help you short of writing the paper for you?
January 29, 2015

chemistry
q = mass x specific heat x delta T #1. q = 10.0g x 0.897 U/g x 25 = ? Calculate q for each then rank from low to high.
January 29, 2015

Chemistry
Use your numbers for this. Adding NaIO3 dropwise to the solution will continue until the most insoluble material starts pptng. That will be Pb(IO3)2. Pb(IO3)2 will continue to ppt until the IO3^- rises high enough to begin pptn of Cu(IO3)2. At that point, what is the (IO3^-)? ...
January 29, 2015

Chemistry
What Ksp values are you using? The answer depends upon those value you use.
January 29, 2015

Science
I'm having trouble believing 3d is correct. I think A is a better answer.
January 29, 2015

chemistry
Do you want the entropy of the reaction? dSrxn = (n*dSo products) - (n*dSo reactants). Look up the standard S values in your text/notes and plug into the above equation and solve for dSrxn.
January 29, 2015

Chemistry
The equation is delta T = i*Kf*m i = van't Hoff factor which is the number of particles. CoCl3 is 4, K3CO3 is 3, KNO3 is 2. Kf is a constant The problem tells you m is constant, so.....
January 29, 2015

chemistry
2H2 + O2 ==> 2H2O mols H2 = grams/molar mass Using the coefficients in the balanced equation to convert mols H2 to mols O2. Now convert mols O2 to what you meant by "how much". If you want grams O2, g O2 = mols O2 x molar mass O2. If you want volume at STP it is L...
January 29, 2015

Chemistry
If those two substances were the only ones in the solution there will be no reaction. Reactions occur for one of just a few reasons. 1. A ppt is formed. Nothing insoluble here. 2. A gas is formed. No gas can be formed here. 3. A slightly ionized material is formed. Both NaCl ...
January 29, 2015

college chemistry
P1V1 = P2V2
January 29, 2015

Science
I agree
January 29, 2015

Science
I think the correct answer COULD be any of these. I think most cold fronts produce A sometimes if enough humidity is present, I think B if more water vapor is in the air, D is conditions are right. and C if there is not enough moisture in the air.
January 29, 2015

Chemistry
What do you want? The cation is NH4^+ and the anion is Cl^-. Probably that isn't what you want. And you want the molarity of what? the cation? the anion? NH4Cl? The molarity of NH4Cl is mols/L. mols = grams/molar mass Then mols/0.0199 = ?M
January 29, 2015

Science
I only checked those two.
January 29, 2015

Science
I agree with 2 and 4.
January 29, 2015

Chemistry
q1 to melt ice = mass ice x heat fusion. q2 to raise T to 100 C = mass H2O x specific heat H2O x (Tfinal-Tinitial) q2* to torn liquid H2O at 100 C to steam at 100 C = mass H2O x heat vaporization. Total to melt ice = q1 Total to raise T from zero to 100 and turn steam is q2 + ...
January 29, 2015

Chem
I think you have too many minus signs there. I would have done (1/4)*-0.41 = - 0.10 M/s
January 29, 2015

chemistry
volume of box = 4 x 2 x 2 = ? m^3 Then 1500/?m^3= ?
January 29, 2015

science
I think you need to read this post and clarify it.
January 29, 2015

chemistry
This may be the long way but I would convert 0.26m to cm. That's 26 cm. volume = 26cm x 26 cm x 26 cm = ? cc. Then mass = volume x density Then convert g to kg.
January 29, 2015

Chemistry
Stacyy09, you can check these yourself. Check atoms and left and right of the arrow and if the left side and right side don't agree the equation isn't balanced.
January 29, 2015

Chemistry
dSsys = (n*dS products) - (n*dS reactants) dSsurr = -dH/T dSuniv = dSsurr + dSsys Note: dH in kJ/mol but dS usually in J/mol. keep the units straight.
January 29, 2015

chemistry 116
How in the world did you arrive at 401.65? 159.0J = 8.4g x sp.h. x 21.1 Solve for sp.h. = [159.0/(8.4*21.1)]
January 29, 2015

chem
What about 1/2 that? The equation tells you that 2 mols HBr were formed with the release of 72 kJ. So 1 mol must release just 1/2 that? right?
January 28, 2015

Chemistry
For solutions use the dilution formula of mL1 x M1 = mL2 x M2 For solids, calculate how many moles you need which is mols = M x L = 0.15 x 1.90 = ? Then mols = grams/molar mass. You know mols and you have molar mass, solvel for grams. Note that c wants Nicl2 but weighs NiCl2....
January 28, 2015

Chemistry
You want 100 mL of 0.2M so weigh out 0.2 mol NaHCO3, dissolve in some water, add 0.1M NaOH dropwise until the pH is 9.8. Transfer quantitatively to a 100 mL volumetric flask and dilute to the mark. Mix thoroughtly.
January 28, 2015

Science-Chemistry
You are correct.
January 28, 2015

Chemistry
Answered above.
January 28, 2015

chemistry
mass = volume x density so density = mass/volume = ? Can you do the s.f.?
January 28, 2015

Chemistry
We can't draw these things on this forum. What problem are you having doing this. Probably you can google and find them on the web.
January 28, 2015

Chemistry
You didn't write all of the question. The reaction (only one was written) can't shift unless you do something to it. What did you add or remove? BTW, you need to inform your prof that the sentence of "By convention, no units are reported for K values" is not ...
January 28, 2015

chemistry
Look it up on the periodic table. You get the individual atomic masses as well as adding them to obtain the molar mass.
January 28, 2015

chemistry
pH = 4.53 = -log(H^+). Solve for (H^+) and that's approx 1E-5 but that's just close so you need to do it more accurately. .........HClO ==> H^+ + ClO^- I........x........0......0 C.......-y........y.......y E........x-y......y........y The problem tells you (...
January 28, 2015

chemistry
Do this the same way as the HClO problem.
January 28, 2015

chemistry
Done the same was as the HClO problem.
January 28, 2015

chemistry
I believe the problem asks for Ka.
January 28, 2015

Chemistry
The planetary model came from Bohr primarily was was displaced by Shroeder et al with wave mechanics. I think if you Google wave mechanics you can see what fits.
January 28, 2015

oops--chemistry
http://en.wikipedia.org/wiki/Nuclear_magnetic_resonance
January 28, 2015

chemistry
I think B and D are eliminated because of the "ultraviolet rays" part of the answer. The nuclei are irradiated by VHF or UFH RADIO frequency as per this site. High and low are relative terms but I think of UHF and VHF as high. Here's the site. And I don't see...
January 28, 2015

chemistry 116
1 g thermite--25% Al; 75% Fe2O3 makes 0.25g Al and 0.75g Fe2O3. q = [mass Al x specific heat Al x (Tfinal-Tinitial)] + [mass Fe2O3 x specific heat Fe2O3 x (Tfinal-Tinitial)] Substitute and solve for q.
January 28, 2015

chemistry
https://www.google.com/search?q=shapes+O3&ie=utf-8&oe=utf-8 Google the others.
January 28, 2015

chemistry
What's your problem here.
January 28, 2015

chemistry
All but AlCl3.
January 28, 2015

chemistry
Na to CN is a single ionic bond. C-N is a triple covalent bond.
January 28, 2015

chemistry
The easy way to do this is to use the dilutiong formula of mL1 x M1 = mL2 x M2 mL1 x 4 = 1000mL x 0.1
January 28, 2015

chemistry
http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/menfre.html#c3
January 28, 2015

Physical Science
A is not true. B is true. C MAY be true. D is true.
January 27, 2015

Chemistry
a)The reaction will shift to the left in order to try and decrease the added OH. b) Write the expression for Q and see if increased OH will caue Q to go up or go down.
January 27, 2015

chemestry
85.0 x 0.052.02 = ?
January 27, 2015

science
T goes up, V goes up.
January 27, 2015

SCIENCE HELP NEED ANSWERS FAST!!!!!!!
How can we help you with this short of giving you all of the answers?
January 27, 2015

chemistry(limiting reagent)
I do these the long way. Moles Al2*SO4)3 = grams/molar mass = ? mols NaOH = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols Al2(SO3)3 to mols Na2SO3. Do the same for mols NaOH to mols Na2SO3. I think the answers will not be the same which ...
January 27, 2015

Chemistry
Your post needs clarification. You omitted some word or words in the post.
January 27, 2015

Chemistry
How many moles of naphthalene do you have? That's grams/molar mass. Now remember there are 6.02E23 molecules in 1 mole of any material.
January 27, 2015

chemistry
I would convert 5 ft to nm, convert 10 inches to nm, add them to find the total. Then total nm/2.5 = DNA molecules.
January 27, 2015

Chemistry
Use the Clausius-Claperyron equation. Using p1, p2, T1 and T2, solve for delta H vaporization. Then plug into a new Clausius-Claperyron equation EITHER p and T pair, and plug in 760 mm and Tboiling for the other pair. Solve for Tboling.
January 27, 2015

pharmacy tech
Do you want % w/w or % w/v. I will assume % w/w; I don't think you can calculate the %w/v. Also, I assume the density of the sterile water is 1.0 g/mL which makes the 1 L have a mass of 1000g. % = (g solute/g solution)*100 = ? %KI = [22/(22+1000)]*100 =
January 27, 2015

chemistry
mols urea = grams/molar mass = ? mols H2O = 100 g/molar mass = ? Total mols = nurea + nH2O mole fraction H2O = XH2O XH2O = nH2O/total mols psolution = XH2O*PoH2O
January 27, 2015

Chemistry
Use the coefficients in the balanced equation to convert anything to anything. 7.2 mol Fe x (3 mols O2/4 mols Fe) = 7.2*3/4 = ?
January 27, 2015

physics --chemistry
zero. Work is force x distance. d is zero, force x zero = zero.
January 27, 2015

chemistry 116
heat lost by Cu + heat gained by H2O 0 [mass Cu x specific heat Cu x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 Substitute and solve for Tfinal
January 27, 2015

chemistry
If that is 58 J/C, the specific heat is 58/126 J/g*C.
January 27, 2015

college chemistry
The HNO3 and NaOH exactly neutralize each other to produce H2O. The remainder can be calcualted by the Henderson-Hasselbalch equation pH = pKa + log (base)/(acid) base is CH3COONa acid is CH3COOH pKa is 4.74
January 27, 2015

chemistry
For #2, use the HH equation and solve for the ratio base/acid
January 27, 2015

chemistry
This is a limiting reagent (LR) problem since amounts are given for BOTH reactants. AgNO3 + NaBr ==> AgBar + NaNO3 mols AgNO3 = M x L = ? mols NaBr = M x L = ? Convert mols AgNO3 to mols AgBr Convert mols NaBr to mols AgBr. It is likely the two values will not agree which ...
January 27, 2015

chemistry
1 mol ascorbic acid reacts with 1 mol I2 so the ratio is 1:1. mols ascorbic acid = grams/molar mass = ? mols I2 = mols ascorbic acid from the equation. M I2 = mols I2/L I2.
January 27, 2015

chem
4NH3 + 3O2 ==> 2N2 + 6H2O dHrxn = (n*dHf products) - (n*dHf reactants)
January 27, 2015

chemistry
See your other post.
January 27, 2015

chem
Yes, it's what I meant but 284 isn't the right answer if that is 284 J/min. Punch those numbers into the calculator again and remember the answer should be in kJ.
January 27, 2015

chem
Assuming the fluid is H2O and not ethylene glycol, then q in joules = mass H2O x specific heat H2O x (Tfinal-Tinitial) and I would substitute 17,000 g for mass H2O
January 27, 2015

chem
For #1 you didn't list the choices. 190 = 4.51 x Z x (315.7-21.3) and solve for Z. For #2, your numbers are ok but you have too many significant figures.
January 27, 2015

chem
I think so but you have too many significant figures. If your prof is picky about s.f. s/he will count off points.
January 27, 2015

chem
CH4 + 2O2 --> CO2 + 2H2O So you get 686 kJ for 13.7 g CH4. How much heat will you get for 1 mol (16 g)? Thats 686 kJ x 16/13.7 = ? kJ
January 27, 2015

Chemistry
The ice at zero is to melt and remain at zero. So the heat fusion must be enough to lower the liquid water from 45.0 to zero C. How much heat must be removed from the water. That's q = mass water x specific heat H2O x (Tfinal-Tinitial). That gives you q in J. Now convert ...
January 26, 2015

chem
A radius of 124 pm means a diameter of 248 pm and that is 2.48E-7 mm. So #atoms x (2.48E-7 mm/1 atom) = 1.75 mm Solve for # atoms.
January 26, 2015

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