CHEMISTRY COMMUNITY

kennedyp

It's been an honor having you as a professor this quarter. Thank you for the work that you do and for sharing your passion for chemistry with us. I hope we cross paths again soon!

kennedyp

he finds the net production of gas because there are 3 mols of gas on the right side (products), 2 mols of gas on the left (reactants). Because this is a standard 1.00 mole reaction of O2, meaning the equation presented is what is occurring, you find the total production with a 3-2=1 mole of gas. t...

kennedyp

Actually nvm, I see my mistake now!

kennedyp

How does Lavelle find that there is deltan=1 mole of gas when there's 3 moles of gas on the right side of the equation?

kennedyp

Can someone explain exactly what a pseudo 1st order rxn is? The book was kind of confusing for me.

kennedyp

(Really sorry if this is in the wrong section!)
When setting up the chemical equation, how do we know that Br- doesn't go in because it doesn't affect the ph? I guess my question is how do we know what affects the ph?

kennedyp

it's e to the power of the other side! (x=e^lnx)

kennedyp

You would only add OH- to a reaction to balance the amount of H2O that was added (in general, for every H2O added, one OH- needs to be added).

kennedyp

I found a really good video explaining how to find them if you have the time to watch before Final real quick! I post the link below. Good luck! https://www.youtube.com/watch?v=-a2ckxhfDjQ

kennedyp

I think it's safe to always use Kelvin unless told otherwise. Chemistry pretty much prefers Kelvin over other temperatures.

kennedyp

Because it doesn't allow for the exchange of matter. For example, let's say you have a shampoo bottle and it falls off the rack while you are taking a shower. Assuming the bottle is capped (closed system) the shampoo will not leak out of the bottle because the bottle doesn't allow that to happen!

kennedyp

I would assume mostly free response but also a little bit of multiple choice, like how it was for the midterm.

kennedyp

Balancing chemical equations and chemical equilibrium!

kennedyp

WGaines_2E wrote:so the reaction looks like its gonna be COBr2 <> CO(g) + Br2(g)
you have the final concentration of CO
solve using ICE table

I figured it was an ice table question, but how would we solve if we weren't given K? Unless the og poster accidentally left K out?

kennedyp

I think you have to compare two experiments where everything is constant except for one thing. For example, say for two experiments you have the same concentration of reactant A and B, but reactant C has a different concentration. You would focus on comparing those two experiments.

kennedyp

Michelle Song 1I wrote:I don't think you can multiply both sides in k1 cause the left side of the Van't Hoff equation is ln(k2/k1) so you'd have to change that to ln(k2)-ln(k1) and add ln(k1) to both sides.

Oh okay my bad!! :(((

kennedyp

For part b I'm a bit confused. The book states that the reaction rate increases by a factor of 2 if H2 is doubled, however I remember the book saying that if you have a second order reaction and double the reactant, the rate increases by a factor of 4. PLease help!

kennedyp

You would use the Van't Hoff equation! (ln K2/k1= delta Hr {1/T1-1/T2}); multiply both sides by k1 and remember that K=e ^lnK

kennedyp

For part b in 7A.3, wouldn't the answer be negative? The solution manual has it as positive 0.88 mol/l*s but I thought you would have to get ride of the negative on the other side since rate of formation is +delta [P]/delta t.

kennedyp

Can someone do a detailed walkthrough of how to do this problem? I keep getting the wrong answer :( 7A.13) In the reaction CH Br(aq) 1 OH2(aq) S CH OH(aq) 1 33 Br2(aq), when the OH2 concentration alone was doubled, the rate doubled; when the CH3Br concentration alone was increased by a factor of 1.2...

kennedyp

Does anyone know how the final is going to be given? Will it be a pdf that we have to print out and then take pictures of our answers or is it like through that respondus webcam thingie?

kennedyp

For letter f, how is it that adding water will not shift the reaction towards products? Is it because water is not apart of the eq constant?

kennedyp

How do we know the physical states of the elements after balancing the reaction?

kennedyp

When balancing a redox reaction, how do we find the oxidation number? The book doesn't really say how, unless this was something that I was supposed to have learned before??

kennedyp

What's the equation needed to convert K back to Kc? I assumed you would just rearrange the Kc to K equation, but I wanted to ask just to be sure. aren't those the same Not according to the book :( Look at the very last part of section 5J.3, it talks about converting K to Kc when using Van't Hoff eq...

kennedyp

For the first part of part a , I used the standard gibbs free energy equation and was able to correctly find the first K, but I'm using the Van't Hoff equation to find the second K and I keep getting one. I don't know if the book made the mistake or if I'm doing something wrong in my calculations (t...

kennedyp

For question letter b, the book is gives a rxn ( X2 (g) --> 2 X(g) )and tells us that X is a halogen. How would we know how a halogen would affect the K? Because I don't remember halogens being discussed anywhere in that section (section 5J.11).

kennedyp

I keep getting the wrong answer for this homework problem and I don't know what I am doing wrong. ( 5G.15 (a) Calculate the reaction Gibbs free energy of N2(g) 1 3 H2(g) S 2 NH3(g) when the partial pressures of N2, H2, and NH3 are 4.2 bar, 1.8 bar, and 21 bar, respectively, and the tempera- ture is ...

kennedyp

When calculating the gibbs free energy using this equation (delta G = standard delta G + RTlnQ), how do you know which R to use?

kennedyp

Does the Gibbs free energy have to be reported in kJ per mol or can we report in J per mol?

kennedyp

Will we ever be asked to use the equations that are in the book that relate Temp to the EQ constant using kinetics vs. thermodynamics? To be a tad more specific, the equations in the yellow box that we are given before the book rearranges them into the Van't Hoff Equation.

kennedyp

Also, do you guys think points would be deducted on the test if we don't convert back to Kc after finding the new K?

kennedyp

What's the equation needed to convert K back to Kc? I assumed you would just rearrange the Kc to K equation, but I wanted to ask just to be sure.

kennedyp

I have developed such a weird love for chemistry jokes, I love this thread lol I'll try to add some every now and then, here's the first one!

Man, I hate when I tell a chemistry joke and I don't get a...REACTION!

This was horrible, I'm so sorry!! :((((

kennedyp

Q8 was very similar to a homework problem on Entropy. It asked for the total, system, and surroundings entropy change for reversible vs irreversible expansion.

kennedyp

I don't know if we all had the same midterm, but there was one question about concentrations and ph that I genuinely had no idea how to solve. It was about a molecule that would turn into a salt I think, and then i remember something about the ph of the stomach and the question asked us to find the ...

kennedyp

So this might sound bad especially since we just took our midterm on it, but I'm still having a little trouble understanding exactly what Gibbs free energy is? Like what does it tell us about a system or the surroundings and why is it an important concept to know for chemistry? I can do the equation...

kennedyp

Can someone explain 2 D? For some reason I'm not getting the right answer for the reaction quotient :(

kennedyp

Is there a difference between an isolated system and an insulated system?

kennedyp

Does anyone have the notes from class on Friday ( Jan 31st) and Monday (Feb 3)? I had a cold and couldn't make it to class. :(

kennedyp

Does anyone know if there will be a Step-up session this Sunday at Covel? I know there's a midterm review going on but I couldn't make it :(

kennedyp

If you are given concentrations, then you should use Kc. If you are given gases, then you should use Kp.

kennedyp

Can someone explain how to do problem 5 on the test? (Problem: The pkb of fluoride is 10.8. A 0.12 M solution of hydrogen fluoride was made for silicon wafer processing. What is the pOH of this solution at equilibrium?)

kennedyp

Can someone breakdown how to do problem #6? (Problem: The pH of a 0.10 M solution of hydrofluoric acid is 2.63. What are the Ka and % ionization?)

kennedyp

What key words should we look for in a word problem that would help us know whether the formula for work should be the reversible or irreversible one?

kennedyp

Internal energy (U) is a state property because the value doesn't change no matter the path you took to get there.

kennedyp

I remember the book saying that it's possible to have a negative pH or a pH higher than 14, but that they wouldn't ask us questions outside the scope of a pH value from 1-14. Any acid that has a concentration of hydrogen ions with a molarity greater than 1 will likely be calculated to have a negativ...

kennedyp

Why are systems at equilibrium reversible?

kennedyp

Can an isolated system have a change in energy?

kennedyp

How do we know that a molecule is in its "standard form"?

kennedyp

Why exactly aren't solids and liquids included in the eq constant?

kennedyp

The problem asks us to find both the desired ph and then then actual ph. I know to find the actual ph I would need to the amount of substance added (in moles), but how do I go about finding that?

kennedyp

Why exactly is the standard of formation of an element in its most stable form 0?

kennedyp

When explaining how to find the concentration of OH- ions, the book wrote that 1 mol Ba(OH)2 ≏ 2 mol OH2. What does the ≏symbol mean?

kennedyp

Is it possible for a molecule to be both amphoretic and amphiprotic?

kennedyp

How do you write the chemical equation for a proton transfer?

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