CHEMISTRY COMMUNITY

Ariana de Souza 4C

Hey Dr. Lavelle, Thank you SO much for everything you do for 14A/B students! I cannot tell you how many times I've gone to peer review learning sessions, ta meetings, office hours -- they were incredibly helpful, and I'm so thankful that you and all of your ta's and ua's put that time in. You really...

Ariana de Souza 4C

But then in the 2016 final problem 2A, we use the standard gibbs free energy and use this equation -- $\Delta (G^o) =-RT lnK$ -- with the standard gibbs free energy when T=1943. Why can we do that?

Ariana de Souza 4C

Hello! I just wanted to get something cleared up -- what is the relationship between the standard condition of G and H and S and temperature? We can still say that it is (delta G)^o if the temperature isn't 298 K, right? And all we need for standard conditions is the pressure to be 1 atm and for the...

Ariana de Souza 4C

If you are referring to the first problem set, because it places the largest substituents anti to each other. But can't you have the largest groups still anti each other but then on the left side of the newman projection have CH3 and H and then on teh right side have CH3 and H so that one side does...

Ariana de Souza 4C

you don't need to know the common names -- you have the IUPAC names in that same order, so you know the IUPAC name for the respective common name, and can just use that for identifying the structure

Ariana de Souza 4C

for #1, why do we need "iso" infant of propyl? wouldn't the 4- signify the branching? No, because the 4 signifies from what carbon on the MAIN BRANCH you're substituent is on. WIthin the substituent itself, though, there is branching, and that's why you'd either say iso-propyl (common nam...

Ariana de Souza 4C

when we name something, for example, "tert butyl" does the t count in the alphabetical order? or does it not? I thought it would, since it's a common name, and for other common names like isopropyl or neopentyl, we include the prefix for alphabetic consideration? And for number 1.17 in th...

Ariana de Souza 4C

For the first question, how do you know it is 4- isopropyldecane? I thought that it was just 4-propyldecane Can someone please address this? Why do we need the "iso" prefix? Isn't it just a propyl functional group attached to the 4th carbon of a decane compound? The reason we can't just s...

Ariana de Souza 4C

Can someone help me with #3 I don't understand how both of them are nucleophiles? Are you referring to #6? Nucleophiles are species rich in electrons. For the benzene ring, this electron richness comes from its double bonds. For CH_{3}OCH_{3} the oxygen in the center of the compound can only be att...

Ariana de Souza 4C

Will we be responsible for knowing how to solve questions 5-8 on the practice quiz #3 even though we didn't go over that kind of thing in lecture? we went through numbers 5-8 in class.. the only thing we havent is number seven when it says 2-butene. that just means you have a butene and then your d...

Ariana de Souza 4C

For number 1, I wrote down 4-isopropyldecane as my answer, but I don't understand why it can also be 4-(1-methleythyl) decane the second answer would be if you're writing it by IUPAC rules. you can see the isopropyl as a long ethane (that's your longest chain) with a methane coming out of the first...

Ariana de Souza 4C

Jocelyn_Dao_2N wrote:Hi! Why is the answer for number 4, 4-butyl-1,2-dimethylcyclohexane and not 1,2-dimethyl,4-butylcyclohexane?

When naming a compound, do the lower numbers do first?

remember that you have to do it alphabetically. butyl comes before methyl

Ariana de Souza 4C

when we name something, for example, "tert butyl" does the t count in the alphabetical order? or does it not? I thought it would, since it's a common name, and for other common names like isopropyl or neopentyl, we include the prefix for alphabetic consideration? And for number 1.17 in the...

Ariana de Souza 4C

so it isn't equivalent numbering. you have either 2, 1, 1, or 2, 2, 1. you choose the first because 1 < 2 and you have more 1's in the first one than you have in the second one.

Ariana de Souza 4C

oh! thanks !!

Ariana de Souza 4C

Hey guys,
im feeling like this is a dumb question, but for 1.12 c, why is it 3,4,4 - trimethyl-2-pentene and not 2,2,3 trimethyl-3-pentene ?
thanks :)

Ariana de Souza 4C

so on page 157 in the green o chem book, it says that we should refer to the delta G double dagger of the second transition state not in reference to the intermediate, but in reference to the reactants. so you would have the delta G be from the reactants to the energy of the second transition state....

Ariana de Souza 4C

And I'm pretty sure you have delta S as negative because you're making the molecule into one particular orientation for it to be a transition state, so there is a decrease in entropy. I don't know why you would have a positive delta S though...

Ariana de Souza 4C

If the answer to #2 if false, what other possible units can be used to signify rate constant? It depends on what order the reaction is. you can just check this with the rate equations. ZERO ORDER: Rate=k the units of the rate are M/s so k must be M/s too for zero order reactions FIRST ORDER: Rate =...

Ariana de Souza 4C

Can someone explain the graphing part of question 4 on the practice quiz? It tells you that you have a graph where you're plotting the natural log of NOBr against time, and you get a straight line. on page 63 in the course reader, you can see that that's basically how you know that the reaction is ...

Ariana de Souza 4C

but the book on page 634 goes over a steady state approximation for a reaction with a fast first step and a slow second step... whats going on there?

Ariana de Souza 4C

but the slope is -k. So wouldn't k have to be positive, for there to be a negative slope?

Ariana de Souza 4C

Could someone explain to me how to do #6? So this one you need to split into two problems. The first step will be to determine what k is. 1) you have your initial concentration (0.95 M) and your final concentration (0.44 M) and the time it takes (11 minutes) you use your equation 1/(At) - 1/(A0) = ...

Ariana de Souza 4C

Hey guys in the course reader on page 60, it says that we're only going to be focusing on initial rates that are a function of only reactant concentration. but in the textbook, on page 621, it says that rate laws may depend on the concentrations of prouctsa s well as those of reactants. It uses O3 -...

Ariana de Souza 4C

For rxn mechanisms will we have to infer the intermediate for a rxn or will it be given to us? Pretty sure the mechanism will be given to us. The intermediate will be the compound that is in the products of the first reaction and in the reactants of the second, and so will be canceled out -- it sho...

Ariana de Souza 4C

for number 8, is it okay if we express it in seconds, since the question gave the rate constant in seconds?
Additionally, do we need to know how to do numbers 5, 9, and 11 ? They all have to do with enzymes and the arrhenius equation, and i thought we didn't have to know that

Ariana de Souza 4C

So it's because the equation for the second order half lives include the concentration of the initial substance? Then the reason we can multiply half lives for problem 15.27 is because, there, it's talking about a first order reaction, which only concerns the rate constant? For reference, 15.27 : &q...

Ariana de Souza 4C

Hey everyone
Not sure if this has been asked before (it probably has) but does the mantissa rule still apply for natural logs?
And do we use that rule whenever we need to use an equation that uses a natural log? Does the rule change when we have to do e^x to get rid of the natural log?
Thanks

Ariana de Souza 4C

at the end of the problem, how come we take the square root of K? it says
Ka= sqrt(K)

Ariana de Souza 4C

standard e potential (E^o) is when you are at standard conditions, so when you know that everything is at 1 molar. when you're just asked for cell potential, it's probably not at standard conditions -- meaning you probably have to use the nernst equation, because it's a concentration cell. hope that...

Ariana de Souza 4C

You separate them with a comma when they are in the same state, and with a "I" when it's in different states. for example: 14.13 a) Zn (s) I Zn 2+ (aq) II Ni 2+ (aq) I Ni (s) vs. b) Pt (s) I I- (aq) I I2(s) II Ce 4+ (aq), Ce 3+ (aq) II Pt both Ce's are aqueous, so we separate them with a c...

Ariana de Souza 4C

In the same vein as the question posted, in the course reader, we put an inert conductor on only one side of this diagram 2Fe 3+ (aq) + Cu (s) --> Cu 2+ (aq) + 2 Fe 2+ (aq Cu (s) I Cu 2+ (aq) II Fe 3+ (aq). Fe 2+ (aq) I Pt(s) I'm assuming this is because the left side of the equation has a solid, bu...

Ariana de Souza 4C

We are supposed to come up with the anode and cathode reaction for 1 M NiSo4 solution electrolyzed. When it comes to choosing the anode, the solution manual says to choose the oxidation reaction with the most negative reduction potential. so why did we choose 2H20 --> O2 + 4H+ +4e- with an standard ...

Ariana de Souza 4C

Oh! That does make sense, thank you!

Ariana de Souza 4C

a) O3 + Br(-) --> O2 + BrO3 (-) for the oxidation reaction, when balancing out the hydrogens, the solution manual goes from 3 H20 + Br(-) --> BrO3(-) to 6 OH (-) + 3 H2O + Br(-) --> BrO3(-) + 6H2O I don't understand why they are adding the hydroxide and the water to the equation instead of balancing...

Ariana de Souza 4C

okay, thanks Emma!

Ariana de Souza 4C

right, because q=-w. But then using that equation, we don't factor in pressure. Do you ignore the values of pressure that are given in the problem?

Ariana de Souza 4C

IF 2 mol of an ideal gas at 300 K and 3 atm expands isothermally and reversibly from 6 L to 18 L and has a final pressure of 1.20 atm, what is w, q, and delta U?

What do we do if both volume and pressure are changing? What equations should I be considering? Thanks

Ariana de Souza 4C

So I get that from the table. But from the math, are we supposed to assume that since we get a negative K value, it's impossible? And from that should we know that it would never be spontaneous? And additionally, when we get values for T, is it always that when T is greater than that value, it's spo...

Ariana de Souza 4C

Initially a sample of ideal gas at 323 K occupies 1.67 L at 4.95 atm. the gas is allowed to expand to 19.44 L. a) it expands isothermally, reversible expansion b) isothermally, IRREVERSIBLE free expansion calculate delta S total delta S, and delta S surroundings for each pathway I understand a, but ...

Ariana de Souza 4C

this is all so incredibly detailed, and bless your soul, but one question-- ΔH*rxn = [1mol(ΔH*f(H2)) + 1mol(ΔH*f(Zn2+))] - [2mol(ΔH*f(H+)) + 1mol(ΔH*f(Zn))] ΔH*rxn = [1mol(ΔH*f(0)) + 1mol(ΔH*f(-153.89KJ/mol))] - [2mol(ΔH*f(0)) + 1mol(ΔH*f(0))] ΔH*rxn = -153.89KJ how come you have an enthalpy of form...

Ariana de Souza 4C

I don't get that problem either, but can you explain why you need to find the limiting reactant and how you then find the enthalpy?

Ariana de Souza 4C

and in that same vein of "Releasting" vs "absorbing" -- for 8.99, the solution manual uses the specific heat capacity of water (we're assuming that HCL has the same specific heat capacity as water) as -4.184. I'm not really clear as to why we are using negative? 8. 99) a piece of...

Ariana de Souza 4C

yes, thanks so much!

Ariana de Souza 4C

Ohhhhhhhhhhhhhhhhhhhhhhhhh. That makes sense. Thank you hahah

Ariana de Souza 4C

8.51) the enthalpy of formation of TNT is -67 kj?mol and the density is 1.65 g/cm^3. explore its potential as a rocket fuel by calculating its enthalpy density (enthalpy released per liter) for the reaction 4 C7H5N3O6(s) + 21 O2 (g) --> 28 CO2(g) + 10 H2O (G) + 6 N2(g) The energy released per mole o...

Ariana de Souza 4C

Yeah, it does! I appreciate the explanation. So when you're doing the math part, you're doing --

q(reaction) = -q(calorimeter)
q(Reaction)= -q*C*deltaT
so are you calculating the heat of the reaction then by saying it's the opposite of the heat of the calorimeter?

Ariana de Souza 4C

CO(g) + H20(g) --> CO2(g) + H2(g) reaction of 1.4 g of CO in a bomb calorimeter causes the temp to go from 22.113 C to 22.799 C. The calorimeter assembly is known to have a total heat capacity of 3.00 kJ/C b) calculate the internal energy change, delta U, for the reaction of 1 mol CO So the solution...

Ariana de Souza 4C

how do you know to write those three equations from what they give you? Sorry if this is a silly question

Ariana de Souza 4C

I dont understand how the solution manual does this question. A constant volume calorimeter was calibrated by carrying out a reaction known to release 3.5 kJ of heat in 0.2 L of solution in the calorimeter, resulting in a temperature rise of 7.32 C. In a subsequent experiment, 100.00 mL of 0.2 M HBr...

Ariana de Souza 4C

I dont understand how the solution manual does this question. A constant volume calorimeter was calibrated by carrying out a reaction known to release 3.5 kJ of heat in 0.2 L of solution in the calorimeter, resulting in a temperature rise of 7.32 C. In a subsequent experiment, 100.00 mL of 0.2 M HBr...

Ariana de Souza 4C

you're right -- must have missed that. sorry! then all the calculations after that are off by a bit -- sorry again

Ariana de Souza 4C

dude ive been doing this problem for around an hour and i finally got it. so first you find the moles of HCl (Because it's at the stoich point, and since NaOH is impure, we're gonna use HCl to find out NaOH) 0.0695 mol HCl x 0.03420 L = 0.0023769 moles HCl so that means that there are 0.0023769 mole...

Ariana de Souza 4C

okay i've kind of gotten it but am still confused a little about how to get the final point so for the initial point.. Initial Point -- it's only gonna be NaOH (no HCL added yet) so pOH= -log(0.01M)=2 pH=14-2=12 and then Stoich Point-- moles NaOH=molesHCl pH is gonna be 7 (Strong base and strong aci...

Ariana de Souza 4C

hey im having a lot of trouble with this question. I looked at the textbook explanation for a similar problem but I'm extremely confused "a) Sketch the titration curve for the titration of 5 mL 0.020 M NaOH with 0.005 M HCl, indicating the pH of the initial and final solutions and the pH at the...

Ariana de Souza 4C

oh! I see. thanks so much!

Ariana de Souza 4C

Hiya
so for question 21 a, the solution manual does something and i keep getting the wrong answer.
log ([CO3 2-]/[HCO3-]) = 0.75
[CO3 2-]/[HCO3-]=5.6
but when i take the antilog of 0.75 (which is (10^(-0.75))) and I keep getting 0.1778!! I don't know where 5.6 comes from??

Ariana de Souza 4C

I think (I'm not sure, someone please correct me if im wrong) that it's because you're adding OH, right? So that's going to react with the acid, which is CH3COOH. That is going to cause the forward reaction to occur, which would decrease thea mount of CH3COOH and increase theamount of CH3COO-. And b...

Ariana de Souza 4C

I also have a question on this part.
I have (x*y)/(2x)=3.02x10^(-4)
This is probably a simple mistake on my part but how come you end up with 2*Ka?? the x's don't cancel out -- so how does that math work?

Ariana de Souza 4C

ohhh, i see!! Thanks!!

Ariana de Souza 4C

Hiya
So question 69 b) asks for the pH of 0.055 M AlCl3. The solutions manual then lsits this chemical equation
Al(H20)6 (3+) + H20 <--> H3O + Al(H2O)5 OH)(2+)
I am just completely lost as to where this equation came from. Thanks!!

Ariana de Souza 4C

So in the course reader it says that alkali metals and alkali earth metals form hydroxides and oxides that make strong bases. but then it shows this equation --- CaO +H2O <--> Ca + 2OH- wouldn't it not be <---> because that shows equilibrium, but just --> if it's a strong base?? Since it's dissociat...

Ariana de Souza 4C

okay, thanks guys!

Ariana de Souza 4C

but how come, then, when we are given a table of Ka values, we can choose the strongest acid based on the biggest Ka value? Why is there a Ka value then for a strong acid?

Ariana de Souza 4C

I'm confused about why when a problem gives you Ka, you know it's going to be a weak acid. Why do we know this? Thanks

Ariana de Souza 4C

This problem is as follows: "the following plot shows how the partial pressures of reactant and products vary with time for the decomposition of compound a into compounds b and c. all three compounds are gases. use this plot to do teh following a- write a balanced chemical equation for the reac...

Ariana de Souza 4C

yes, it does help! thank you so much

Ariana de Souza 4C

Are you sure they aren't polydentates? I haven't been able to find out what kind of dentate they are though

Ariana de Souza 4C

Thanks so much! I understand i tnow -- I looked in the notes and we haven't gone through that stuff yet. So I shouldn't expect that in the quiz, right? Some of the practice quizzes have it...

Ariana de Souza 4C

Am I going crazy? Because i"m looking at the practice quiz for quiz 3 that we're supposed to turn in and 2 includes material we haven't learned yet and 3 tells us to draw the structure for a coordination complex. Has anyone else run into this problem, or am I just woefully prepared?

Ariana de Souza 4C

What do the asterisks next to the last few ligands refer to? Is there specific knowledge about these ligands that we are supposed to know? Thanks

Ariana de Souza 4C

One question had ferrate in it. To be specific, question 17.29 a) had "Ferrate" in the answer. Are we supposed to know the latin prefixes for atoms??

Ariana de Souza 4C

Chapter 11 Question 43 asks "consider the reaction 2 NO(g) <--> N2 (g) + O2 (g) if the initial partial pressure of NO (g) is 1.0 bar, and x is the equilibriumconcentration of N2, what is the correct equilibrium relation? a) K=(x^2)/(1.0-x) b) K=x^2 c) K=(x^2)/(1.0-2x)^2 d) K=(4x^3)/(1.0-2x)^2 e...

Ariana de Souza 4C

But take, for instance, Chapter 11 Question 13. Part a has a gas in the reactant (The rest are liquids and solids) and the question asks to write the reaction quotient Q. The answer key shows Q in Pressure values. Then comes b, where there are solids, liquids, and aqueous solutions. Then the answer ...

Ariana de Souza 4C

For 17.33 d) why is oxalate bidentate? the structure is two carbon atoms with two oxygen atoms each double bonded onto the carbons. why can a ligand only bond at two places?

Ariana de Souza 4C

this may be a stupid question, but for example 17.29 a) [Fe(CN)6]4- why is Fe the anion?? As in why is it ferrate?

Ariana de Souza 4C

Yeah, he said today that we're supposed to know them

Ariana de Souza 4C

Thanks! that helped a lot

Ariana de Souza 4C

Thanks, colin!

Ariana de Souza 4C

Question 75 asks you to write the hybridization orbitals for CH4O. I know that both carbon and oygen are sp3 because they each have four electron regions around them, but since oxygen has six valence electrons, would the electron config for the hybridized sp3 oxygen orbital look something like this?...

Ariana de Souza 4C

Number 99 asks "Just as AlCl3 forms dimers, in the [Bi2Cl4]2- ion two of the chlorine atoms form "bridges" between the two Bi atoms. Propose a structure for the ion." What is this talking about? I tried to go back into the book to look up dimers and bridges, but I didn't understa...

Ariana de Souza 4C

I know that Professor Lavelle said something about the orbital theory not being on the midterm, but I just wanted to clarify that the midterm will only be up to hybridization? So nothing will be on there regarding antibonding and bonding?
Thanks

Ariana de Souza 4C

I think i understand now! I didn't quite get that the orbitals were merging together and becoming one when they hybridize. Thanks so much for the explanation!

Ariana de Souza 4C

I don't quite understand why 5 bonds on the atom in question means that it has a hybridization of sp3d. I get that the number of electron regions = number of orbitals, but I don't get why. Why can't you just keep filling up the p orbital? Take, for example, BrF3 in problem 4.35 a. Why is it sp3d??? ...

Ariana de Souza 4C

I also had a question on O3
Why is the structure linear, and not like a triangle? Wouldn't it be more stable that way, because then the middle one wouldn't have a charge of +1?

Ariana de Souza 4C

I feel like it would be Xe, not Kr -- it just makes more sense that way

Ariana de Souza 4C

I have a question about tungsten (W). Why is its configuration [xe] 4f^14 5d^4 6s^2 and not [xe] 4f^14 5d^ 5 s^1 and take an electron from the s orbital to complete a half d orbital like Chromium???
thanks

Ariana de Souza 4C

Will we be expected to be able to know the formula for polyatomic and other species for the second quiz? Or will the formulas be explicitly given to us? Thanks

Ariana de Souza 4C

Oh, i never even thought of that! Thanks so much!!

Ariana de Souza 4C

This isn't exactly about electronegativity. Question 67 asks "which element of each of the following pairs has the higher electron affinity?" and letter b) asks nitrogen or carbon. Wouldn't it be nitrogen, since it's on the right hand side? Why is it carbon?
Thanks so much :)

Ariana de Souza 4C

Thanks, Andrew! I didn't realize that Chlorine doesn't have the octet rule. Thanks for the help!

Ariana de Souza 4C

Question 59 talks about radicals, and asks you to write the lewis structure of ClO. For ClO, why is Chlorine the one that gets the unpaired electron? Based on the Formal Charge, wouldn't it be better if Oxygen got the unpaired electron?
Thanks!

Ariana de Souza 4C

Oh, I get it now, thanks!
Do all metal ions steal the electrons from the s orbital if the d orbital has not been filled yet?

Ariana de Souza 4C

For question 11 in chapter 3, the question is "Which M3+ ions (where M is a metal) are predicted to have the following ground state electron configurations?"
I don't understand why a) [Ar] 3d^6 is Cobalt 3+ and not Iron 3+. Please help! Thanks :)

Ariana de Souza 4C

You have to use both. For example, (2.34+3.45)/1.5 = , use the addition/subtraction rule for (2.34+3.45), which gives you 3 sig fig and use multiplication/division rule for the next step, which gives the final answer with 2 sig fig. I thought that we were supposed to keep as many digits as we could...

Ariana de Souza 4C

If a problem requires us to use both multiplication/division and addition/subtraction, which rule do we follow?

Ariana de Souza 4C

We won't get a periodic table? So we have to memorize the masses?

Ariana de Souza 4C

Hey ! I'm in Rieber Vista, and I'd love to be a part of this... only thing is I don't have GroupMe and my phone can't download it. Could we do like a facebook message group thing too? Thanks!

Ariana de Souza 4C

Is it necessary to be fluent in nomenclature right now, or are we going to be going over it in lectures and discussion groups in the future?

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