CHEMISTRY COMMUNITY

ashwathinair

Wasn't sure where to put this, but is there anything that can alter a reaction's rate constant (for example, temperature or pressure)? Or does the rate constant remain the same in all situations?

ashwathinair

Wait never mind, I found the unimolecular/bimolecular info in my notes! Thanks!

ashwathinair

Rate laws can be used in this question because for bimolecular reactions like the one in part a, the rate is simply equal to k[NO}^2, because there are two molecules of NO reacting and colliding with each other. This makes the coefficient for NO 2, and thus that becomes the exponent in the rate law...

ashwathinair

Do you guys think it will be all MC questions with a purely correct/incorrect grading style? I'd imagine there would be some multiple choice and some fill-in-the-blank, but I think since we probably can't show work it would be a full correct/incorrect grading scale. Also, since Prof Lavelle also me...

ashwathinair

How do you use rate laws to find the rate of a specific reaction? For example, in 7C 1:
Each of the following is an elementary reaction. Write its rate law and state its molecularity. (a) NO + NO --> N2O2; (b) Cl2 --> Cl + Cl.

ashwathinair

Ooh, I'm not sure about that, but I know usually when we do problems it's best to just keep all of the decimal points in intermediate answers before we get to the final answer. So only round to sigfigs at the final product.

ashwathinair

It's open book/open note, is 30 qs/5 pts each, starts at 11:15 on CCLE, and lasts 3.5 hours. Prof Lavelle said most people should finish it in 2 so that should be a good sign.

ashwathinair

Determine the rate constant for each of the following first order reactions, in each case expressed for the rate of loss of A: (c) 2A --> B + C, given that [A]0 = 0.153 mol/L and that after 115 s the concentration of B rises to 0.034 mol/L. I was able to do parts (a) and (b) for this problem, but I'...

ashwathinair

When creating a possible reaction mechanism, do we generally just have to find one by trial and error? Are there any specific guidelines to keep in mind for developing a reaction mechanism?

ashwathinair

805312064 wrote:Okay that makes sense. One more question, what does adhesion/adsorption have to do with catalysts?

Basically, when an enzyme is catalyzing a reaction, the substrates are not absorbed INTO the enzyme. Rather, they sit on top of it in a specific active site.

ashwathinair

Why do we only use reactant rate for initial rate (and not product)? Also, in which reactions is this rule used (like is this used only when calculating a specific order reaction or is this used for all reactions)?

ashwathinair

How do we know what the rate limiting reaction within a proposed reaction mechanism is? I know that it has the slowest rate, but is this something we generally calculate ourselves (if so, how?) or not?

ashwathinair

Will we need to know how to derive 0-, 1- or 2-order reaction equations for the final?

ashwathinair

I think it mostly just depends on what they give you. If you're given a table with delta G of different molecules, then you use the second one. I understand this, but for one of the homework questions (5J 15), we were supposed to use different methods of finding deltaG at different temperatures (25...

ashwathinair

(a) Write balanced half-reactions for the redox reaction of an acidified solution of potassium permanganate and iron(II) chloride. (b) Write the balanced equation for the cell reaction and devise a galvanic cell to study the reaction (write its cell diagram Why do we not include the Cl and the K in ...

ashwathinair

The n value should always be the same for a specific redox reaction, as half reactions are multiplied by a scalar in order to equalize number of electrons on both sides before they are added to create a fully balanced reaction. This equivalent number of electrons is what should be used in Nernst.

ashwathinair

For cell/redox problems, when do we use deltaG = deltaH - TdeltaS and deltaG = deltaG(products) - deltaG(reactants)?

ashwathinair

Do the sides of galvanic cells (anode and cathode) have different pH, and if so, how might that affect how we solve for half reactions?

ashwathinair

Write the half-reactions and devise a galvanic cell (write a cell diagram) to study each of the following reactions: (a) AgBr(s) <---> Ag+(aq) + Br-(aq), a solubility equilibrium (b) H+(aq) + OH-(aq) ---> H2O(l), the Brønsted neutralization reaction (c) Cd(s) + 2Ni(OH)3(s) ---> Cd(OH)2(s) + 2Ni(OH)2...

ashwathinair

Do you guys think for this upcoming test we are going to have to look up Eo values on a table like we had to for the midterm?

ashwathinair

D is actually deuterium and the values can be found in the Appendix You could use that formula at 25 degrees celsius since the values in the appendix are at that temperature. However, for 150 degrees celsius, you'll need to use the equation delta G= delta H-T(delta S) Hope that helps! Oh ok, thanks...

ashwathinair

Calculate the equilibrium constant at 25 8C and at 150 8C for each of the following reactions, using data available in Appendix 2A: (a) NH4Cl(s) <--> NH3(g) + HCl(g) (b) H2(g) + D2O(l) <--> D2(g) + H2O(l) How do we calculate for (b)? What values do we use for this, as D2O and D2 obviously are not te...

ashwathinair

I wasn't in class for lecture this week so I don't fully understand the cell diagram for a galvanic cell. Exactly how does a galvanic cell work (through redox reaction, salt bridge/porous disk, etc)?

ashwathinair

We need to assume 273 K/0 C temperature and 1 atm pressure under STP.

ashwathinair

Why exactly is Eo intensive?

ashwathinair

In what situations would we assume 1 M solution or 1 atm at 25 degrees Celsius?

ashwathinair

AngieGarcia_4F wrote:I think what equation you'd use would depend on what info the question provides

Specifically what info would you need to know from the question to distinguish between the two? What if you don't necessarily have all of the info you might need?

ashwathinair

Can someone explain conceptually what the overall Gibbs Free Energy of a system equation means?
deltaG = deltaG* + RTlnQ

How does this relate to deltaG = deltaH - TdeltaS? Are these equal to each other or is the second equation supposed to be deltaG* in the first equation?

ashwathinair

How/why does K as the equilibrium constant relate into the Van't Hoff equation? What does that mean conceptually?

ashwathinair

So would this be similar to how in Hess's law we would add intermediate equations to make the final reaction?

ashwathinair

Just to clarify, when you are trying to figure out how many electrons are in a compound (for redox reactions), no matter if the compound is covalent or ionic you usually just use the butterfly method (for H2O, the 1 subscript from O goes to the top of H - making it +1 - while the 2 subscript from H ...

ashwathinair

In oxidation, an atom loses electrons while in reduction electrons are gained (OILRIG). Specifically in situations where the electrons are in compounds, the best way to be able to tell if some atom has been oxidized or reduced is by figuring out how many electrons each atom in a compound has through...

ashwathinair

Other than del(S surr) + del(S sys) = del(S univ), how are del(S surr) and del(S sys) related? Like how can you find del(S surr) if you only have del(S sys) or vice versa? What other information would you need for that? Also, under what conditions might del(S surr) = -del(S sys) be true - in other w...

ashwathinair

I wasn't super sure where to put this, but I wanted to know how to tell the difference between reversible and irreversible reactions. Are phase changes reversible? What are the markers to know whether a chemical reaction is reversible or irreversible?

ashwathinair

Sometimes I post multiple times on the same thread - is this counted as separate posts or as just one?

ashwathinair

Do we know how much of each topic will be on the midterm? Will it be similar to Pizza Rolls where there was a clearly heavier focus on more recent stuff or will it be more equal between equilibrium and enthalpy/entropy/Gibbs free energy?

ashwathinair

Delta S = q(rev)/T can only be used for reversible reactions, right? Does this mean other ways to find delta S, such as nC(T2/T1) or nR(P1/P2) etc only apply to irreversible reactions, or can this be used for both?

ashwathinair

Why can we use mass and moles in different heat capacity equations and still get an equivalent result?

ashwathinair

I've noticed that change of entropy calculations using moles/temperature/volume etc tend to be much larger than entropy calculations using degeneracy and Boltzmann's constant - are these two types of calculations calculating entropy at different levels, and if so, what are they?

ashwathinair

Hey everyone! I was wondering how to best approach studying for the upcoming midterm? I feel like there is so much to remember and understand how to use and I'm not very confident in the studying I'm doing (redoing all the homework questions) because it just feels like a lot of busy work and I don't...

ashwathinair

I have another question related to this - in Lyndon's review session for Pizza Rolls today he used Cv for a problem that had changing volume (problem 5) and I don't understand why. He said you usually use Cv (he might have offered an explanation but I didn't really hear/understand).

ashwathinair

How can we use Cv and Cp when looking into heat required to change the temperature of a system (qp = n(Cp/v)(DeltaT))? I know one of them is for constant volume and the other is for constant pressure, but are there calculation-based differences between the two, or are both found the exact same way?

ashwathinair

How do you calculate the change in U for different situations: constant/changing pressure, temperature, volume etc?

ashwathinair

A piston confines 0.200 mol Ne(g) in 1.20 L at 25 8C. Two experiments are performed. (a) The gas is allowed to expand through an additional 1.20 L against a constant pressure of 1.00 atm. (b) The gas is allowed to expand reversibly and isothermally to the same final volume. Which process does more w...

ashwathinair

Thanks so much for sharing your story with us and being open to questions! It sounds like being able to learn about disease and do some work in the hospital is a blast. I have heard a lot about medical school - namely, that it requires a lot of rote memorization - but I believe I learn better by und...

ashwathinair

In some homework questions, a pressure unit is mentioned to calculate work over some time, but there is no other pressure unit to compare it with. Are we right to assume that it should be constant pressure?

ashwathinair

I know that delta H alone is a reaction's enthalpy and that delta Hf is standard enthalpy of formation, but in one of the homework problems (4D15) I came across delta Hc; does anybody know what this means?

ashwathinair

How should we go about trying to find the pH or pOH of a solution where a strong acid or base is poured into water? Like I know the pH or pOH shouldn't change much and we don't use an ice table, but then what can we do to find the pH?

ashwathinair

What is the equation to find percentage protonation? What does percentage protonation measure?

ashwathinair

(a) Complete the following table. (b) Rank the four solutions in order of increasing acidity. [H3O+] [OH-] pH pOH (i) [H3O+] is 1.50 mol/L (ii) [OH-] 1.50 mol/L (iii) pH is 0.75 (iv) pOH is 0.75 When calculating pH for the first two rows, the pH and pOH were either negative or over 14. Is this possi...

ashwathinair

A student added solid Na2O to a volumetric flask of volume 200.0 mL, which was then filled with water, resulting in 200.0 mL of NaOH solution. Then 5.00 mL of the solution was transferred to another volumetric flask and diluted to 500.0 mL. The pH of the diluted solution is 13.25. (a) What is the mo...

ashwathinair

I understand the steps to do chemical equilibrium problems for chemical equations that aren't acids and bases; in general, what is added to the basic framework of solving regular chemical equilibrium reactions when trying to find chemical equilibria (and related pH/pOH) for acid base reactions?

ashwathinair

A sample of ammonium carbamate, NH4(NH2CO2), of mass 25.0 g was placed in an evacuated flask of volume 0.250 L and kept at 25 C. At equilibrium, 17.4 mg of CO2 was present. What is the value of Kc for the decomposition of ammonium carbamate into ammonia and carbon dioxide? The reaction is NH4(NH2CO2...

ashwathinair

How can Le Chatelier's principle be applied to partial pressures?

ashwathinair

Can someone explain how and when we use approximation for ICE tables? Are there other situations you can use them as well? Is this only for acids and bases?

ashwathinair

The value of Kw for water at body temperature (37 C) is
2.1 * 10^-14. (a) What is the molar concentration of H3O+ ions at
37 C? (b) What is the molar concentration of OH- in neutral
water at 37 C?

I understand that Kw = [H3O+][OH-], but I am not sure where to go from here.

ashwathinair

What factors change a K value of an equilibrium reaction (other than temperature), and why?

ashwathinair

In what situations should we use the ICE method; in what situations should we use regular equilibrium concentrations?

ashwathinair

What effect does temperature have on the K value, and why does the K value change with temperature?

ashwathinair

Can there never be any reactions that only contain pure substances (purely liquid or solid)? For example, are reactions like the ones modeled below never possible? If so, why?
Solid + Solid <--> Solid
Liquid + Liquid <--> Liquid
Liquid + Solid <--> Solid + Liquid

ashwathinair

What is the difference between bars and atmospheres as units for finding Kp or Qp? Which one is used, and if it is either, why are both applicable?

ashwathinair

Riya Sood 4C wrote:Acid rain can be reduced by reducing burning of fossil fuels. Also, neutralizers like limestone can be used

is that all we have to know for the final about neutralizing acid rain? Are there any specific chemical concepts we should know behind these options to reduce acid rain?

ashwathinair

We have the formulas to find pKa and pKb, but if we are given an acid or base without the Ka or Kb how do we find the pKa or pKb? Or do we need to be given the Ka or Kb to find this?

ashwathinair

When we say a chelating ligand forms a ring around the central metal atom, do we mean that the metal atom is a part of the ring created? How do we know is something is a chelating ligand without knowing the drawing of it? Also, how do we know how to draw a chelating ligand knowing only the chemical ...

ashwathinair

How can we draw coordination compounds and know the VSEPR geometry of the compound? How can we tell the number of valence electrons on the transition metal in the center of the compound?

ashwathinair

What are some ways we can reduce acid rain?

ashwathinair

Which complexes should we know in terms of biological significance (and which formulas should we memorize)?

ashwathinair

Which ligands should we know the formulas for by heart other than edta, en and ox?

ashwathinair

How do we denote hybridization for sigma and pi bonds (something like sigma(C2sp, C2sp) or smth)?

ashwathinair

What are the main differences between sigma and pi bonds? What do we need to know and why are these differences important?

ashwathinair

Exactly what is a ligand, and what do we need to know about ligands from lectures for the final?

ashwathinair

Yes, bronsted definitions are based on proton accepting or donating (in contrast to lewis definitions based on electron accepting and donating).

ashwathinair

I've heard that the final can be very specific, so I think studying the notes or even the textbook in depth will really help.

ashwathinair

Sigma bonds are always one of the (up to three) bonds in a bond between two atoms. Specifically, there is one sigma in a single bond, one sigma in a double bond and one sigma in a triple bond.

ashwathinair

Proton acceptors are bases and proton donors are acids

ashwathinair

Resonance should not affect how we name a compound. However, having different versions of the compound's composition (such as through cisplatin and transplatin) can affect naming of a compound.

ashwathinair

This depends on if there is greater repulsion of bonds based on polarity and lone pairs. For example, H2O has slightly less than 109.5 degrees bond angle because the lone pairs on the oxygen repel the hydrogens away from the lone pairs and closer together to each other.

ashwathinair

(a) 2 sigma bonds
(b) 2 sigma and 2 pi bonds

You can tell based on the lewis structure - single bonds are one sigma bond, double bonds are one sigma and one pi bond, and triple bonds are one sigma and two pi bonds.

ashwathinair

You should know cisplatin has a different structure than the trans version of the molecule because of sigma and pi bonds and the lewis structures of each.

ashwathinair

Im pretty sure Lewis acids and bases are the same as regular acida dn bases. Lewis acids are proton donors and electron acceptors; lewis bases are proton acceptors and electron donors.

ashwathinair

I'd assume we need to memorize them all along with whatever electron configuration they go with for test 2.

ashwathinair

Rod-shaped molecules have stronger London dispersion bonds because they have more surface area as well as more extreme electron clumping/shifting.

ashwathinair

Essentially, does this mean that boiling points have a direct correlation to electronegativity? I would think that if an atom is more electronegative then there is a stronger bond and thus a higher boiling point. I would say it is more about the difference in electronegativities between atoms in a ...

ashwathinair

No - polarity depends more on whether the individual polarity between atoms in a single molecule cancel out or not. You cannot just assume that all molecules with lone pairs are polar as a whole.

ashwathinair

I'm pretty sure it's everything we covered after the midterm up until but not including hybridization.

ashwathinair

Since we don't have school on Monday, is there anything we need to prepare for the Friday lecture or no?

ashwathinair

Does anybody know when Test 2 will be?

ashwathinair

Why do hydrogen bonds only form between N, F and O? Why do they not form with elements in lower periods?

ashwathinair

Can someone explain how the interaction potential energy equations for different types of bonds work? I know that r is distance and alpha is polarizability, but how do the two interact to form the potential energy? Also, in what context would these equations be used?

ashwathinair

What do we need to understand conceptually about the Shrodinger equation and the Hamiltonian? How do these concepts interact, and do we need to know the equation/how to solve the Hamiltonian?

ashwathinair

At the review session on Friday, we went over 8a on the Dino Nuggets packet and found an equation derived from E(photon) = (threshold) + E(kinetic) that was equalled to frequency. Why did the equation need to be equalled to frequency? Could any other form of this equation still work to show the cons...

ashwathinair

If a bond is ionic, why would it have more or less covalent character? Is this because the electron being pulled on by the cation has more or less polarizing power/the anion has more or less polarizability?

ashwathinair

Exactly what does it mean for an electron to be distorted?

ashwathinair

Exactly what is a sigma and pi bond, and how do we know which molecules have which type of bond?

ashwathinair

Exactly what are the elements that are exceptions to the octet rule?

ashwathinair

Compounds naturally want to be at their most stable form. By using formal charges and equalling them to 0, we are better able to find what is ACTUALLY the most stable structure of the compound so that we know what the structure of the compound actually is in nature.

ashwathinair

What are the exceptions to the orbital rules we went over in class? I vaguely remember that d5 and d10 have different energy values so their orbital sequences are different.

ashwathinair

I don't know if I just didn't label it down in my notes but I am not completely sure what this experiment entails. Would someone be able to explain particle in a box to me?

ashwathinair

Exactly what is black body radiation, and what do I need to know about it?

ashwathinair

Just curious, would wave properties such as constructive and destructive interference apply to things other than light, like sound? If so, what would be an example of that?

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