CHEMISTRY COMMUNITY

Sue Bin Park 2I

do we know if the final is going to be timed? or will he post it and give us more than the 1.5 hours he said it would take?

Sue Bin Park 2I

and i guess to extend the question, would there be cases in which scenarios change enough to change rate equations describing the current state of the system?

Sue Bin Park 2I

one of the examples/scenarios given by prof. lavelle of a 0th order rxn was in the case of a catalysed reaction, in which the catalyst is always saturated by reactant particles and the rate is dependent on the availability of catalyst rather than concentration of reactants. my question is, is there ...

Sue Bin Park 2I

could we not just set [A] = 1/16 and [A]initial = 1?
EDIT: oh nvm we are given [A]initial. my bad

Sue Bin Park 2I

i got up to the new concentration of A to be .085, but i don't understand why we are applying the natural log to (.153/.085) before dividing by time.

Sue Bin Park 2I

as we haven't heard anything from chem dept professors overall, i doubt anything will change until/unless ucla admin mandate moving schooling online.

Sue Bin Park 2I

will we have to work with the big equation for rate constant given in this section? from my understanding, we just need to be familiar with qualitative concepts of the collision theory (and activated complex model), right?

Sue Bin Park 2I

i third that. definitely an error.

Sue Bin Park 2I

by balancing the redox reaction and using the resulting coefficients, i end up with crazy large exponents and my calculator gets overflow error...i'm not sure what i'm doing wrong? i multiply the reduction of MnO4- by 2 and the oxidation of Cl- by 5 to get 10 e- total

Sue Bin Park 2I

So how does the charge of cl go from 0 to -1, don't both the cl2 have an oxidation number of 0? the way i figured was the e- had to come from somewhere. this takes place in an acidic solution so theres no free OH-s to take from, it must go to Cl- but thats a valid question, honestly i made the leap...

Sue Bin Park 2I

i believe using the first table in appendix 2B (Potentials in Electrochemical Order) is most helpful for these questions. e.g. for 6M.7a), in order to find if Fe or Cu have greater reducing capacity, we check for the highest instance of Fe and the highest instance of Cu (in the direction of the redu...

Sue Bin Park 2I

to add on, the charge of the reactant on its own doesn't indicate anything about whether or not it is an oxidising or reducing agent; it is rather its relation to the charge of the counterpart in the products that indicates it. here, the Cl becomes both positively and negatively charged after the ar...

Sue Bin Park 2I

the answer for the cell diagram given by the back of the book is:
Hg(l) | Hg2 2+(aq) || NO3 -(aq), H +(aq) | O(g) | Pt(s)
I understand everything except why there isn't a Pt(s) electrode on the left...what would the cell actually/practically look like if it just had Hg in liquid and aqueous form?

Sue Bin Park 2I

the given cell diagram is M(s)|M1(aq)||Cu21(aq)|Cu(s), so in using the Ecell = E(right)- E(left) i set the copper as the cathode/right electrode and calculated as usual. i got -1.029 V instead of the answer the book gives. the solutions manual reverses the anode and cathode roles--is this because th...

Sue Bin Park 2I

i'd guess KOH is used because it is a completely soluble salt of OH- that does not interact with the desired reaction in any way. it probably could have also been NaOH? i don't really understand why we can't just write OH- like we did in 6L.7b but maybe someone else can chime in on that...

Sue Bin Park 2I

bumping this post so i can track it...

Sue Bin Park 2I

in the process of oxidation in the anode, you will be going from I-(aq) to I2(s). the half rxn is 2I-(aq) -> I2(s) + 2e- before the redox begins, you will have, as an anode, only an aqueous solution of I-(no I2 present yet). therefore you will need some inert conducting metal to carry the current in...

Sue Bin Park 2I

in questions like 6L.5c where you draw cell diagrams given a redox equation: (c) Cl2(g) 1 H2(g) _> HCl(aq) how do you know what order each component goes in the anode and cathode? e.g. with the answer: Pt(s)|H2(g)|H1(aq)||Cl2(aq)|Cl2(g)|Pt(s) do the gas phases always go on the outsides and aqueous o...

Sue Bin Park 2I

i know the definition of the coulomb has to do with the ampere but when i look for what an ampere is i'm referenced to the same definition involving coulombs...i'm a bit confused lol. could someone summarize the significance of these units and what exactly they measure? thanks!

Sue Bin Park 2I

why is the splitting of a halogen assumed to be an endothermic reaction in this question?

Sue Bin Park 2I

If we are given a non isobaric process, e.g. an irreversible isothermal expansion, how would we find the enthalpy (delta H) of the process? does delta H exist for a non isobaric reaction? in particular, i'm dealing with a type of question where you open a valve between two containers of gas. I know ...

Sue Bin Park 2I

question 4.43b defines the situation as being at standard ambient temperature and pressure, which i believe is 298.15, 1 atm; but the answer manual computes it using STP and in fact states the conditions of STP first...is this a typo? am i correct in using T=298 rather than 273?

Sue Bin Park 2I

the constants and equations sheet doesn't actually give the Cv or Cp of diatomic gas molecules, only calling the monoatomics "ideal gases" - will he differentiate/expect us to use the diatomic values at all during the test?

Sue Bin Park 2I

oh wait...did you use the ∆S = nR ln(V2/V1) but replace volume ratio with (P1/P2)?

Sue Bin Park 2I

was wondering this too. also, how did you find entropy from change in pressure exactly?

Sue Bin Park 2I

not sure if this belongs here, sorry.
but when is "Ideal gas, U = 3/2 nRT" true? is there an iso-something condition to this statement? in what kind of question would I use this?

Sue Bin Park 2I

ΔS= nRln(V2/V1) is used when we are calculating change in entropy from a change in volume ΔS= Cln(T2/T1) is used when we are calculating change in entropy from a change in temperature. C is Cv if volume is constant (isochoric), Cp if pressure is constant (isobaric). Note that occasionally we have a ...

Sue Bin Park 2I

the textbook has this passage in 4j.2, pg 332: "The molar Gibbs free energy of a substance in a mixture depends on what molecules it has as neighbors, so the molar Gibbs free energies of NH3, N2, and H2 change as the reaction proceeds. For example, at an early stage of the reaction, an NH3 mole...

Sue Bin Park 2I

so i'm reviewing prof. lavelle's lecture from feb 3rd and i'm following along with his derivation of the link between "accessible microstates and a macroscopic property" (specifically V). i understand most of it up until he basically replaces the boltzmann constant with nR in which n = mol...

Sue Bin Park 2I

in part a of the question, the answer key's result requires you to assume that water vapor is produced in the reaction (to get the right delta n of gaseous products). however, in part b to get the provided solution you have to use the enthalpy of formation of liquid water to get the "correct&qu...

Sue Bin Park 2I

I know the question requires the use of deltaS = Cp*ln(T2/T1), but I'm not sure how I'm supposed to solve this without a given specific heat for the unnamed gas?

Sue Bin Park 2I

AMahadi wrote:Do we have to know this info for the midterm?

it was in his topic outline

Sue Bin Park 2I

do the TAs collect them on mondays? fridays?

Sue Bin Park 2I

will we have to know all the stuff in the "molecular interlude" chapter, with translational/vibrational/whatever energy? i didn't see any of that in the outline/objectives list prof. lavelle gave us, and he didn't lecture at all about it?

Sue Bin Park 2I

prof lavelle said in his email today that we'd spend this week going thru the rest of the thermodynamics outline, so i'd assume all of it is going to be fair game for the midterm.

Sue Bin Park 2I

also, why does the area under the P-V graph = work?

Sue Bin Park 2I

i kind of understand the definitions of the two and the conditions in which they are true, but why do the curves look so different?

Sue Bin Park 2I

sorry i'm completely clueless, is there a book section/chapter about this topic?

Sue Bin Park 2I

If you use a weak acid or weak base, wouldn't it's conjugate be a strong base/acid? So if the buffer demands equal concentrations of weak acid and base, how would it be created? i'm pretty sure the conjugate seesaw is only relative; if the acid is weakER then its conjugate base is strongER, etc. ir...

Sue Bin Park 2I

I believe if you are calculating x using the information from Table GE.2, the values you would get for x are 1.47x10^-2 or 6.81x10^-3. But you would use 1.47x10^-2 since anything around 10^-3 is too small (I might be wrong about that, but thats my general rule of thumb lol) which value of K are you...

Sue Bin Park 2I

That makes sense, in a problem would that value be given or is there a way to calculate it? it would likely be given but i guess if they did want us to calculate the ions' concentrations they could provide us with a dissociation constant and the amount of ionic compound added to the soln. that woul...

Sue Bin Park 2I

Do you have to account for the amount of H+ already present from the first deprotonation in the Initial row of ur second deprotonation ICE table?

Sue Bin Park 2I

gases behave most ideally when they are as inert and non-interacting as possible. this is why @high temperatures and low pressure they behave most ideally; the potential energy of intermolecular forces is lessened. high temp = greater kinetic energy/moving around faster, and low pressure = less coll...

Sue Bin Park 2I

what exactly is the practical definition of a buffer? wouldn't any solution of a weak acid/base be a buffer because the acid/base and its conjugate would exist in solution? or am i getting this all confused lol

Sue Bin Park 2I

the term 'conjugate acid/base' is arbitrary and based on whatever we want to be focusing on. if HA + H2O <-> A- + H3O+ is our reaction, we could call HA our acid and A- our conjugate base, or A- our base and HA our conjugate acid. the word 'conjugate' just establishes the fact that one species is re...

Sue Bin Park 2I

An exothermic reaction will result in products which are more thermodynamically stable than its reactants; lower energy bonds are more stable than high energy bonds, so if you have some knowledge of which side has the more "common" or "stable" species (e.g. O2 is much more common...

Sue Bin Park 2I

Can't figure out why I'm getting an impossibly small amount of NO2...using Kc from 5G.2. Could someone outline the solution? thanks.

Sue Bin Park 2I

using PV=nRT for these types of problems, you usually assume the number of moles (n) remains the same, R is a constant, and in these questions you usually have a closed system with a constant volume. if you don't have T, you'd be solving for more than one unknown, which is impossible. so most likely...

Sue Bin Park 2I

am i getting ahead of myself or is there a connection between these concepts/values?

Sue Bin Park 2I

In regards to the activity of each ion, I believe they are referring to the ion's respective concentration. I hope this helps! That makes sense, in a problem would that value be given or is there a way to calculate it? it would likely be given but i guess if they did want us to calculate the ions' ...

Sue Bin Park 2I

he was talking mainly about if you are trying to figure out how an equilibrium reacts to a change in pressure. example equation: A(g) + 2B(g) <-> 2C(g) if pressure is increased : the equilibrium will shift to produce more of the side that has less overall moles of gas . in our example, it's the righ...

Sue Bin Park 2I

So is this why when the amount of reactant is increased, K remains the same for the reaction? i don't think this has to do with why K remains unchanged. the eq constant just describes the behavior of a reaction, no matter the amounts of reactants or products you have in your given situation. the va...

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