CHEMISTRY COMMUNITY

Peter Dis1G

Can anyone explain why does reduction take place at higher concentration?

Peter Dis1G

Think this way, two half-reactions, one reduced and the other oxidized. Reducing agents themselves are oxidized because their electrons are taken away so to facilitate the other reduced reaction.

Peter Dis1G

I see. I thought their values are already determined so I could just plug in and find out, but why can't I do that?

Peter Dis1G

Hi,I don't understand how there's a manipulation done on the arrhenius equation.

Peter Dis1G

Thanks!

Peter Dis1G

There are HW problems included but on the syllabus I don't see there's a requirement to know about electrolysis in terms of knowing how to calculate.

Peter Dis1G

"Predict the effect of changes in concentration of reactants and products on the cell potential." What is that referring to? the ln K=nFE/RT?

Peter Dis1G

I know there are other posts about this question. I read them and still don't understand in some aspects. I know that for electrolytic cell, the cathode is negative and anode is positive, and so Ni and SO4 are competing with water for to be in either cathode or anode? (I am not sure if I understand ...

Peter Dis1G

Since it is basic reaction, you have to get two half equations to find out the electrons, which is n.

Peter Dis1G

I am not sure how do the last two. Is there part of the text I can refer to? Thanks.

Peter Dis1G

On chapter 15.14 it says "a catalyst has no effect on the equilibrium composition. both forward and reverse reactions are accelerated on the catalyzed path,leaving th equilibrium constant unchanged." Does it mean the catalyst has no effect on K?

Peter Dis1G

Enzymes affect the rate of the reaction in both the forward and reverse directions; the reaction proceeds faster because less energy is required for molecules to react when they collide. Thus, the rate constant (k) increases.

Peter Dis1G

Since it's not the rate-determining step, I don't think there's an effect right? By the way, if it is on the rate-determining step, it simply lowers the rate constant right? Thanks.

Peter Dis1G

Thanks!

Peter Dis1G

Don't get what the question is asking. I only know that the slow step determines the reaction rate.

Peter Dis1G

Divide the catalyzed over uncatalyzed since it says all other factors equal.

Peter Dis1G

thanks, I thought rate constant and rate of reaction didn't mean the same thing.

Peter Dis1G

why is the rate of reaction referring to the e^-Ea/RT?

Peter Dis1G

Activation energy is the minimum amount of energy needed for a reaction to take place. Think of it as an entrance fee to a party. Increasing temperature refers to adding heat. Since heat is considered a form of energy, increasing the amount of heat means to increase the amount of energy available in...

Peter Dis1G

Hi, for 15.26,I don't understand why is there a peak following a sudden drop and for 15.27, I don't understand how Boltzmann distribution formula e^-Ea/RT explains this graph. Thanks!

Peter Dis1G

Thanks ! So we just ignore those elements with big concentrations in the rate law?

Peter Dis1G

On Friday 3/2 lecture one slide wrote "but making one reactant concentration small and the others large makes reaction rate dependent only on small concentration reactant.". Can someone explain? Thanks!

Peter Dis1G

it has been answered.
viewtopic.php?t=20120

Peter Dis1G

Can anyone explain the approach as to how to interpret the diagram of the steps? Thank you.

Peter Dis1G

I think instantaneous rate is the general but more accurate measure of the rate of change of concentration, and unique rate is like the instantaneous rate of individual species. (so the name 'unique')

Peter Dis1G

Doesn't matter, just beware of the units cancellation when calculating

Peter Dis1G

Thanks in advance!

Peter Dis1G

Why can the oxidized species on the left side of the equation oxidize those reduced species below that oxidized species' equation? And why can the reduced species reduce the oxidized species lying above that reduced species? I know that the positive standard reduction potential tells us it's spontan...

Peter Dis1G

So can I understand it as when solid is left a single element it has no charge. When it functions as a compound, say NaCl, it (Na (s)) has charge.

Peter Dis1G

Going through some examples, I find that only aqueous solutions and liquids can have charges, just curious if solids can have, why or why not? Thanks in advance!

Peter Dis1G

The whole reaction for this example is 6MnO4-(aq)+11 H2O(l)+10Cr3+(aq)---> 6Mn2+(aq)+22 H+(aq)+5Cr2 O7(-2) (aq) Why is the cell diagram Cr2O7 (-2), Cr (3+)(aq),H+(aq)|| H+(aq),MnO4- (aq_,Mn 2+( aq)? I understand that on the left is oxidation, and on the right is reduction, but why is H+ also included?

Peter Dis1G

Why is that the case "the more negative the standard potential of a couple, the greater is its reducing strength"?

Peter Dis1G

That answers my question, thank you!

Peter Dis1G

I know that on the left is anode and on the right is cathode. So does the order of those elements matter when writing the cell diagram? (I mean since the left is a oxidation, does the elements have to be in order like the oxidation reaction form?) Thanks.

Peter Dis1G

That helps alot!

Peter Dis1G

I fail to understand the number of mols. How to figure that out from the equation? Thanks.

Peter Dis1G

How do we know at first hand? Thanks.

Peter Dis1G

No way to figure out at first hand, read the Toolbox 14.1 and do it step by step.

Peter Dis1G

Yeah, it's 0.

Peter Dis1G

1. write and balance half-reactions except O and H 2. For acidic solution, balance O by H2O; H by H+. For basic, balance O by H2O; H by H2O to the side that needs H and add OH- to the other 3. balance electric charges by adding electrons to left for reduction; right for oxidation. Hope it's straight...

Peter Dis1G

Also what's the difference between reversibility of work? Is that for the reversible, the pressure is not constant,and for the irreversible, the pressure is constant? Thanks in advance!

Peter Dis1G

There is a chart back in 8.8 i think that will help you understand.

Peter Dis1G

Hi, it's because according to ideal gas, PV=nRT. It says independent of temperature, which means that there is no relation between pressure and volume for that equation and therefore we shouldn't have to account for the volume.

Peter Dis1G

Do we have to be able to distinguish and identify those kinds of compounds?

Peter Dis1G

So for this one, can someone explain why we are treating one (either hot or cold water) as system and the other as surroundings? Because the heat transfer is happening only at those two?

Peter Dis1G

The Boltzmann constant is used to calculate simpler entropy, so it is more precise than the Q rev/T. The Q rev/T is to calculate the bulk change(so less precise) and therefore there is a delta sign.

Peter Dis1G

No, I don't think so. If the temperature is constant, there should be some calculation for the change in volume or pressure. Since the formulas in the book doesn't specify those conditions you said, there shouldn't be that condition to consider. Going over examples will help you develop a further un...

Peter Dis1G

I think it is the energy associated with a chemical reaction that can be used to do work.

Peter Dis1G

Thanks in advance!

Peter Dis1G

By the way,is the reversible work equation also used for isothermal situation only?

Peter Dis1G

Can anyone explain this? Thanks in advance!

Peter Dis1G

I think knowing the formula for work,change in internal energy, change in enthalpy, and calculation of heat are most important that many other equations can be derived from those.

Peter Dis1G

So,at the starting point it's an ice. According to the phase change in enthalpy, there is energy spent on breaking the bond to level to next phase. So from the table 8.3 you know the change in fusion of enthalpy and vaporization of enthalpy, then you can use those values to calculate the individual ...

Peter Dis1G

Thanks a million in advance, that would be really helpful!!

Peter Dis1G

Hey guys,for this chapter,there are many situations in which we are taking the change in temperature,volume and pressure into account. I am always confused when we should assume which change is zero under which situation. For example, I know that in an isolated system the internal energy is constant...

Peter Dis1G

OMG lots to cover. Thanks!

Peter Dis1G

What are some standard states of substances that we have to remember? And what kind of question do we use standard states? I know that for O2 the standard state is O2, for carbon it is graphite. Thanks!

Peter Dis1G

Same question. In addition, will formulas such as irreversible be given?

Peter Dis1G

A Thermochemical Equation is a balanced stoichiometric chemical equation that includes the enthalpy change, ΔH. In variable form, a thermochemical equation would look like this: A + B → C. ΔH = (±) #

Peter Dis1G

Sorry I forgot to add, I am referring to reaction enthalpies.

Peter Dis1G

I know this formula is for the ideal gas. So when there is a reaction related to gas, say combustion reaction, and question tells us to find the internal energy, is that the correct way of applying? Thanks.

Peter Dis1G

https://lavelle.chem.ucla.edu/wp-conten ... mistry.pdf
It doesn't say we have to draw, but to identify yes.

Peter Dis1G

Hi,this is Peter. I missed two lectures this week and curious if someone can give me his/her notes. My email is yfzucla21@g.ucla.edu. Thank you so much in advance!

Peter Dis1G

On Pg 279 it says "melting requires energy to overcome the intermolecular attractions and therefore endothermic." So in order to get the energy it has to absorb and therefore endothermic.

Peter Dis1G

Hey,guys, that equation I saw on the fundamentals J. HCl+NaOH--->H2O+NaCl. HCl I remember contains 3.64 g and NaOH has 2 g. Is that we have to find pH=-log(H2O)?

Peter Dis1G

And pure solids and liquids are not counted in the reaction.

Peter Dis1G

But why CBr2Cl2 is polar? Don't they cancer each other out?

Peter Dis1G

My understanding is there is no electron pairs around central atom, so there is no electrons to donate and therefore acts as a Lewis acid.

Peter Dis1G

What is specific about 5% rule in calculating chemical equilibrium of Kw?

Peter Dis1G

Will the test tell us whether it's strong acid/base or not or we need to remember some?

Peter Dis1G

I am confused exactly how many elements do the diagonal line cover are amphoteric?

Peter Dis1G

That's so helpful! Thanks.

Peter Dis1G

How to identify Lewis acid and base, can anyone give some examples? Thanks!

Peter Dis1G

From the experience of Test 4,I feel like we definitely need to remember that.

Peter Dis1G

Cool,appreciate it!!

Peter Dis1G

Can anyone give some examples? Thanks a lot~

Peter Dis1G

Basically a ligand is a Lewis base(which donates electrons) that attaches to the central metal atom. Ex:[Fe(CN)6]^-4. [CN] is a ligand that bings to iron. And the coordination number(number of points ligands attach) is 6. Hope other people can add more.

Peter Dis1G

Stuck on the same one...OH2 is neutral so why is it in the middle?

Peter Dis1G

Thanks y'all!

Peter Dis1G

So does it mean we need to draw Lewis Structure to count the lone pairs first?

Peter Dis1G

Cynaide is an anionic ligand, which follows rule #3 on Tool box 17.1.
For second question, yes there are two ligands.
Suggestion:Try to break down the procedure on the book as simple as possible.I read like more than 10 times and form an idea.

Peter Dis1G

Wait, do we need to know the names?

Peter Dis1G

Reading textbook+watching online sources are helpful to me. Only reading the textbook gains little help.

Peter Dis1G

I was going to ask the same question...Nice picture!

Peter Dis1G

I hope I should have known that earlier or the points will not be lost. This is an important concept and it might be in the final again.

Peter Dis1G

Thanks for both wonderful explanations!

Peter Dis1G

Ionic bonds are usually metals+nonmentals. NaCl,NaF,LiF are good examples. Covalent bonds are usually two nonmetals. CH4,H2O and CO2 are good examples.

Peter Dis1G

From the answer key, it seems like it's referring to Group 5 counting from the transition metals. It says (n-1)d^5 ns^2. I was confused by that at first.

Peter Dis1G

Most of the time quantum numbers are written in order,except for 2 elements,Cr and Cu.

Peter Dis1G

Just a quick note s subshell can hold 1 orbital(2 electrons), p subshell 3 orbitals(6 e), d subshell 5orbitals (10e),f subshell 7 orbitals(14 e).

Peter Dis1G

I have the same question. Thanks guys for explaining!

Peter Dis1G

Thanks!

Peter Dis1G

Calculate the de Broglie wavelength of a 0.155 kg ball travelling at 85.0 m.s-1. Can we detect this wavelength or observe the wavelike characteristics of this ball? I am stuck on second one. Can anyone tell me when we can or can't detect wavelength? Thanks.

Peter Dis1G

Counting the vowel is cool. I start to remember that. Thanks!

Peter Dis1G

But overall,it's still an important concept.I recommend looking at it even if not tested.

Peter Dis1G

Agree with the above. Saving decimals until the answer

Peter Dis1G

wait,so what's the answer?is that D? I found from the internet that the shorter the frequency,the larger the radiation energy.

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