CHEMISTRY COMMUNITY

CNourian2H

oh that makes sense, thanks

CNourian2H

can someone explain why first order graphs have a slope thats pos but 2nd order graphs have a neg slope (without using eq).

CNourian2H

Oh i guess pseudo rate constant k' is just using the reactant concentration that the rate is dependent on. that would be [B].

CNourian2H

Ya I dont understand how to get it directly.

CNourian2H

I was just confused on 14f if anyone can explain it.

CNourian2H

This was very helpful, thank you!

CNourian2H

He said that we submit the test online, so i dont think we even need to scan or print anything anymore

CNourian2H

Ya his email says it is. Just make sure you log on at 11:15(i think that is the time)!

CNourian2H

can someone explain how you know something is a catalyst? im confused on that.

CNourian2H

Oh that makes sense, so rate law and rate constant are proportional to each other?

CNourian2H

yes, just remember that the lower concentration is always in the products.

CNourian2H

I am pretty sure cathode is always on right and anode is always on left. that is how it is always shown for problems. but i guess you can make cathode on left if you make electrons flowing towards left.

CNourian2H

When delta G is negative, there is energy free to do work. Cell potential wants to go down. IF cell potential goes down there is a release of energy free to do work. I don’t think this is a correct. In the equation delta G= -nFEcell, if cell potential is higher, and more positive, then Gibbs free e...

CNourian2H

Basically, the electrons flow through the different concentrations, where it goes from a higher to a lower concentration. The lower concentration will always be for your product.

CNourian2H

Ya, so since Ecell is more negative for the lithium equation, the anode is lithium equation.

CNourian2H

just to clarify, the slow step determines the rate of the overall rxn by determining the reaction order?

CNourian2H

Think about them as something necessary to get from the reactants you want to products you want. they come along in process, but arent part of initial reactants or final products.

CNourian2H

if you think about the rate equation...

rate= k [A]

increasing the concentration will increase the rate of the rxn as they are proportional to each other, but that does not mean it will affect k, the rate constant. also k is a constant, so it does not change over course of rxn.

CNourian2H

7E.3 The presence of a catalyst provides a reaction pathway in which the activation energy of a certain reaction is reduced from 125 kJ*mol−1 to 75 kJ*mol−1. (a) By what factor does the rate of the reaction increase at 298 K, all other factors being equal? (b) By what factor would the rate change if...

CNourian2H

can someone explain how the frequency factor comes into play with everything?

CNourian2H

I am confused on how to determine if something is a catalyst. If you are given a reaction or multiple steps for a reaction, how do you know what the catalyst is?

CNourian2H

I am confused: if we are getting a time limit for this, then how does he track that we only take 3-4 hours to take the test from when he posts the test on the website.

CNourian2H

Do you know what time tomorrow he is going to send the test out?

CNourian2H

Ya, I am not as afraid for my grade as just being prepared going into the test.

CNourian2H

Just to add on, I never used this equation or others like this in the homework problems, so I want to know its usefulness for the final

CNourian2H

Im confused, do we ever actually use the equations with dt?

ex: d[A]/-[A]^2 = k dt

CNourian2H

I am getting a little anxious because I do not know general details about this final. What is the exact time limit? How are we going to be tested, is it all online and are we using zoom/video recording site while taking the test? How is the test formatted? I just feel like I do not know all the info...

CNourian2H

I think my main issue was freaking out when I enter the test. Just remember to breathe and relax before starting each assessment so you can answer each question with a clear mind and right direction. Good luck everyone!

CNourian2H

Thank you, this was so interesting and uplifting.

CNourian2H

Does anyone know what Lavelle's office hours are like? Is it going over general HW problems and information, or do we need to ask him questions and bring our own HW problems in?

CNourian2H

Since Test 2 has been postponed to a week later, does that mean we will also be responsible for all the info we learn next week?

CNourian2H

Whether you use delta H or C*delta T depends on the information you are given. If you have delta H reaction, for example, then you will use that value. If you don’t have that information and instead just have the material and it’s specific heat, as well as the temperature change, you will use that ...

CNourian2H

that is true for reversible isothermal expansion. for an irreversible rxn, delta s is greater than 0 and delta s surroundings is =0.

CNourian2H

it is natural for entropy to increase abd be greater than 0 because the world naturally will always has disorder. Only in conditions that aren't related to the real world, that is when entropy is =0.

CNourian2H

how do the terms anode and cathode relate to oxidation and reduction. He used the latter pair of terms to define anode and cathode, but can someone explain this further?

CNourian2H

What did the bartender say when oxygen, hydrogen, sulfur, sodium, and phosphorus walking into the bar? OH SNaP!

CNourian2H

Here is a joke:

CNourian2H

when do we know when to write delta G r (with r as the subscript)? I see both but never understand when to write what when calculating it.

CNourian2H

Can you explain how to tell which is being oxidized and which is being reduced in a redox rxn?

CNourian2H

Maya Pakulski 1D wrote:What are oxidation numbers used for?

I am also partly confused with this. I understand we use the oxidation numbers for redox reactions, but can you explain how it in an example?

CNourian2H

I think there is an error also. Yours looks correct.

CNourian2H

You put the H+ for the acidic solution on the opposite side of the H20 (when applicable to add it).

CNourian2H

i never saw this in our notes. will we be tested on this?

CNourian2H

what does it mean to b thermodynamically stable? how does this relate to gibbs free energy?

CNourian2H

why does a monoatomic gas have higher entropy than a diatomic gas?

CNourian2H

Not necessarily. Isothermal means that there is no temperature change (aka deltaT = 0) whereas reversibility has to do with entropy and if total entropy is 0 (aka in a reversible system) or if entropy of the surroundings is 0 (aka in an irreversible system). Can you explain further how entropy rela...

CNourian2H

What is the difference between reversible and irreversible expansions?

CNourian2H

Why do you use the specific heat capacity for liquid water instead of solid water in this problem?
4C.11 How much heat is needed to convert 80.0 g of ice at 0.0 8C into liquid water at 20.0 8C (see Tables 4A.2 and 4C.1)?

CNourian2H

4C.3 Calculate the final temperature and the change in enthalpy when 765 J of energy is transferred as heat to 0.820 mol Kr(g) at 298 K and 1.00 atm (a) at constant pressure; (b) at constant vol- ume. Treat the gas as ideal.

How do you differentiate what to do for constant pressure vs constant vol?

CNourian2H

Also, isn't it usually qsys = -qsurr
so how is this different from the problems using that equation.

CNourian2H

Hi. Im confused why we would add the heat of kettle and heat of water together for this problem in (a). 4A.7 (a) Calculate the heat that must be supplied to a copper kettle of mass 400.0 g containing 300.0 g of water to raise its tem- perature from 20.0 8C to the boiling point of water, 100.0 8C. (b...

CNourian2H

Mariah wrote:
Abhi Vempati 2H wrote:Adding on to what @Hui Qiao Wu 1I mentioned, the lower the pk_a of an acid, the higher the pK_b of its conjugate base. This is because of the equation pk_a + pK_b = 14. Hope this helps!

14 is the same as p[sub]w right?

Yes, Pkw=14

CNourian2H

Can someone explain the relation btwn pkA/pkB and how strong the acid/base is. If I have a higher pkB, does that mean I have a weaker base?

CNourian2H

5J.13 A gaseous mixture consisting of 2.23 mmol N2 and 6.69 mmol H2 in a 500.-mL container was heated to 600. K and allowed to reach equilibrium. Will more ammonia be formed if that equilibrium mixture is then heated to 700. K? For N2(g) + 3H2(g) --> 2NH3(g), K=1.7 x 10^-3 at 600.K and K=7.8 x 10^-5...

CNourian2H

what are the general units for partial pressure? I have seen bar and atm, so do both work depending on what the problem gives you?

CNourian2H

5G.1 State whether the following statements are true or false. If false, explain why.
(c) If one starts with a higher pressure of reactant, the equilibrium constant will be larger.

Can someone explain C to me? I understand it is false but i want to know the best way to explain it.

CNourian2H

5J.5 State whether reactants or products will be favored by an increase in the total pressure (resulting from compression) on each of the following equilibria. If there is no change, explain why that is so.  (c) 4NH3(g)+ 5O2(g) -> HNO(g) + 6H2O(g) How do I know the reactants are favored in this case...

CNourian2H

So it is involving electronegativity...Im guessing.

CNourian2H

Oh I think I got it. It's because of the CH3 in acetic acid is electron donating, and it contributes e- density towards the O-H bond making the bond stronger to break and H+ ion less wanting to go and attach to another compound.

CNourian2H

I get it now. The rod shaped molecs have greater surface area bc of more pts of interaction btwn 2 polar molecs, which causes a stronger interaction btwn the 2 molecs. therefore, a higher BP would be needed to break up the 2 molecs.

CNourian2H

Naren_Ramesh_4D wrote:On question 2b of the mini marshmallow, does the order of the ligand in the coordination complex matter?

I dont think so

order of ligands matters in writing the name- alphabetical order
not in writing formula

CNourian2H

6D.11 Decide whether an aqueous solution of each of the following salts has a pH equal to, greater than, or less than 7. If pH . 7 or pH , 7, write a chemical equation to justify your answer. (e) AlCl3;

I am confused how to write the equation for Al +3. Why does it combine with H20 first?

CNourian2H

Problem 6C.21b: Why is formic acid stronger than acetic acid? I'm confused with the electronegativity/polarity aspect of it.

CNourian2H

Also, if anyone knows the full list of strong and weak acids and bases we need to memorize.

CNourian2H

Does anyone have a good list that simply puts what to look for when trying to decide whether one acid/base is stronger than another?

CNourian2H

How do i know if a transition metal is amphoteric? Do we need to know specific ones for the final?

CNourian2H

We are asked to write the formula for sodiumbisoxalato(diaqua)ferrate(III)

I'm confused how we know which ligand to put first and which to put second in the formula for the compound.
Also, why is diaqua in parentheses?

CNourian2H

So the problem asks to write the formula for potassium hexacyanidochromate(III) I understand how to get the formula from this coordination compound name but I want to clarify a few things. 1)the -3 charge for hexacyanidochromate is not written outside the brackets bc it cancels out with the +3 charg...

CNourian2H

In Homework question 2.45, it asks to write the hybridization of each lone pair in the bonding in H2C =(double bond) CHCHO. The drawing in the answer key says the lone pairs of O have a hybridization of sp2 but the hybridization of O when its bonded is 2sp2 (difference is the 2 in front). What does ...

CNourian2H

Problem 2F.13 asks to draw Acrylonitrile, which is CH2CHCN, and then state the bond angles. How do I know which element is the central atom and how to organize the surrounding molecules? The drawing affects what bond angles I put, so is there a way to ensure I draw it correctly with all compounds si...

CNourian2H

3F.5 Suggest, giving reasons, which substance in each of the fol- lowing pairs is likely to have the higher normal melting point (Lewis structures may help your arguments): (a) HCl or NaCl; (b) C2H5OC2H5 (diethyl ether) or C4H9OH (butanol); (c) CHI3 or CHF3; (d) C2H4 or CH3OH. In B, why can buthanol...

CNourian2H

Do you think it will also have some information from the midterm as well? Or only new untested topics?

CNourian2H

Maybe we should ask Dr. Lavelle on Wednesday during the lecture, the test is coming up and I want to start preparing for it.

CNourian2H

I feel like the homework is pretty flexible in which concepts you can do it on that are relatively recent- I'm thinking concepts like dipole moments, intermolecular and intramolecular forces, and whatever is around that is all ok.

CNourian2H

Hiba Alnajjar_4B wrote:Not sure when they'll be posted, but Dr. Lavelle announced that we would be getting them back during Wednesday lecture, so maybe after Wednesday?

Are we reviewing the questions on the midterm during the lecture or just getting them back?

CNourian2H

Can someone explain what a temporary dipole is and how it occurs? How does it happen on a nonpolar molecule?

CNourian2H

I know the De Brogile Equation is used in certain circumstances, what are those? How do you know based on the wording of the question that you need to use this equation for your answer?

CNourian2H

What elements have exceptions to the octet rule other than the ones that are past the 3rd period and can have more than an octet? I know there are specific elements that also like specific types of bonds, what are those elements?

CNourian2H

Can someone explain the key differences between rod shaped and spherical shaped molecules?

CNourian2H

Can someone explain why hydrogen bonding is so common in biological systems? I'm confused

CNourian2H

Technically, if the question asks if the wavelength is detectable, or more often it will ask if there are "detectable wavelike properties" that means that it wants to know whether the wavelength is greater than 10e-15 or not. That makes a lot of sense! A good thing to look out for, thanks!

CNourian2H

All these worksheets were really helpful for reviewing for the midterm, thank you! Will any worksheets be posted to review for the upcoming Test 2? Thanks!

CNourian2H

Wow! I just read some of these articles and they're so interesting! Thank you for sharing, keep them coming!

CNourian2H

Hey guys! Does anyone know the full range of topics covered on Test 2? I know it is coming up next week starting the 19th but I am unsure what exactly is on it.

CNourian2H

I'm pretty sure Dr. Lavelle doesn't offer any extra credit or other opportunities to boost up your grade, but I just wanted to make sure on Chem Community. Thanks!

CNourian2H

Are there any review sessions and workshops available for the upcoming Test 2? Really nervous and wanted to get extra practice.

CNourian2H

Does anyone know when our midterm grades will be posted onto myucla?

CNourian2H

1D.23 How many orbitals can have the following quantum numbers in an atom: (a) n=2, l=1; (c) n=2?

I am confused with how to answer a and c because they don't give a mI value so there are multiple orbitals that can have those quantum numbers.

CNourian2H

If it says to write the full electron configuration in the ground state for an element, do you ever need to include the different subshells that show unpaired electrons? for example: for the full electron configuration of nitrogen, in the 2p-orbital do you write it out as [2px1 2py1 2pz1] or just [2...

CNourian2H

When you don't get the amount in grams of each element in the question, what is the best way to find out those amounts? You would get the molar mass of the compound and the amounts of the other molecules in the equation. There was a question like this on the midterm.

CNourian2H

Has anyone began reviewing for the final? If so, what are you doing to slowly prepare?

CNourian2H

Quick question! Why does the # of orbitals increase by 2 per level? For example, why does S have 1 orbital and the next level, p, has 3 orbitals, d has 5 orbitals, etc? It increases by 2, why can't it increase by 1?

CNourian2H

I am really confused with the spin up and spin down aspect we discussed in class. Can someone clear it up for me?
I also remember him saying that when both electrons are spin up, they interact differently than when they are spin down. Why?

CNourian2H

In class, Dr. Lavelle said that elements like Neon are not good at building bonds. Why is this so?

CNourian2H

The series is from the spectrum of hydrogen, as sequences of lines correspond to atomic transitions that each begin or end with the same atomic state in hydrogen. The Balmer series- all of the lines are in the visible region The Lyman series- ultraviolet region The Brackett series, Pfund series, Pas...

CNourian2H

The 4s sublevel is filled before the 3d sublevel because the 4s subshell is lower in energy, and it is farther from the nucleus than the 3d subshell.

CNourian2H

I am confused why light sources with long wavelengths of light cannot eject electrons in the photoelectric experiment, but why light sources with short wavelengths can. Can someone clear this up for me?

CNourian2H

I thought of this to mean that electrons behave both like particles and like waves. De Brogile explains that all material particles in motion have wave characteristics, but for microscopic bodies like electrons this observation is important. Electrons are under high speed, showing a wave-like appear...

CNourian2H

Hi guys, I'm confused with this textbook problem. Can anyone describe the steps needed to complete the problem? 1B.19 Protons and neutrons have nearly the same mass. How different are their wavelengths? Calculate the wavelength of each particle when traveling at 2.75 x 10^5 mxs^-1 in a particle acce...

CNourian2H

We use quantum mechanics to describe the behavior of very small objects that can accept energy only in discrete amounts. These discrete amounts are called quanta. It's easy for me to think about quanta as the smallest unit of any physical property- whether that is energy, matter, etc. It is like a p...

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