CHEMISTRY COMMUNITY

Jordan Lo 2A

We can use the 5% rule to ignore x in the denominator of the fraction that you get from the ICE table

Jordan Lo 2A

Is this like the elementary steps reactions where you use the coefficient to determine the power of the concentration?

Jordan Lo 2A

pKa and pKb are the -log of Ka and Kb. As the exponent of the K becomes more negative, pKa or b increases

Jordan Lo 2A

Will we be performing calculations where we find the derivatives?

Jordan Lo 2A

Do we know how to find the order or will it be given?

Jordan Lo 2A

A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change by decreasing the activation energy of a reaction

Jordan Lo 2A

A greater E on the standard reduction potential list means reduction is more favorable. For example, Lithium is a metal that likes to "give away" its electron so reducing it (adding an electron) is very unfavorable and E is very negative. When E is negative, the reverse reaction is more fa...

Jordan Lo 2A

Platinum electrodes are used because they aren't very reactive, so they won't be involved in the oxidation/reduction. We use them when we have two ions involved so that electrons can flow between the cells

Jordan Lo 2A

A salt bridge is made of ions that flow into the solutions produced by the oxidation/reduction to prevent charge build-up, allowing electrons to continue flowing between the two cells

Jordan Lo 2A

The question is: (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) There are multiple reduc...

Jordan Lo 2A

What number is this in the 6th edition?

Jordan Lo 2A

You add similar to Hess's Law, with the sum of the products minus the sum of the reactants

Jordan Lo 2A

I believe that delta G is a state function because delta G not is a state function

Jordan Lo 2A

Do you mean when you are calculating Gibbs free energy and they want you to find it for a certain temperature using Q? in that case, you need to calculate Q and either compare it to K or delta G to 0 to answer the problem

Jordan Lo 2A

Gibbs free energy is delta G, and standard is delta G not at certain conditions. I believe it's 1 atm and 273.15 Kelvin

Jordan Lo 2A

Can someone explain #4? Is this because q=0 when delta T=0, and w=0 when -PdeltaV=0?

Jordan Lo 2A

katherinemurk 2B wrote:Can someone explain how to do #1. I found the heat gained by the water but without the final temperature of the metal how would I find the specific heat??

Final temperature of the metal and water are equal

Jordan Lo 2A

Reading other people's questions on Chemistry Community about homework problems while I'm doing them helps me a lot because I can see how else to approach the problem

Jordan Lo 2A

I would know the Lewis structure just in case it isn't obvious what kind of bonds are being broken and formed, especially if there is a lot of change between products and reactants

Jordan Lo 2A

The strong acid/strong base comes from the salt, right?

Jordan Lo 2A

Do we need to know this for the midterm? It's not on Outline 3

Jordan Lo 2A

Changes in pressure and volume most affect gases because the particles move most freely. Changes in pressure and volume would affect gas particle motion more than it would for liquids and solids, so work is only affected a negligible amount for non-gaseous reactions

Jordan Lo 2A

Does anyone know if Lyndon is doing a review session for the midterm?

Jordan Lo 2A

U is a state property because changes in internal energy are functions of final and initial states

Jordan Lo 2A

If you imagine a double bond as the sigma and pi bond that we learned in 14A, I think it makes sense that you can't just halve the value of a double bond to get the value of a single bond because the first and second bonds hold the atoms together in different ways

Jordan Lo 2A

What is the difference between q and delta H?

Jordan Lo 2A

I copied and paraphrased the following information from Friday's slides, but I'm not sure what I meant by this: -reaction constant P: that involves change in number of moles of gas, so P deltaV is significant -reaction constant P: that involves solids/liquids, so P deltaV is significant (calorimetry...

Jordan Lo 2A

Do we use bond enthalpy for 8.51 in the 6th edition? I'm having a hard time with the Lewis structure, and the solution manual doesn't explicitly state that they used the bond enthalpies

Jordan Lo 2A

A periodic table that's color coded by state of matter might help if you want to memorize them, but you don't need to

Jordan Lo 2A

If you mean delta H formation, I think it's because we measure delta H formation relative to what the compound "normally" is. At 25 degrees Celsius and 1 atm, oxygen is usually O2(g). So, it doesn't take any additional energy to transform O2(g) from O2(g)

Jordan Lo 2A

Another aspect of this is thinking of the heat as a product or reactant, where in an endothermic reaction (+) it would require heat which can be considered as a reactant. In an exothermic reaction (-), where heat is given off, we can think of it as a product. This strategy is also helpful when thin...

Jordan Lo 2A

I think we only need to learn these terms to identify if systems are closed, open, or isolated (like in 6th edition 8.1)

Jordan Lo 2A

Can someone explain why we use 101.325 J/L*atm to convert w into joules for 8.3, but not for w in 8.9?

Jordan Lo 2A

b) work is positive because a force is being applied to it that causes it to change volume
c) change in internal energy is the sum of heat energy and work energy. Since there isn't a change in heat, the change in internal energy is solely the work done on the system

Jordan Lo 2A

I think the buffer reactions are the calculations with salts that he listed on outline 2

Jordan Lo 2A

Is test 1 the entire outline 2? I could be wrong but I don't remember going over polyprotic acids (last couple exercises in 6th edition) or examples (last bullet points under concepts)

Jordan Lo 2A

if the x (change in concentration) is less than 5% of the initial concentration, you don't have to include "-x" in the denominator when solving the ICE table

Jordan Lo 2A

Will we be solving problems where we take a polyprotic acid and calculate for both dissociation reactions? i.e. for both H2SO4 and HSO4-

Jordan Lo 2A

Is it ok to just write K or do we have to specify which K we are using?

Jordan Lo 2A

Are there any differences in solving ICE tables for acid-base reactions and gases? Other than keeping in mind partial pressures

Jordan Lo 2A

Do we need to memorize the formula in the book for converting between the 2?

Jordan Lo 2A

I think both phrases mean that "to the right" has more products than reactants since products are on the right side of the equilibrium equation

Jordan Lo 2A

I couldn’t find a specific forum to post about changing discussion sections, so I’m posting here. I’m in discussion 2A (T 8-9) and I’m looking to change into discussion 2E because of class conflicts. Is anyone willing to switch?

Jordan Lo 2A

you put "bis" to replace "di" if the ligand already has "di" in its name (ex: ethylene diamine)

Jordan Lo 2A

Which is the stronger base, the hypobromite ion, BrO-,or morphine, C17H19O3N? Justify your answer.

Is there a way to solve for this without using data from the textbook? The answer key just lists the pKb

Jordan Lo 2A

If so, I assume that we would need to know everything on the periodic table that is commonly used. However the periodic table on his website has both the name of the element used and the symbol

Jordan Lo 2A

Are you referring to something like silver versus Ag?

Jordan Lo 2A

Will we get marked off if we don't write OH2?

Jordan Lo 2A

thanks! this is very helpful because I was confused as well

Jordan Lo 2A

Are stronger acids/bases stronger because they have weaker intermolecular forces, and dissociate more completely?

Jordan Lo 2A

Hey so does anyone know how the grading in this class is done. Is the class curved or is there a specific rubric. I've been asking around but still can't seem to find out. Weekly Homework (7 pts per week) 70 pts Weekly Online Discussion (3 pts per week) 30 pts Three Discussion Section Tests (3 x 40...

Jordan Lo 2A

Thank you!

Jordan Lo 2A

Dr. Lavelle said that we would go over naming on Wednesday. Does that mean that it will be on the test?

Jordan Lo 2A

Should we consider lone pair as sigma or pi bond when we do hybridization? For example if an central atom is linked with 3 atoms (sigma bond) and 1lone pair is it s1p3 or s1p2 hybridization? Thank you very much! I believe that the hybridization would be s1p3 because of the four regions of electron ...

Jordan Lo 2A

Are all square planar structures polar unless they have 4 of the same type of atom?

Jordan Lo 2A

The solid wedge is the one in the foreground, and the dashed wedge represents the one in the back

Jordan Lo 2A

Thank you Joyce

Jordan Lo 2A

not electronegative* just smaller cations

Jordan Lo 2A

In general larger atoms have greater polarizability and more electronegative atoms have greater polarizing power

Jordan Lo 2A

Adrian C 1D wrote:A)What is the shape of a ClO2+ ion?
B)What is the expected OCLO bond angle?

I know the bond angle would not be 180 degrees since the shape is not linear, but the answer says it is slightly less than 120 degrees. How did they arrive at this answer?

Because the molecule has lone pairs, it is bent

Jordan Lo 2A

1. count total number of electrons
2. put element with lowest IE in the center
3. arrange electrons symmetrically around central atom
4. draw resonance if applicable

Jordan Lo 2A

4s has a lower energy than 3d, so we fill that first. That's also why we generally take electrons from 4s first as well

Jordan Lo 2A

Porus_Karwa_3C wrote:Hi just confirming for the midterm we'll only have to be responsible for the configuration of all of the s-block, all the p-block, and just the first row of the d-block?

My TA also mentioned that we should know/be able to draw the shapes of s, p, and d

Jordan Lo 2A

This is from homework problem 3.21 c from the 6th edition. The shorthand used for Te 2- is [Xe], which comes after tellurium in the periodic table. When does an ion use the noble gas that comes before in its electron configuration and when does it use the noble gas which comes afterwards? Sorry, I ...

Jordan Lo 2A

viewtopic.php?t=427

This is a similar question answered by either a TA or Dr. Lavelle

Jordan Lo 2A

Arshia Ramesh 1G wrote:Why is it that chromium's electron configuration is [Ar]3d^5 4s^1? I get the [Ar] but why is it 3d^5 instead of 3d^4?

I believe that it is the element is more stable this way. The electrons are more evenly distributed because none are paired.

Jordan Lo 2A

I'm confused about this statement from the 6th Edition Ch 2 #37b homework problem: Electrons in an s-orbital are more effective than those in other orbitals at shielding other electrons from the nuclear charge because an electron in an s-orbital can penetrate to the nucleus of the atom. Is this beca...

Jordan Lo 2A

The second equation is to calculate energy of an electron at t a certain level. The Rydberg equation measures the frequency of energy released when electrons move between levels.

Jordan Lo 2A

I believe Dr. Lavelle said it wasn't necessary, but I'm not sure

Jordan Lo 2A

Why are symmetry and nodal planes important in determining electrostatic interactions?

Jordan Lo 2A

I'm confused about this statement from the 6th edition in chapter 2: In other words, an s-electron is bound more tightly than a p-electron and has a slightly lower (more negative) energy Wouldn't an electron that is more tightly held have more positive energy because the nucleus "cancels out&qu...

Jordan Lo 2A

What steps did you take to solve the following problem (continuation of #18): Use the above uncertainty in velocity to calculate the electron's uncertainty in kinetic energy. Then calculate the uncertainty in kinetic energy per mole of electrons (that is, per mole of hydrogen atoms). Comment on your...

Jordan Lo 2A

Do you know how many significant figures we should use when solving problems, or should we just match the given information?

allisoncarr1i wrote:They are given on the exams but it might be helpful to familiarize yourself with some of the more frequently used constants just as a time saving technique.

Jordan Lo 2A

So each outline corresponds with one test?

Sona Hakobyan 3J wrote:Everything regarding test 2 should be on outline 2 :)

Jordan Lo 2A

I am wondering the same thing. Certain homework questions imply that we should memorize them, and they're not included in the constant worksheet on Dr. Lavelle's webpage Do we need to memorize which colors corresponds with which frequency/wavelength/energy of photons? For example, if given a wavelen...

Jordan Lo 2A

Thank you so much!

Chem_Mod wrote:Week 2 worksheet for this week! We will go over quantum world material up to (not including) debroglie's wavelength.

Jordan Lo 2A

I used the equation E=hv and v=c/lambda to find energy of the photon, but my answer for energy is 1.02*10^34 J. Is this correct? It seems like it's too small of a number but I can't find my mistake

Jordan Lo 2A

Do you know if other UAs will be posting their worksheets? I know that it's best to go to as many peer learning sessions as possible, but I have some class time conflicts and would like to still get a lot of practice work done.

Jordan Lo 2A

Is test 2 solely going to be Quantum World material, or will it be cumulative? I'm trying not to fall behind in Chapter 1, but I also want to continue studying the review topics

Jordan Lo 2A

I believe that that it's better to air on the side of caution and always show units. On Lavelle's website, he included a link to an article about how important units are https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14A/14aflip.pdf Also, I find it much easier to solve problems (for n...

Jordan Lo 2A

I'm also confused about formula units. Are they synonymous with "parts" within a salt? Why and when would a chemist use the word formula unit in place of the word atom? See my answers here: https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=26&t=32772&p=105307&sid=7e485d68778f...

Jordan Lo 2A

For significant figures:
-zeros between two significant figures are significant (8009 has 4 sig figs)
-zeros before a decimal point are significant (250. has 3 sig figs but 250 has 2)
-trailing zeros after a decimal point are significant (0.0080 has 2 sig figs but 0.008 has 1)

Jordan Lo 2A

I assume that this week is the review given what my TA went over on Friday. However, I'm not positive and I plan to ask during office hours.

Jordan Lo 2A

I purchased the 6th edition solutions manual, but it only has odd-numbered answers. Is there a way to check even answers, or am I looking in the wrong place?

Jordan Lo 2A

I tried G.21 part A and I got 4.58 * 10^-2 M for my answer. Do you think the masses of your compounds could be slightly off because you're using a different periodic table?

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