CHEMISTRY COMMUNITY

Kennedi2J

What does it mean for a reaction to be pseudo-first-order?

Kennedi2J

If I'm thinking of the same problem, it seems to be asking about the rate of disappearance of oxygen. In that case you would multiply the rate given by the ratio of oxygen shown in the reaction.

Kennedi2J

You shouldn't confuse the two when doing calculations. When a question is asking about thermodynamics and kinetics at the same time it is most likely a conceptual problem that has to do energy profiles.

Kennedi2J

The rate constant, k, is dependent on temperature and directly proportional to it. An increase in temperature would increase k and speed up a reaction.

Kennedi2J

How exactly will be turning in our finals? If we're going to scan them, does anyone know how that works?

Kennedi2J

By looking at energy profiles, how can you tell if it is showing an endothermic or exothermic reaction?

Kennedi2J

How can you determine which step is the slow by just looking at the reactions alone? For this problem step 2 is the slow step but I'm not understanding how you can determine that with just the reactions given.

Kennedi2J

The solution ti this problem uses the word "pseudo-first-order" to describe the rate mechanism. What does that mean? And how are you able to tell the other of the reaction from the elementary steps alone?

Kennedi2J

This problem asks to distinguish which product has the larger activation energy and the only information given besides the molecule is temperature. Since temperature increases k and speeds up the run shouldn't the product with the lower temperature have the larger activation energy? The answer says ...

Kennedi2J

A lot of people are saying Karen has good review session but I don't see her name or where and when her sessions are on the peer learning sessions link. Does anyone know where and when her review sessions are?

Kennedi2J

Which method for calculating the standard cell potential can be used for both galvanic and electrolysis cells?

Kennedi2J

Will we ever need to use the equation E = E* - (0.0257/n) lnQ ? Or is it only the other equation E = E* - (0.0592/n)logQ ?

Kennedi2J

For this homework problem, the cell notation includes Pt(s) and I2(s) on the same side of the cell diagram. Why is Pt added if there is already a solid (Iodide) in that half reaction?

Kennedi2J

For this homework problem, the Ni reduction reaction is flipped so the cell potential should also be flipped from -0.23 to +0.23 but the solution says it remains as -0.23. Why is that?

Kennedi2J

Why do we not include H20 (l) in the cell notation for a reaction?

Kennedi2J

When does the information for test 2 stop in terms of lecture material?

Kennedi2J

Besides G(not) being in standard conditions and G not being in standard conditions, do we calculate them both the same way?

Kennedi2J

It's typically because both sides of the reaction require a metal conductor. If one side lacks a metal, you add Platinum which a good inert conductor.

Kennedi2J

It's usually stated next to the molecule as in N2 (g) or Fe (aq).

Kennedi2J

Can anyone explain when we use , between 2 molecules vs. when we use | between molecules. For example Fe , Fe || Cl | Cl.

Kennedi2J

When using the Van't Hoff equation why is delta H in the equation if we're assuming change in enthalpy is constant?

Kennedi2J

Why do we assume change in entropy is constant in this equation?

Kennedi2J

For the equation G = G* +RTlnQ are we actually using this equation or only/primarily the 0=G* + RTlnK ?

Kennedi2J

Can anyone explain the end result for the reaction Dr. Lavelle did in class with permanganate and iron?

Kennedi2J

There technically is no temperature change at the plateaus where phase changes occur (i.e. melting is 0 degrees---> 0 degrees). For phase changes you use q=m(delta H) and for a temperature change you use q= mCAT.

Kennedi2J

I had my AirPods with a Louis Vuitton case on them in my backpack right before I started the Chem 14B midterm yesterday. I was in Franz 1178 and I believe someone took them because they were in my bag right next to all of the other bags in the front and now they’re not. If you took my AirPods or hav...

Kennedi2J

Does R always equal 8.314 when using Cv=3/2R and Cp=5/2R?

Kennedi2J

w = (+) when work is done on the system (compression)
w = (-) when work is done by the system (expansion)

Kennedi2J

How do you know when to use R=8.314 vs. R= 0.08206

Kennedi2J

I know that Cv= 3/2R and Cp=5/2R but how do know which one to use when calculating q=mCAT when it doesn't specify constant volume/pressure?

Kennedi2J

For the midterm will we be given the change in enthalpy for vaporization/fusion of water or do we have to memorize it?

Kennedi2J

When calculating bond enthalpies, how can you tell which bonds are broken and which ones are formed?

Kennedi2J

Why don't we consider the C--H bonds when calculating the bond enthalpies for this question?

Kennedi2J

For this problem, can anyone explain why q is negative in the final calculation?

Kennedi2J

What is the difference between q=mCAT and q=CAT?

Kennedi2J

How do you know when to use q=mCAT/nCAT vs. q=CAT?

Kennedi2J

Dr. Lavelle mentioned in lecture that because enthalpy is a state function it MUST be additive. Why is that? and what does that mean?

Kennedi2J

Has anyone picked up their Chem 14A final from Young Hall yet? Are we still able to pick them up this week?

Kennedi2J

Wow I thought they'd be available sooner. Thanks.

Kennedi2J

I think another is by looking at the energy graphs he's gonna cover soon.

Kennedi2J

Does anyone know when the grades for Test 1 will be available?

Kennedi2J

What is the process for determining which way the reaction is going when we're not dealing with a gas and not a concentration?

Kennedi2J

You can think of Q on a "number line" with K where Q is on either side of K and K is in the middle like 0. When a reaction is not at equilibrium you want to find Q to determine which way the rxn will shift to reach K at equilibrium. If Q is less than K the rxn will move right towards K, th...

Kennedi2J

When a concentration value is less than 10^-3 you can approximate that the value is so small that it will not be significant in the problem so you disregard it in the calculation. This approximation is valid if it's less than 5% of the initial concentration.

Kennedi2J

If two different reactions are given with a K value for each and you are asked to calculate the K value of the third reaction based on what is given, how would you know when to combine or how to combine the reaction the get the K value?

Kennedi2J

For test 1, will we need to know how to calculate the partial pressure of a gas if it isn't given?

Kennedi2J

You wouldn't necessarily use the principle in a calculation, it's more so to predict which way the reaction will shift given an increase or decrease to the products or reactants.

Kennedi2J

Does anyone know of a good homework question that involves applying Le Chatelier's Principle to an actual equation/problem?

Kennedi2J

Dr. Lavelle also hasn't covered nor mentioned any of the other gas laws so I don't think we would need to explain the definition or specifics of any of them besides the ideal gas law.

Kennedi2J

How do we distinguish when to calculate Q instead of K or vice versa?

Kennedi2J

You can get the same answer either way you write it but using P=(n/V)RT makes it easier when you need to convert between the concentration and partial pressure of a compound.

Kennedi2J

An example would be ethylenediamine (en) which binds to a transition metal at 2 sites.

Kennedi2J

Can we use the same formulas for pOH/pH to calculate pKa and pKb?

Kennedi2J

Is there any examples of this in the textbook? It would make more sense if I saw problem related to this topic

Kennedi2J

No ICE tables are only used for weak acid/base calculations which we won't be doing for this class.

Kennedi2J

Does anyone know if we will have to use ICE tables for the final in order to calculate pH of strong acids/bases or is this only for weak acids/bases.

Kennedi2J

kA is just the constant for acids. pkA refers to the pH of kA which is just -log(kA).

Kennedi2J

There's also a chart for this online if you look it up. There a list of the strong acids and strong bases that conjugate bases/acids come from.

Kennedi2J

Do you guys know if we would actually have to know that for the final?

Kennedi2J

Will we have to know how to write the formula for a coordination compound from the name? Like if we're given a long name would we have to write (C6H4)2 or something like that ?

Kennedi2J

Also, there may be some things not listed on his sheet that may be need to be used in naming like ferrate,etc. is not listed on there.

Kennedi2J

Does anyone know if calculations for acids and bases will be on the final?

Kennedi2J

Also can anyone explain what oxidation is? And what Dr. Lavelle meant by oxidation states? I don't remember him explaining the concept in class.

Kennedi2J

Does anyone know when test 2 will be handed back for sections on Wednesday-Friday since we'll be on break next week?

Kennedi2J

If hydrogen bonding is present does that always mean the molecule is polar?

Kennedi2J

Will we need to know how to determine the polarity of large compounds/molecules? For example, CH3COOH?

Kennedi2J

Will we need to know how to draw/know the shape of a molecule with more than one central atom?

Kennedi2J

Will we have to know about dispersion and induced dipole for test 2? Or is it only london forces, dipole-dipole, and hydrogen bonding?

Kennedi2J

Whenever the dipole moments don't cancel can we assume that it is a polar molecule.

Kennedi2J

How do you make sure your'e using the correct Lewis structure when estimating the bond angle?

Kennedi2J

I believe he doesn't make the curve until after the final so it changes each quarter but I'm hoping there's some type of curve because that's not a great average.

Kennedi2J

You should draw the most stable Lewis structure when doing calculating the bond angle.

Kennedi2J

Does anyone know the grading scale for this class? I know that 50% is a C- but are the other grades also a lower percentage?

Kennedi2J

Do we need to know the bond order or how to find it when finding the bond angle? Or is the bond order for bond length

Kennedi2J

Do lone pairs also count as a region of electron density?

Kennedi2J

Does anyone know if test 2 is only covering outline 4? Or is it also outline 3?

Kennedi2J

There was also a question: How many electrons can have the following quantum numbers in an atom?
a) n=5, l=3, ml= -1 and the answer was 2 electrons
Can anyone explain why the answer is 2 electrons and not 14 since l corresponds to f orbital and f orbital can hold 14 electrons?

Kennedi2J

What is distortion in terms of electrons?

Kennedi2J

Is it always the case that N has a higher ionization energy than O?

Kennedi2J

What's the difference between ionic character and covalent character?

Kennedi2J

Does this apply to both ionic and covalent bonds?

Kennedi2J

Does polarization power only apply to ionic bonds?

Kennedi2J

I was looking for an answer to that, that explanation was very helpful!

Kennedi2J

Is this the same for ionization energy?

Kennedi2J

Dr. Lavelle said in lecture that p-block non-metals form anions and gain p valence electrons until the following noble gas electron configuration is reached. Can anyone explain this?

Kennedi2J

Dr. Lavelle said in lecture that main group metals form cations and lose s & p valence electrons. Can anyone explain this ?

Kennedi2J

What did Dr. Lavelle mean when he said non-metals do not form cation because their ionization energies are too high?

Kennedi2J

Does anyone know if all the equations are typically given on the midterm like they were on the test?

Kennedi2J

Oh wow I had no idea there was solution manual. Thanks!

Kennedi2J

In the equation, E= work function + KE (kinetic energy), how do we know when kinetic energy is equal to 0?

Kennedi2J

Does anyone know what the actual constant is for Rydberg's constant? Or is it the (1/n1 - 1/n2)?

Kennedi2J

When studying by doing practice problems from the textbook, how do you guys check if your answers are correct? For me many times I may think I got the correct answer when I really didn't.

Kennedi2J

Good response! that explanation helped a lot.

Kennedi2J

Are we able to review the test up until the midterm?

Kennedi2J

Does anyone know if Sapling is mandatory?

Kennedi2J

Can anyone explain how to list the orbitals for an element. Dr. Lavelle went over it in lecture but he did not explain the process fully.

Kennedi2J

I believe it’s not because it’s not in the U.S. metric system but I doubt Dr. Lavelle would expect us to know why it’s not.

Kennedi2J

Do you guys think that would be asked explicitly in the problem so we would know when to use it ?

Kennedi2J

Is there a contact number for their tutoring ? Or an email? I can’t find it anywhere.

Kennedi2J

Does anyone have a picture of the slide Dr Lavelle showed in class with infrared radiaton experimental data?

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