CHEMISTRY COMMUNITY

Katherine Grillo 1B

If a catalyst doubles the reaction rate, what's the new activation energy? Would it be half?

Katherine Grillo 1B

What would the units of the frequency factor be?

Katherine Grillo 1B

What is the collision model and activated complex model?

Katherine Grillo 1B

Given general reaction mechanism like

Step 1 (Fast): 2A + B -> C
Step 2 (Slow): C + D -> 2E

Would the expression for the rate of formation of the product E using the pre-equilibrium approach be equal to (2k1k2/k1')[A]^2[B][D] ?

This is question 12 from Lyndon's practice final btw

Katherine Grillo 1B

If given a general reaction mechanism like

Step 1 (Fast): 2A + B -> C
Step 2 (Slow): C + D -> 2E

How do we determine what the intermediates and catalysts are?

This is question 12a on Lyndon's practice final btw

Katherine Grillo 1B

Joon Chang 2F wrote:You can use the equation $ln K=\frac{nFE^{\circ}}{RT}$

Would that be the same if you're asked to find Ka?

Katherine Grillo 1B

If you're balancing redox reactions, does it matter if it's acidic or basic conditions?

Katherine Grillo 1B

If we're just given a galvanic cell with the cell potential, how do we find K for the cell?

Katherine Grillo 1B

What's the purpose of the porous disk in a concentration cell?

Katherine Grillo 1B

Why is the change in Gibbs free energy negative when ice melts? Isn't it gaining heat or in other words, isn't delta H positive?

Katherine Grillo 1B

Why do we know that the delta G of galvanic cells will always be less than 0?

Katherine Grillo 1B

I'm confused as to when the Nernst equation would be applicable? When do we know to use it?

Katherine Grillo 1B

For question 6 on the midterm, how do you know that the reaction will do expansion work?

Katherine Grillo 1B

How do you determine which step is the fastest and which is the slowest? I'm specifically asking for the pre-equilibrium approach. Are we usually given that information? Or is there a way to figure it out with the information we're given? Like in class we were given 2NO + O2 -> 2 N02 with the observ...

Katherine Grillo 1B

How do you determine reducing and oxidation power?

Katherine Grillo 1B

When is the last day to finish posting on Chemistry Community? For it to count for points this quarter.

Katherine Grillo 1B

Balance the following redox reactions in acidic solution.

Br–(aq) + MnO4–(aq) -> Br2(l) + Mn2+(aq)

I got 5Br- + Mn04- + 8H+ -> 5/2(Br2) + Mn^2+ + 4H2O and I just want to know if it's correct

Katherine Grillo 1B

How do you find the oxidation number of certain atoms in a molecule? Are there just some oxidation numbers that are certain?

Katherine Grillo 1B

Will we be given the Vant Hoff equation for the test? I can't find it on the posted equation sheet

Katherine Grillo 1B

In the equation delta G = -RT*ln(K), K is the equilibrium constant right? But it's stated that a reaction is at equilibrium when delta G equals zero or when K equals 1. There are many reactions that have an equilibrium constant that is not equal to one but is in equilibrium. So I'm confused with thi...

Katherine Grillo 1B

Why is delta G 0 at equilibrium? I don't understand conceptually why that's the case

Katherine Grillo 1B

Why does a positive delta S favor the forward process in a reaction?

Katherine Grillo 1B

I was wondering if my answers are correct for this practice problem. Specifically a and c. The exothermic reaction of carbon disulfide with chlorine is as follows: CS2 (g) + 3Cl2 (g) ⇋ CCl4 (g) + S2Cl2 (g) delta H = -238 kJ Predict the effect of the following changes to the system on the direction o...

Katherine Grillo 1B

I'm confused about the different delta S equations. When does delta S equal q/t vs nRln(V2/V1) vs nCln(T2/T1)?

Katherine Grillo 1B

What does it mean that an isothermic reaction has maximum work? Why is that the maximum?

Katherine Grillo 1B

What does it mean that a system can only be prepared in one way? And why does that mean S=0?

Katherine Grillo 1B

When calculating degeneracy, does the number of available particles mean the number of UNIQUE available particles? For example would n=2 or 1 if the molecule is 02?

Katherine Grillo 1B

My TA was talking about the difference in entropy when comparing N2 and CO. Why does CO have more positive entropy? N2 also has two atoms so wouldn't they be able to take up the same amount of states?

Katherine Grillo 1B

I have the equation delta U= 3/2 nR delta T = 0 written in my notes and I can't remember what that's in reference to. When does that equation apply?

Katherine Grillo 1B

How do I know when to use w=-pv vs w= -nrT ln(V2/V1) ?

Katherine Grillo 1B

Why doesn't temperature change during a phase change? I understand how to interpret the heating curve for water but why is a substance able to absorb so much heat without changing temperature?

Katherine Grillo 1B

What does it mean that entropy is a maximum at equilibrium? Why is it at its maximum?

Katherine Grillo 1B

What does it mean when an expansion is isothermal/reversible? What would be an example of an irreversible expansion?

Katherine Grillo 1B

So when Ka is less than 10^-3, it is a weak acid right? So how does pKa work and what's the scale? If pKa is small, then is it a strong acid? And is it the same for pKb?

Katherine Grillo 1B

Are we supposed to just know the list of strong acids and bases? Or is there a way to figure out if the acid/base is strong and completely dissociates based on the chemical equation we're given?

Katherine Grillo 1B

I'm confused as to why heating will favor R formation if the reaction is exothermic. If the reaction releases heat, wouldn't the extra heat favor P formation?

Katherine Grillo 1B

So I'm in discussion 1B and my TA (Wang) posts his slides on here and I don't know how to access them. Does anyone knows what I'm supposed to specifically search for or where I can find them?

Katherine Grillo 1B

Why aren't solids and liquids included in K expression? Wouldn't it significantly change K?

Katherine Grillo 1B

When you're calculating K and all the R and P are gases, does it really matter whether or not you use partial pressure or molar concentrations? You would get the same calculation right?

Katherine Grillo 1B

How do the different definitions of Lewis acids and Bronsted acids help us conceptualize acids and bases? Would each term be applicable in different problems?

Katherine Grillo 1B

Why are transition metals able to have many oxidation states?

Katherine Grillo 1B

I'm confused about how to calculate the oxidation state of a molecule. I don't know if we went over rules in lecture and I just missed it? But when we were talking about the coordination number of the molecule [Fe(CN)6]^4- he mentioned that the oxidation state is +2 and I have no clue where he got t...

Katherine Grillo 1B

What does it mean that sigma bonds allow bound atoms to rotate? What are they rotating between and why don't pi bonds allow rotation of bound atoms?

Katherine Grillo 1B

Why is hydrogen bonding one of the strongest types of intermolecular forces?

Katherine Grillo 1B

Why are the instantaneous dipoles in rod-shaped molecules stronger than those in spherical molecules?

Katherine Grillo 1B

When would we need to calculate this on an exam? And what useful information does it provide?

Katherine Grillo 1B

How does dispersion work? How can a dipole be induced then induce another?

Katherine Grillo 1B

Which ions cause large distortions? Do the ions increase in polarizing power as they increase in atomic radius?

Katherine Grillo 1B

What does it mean that highly distorted electrons are highly polarizable?

Katherine Grillo 1B

So I understand that a radical is a compound with an unpaired electron but I don't understand how this occurs. Why would a radical form? Are there few compounds that can support an unpaired electron? And when Lavelle says that they only exist for a short time, what happens to them?

Katherine Grillo 1B

Which atoms accommodate more than 8 valence electrons? And why? I know that P, S, and Cl have expanded valence shells but why? And what are the others that have expanded valence shells?

Katherine Grillo 1B

Why does the atomic radius decrease across a period and increase down a group? I'm confused about the relationship between electrons/shells and size.

Katherine Grillo 1B

Why isn't a double bond twice as strong as a single bond? It seems like there isn't a linear relationship between the amount of bonds and bond strength. Why is that?

Katherine Grillo 1B

Is there an explicit relationship between the strength of a bond and whether it's a solid, liquid, or gas?

Katherine Grillo 1B

I don't quite understand how you would calculate the probability of finding an electron. I understand that it's psi squared but what does that mean exactly? What would you need to know to calculate that?

Katherine Grillo 1B

Why is removing a second electron always harder than the first? Does this logic apply to the third electron, meaning the third is even harder to remove than the second?

Katherine Grillo 1B

How can chlorine exist in both positive and negative oxidation states? And how do you find the maximum and negative oxidation number that chlorine can have?

Katherine Grillo 1B

In lecture, Lavelle said that group 13 elements need 5 electrons to complete their octet. What does this mean? They only need 5 electrons in total or need 5 more to complete an octet?

Katherine Grillo 1B

Can someone explain the definition of degenerate orbitals? How do you find how many degenerate orbitals a specific orbital has?

Katherine Grillo 1B

How does Schrodinger's equation related to orbitals and quantum numbers?

Katherine Grillo 1B

Lavelle worked through an example in class about the wavelength of a car moving at a certain velocity. He asked if the car has "any measurable wavelength properties." What does that mean and how do you determine if there are measurable wavelength properties?

Katherine Grillo 1B

What does it mean that the empirical equation En= -hr/n^2 only works for the H spectrum?

Katherine Grillo 1B

I'm confused in regard to the connection between the Bohr frequency condition and the empirical equation for H-atom. Do they give you the same solution? The change in energy? And you just use either one depending on what information you're given? Or are they two separate, unconnected formulas?

Katherine Grillo 1B

Zeros between non zero digits are always significant

Katherine Grillo 1B

If there's a decimal point, start counting digits from the left starting with the first non-zero digit. If there isn't a decimal point, start counting digits from the right side starting with the first non-zero digit. Just think of a map: Pacific = left, Atlantic = right.

Katherine Grillo 1B

F 13 asks for the name of the compound for which we find the empirical and molecular compound. Are we expected to know how to determine the name of compounds given this information? If so, what are the rules for the nomenclature?

Katherine Grillo 1B

E. 15 asks "The molar mass of the metal hydroxide M(OH)2 is 74.10 g*mol-1. What is the molar mass of the sulfide of this metal?"

I'm confused by the term "sulfide" in this question. Is there a typo in the book or can a sulfide refer to something other than the anion of sulfur?

Katherine Grillo 1B

How do we know when to write solutions using scientific notation? I usually do so as a default but when checking the solutions manual, I noticed that sometimes answers like (for example) .0623 is left just like that and not written as 6.23 * 10^2. Is there a reason for that? Are there specific rules...

Katherine Grillo 1B

Yes, you're right. You would only have to use Avagadro's number if it asked you to calculate the number of molecules or formula units as it did in question E21. In this case, the question is just asking for the number of moles so no need to use Avagadro's number.

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