CHEMISTRY COMMUNITY

LyahFitzpatrick 2E

Hello, I think the best things to remember are: - anode components on the left of the salt bridge, cathode components on the right - salt bridge is || - components of different state separated by |, of same state separated by comma - usually, the solid components are towards the edge hope these quic...

LyahFitzpatrick 2E

Are there ways to mathematically model the situation even when the reverse reaction comes into play?

LyahFitzpatrick 2E

Hi, I know there's a bunch of replies but I asked this on a midterm and I was told to always assume 25C/298K unless otherwise specified :)

LyahFitzpatrick 2E

Once calculating the half life of a reaction, how do you determine how much of the reactant disappears in a certain amount of time using the reactant? Here's the problem.. Dinitrogen pentoxide, N2O5, decomposes by first‑order kinetics with a rate constant of 3.7×10−5 s−1 at 298 K. If [N2O5]0=0.0603 ...

LyahFitzpatrick 2E

It's a bit late, but I'm still stuck on getting the final balanced equation for this problem.. right now I have: S^{2-}(aq) + MnO_{4}^{-}(aq) + 2H_{2}O(l) -> S(s) + MnO_{2}(s) + 4OH^{-}(aq) How come this isn't working out? Here is the reaction, taking place in a basic solution... MnO−4(aq)+S2−(aq)⟶S...

LyahFitzpatrick 2E

How come all concentration cells automatically have a standard reduction potential = 0 when solving for E?

LyahFitzpatrick 2E

If entropy and enthalpy are both spontaneous and positive values, why is deltaG spontaneous when negative?

LyahFitzpatrick 2E

In the terms reversible and irreversible expansion, what does "reversible" mean? And why are all real processes reversible?

LyahFitzpatrick 2E

Do you mean K or k? To find k, you must determine the order of the reaction, then use either the zero order [A] = -kt + [A]₀ or the first order ln[A]=-kt+ln[A]₀, second order 1/[A]... and so on.

LyahFitzpatrick 2E

I think this may be more of a biological question than a chemical one, about the catalyst's abilities to manipulate different molecules. However, both rates increase because both activation energies are decreased.

LyahFitzpatrick 2E

Oh, actually, I don't have the first 3(aq).

LyahFitzpatrick 2E

Hi, I used all the same numbers/coefficients and it worked, so you must have a states/charge issue!

LyahFitzpatrick 2E

Hi! For a reaction to be spontaneous, you could focus on numerous things such as change in free energy (G) -- negative = spontaneous, enthalpy (H) -- exothermic = spontaneous, or entropy (S) -- positive = spontaneous.

LyahFitzpatrick 2E

Generally, Nitrogen has a negative oxidation number because it is highly electronegative, but when paired with Hydrogen in this format does it mean it can act as if it had a positive oxidation number?

LyahFitzpatrick 2E

Would it be positive or negative? How can we determine this? Is it based off of the notation?

LyahFitzpatrick 2E

We learned that the cathode grows larger because the material in the solution takes on the electrons and latches on to the cathode...Why don't the molecules of the cathode itself just take on the electrons?

LyahFitzpatrick 2E

Are there any situations when solving electrochemical equations in which we will not use 8.314?

LyahFitzpatrick 2E

If q = deltaH, what is the difference between heat and enthalpy? How come we keep using these variables interchangeably throughout thermodynamics?

LyahFitzpatrick 2E

How do we know which elements or molecules to single out for our half reactions? For example why Cu versus SO4?

LyahFitzpatrick 2E

Does anyone know if Professor Lavelle mentioned utilizing the pressure/volume, work integral on the midterm?

LyahFitzpatrick 2E

I noticed some Achieve problems using kJ and some using J... is there one we should mostly stick to, or will it be variable for the rest of the quarter?

LyahFitzpatrick 2E

Does this mean that under pressure these gases are deemed liquid? Also, just an additional question for thought.. there was a table in the Achieve problems that related the 'constant‑pressure molar specific heat' to R.. how was this relationship established and proven?

LyahFitzpatrick 2E

By "standard" conditions, I mean 1 atm and most standard state

LyahFitzpatrick 2E

It seems that it would be more accurate to be handling specific values and bond numbers... why is it less accurate?

LyahFitzpatrick 2E

Hello,
I think that this is simply a characteristic of entropy. Similar to asking why energy is at its minimum at equilibrium; it is simply a part of what makes entropy, entropy. Greater entropy means more likelihood for equilibrium; entropy is associated with stability.
Hope this helps!

LyahFitzpatrick 2E

Hello, yes! Multiply the C(cal) by the shift in temperature for a new q value... because -q(cal)=q(reaction), adjust your answer accordingly.

LyahFitzpatrick 2E

U is also equal to U=nCVdeltaT

CV is the constant‑volume molar specific heat of the gas, and is related to CP by CV=CP−R.

(I think you can also use the method U = q + w and solve for work)

LyahFitzpatrick 2E

Hello, Although I am not sure of the exact math, I do know that in a reversible isothermal expansion, external pressure must be reduced in step with the change in volume so that at every stage in the expansion the external pressure is equal to the pressure of the gas. This may explain the funky natu...

LyahFitzpatrick 2E

Problem: A sample of an ideal gas in a cylinder of volume 4.21 L at 298 K and 2.47 atm expands to 8.95 L by two different pathways. Path A is an isothermal, reversible expansion. Path B has two steps. In the first step, the gas is cooled at constant volume to 1.42 atm ..... I calculated the moles of...

LyahFitzpatrick 2E

I remember learning this in 14A, but does anyone have an easy method they use?

LyahFitzpatrick 2E

What is the purpose of having a reaction with elements that neutralize both acids and bases? And how come you want equal amounts of both? Is the purpose to neutralize, and if so, how come a solution like water isn't used?

LyahFitzpatrick 2E

In the example problem in Friday's lecture for finding the pH of a NH4Cl solution, NH4Cl acted as an acid (as a proton donor) so we solved for Ka by using the equation Ka*(Kb for NH3)=Kw. However, since we set up the equation with NH4 in the reactants and NH3 in the product, wouldn't we need to use ...

LyahFitzpatrick 2E

Hi! Sometimes to deal with burnout I'll switch up the location where I attend online class... for example, I'll take my notebook and laptop to the Study, an open table by Cafe 1919, or even to campus by Kerchoff/Janss. I'll also take notes in different ways sometimes (i.e. computer vs paper, using c...

LyahFitzpatrick 2E

This problem has been brought up before, but I can't seem to calculate the right answer... how should I approach this? Is the information about the weight of the solid even useful? I set up an ICE table but I don't know where to go from there. Any help is much appreciated! 11.41. A 25.0-g sample of ...

LyahFitzpatrick 2E

Hello, to calculate the overall K value you have to manipulate the equations/K-values of the components so that they match your goal reaction. In some cases, (like in the achieve homework), you then have to multiply the manipulated k-values together (which is the same thing as multiplying their frac...

LyahFitzpatrick 2E

In question 4, the reaction shifts left and the concentration of product PCl5 decreases as the concentration of reactants PCl3 and Cl2 increase. When calculating the equilibrium constant, we are instructed to still put the concentration of PCl5 in the numerator as a "product." What exactly...

LyahFitzpatrick 2E

Doesn't a small K mean that the products are favored, so more product is being made than reactants.. wouldn't the reactants have to decrease to create the favored products?

LyahFitzpatrick 2E

In my discussion section we went over an example in which the reaction had a single arrow towards the products. Should reactions with double versus single arrows be approached differently?

LyahFitzpatrick 2E

I know we are given partial pressure values in problems, but how can we measure the pressure of different gases within the same reaction? Don't the gases have to be in the same environment to react?

LyahFitzpatrick 2E

Does the value of k relate to the amount of the reactants and products or the concentration? Or do those two amounts mean the same thing because we can ignore the effect of water?

LyahFitzpatrick 2E

I know this is old material, but how does the resonance of an acid's conjugate anion relate to the acid's strength? Why do resonance structures correlate with stability?

LyahFitzpatrick 2E

Cations are looking to get rid of electrons, not attract them... how do cations weaken the O-H bond, leading to the eventual release of a hydrogen atom?

LyahFitzpatrick 2E

In class we learned that there is a band of amphoteric oxides closely matching the band of metalloids. Are all amphoteric compounds oxides? Why?

LyahFitzpatrick 2E

Should we memorize the strong bases and acids in the chempendix of the textbook?

LyahFitzpatrick 2E

I know there is a textbook section with a list of common ligands and their charge, but will we have to have any of this memorized for the final?

LyahFitzpatrick 2E

When we say a ligand is "polydentate," do we mean that one ligand molecule is binding on a cation in multiple positions, or are multiple of the same ligand molecule binding to different sites of the cation?

LyahFitzpatrick 2E

How come 4 ligands can sometimes form a square planar complex and sometimes form a tetrahedral complex? Does it have to do with lone pairs on the cation?

LyahFitzpatrick 2E

I understand that cis- coordinate covalent structures have identical ligands adjacent to each other, while trans- structures have identical ligands across from each other, but how does this affect the function or shape of the molecule, if at all?

LyahFitzpatrick 2E

In class, Professor Lavelle said that when naming anions you should drop the "ide" and add "o." How come in the naming of the first example ( [Co(NH3)5Cl]Cl]Cl . 2H20 ) the anion chlorine atom is named "chloride" (...cobalt (II) chloride dihydrate) instead of chloro?

LyahFitzpatrick 2E

I understand how cisplatin has NH3 and Cl lined up, but how does this actually inhibit cell division (and prevent DNA transcription)?

LyahFitzpatrick 2E

In class, an example included a charged cation acid NiCl2, the ligands Cl2(NH3)4, and 2H2O outside the coordination sphere. What does the H2O do in this situation?

LyahFitzpatrick 2E

Just because both electrons are contributed by a ligand in a coordinate covalent bond, does that change the behavior or structure of the molecule at all? Or does it act like a normal covalent bond?

LyahFitzpatrick 2E

I understand that a double or triple bond means the existence of pi bonds. How come these are formed with electrons in a hybridized orbital unlike the initial, hybridized orbital bond?

LyahFitzpatrick 2E

How do orbitals "combine"? We learned that orbitals do not describe position; they describe the "state" of electrons. So what does a hybridized orbital mean in terms of the state of the electron?

LyahFitzpatrick 2E

How do neighboring atom lone pairs cause bonds to weaken? By neighboring, it doesn't mean bonded, right?

LyahFitzpatrick 2E

In class, a line on one of Dr. Lavelle's slides said the above. Many covalent molecules have nonmetals, so why was this shared?

LyahFitzpatrick 2E

When are these values different?

LyahFitzpatrick 2E

Why can't p orbitals accept extra electrons when unfilled by an atom's standard electrons?

LyahFitzpatrick 2E

When solving for the electric dipole moment in debyes, where does the "charge" come from? It's a covalent molecule, so I'm wondering what exactly the charge refers to. Formal charge, as in number of electrons gained/lost?

LyahFitzpatrick 2E

I know we learned about positive and negative electronegativity in class, but is the dipole moment of a molecule gradual?

LyahFitzpatrick 2E

It seems like atoms can bond by use of added or subtracted electrons.. can any molecule technically be created in this way or are there exceptions?

LyahFitzpatrick 2E

It seems as if a molecule had a double bond rather than a single bond, the shift in electron positioning would affect the bind angles. However, Prof. Lavelle said that no matter the bond quantity the shape stays the same. Why is this?

LyahFitzpatrick 2E

It seems as if these two quantities function similarly.

LyahFitzpatrick 2E

Hi! Because water is a polar molecule, it has a strong dipole effect. In other words, there is a slight offset in charge; one end is more positively charged, while the other is more negatively charged. Consequently, water can dissolve molecules by separating positive ions (that are attracted to the ...

LyahFitzpatrick 2E

How can I look at a structure/formula and determine whether it's a Lewis acid/base? Is there something special about the molecule?

LyahFitzpatrick 2E

What is the actual meaning of "bond length?" Is it center to center of atoms? I'm wondering how this is measured too...

LyahFitzpatrick 2E

For anyone who did well on the conceptual questions of Midterm 1... what sort of studying did you find helpful? Did you read the textbook? I did all the homework problems so the calculations were understandable, but the conceptual questions seemed more obscure.

LyahFitzpatrick 2E

I realize that once an atom obtains five electrons, they are able to occupy space in each s and p orbital with at least one electron. However, how does this then enable the d orbital to be used? Shouldn't the p orbital fill first? Is this just a phenomenon that happens to make covalent bonds work out?

LyahFitzpatrick 2E

Are there elements in the periodic table (other than the d5 d10 situation) that don't follow the electron configuration setup by row and period? Maybe these lie in the f group we have not talked about much?

LyahFitzpatrick 2E

If the wave function is a list of four values, then how do you square the wave function to get probabilty density? Do you square each value in the list?

LyahFitzpatrick 2E

How come p orbitals have more energy than s orbitals in the same shell? Why is there a hierarchy within the same shell?

LyahFitzpatrick 2E

If electrons dropping energy levels produces a spectrometer, doesn't that mean that a steady stream of electrons would have to be dropping levels for a steady line to show up in a spectroscopy? Do the electrons constantly jump levels as well to continue the cycle of emitting photons? How does this w...

LyahFitzpatrick 2E

I think the labeling of n1 and n2 doesn’t have to do with the beginning versus end in this case— it just fits with the formula v=R(1/n1^2 - 1/n2^2), where the first term in the parentheses has to have a lesser n value in order for frequency (v) to output positive. (1/a lesser value > 1/a greater val...

LyahFitzpatrick 2E

How do I approach a molarity/solution problem when the solute is specified as “molecule•#H2O”? (there was an instance in the Week 1 textbook problems)

LyahFitzpatrick 2E

In class, professor Lavelle would write some configurations with the s orbital represented before the d one. Is there a reason for this? Does it matter?

LyahFitzpatrick 2E

What does spin refer to? Do electrons really spin in certain directions? Does it have to do with magnetism?

LyahFitzpatrick 2E

Also, how do we know what series a spectroscopic line belongs to?

LyahFitzpatrick 2E

Why does the balmer series consist of a spectrum with n1=2 while the lyman series has n1=1?

LyahFitzpatrick 2E

If spectral lines are created by electrons dropping energy levels, then how come the spectroscopic possibilities for all elements with the same number of energy levels aren’t the same?

LyahFitzpatrick 2E

I know that Dr. Lavelle made it clear that the orbitals represent “state” not position, but what does it mean for an electron to be in the state represented by say the center of a lobe versus the edge?

LyahFitzpatrick 2E

Just curious, does anyone know how Planck’s constant was derived? How do we know that there is this variable that properly converts frequency to a value that proportionally represents Joules of Energy?

LyahFitzpatrick 2E

I was sick and had to miss discussion section this week… what topics should I focus on to make up for this week’s example problems/discussion topics?

LyahFitzpatrick 2E

Can any of the homework week 2 questions be solved using enthalpy equations of any sort? Or can we only use the photoelectric equations. Just curious if there are multiple methods.

LyahFitzpatrick 2E

I keep seeing the word “unusual” and “unexpected” when describing how greater intensity does not make any difference in freeing electrons from a metal plate when frequency is not low enough… wouldn’t this be expected, as intensity is simply more of the photons shot at the plate, not a different kind...

LyahFitzpatrick 2E

What exactly is the intensity of light? Is it the amount of photons hitting the surface? Or is it the amount of energy the photon holds?

LyahFitzpatrick 2E

Does the Φ (energy required to remove the electron) mean the same thing as the "threshold energy?" What exactly does "threshold energy" mean?

LyahFitzpatrick 2E

Does anyone know if the homework questions for the next few weeks are evenly split 10, 10, and 10? Trying to schedule it out now.

LyahFitzpatrick 2E

Angela Harrington 2L wrote:I'm not 100% sure, but I don't think so. I would still do 5 posts/replies this week just to be safe and make sure you get full points for the week.

Is it 5 posts and 5 replies or either/or?

LyahFitzpatrick 2E

In the compound, CuSO_{4}\cdot 5H_{2}O The above formula simply says that for every 1CuSO 4 molecule, there are 5 water molecules associated with it. The dot does not represent multiplication like it does in math or physics. Hope that was helpful! Yes it was! Thank you... doesn't that ratio determi...

LyahFitzpatrick 2E

What is the variable/unit t in problem L.35? The phrase is "d to produce 2.50 t of...".

LyahFitzpatrick 2E

Does anyone know what it means when two molecules are "multiplied" with the small dot in between?

LyahFitzpatrick 2E

You may want to read the problem carefully and see how "volume" is used throughout... when they say "taking volume out" they might be referring to volume of solvent, in which case it would concentrate the solution (I think you got that). But if it says taking volume from the solu...

LyahFitzpatrick 2E

Problem G5 is this: A student prepared a solution of sodium carbonate by adding 2.111 g of the solid to a 250.0-mL volumetric flask and adding water to the mark. Some of this solution was transferred to a buret. What volume of solution should the student transfer into a flask to obtain (a) 2.15 mmol...

LyahFitzpatrick 2E

Hello,
So I just completed the Achieve/MacMillan homework and received 10/10, but checked the CCLE grade section and saw I was scored 4.5/5. Does someone know why this happened? I solved all the problems correctly first try... Please let me know!
Thanks

LyahFitzpatrick 2E

Hello, In order to find the amount of Oxygen from the caproic acid, you should first find the amount of grams of Carbon and Hydrogen. After, you can subtract the amount of grams of carbon and hydrogen from 1.00 gram because that is the weight of the sample given. The remainder must be the amount of...

LyahFitzpatrick 2E

The way I went about doing this one was that I tried to find the masses of C, H, and O in each of the products. You are right that combustion means that oxygen gas is the second reactant, and it is for this reason that we have to look at just the amounts of C and H for the time being. Once you have...

LyahFitzpatrick 2E

I'm still trying to figure out this site and how it works, but it seems Dr. Lavelle is usually quite active. Is it important to see his posts in Chemistry Community or will I be okay just receiving his emails and listening to in class announcements?

LyahFitzpatrick 2E

Hello, I'm not sure if you'll see this but I'm a current freshman following the pre-med track as an undeclared life sciences major. The pre-med track sounds difficult and daunting, but what are your thoughts on how rewarding it is? Do you think it is only meant for the right person? Also, is there m...

LyahFitzpatrick 2E

So here's the problem... Caproic acid has the odor of goats. (In fact, Capra is the genus of the domestic goat.) The compound contains only C, H, and O and was experimentally found to have a molar mass of 110±10 g/mol . When a 1.000 g sample of caproic acid is burned in excess oxygen, 2.275 g CO2 an...

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