CHEMISTRY COMMUNITY

JohnWalkiewicz2J

For part D, start off with the nernst equation : E=Eo-(RT/nF) *lnQ, and since you have every value other than K, rearrange the equation to solve for K. Since K = ([Ce3+]^2 * [Fe2+]) / ([Ce4+]^2), and you have the concentrations of Ce3+ and Ce4+, you can solve for the missing concentration [Fe2+]. Ho...

JohnWalkiewicz2J

I mean, I don't see a scenario where it couldn't be possible. . but yeah just know that these type of reactions are typically found when a material that is required for a reaction to proceed-surface/catalyst-is saturated by the reactants. Hope this helps! :D

JohnWalkiewicz2J

Yes when the cell potential is 0, and given the deltaG = -nFE, gibbs free energy would also be zero, and the battery is dead! :D

JohnWalkiewicz2J

When solving ICE tables or a equilibrium concentration for a R/P, for what value of Q/K do you approximate x, so you don't have to use the quadratic formula. Thnx in advance!

JohnWalkiewicz2J

Typically, the problem will tell you if it is aslow or fast step, at least the problems in the textbook do : )

JohnWalkiewicz2J

We use ln[A] on the y-axis in order to get a linear graph. If you graph [A] vs t, you get a exponential decay. We use ln[A] to calculate the rate constant, -k, which is the slope on the line.

JohnWalkiewicz2J

If Dr.Lavelle didn't mention/ go over it during lecture, I doubt it'll be on the final : )

JohnWalkiewicz2J

I'm pretty sure Lavelle chooses what problems go on all midterms/finals, but I wouldn't be suprised if the TAs had some input as well.

JohnWalkiewicz2J

I don't think we'll need to, I would just focus on how you derive the differential and integrated rate laws.

JohnWalkiewicz2J

For this problem, I would suggest to start with finding what order C is in. If you compare experiements 1 & 4, you see that when C doubles and A/B stay the same, the rate is the same. So, knowing that C is in 0 order, you know that changes in concentration wont affect the rate. You can find orde...

JohnWalkiewicz2J

Yes, on one side(anode/cathode reaction) if 2 species are in the same phase then you separate them using a comma even if one is a reactant and one is a product. You use a singular line to separate two species that are in different phases ((s) | (aq)). Hope this helps! :)

JohnWalkiewicz2J

Typically, you would arrange the Nernst equation in order to solve for Q, the reaction quotient, and then if the problem gives you the concentrations of other species, you set Q = [P]/[R], and solve for the concentration of [H+] ions. Then to find pH you take -log[H+].

JohnWalkiewicz2J

Typically you include a Pt electrode in the diagram if there is no solid present for either the anode reaction or the cathode reaction. So if there is a solid present on one side (Cu (s)) yet only aqueous solutions on the other (Fe2+(aq)), then you would use a Pt electrode on the side that lacks a s...

JohnWalkiewicz2J

delta G = change in gibbs free energy (energy to do work)
n = (# of moles of electrons transferred)
F = (Faraday's Constant , usually 96,485)
E = (cell potential)
Hope this helps! : )

JohnWalkiewicz2J

I'm pretty sure its 5 per week and I think the deadline is Sunday night !

JohnWalkiewicz2J

How do you write the notation for galvanic cell in which there is no solid oxidizing/reducing agent present:
Ex: H2(g) + Cl2(g) ---> 2HCl(aq). Thnx in advance!

JohnWalkiewicz2J

Typically, a battery consists of multiple Galvanic cells, but yeah they're pretty much the same thing as they both consist of 2 half cells-1 reduction half cell and 1 oxidation half cell.

JohnWalkiewicz2J

What's the main difference between balancing redox rxns that occur in acidic solution and balancing redox rxns that occur in basic solutions?

JohnWalkiewicz2J

Additionally, I'd say that it might help to know that anions flow to the anode to balance the charge and cations flow to the cathode to balance the charge as well. :D

JohnWalkiewicz2J

Yeah, when balancing redox reactions the problem will usually mention if it takes place in an acidic or basic solution.

JohnWalkiewicz2J

Lets say you have a simple reaction 5Fe+2 ---> 5Fe+3
In this case, each iron has lost an electron, so to find the total # of electrons lost you multiply electrons lost per molecule by the stoichiometric coefficient. 1x5 = 5 electrons lost.

JohnWalkiewicz2J

Yeah remember that temperature changes also affect changes in equilibrium (K) which is why there is a seperate T1/K1 and T2/K2.

JohnWalkiewicz2J

So when you have one species as a reactant in the first half-reaction and you have the same species as a product in the second half-reaction, you can cross out/cancel both when you add both reactions to make your overall reaction.

JohnWalkiewicz2J

Yeah I think it ok to turn in homework problems from any of the topics that we had to cover for the midterm.

JohnWalkiewicz2J

Yea I think Lavelle said on Monday that if there is a problem like that, the question will give you the Cv or Cp.

JohnWalkiewicz2J

Haha I think it was something like "When you are under Pressure and Depressed, watch TV and get HUGS

Pressure, Density, Temperature, Volume, Enthalpy, Internal Energy, Gibbs Free Energy, and Entropy in that order.

Hope that helps : )

JohnWalkiewicz2J

Yeah pretty much, since ΔG= ΔH - TΔS and all those components are state functions, you could assume ΔG is also a state function.

JohnWalkiewicz2J

If a reaction is exothermic than ΔH will be negative. If ΔH is negative and the exothermic reaction leads to a increase in entropy of the system(+ΔS) than ΔG will be negative and the reaction will occur spontaneously.

JohnWalkiewicz2J

Yeah i'd suggest drawing the lewis structures for both reactants and products and designated which bonds are broken and which are formed. Then: ΔH(formed) - ΔH(broken).

JohnWalkiewicz2J

Yeah the equation sheet you see on the website will be the one given to us on the midterm.

JohnWalkiewicz2J

You can think of a thermos as an isolated system as well! It can't exchange matter with its surroundings, and given its insulation, it can't exchange energy(heat) either!

JohnWalkiewicz2J

In terms of enthalpy, ΔH = q only when pressure is constant.

JohnWalkiewicz2J

U stands for all energy consisting in my closed system, and is the sum of all heat in or released by a system (H) and all work done or done by a system (w).

JohnWalkiewicz2J

Norman Dis4C wrote:but why is the answer not 490J but 9000J?

The answer is 4.90 x 10^2 J , which could also me written as "490 J" as the sig figs are the same. Im sure it was just a small miscalculation on his part.

JohnWalkiewicz2J

Do we need to know the integral and derivative for the midterm? Im not 100% sure considering we haven't gone over a problem using integrals in class, but I think you should definitely try and study it. If you need help Dr.Lavelle has a page on his website titled "Common Antiderivatives" w...

JohnWalkiewicz2J

Assuming that moles (n) is constant, if you increase the pressure, volume will decrease, and whatever side has more moles of reactants/products, the reaction will shift to the opposite.

JohnWalkiewicz2J

Yeah it usually relies on the problem and if it gives you the calculations in concentration (mol.L) or pressure (bar, atm, etc..) You can calculate both Kp and Kc of water in its gaseous form.

JohnWalkiewicz2J

Yeah it usually relies on the problem and if it gives you the calculations in concentration (mol.L) or pressure (bar, atm, etc..) You can calculate both Kp and Kc of water in its gaseous form.

JohnWalkiewicz2J

Are we able to turn in homework problems from the first two topics considering that's whats going to be on the test this week?

JohnWalkiewicz2J

Yeah I would say go over the homework examples, the examples we did in class, and perhaps take a peak at the online modules on Dr.Lavelle's website. You should be good!

JohnWalkiewicz2J

Should we know how to use ice tables for when the reverse reaction occurs in certain reactions? In what conditions can we tell that the reaction will shift left instead of right?

JohnWalkiewicz2J

No I don't think we need to know about reaction rates for the upcoming test at least.

JohnWalkiewicz2J

Uhh depending on the question being given, you should always assume that they will reach equilibrium yeah.

JohnWalkiewicz2J

One way that you can help figure out if the reaction is proceeding forwards (-x from reactants) or backwards (-x from products) is to look at the the Keq (equilibrium constant) if it provides it in the question. If the Keq is < (1.0 x 10^3), then the reaction will proceed forward(-x from reactants, ...

JohnWalkiewicz2J

In terms of identifying strong acids/bases, I would honestly just memorize them as there are around 7 each, and just know that they dissociate completely in water.

JohnWalkiewicz2J

How do you go about solving for an equilibrium concentration for a product when only given the initial values of the reactants and the value of K?
Ex: Br2 + Cl2 = 2BrCl
Inital concentrations for reactants: 0.200 M
Kc = 7.20 @ 200 C

JohnWalkiewicz2J

Typically you would use Kp when dealing with reactants and products that are both in the gas state(g).
You would using Kc when dealing with reactants and products that are both in an aqueous(aq) state.

Hope this helps! : )

JohnWalkiewicz2J

Typically if Q<K, then the reaction will proceed from left to right (reactants→products)
If Q>K, then the reaction will proceed from right to left (reactants←products)

JohnWalkiewicz2J

Yeah id say just use the exact values the problem give you when calculating Kc and then apply sig figs to your final answer.

JohnWalkiewicz2J

Considering you omit solids and liquids when calculating the equilibrium constant, I would say yes, leave out solids and liquids when calculating the reaction quotient.

JohnWalkiewicz2J

Can someone explain how cisplatin's structure contributes to its function in forming a coordination compound with DNA and stopping cell division? Thnx in advance.

JohnWalkiewicz2J

You should probably convert your answer to nm if you get something like 2.13*10^(-7)m , but, as long as you keep track of your sig figs I don't think you'll get marked down for it.

JohnWalkiewicz2J

A lewis acid accepts an electron pair while a lewis base donates an electron pair.
A Brønsted acid donates a proton(H+) while a Brønsted base accepts a proton (H+).

JohnWalkiewicz2J

There is a table in focus 9C in the textbook that I found pretty helpful when naming coordination compounds, try and practice with some of the problems in 9C as well.

JohnWalkiewicz2J

For coordination compounds I think you should mainly focus on the naming aspect, but I don't think it would hurt to become familiar with the function of some of the compounds like cisplatin.

JohnWalkiewicz2J

Typically for oxidation numbers you can look at trends on the periodic table.
For instance elements group 1 is most likely to lose one electron, so it has a oxidation number of +1.
Elements Group 2 most likely loses 2 electrons, so its +2, etc. . .

JohnWalkiewicz2J

Did prof Lavelle go over Arrhenius acids and bases in lecture? If not will we be expected to know them for the final?

JohnWalkiewicz2J

Can someone explain the difference between a Bronsted acid and a Lewis acid?

JohnWalkiewicz2J

I'm pretty sure Monday-Wednesday we will finish up Acids & Bases and Friday will be a review session.

JohnWalkiewicz2J

How do you calculate the pH when a problem gives you the concentration of a base?

JohnWalkiewicz2J

Typically, you take the negative log of the H+ ion concentration: pH = -log([H+])
Ex: Calculate the pH of 0.040 M HCL
- [H+] = 0.040
- -log([0.040])
- = 1.4

JohnWalkiewicz2J

Does anyone know if we can turn in homework problems from focus 9C during week 9? Thnx in advance!

JohnWalkiewicz2J

I'm pretty sure Dr. Lavelle will offer review sessions before our final, but I'd make sure to ask your TA just in case.

JohnWalkiewicz2J

I'm assuming you're talking about naming coordination compounds? If so, when naming the ligands you usually name them in alphabetical order:
Ex: [Cr(Cl)2(NH3)4]+
Ligands: Chlorine, Ammonia
Naming: tetraammine-dichloridochromium(III) ion

JohnWalkiewicz2J

Lavelle gave us an introduction to coordination compounds, ligands, and their biological importance. Its focus 9C in the textbook if you want to catch up!

JohnWalkiewicz2J

I believe dipole-induced dipole forces are between a polar and nonpolar molecule, while induced dipole-induced dipole can occur between 2 polar or 2 nonpolar molecules, which is the same thing as London forces.

JohnWalkiewicz2J

For the test, are we expected to figure out the molecular geometry of molecules with more than one central atom?

JohnWalkiewicz2J

Can someone explain to me why lone pairs around the central atom have more repulsion than bonded pairs? Thnx! : )

JohnWalkiewicz2J

For the AX2E1 BA, if you look at a trigonal planar (AX3), you see the bond angles are 120. Now imagine substituting one of the bonding atoms with a lone pair (E), considering lone pairs have greater repulsion than bonded pairs, they would repel the two bonding pairs farther away, which would mean th...

JohnWalkiewicz2J

The lewis structure for CH2CL2 would be draw with the Cl atoms grouped together and the H atoms grouped together. I see what you mean, but considering the bonding atoms are different, I don't think they would be placed opposite of each other (i.e. one Cl on top and one Cl on the bottom) and their di...

JohnWalkiewicz2J

I think it'll cover the topics that we go over in lecture after the midterm up until the test. I don't think any topics that we went over before the midterm will be on it.

JohnWalkiewicz2J

Yes, Ion-Ion interactions are also referred to as Ionic Bonds.

JohnWalkiewicz2J

Can someone explain the difference between Dipole-Induced Dipole interactions and Induced Dipole-Induced Dipole interactions and perhaps provide an example? Thanks!

JohnWalkiewicz2J

Yes, typically a molecule will have dipole moments if the electronegativity diffence between the two atoms are between 0.4-1.7. The arrows illustrate the direction in which the dipole moments occur. For instance, in a H-O bond, the arrow will be pointing towards the oxygen atom as it is more electro...

JohnWalkiewicz2J

One factor is the Polarizability of electrons in certain compounds, which is when eletrons in an atom or molecule cause e- distortion in a nearby atom or molecule. As the molar mass of a molecule increases, the strength of dispersion also increases, which is why molecules like I2 are solid at room t...

JohnWalkiewicz2J

To answer your first question, no we don't need to know electron configurations for elements that contain f orbitals. I believe we only need to know electron configurations for elements within the first 4 periods.

JohnWalkiewicz2J

Considering Dr.Lavelle did not cover it in any of the lectures so far, I'd say its highly unlikely questions concerning lattice energy will be on the midterm.

JohnWalkiewicz2J

For the midterm, are we going to need to know how to write electron configurations for elements that contain electrons in f-orbitals?

JohnWalkiewicz2J

Are equations like Rydberg's, De Broglie's, and Heisenberg's going to be given on the exam?

JohnWalkiewicz2J

Do we have to memorize what color each wavelength corresponds to? For instance: 468 nm = blue line.

JohnWalkiewicz2J

Are there any significant exceptions in atomic trends that would be important to memorize for the midterm?

JohnWalkiewicz2J

Yes, considering both increase across a period, and decrease down a group, it is considered a positive correlation.

JohnWalkiewicz2J

Hello, can someone explain to me why some atoms can have expanded octets while others cannot? Thank you!

JohnWalkiewicz2J

At n=2, l can equal 0 or 1, since there is an s and p subshell in that energy level.
2s = 1 orbital
2p = 3 orbitals.
If you add them up, you get a total of 4 orbitals for n=2.

JohnWalkiewicz2J

Resonance occurs when some lewis structures have multiple bonds in different equivalent locations. For instance, for the lewis structure for a Nitrate ion (NO3)- , the double bond can alternate between the nitrogen and the three oxygen atoms. Typically when you draw resonate structures, that compoun...

JohnWalkiewicz2J

One way you could calculate the number of valence electrons: 1. Use a periodic table to find atomic number, which is the # of electrons the element has. 2. Write out the electronic configuration. 3. Count how many electrons are in the last shell. Ex: 1. Chlorine - 17 electrons. 2. Electronic configu...

JohnWalkiewicz2J

When writing electron configurations for atoms in orbital notation, is there a particular way we should write it? I mean, should we write it having shells increase from top-bottom? or from bottom-top? or perhaps linearly? Thanks in advance!

JohnWalkiewicz2J

Hello! First you would have to associate l with the type of subshell, and then figure out how many orbitals are in each subshell:
l=0 - s-subshell - 1 orbital
l=1 - p-subshell - 3 orbitals
l=2 - d-subshell - 5 orbitals
l=3 - f-subshell - 7 orbitals

JohnWalkiewicz2J

Hey!
I would definitely recommend reading the appropriate chapters in the textbook and the problems that go along with them.
In terms of schedule, I usually do the concepts after Dr.Lavelle goes over them in lecture, so that I have a basic understanding of what I am reading.
Hope this helps!

JohnWalkiewicz2J

My bad. Yes I do!

JohnWalkiewicz2J

On problem 1B.27, it gives the indeterminacy of velocity (Δv) as "5.00 ± 5.0 m.s^-1." Why is the indeterminacy of velocity 5 m.s^-1, and not 10 m.s^-1, since it is ± 5.0?

JohnWalkiewicz2J

Typically Planck's constant is given in joule-seconds: 6.626 x 10^-34 J.S.
However, it can also be given as: 6.636 * 10^-34 kg*m^2*s^-1.
Hope this helps!

JohnWalkiewicz2J

Hey! So even though Prof Lavelle taught us the formula: (Δp)(Δx) ≥ (h/4π), I found it easier to use the one given in the textbook: (Δp)(Δx) ≥ (1/2)(ћ), when ћ=(h/2π). For some of the textbook problems, using the formula that Prof Lavelle taught in class resulted in the wrong answer, but that was a p...

JohnWalkiewicz2J

Yes, actual yield should always be given in the problem when calculating the percent yield. The only instance I can think of when you'd have to calculate the actual yield is if both theoretical yield and percent yield are presented in the problem. Hope this helps!

JohnWalkiewicz2J

Some problems in the textbook give the names of the compounds but not the molecular formulas, for instance: "..a vigorous reaction takes place, and elemental molten barium and solid aluminum oxide are formed." Are we expected to know the formulas for compounds like aluminum oxide? or just ...

JohnWalkiewicz2J

The question goes as follows: Calculate the amount of urea molecules, OC(NH2)2 , in 2.3 x 10^5 g of urea. The answer it gives is 3.8 x 10^3 moles, which is correct but I thought the question was asking for the amount of individual molecules of OC(NH2)2. Which should be (3.8 x 10^3) x (6.0221 x 10^23...

JohnWalkiewicz2J

Hey!
Visually, the intensity of the light corresponds to its brightness. If we look at it from a quantum prospective, the intensity of light corresponds to the number of photons. Increasing the intensity increases the number of photons in the light.

JohnWalkiewicz2J

Hey! From my understanding, light below a certain frequency threshold will not cause electrons to be emitted. Light above the certain threshold frequency will always cause electrons to be emitted, and increasing the intensity of this light will cause more electrons to be admitted. If by "high f...

JohnWalkiewicz2J

Hey! If you go to Dr. Lavelle's website for Chem14A, there is a link titled "Everything you want to know about Sig Fig" that I found really helpful! Additionally there is a small section on Sig Figs in your textbook that you can review! Hope this helps! ;)

JohnWalkiewicz2J

During last lecture, Dr. Lavelle was going over Limiting Reactants and I was wondering if it was possible to have no limiting reactants in a chemical reaction. For instance, if you were unable to find a reactant in excess.

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