CHEMISTRY COMMUNITY

Edward Xie 2E

From his website, here is the list of courses that Dr. Lavelle teaches: Chem-10A (General Chemistry for Life Science Majors) Chem-14A (Atomic and Molecular Structure, Equilibria, Acids and Bases) Chem-14B (Thermodynamics, Electrochemistry, Kinetics, and Organic Chemistry) Chem-19 (Fiat Lux Seminar: ...

Edward Xie 2E

According to Dr. Lavelle's website, you can pick it up at "3034 Young Hall, Week 3, Spring quarter"

Edward Xie 2E

I believe Dr. Lavelle curves the final class grade based on how all of the classes did. He did this in 14A, otherwise I would've ended up with a lower grade than I actually did.

Edward Xie 2E

15.19 The following data were obtained for the reaction A + B + C -> products: Initial concentration (mmol*L -1 ) Experiment [A] 0 [B] 0 [C] 0 Initial rate((mmol A)*L -1 *s -1 1 1.25 1.25 1.25 8.7 2 2.5 1.25 1.25 17.4 3 1.25 3.02 1.25 50.8 4 1.25 3.02 3.75 457 5 3.01 1.00 1.15 ? For problem 15.19 pa...

Edward Xie 2E

You would rank them in order of increasing standard reduction potential. So a more positive reduction potential = higher oxidizing power.

Mg²⁺ < Ti²⁺ < Sn²⁺
E^o (respectively) = -2.36 V < -1.63 V < -0.14 V

Edward Xie 2E

Alhough Dr. Lavelle hasn't posted the topics that will be covered on the final, I'm assuming that all of the topics on the Kinetics outline will be present on the final.

Edward Xie 2E

For increasing reducing power, you would list them in order of decreasing reduction potential.

Pt (E^o = 1.20 V) < Cu (E^o = 0.34 V) < Pb (E^o = -0.13 V)

Edward Xie 2E

Use the balanced half-equations to determine how many moles of e- are transferred (n).

Edward Xie 2E

Use the equation [A] = [A_o]e^-kt, which is derived from ln[A]=-kt+ln[A_o]

Edward Xie 2E

You use the differential rate law where rate = k[R]ⁿ. Solving for n would give you the order of the reaction.

In cases where rate = k[R₁]ⁿ[R₂]^m, the overall order of the reaction would be n + m.

Edward Xie 2E

If T is negative, that means it goes below 0 K, which is impossible as you cannot go below absolute zero. So yes, temperature (at least in Kelvins) will always be positive.

Edward Xie 2E

ΔG°_RXN = ΔH°_RXN - TΔS°_RXN
G is Gibb's free energy, H is enthalpy, S is entropy. Enthalpy and work are related through the equation ΔU = q_P + w = ΔH - PΔV.
It's significant in that a negative ΔG means that the reaction is spontaneous, and the sign of ΔG will depend on the values of ΔH and TΔS.

Edward Xie 2E

E°_CELL = E°(Cathode) - E°(Anode)

Edward Xie 2E

does anyone know when Test 3 is???

Test 2 will be in your discussion section and starts Tuesday of Week 8.

Edward Xie 2E

According to Dr. Lavelle's website, Test 3 will cover "Gibbs free energy and electrochemistry up to but not including the Nernst equation"

Edward Xie 2E

A reversible reaction could be something like N₂O₄ ↔ 2NO₂, while an irreversible reaction could be a combustion reaction.

Edward Xie 2E

Just use the equation ∆S = n*C*ln(T2/T1) where C is Cp or Cv depending on if it's constant pressure or constant volume. Cp = (5/2)R and Cv = (3/2)R.

Edward Xie 2E

All the constants should be given to us.

Edward Xie 2E

What are you referring to when you say 0.38 J?

Edward Xie 2E

Since his outline for Thermodynamics lists chapters 9, 11.3, 11.11 - 11.13, I would assume that all of chapter 9 is fair game for the midterm.

Edward Xie 2E

Positive delta U means an increase in the internal energy of the system, while negative delta U is a decrease in the internal energy.

Edward Xie 2E

No, an isolated system allows neither energy or matter transfer, but a closed system allows only energy transfer.

Edward Xie 2E

Using bond enthalpies is the least preferable method because it is the least accurate.

Edward Xie 2E

I think it's talking about how CO2 can cause respiratory acidosis, which can cause death from blood pH becoming too low/acidic.

Edward Xie 2E

A good example of an irreversible reaction is combustion.

Edward Xie 2E

Keep in mind that you can only use the approximation method/shortcut if K < 10^-3.

Edward Xie 2E

And which edition?

Edward Xie 2E

Inert gas is another term for noble gas. Since the noble gases often do not react with many substances, they were referred to as "inert" gases. The noble gases include helium, neon, argon, krypton, xenon, and radon (group 18 of the periodic table).

Edward Xie 2E

Since Test 1 covers Equilibrium and Acid & Base Equilibria, I would guess we would need to know the concepts on their respective outlines (1: Chemical Equilibrium & 2: Acids and Bases).

Edward Xie 2E

Molar concentration of a pure substance (solid or liquid) does not change in a reaction, so solids and liquids are not included in the K expression

Edward Xie 2E

Then, if you were to remove some reactant would the reaction shift left? Towards the reactants to compensate for the loss?

Yep, since Q > K the reaction will shift towards the reactants.

Edward Xie 2E

As Dr. Lavelle said,

Molar concentration of a pure substance (solid or liquid) does not change in a reaction
∴ solids and liquids are not included in K expression

Edward Xie 2E

If it is ethylenediaminetetraacetato, it is (edta).

Edward Xie 2E

I think strength of bond also factors in for bases. If the OH has a weaker bond to the metal, then it is a stronger base since the OH can more easily separate/dissociate.

Edward Xie 2E

Knowing about myoglobin/hemoglobin and the heme complex is probably a good idea as it was also on the Churro practice exam.

Edward Xie 2E

But how would you know which ones lose a proton and which ones gain a proton? See which chemical gains/loses an H + . For example: HCl(aq) + NH 3 (aq) → Cl − (aq) + NH 4 + (aq) HCl would be the acid because it donates a proton to NH 3 and becomes Cl - . NH 3 would be the base because it accepts the...

Edward Xie 2E

A Bronsted acid is a proton donor, and a Bronsted base is a proton acceptor. In this case, NH 3 is a base, HBr is an acid, KOH is a base, H 2 SO 3 is an acid, and Ca(OH) 2 is a base. One tip I generally use is I look at the chemical equation and see which substance loses a proton and which one gains...

Edward Xie 2E

It's a net ionic equation: in solution, NaC₆H₅O dissociates to C₆H₅O^- and Na⁺. Na⁺ is neither an acid or base, so it doesn't reaction with water. And since it's a net ionic equation, anything that appears on both sides (in this case, Na⁺) is taken out of the equation.

Edward Xie 2E

I'm not sure, but I think we're probably expected to know the strong acids.

Edward Xie 2E

Yes, since electrons repel each other.

Edward Xie 2E

Polarizability is the tendency of the anion to be polarized by the cation. Polarizing power is the ability of a cation to attract valence shell electrons from an anion. Polarization is when two oppositely charged ions approach each other and the cation attracts electrons in the outermost shell of th...

Edward Xie 2E

The smaller cation has a more positive charge, so it would pull electrons more strongly.

Edward Xie 2E

I believe they are the same thing.

Edward Xie 2E

Does anyone know of any resources similar to the audio visuals for the other topics this quarter? Do people find Khan academy helpful, or crash course videos?

I think those are helpful for explaining general concepts, but maybe not as good for detailed things.

Edward Xie 2E

Yes. The terms are interchangeable.

Edward Xie 2E

Professor Lavelle hasn't posted the topics yet, but I'm guessing chemical bonds and molecular shape and structure.

Edward Xie 2E

From the syllabus: "Each test and exam has a total score but is not assigned a grade. Only at the end of the class when the class average score (out of 500 points) is known are final grades assigned. This class does not use a curve. Group learning (Chemistry Community, Study Groups, Peer Learni...

Edward Xie 2E

Thank you, Joyce!

Edward Xie 2E

For question 13A, can someone please explain why the answer is 2.681x10^-26? I got the 2.681, but for some reason I got x10^-23.

Did you remember to convert the mass into kg?

Edward Xie 2E

I don't understand why in order of increasing ionization energy, it goes C O N F. I thought it would be C N O F. Anyone know why?

Nitrogen is an exception (so is phosphorus) to the trend in that it has a half-filled subshell, 2p^3, which makes it harder for an electron to be removed.

Edward Xie 2E

What determines the energy of a Lewis structure? Formal charges of all the atoms added together?

Edward Xie 2E

To calculate the number of degenerate orbitals, you can use 2l + 1.

Edward Xie 2E

Wavelength, or lambda, is measured in meters, not meters per second.

Edward Xie 2E

You probably had a rounding error. The method I used was multiplying the molar mass by each percentage to figure out how many grams of C/H/O were present in glycogen, then I divided those masses by their respective element's molar mass to find the molecular formula.

Edward Xie 2E

What are degenerate orbitals, and could I have a few examples? This was on test #2, and I was confused as I don't remember it being mentioned in lecture (to the best of my knowledge).

Edward Xie 2E

The one that Dr. Lavelle talked about can be found on his website: https://lavelle.chem.ucla.edu/wp-conten ... PL_ALL.pdf

Edward Xie 2E

The number of dots is the number of valence electrons the element has. Since most elements obey the octet rule, they would want 8 electrons (whether they're in the form of bonds or lone pairs)

Edward Xie 2E

Since it takes work to pull an electron away from an atom (as electrons are negative and protons are positive), higher orbitals will have higher energy.

Edward Xie 2E

The values of constants are given for quizzes/tests

Edward Xie 2E

You use Heisenberg's Indeterminacy Equation: \Delta p \Delta x\geq \frac{h}{4\pi} The question gives the uncertainty in position (delta x) by stating the diameter of the lead atom, 350 pm. To keep it in SI units, it becomes 3.50 x 10^-10 m. To find the only unknown, delta p (uncertainty in momentum)...

Edward Xie 2E

No. According to the law of conservation of mass, in a chemical reaction, the total mass of products must be the same as the total mass of the reactants.

Edward Xie 2E

Since the question gives the actual yield of 17.5g of CO2, the theoretical (maximum) yield would have to be found in order to calculate the percentage yield. Using stoichiometry, the given mass of CaCO3 is converterd into moles, which is then used to find how many moles of CO2 are produced from the ...

Edward Xie 2E

I normally go by the amount of sig figs of the given numbers. For me, the sig figs given by the problem will generally be fewer than the ones in the molar mass since I go up to thousandths place for it.

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