CHEMISTRY COMMUNITY

Vivian Nguyen

Hi Kellina, I went to Lyndon's review session today, and he said that the only type of reaction we covered in lecture was an SN2 reaction (bimolecular nucleophile substitution), so that might be on the final. The rest was just identifying the functional groups in molecules (ether, alcohol, carboxyli...

Vivian Nguyen

Who knows if it'll be on the final, but considering the final is cumulative, and the chapter outline says "Know the definition of the electromotive force (emf, ℰ) and why it represents the maximum potential difference," I don't think it'd hurt to briefly go over it.

Vivian Nguyen

Hello, I'm having trouble on HW 15.85, which asks us to draw a proposed structure for the activated complex. Could anyone explain what the proposed structure is and how to figure it out? Example: "Rate= k[I]2[Ar] (Products are I2 and Ar; the role of the Ar is to remove energy as the product for...

Vivian Nguyen

The right side would be the anode and then left of the salt bridge would be the cathode. Then within those sections, the reactant is written first then the product.

Vivian Nguyen

I think so. I think Dr.Lavelle said that coming up with the actual steps in the mechanisms is really complicated/advanced, so we would be given it.

Vivian Nguyen

Equilibrium constants depend on temperature. You can see how the equilibrium constant changes with the changes in temperature through the Vant Hoff Equation. In terms of what's qualitatively happening, raising the temperature will favor the formation of more reactants if it is an exothermic reaction...

Vivian Nguyen

A zero-order reaction is one where the rate is independent of a concentration of the reactant, so the rate just relies on k. Meanwhile, a catalyst is not present in the overall chemical reaction, they just participate and are not consumed to provide a separate pathway of lower activation energy. Zer...

Vivian Nguyen

mmol means millimoles, so x10^-3 moles.
However, because they converted all the values to moles, this gave them the 10^-12.
so in terms of experiment 1
8.7x10^-3/(1.25x10^-3)(1.25x10^-3)^2(1.25x10^-3)^2

which would give you
=8.7x10^-3/3.05x10^-15
=2.85x10^12

hope that makes sense! :)

Vivian Nguyen

They depend on [A]o, the initial concentration.

Vivian Nguyen

Well, I'm not sure if this is much help, but for part b the answer has 2 sig figs, but you couldn't really write 3 sig figs, since the answer is simply 710.

As for part c and d it might have to do with logarithmic sig fig rules?

Vivian Nguyen

I believe the pseudo-rate law is included in that section, on page 627 at the end of section 15.4, so I think you should be fine sticking strictly to 15.1-15.6

Vivian Nguyen

The SHE just has to be the left side of the cell diagram (the anode) because it is used to determine the standard potentials of the other half reactions, which in the table is just based on reduction/oxidizing ability. The standard hydrogen electrode is just used as a reference point to measure the ...

Vivian Nguyen

I believe you should find the positive E cell because, like Dr.Lavelle mentioned as a joke in class, we wouldn't shop for a battery with a negative voltage in a store. In this specific case, the question asks to "devise a galvanic cell" to study the reactions, and galvanic cells are "...

Vivian Nguyen

Hello, Here is question 14.43 for reference: "A tin electrode in 0.015 m Sn(NO3)2(aq) is connected to a hydrogen electrode in which the pressure of H2 is 1.0 bar. If the cell potential is 0.061 V at 25 C, what is the pH of the electrolyte at the hydrogen electrode?" Could anyone explain ho...

Vivian Nguyen

Hi, I got the right solution to the self-test question, but I didn't use the method explained in the toolbox. I just found the half reactions in the table and worked from there to write the net ionic equation. I'm not sure if I went about this right either, but I did get the right answer by using th...

Vivian Nguyen

Delta G is usually used with the questions regarding the gibbs free energy of a reaction not at standard conditions. I think 11.15 is a good example.

Vivian Nguyen

According to Lyndon's explanation during the review session "heavier molecules have more vibrational energy states - they're more complex". Homework problem 9.31 tests similar concepts. In this case, Iodine (g) is being compared to Bromine (g), and Iodine has the higher molar entropy becau...

Vivian Nguyen

Hello, Although I can't say for sure either, I remember Dr.Lavelle saying we wouldn't have to derive anything very sparingly because we would still be responsible for knowing how to manipulate equations to be able to solve a problem. I interpret this as not needing to know a formal derivation, but s...

Vivian Nguyen

ΔG° denotes the gibbs free energy at standard conditions which for aqueous solutions is 1M or gases at 1 atm and in terms of the appendix in the book, at 25C
ΔG meanwhile is not at standard conditions.

Vivian Nguyen

The standard molar entropy is the latter definition that you described. It's the entropy for one mole of the substance at standard conditions (1 atm) and the given temperature which is usually 25C in our textbook. To find the standard reaction enthalpy, you would need to use the equation: \Delta S^{...

Vivian Nguyen

Yes ! Both are raised to the power of the stoichiometric coefficients.

Vivian Nguyen

You would multiply by Avogadro's number when you're trying to find the number of microstates in a mole of a substance. For example, if you had 1.00 mole of CO then you would use 2^6.022x1023 since CO has two orientations and you'd have 6.022x1023 molecules. Because it is such a large number, you can...

Vivian Nguyen

Yes, I think you can use them! I also wrote in my notes that Professor Lavelle mentioned the various methods of calculating delta H.

Vivian Nguyen

I'm guessing this has to do with the overall size of the molecule which could hint at the existence of more states /degrees of freedom and therefore more entropy. For example, everything has translational states, but as you get larger the molecules will have vibrational states and rotational states ...

Vivian Nguyen

Hello, the standard enthalpy of a phase change is the change in enthalpy required to supply the energy needed to carry out that certain phase change in a specific substance.
Meanwhile, the entropy of a phase change deals with the change in the number of states (disorder) of the substance.

Vivian Nguyen

The 6 C-H resonance stabilized bonds are not added because the question asks for the difference in the stability/molar energy depending on the types of bonds are considered. As a result the 6 C-H resonance bonds are one calculation while the 3 C double bonds and 3 C single bonds are the calculation ...

Vivian Nguyen

Hello Grace, The environmental impact section is in Box 8.2 and sorta section 8.21 in the textbook if you need further reference. In summary, burning fossil fuels is not sustainable since we are using them at a rate of 5 million times faster than the biomass necessary in the development of fossil fu...

Vivian Nguyen

I believe the answer has "4" significant figures because in the last step, the two values are being added to each other. To do significant figures when you're adding, it depends on how many values are after/before the decimal point. From the worksheet on Dr.Lavelle's website: "Number ...

Vivian Nguyen

Yes^, I believe so because the surroundings in an open beaker are so large that the pressure is constant /unchanging. I might be wrong, but I think this is when Dr.Lavelle used the examples about whether the temperature of the surroundings would be affected by an individual lighting a match. The pre...

Vivian Nguyen

Hello April, I guess the answers are the same thing. I think they're just trying to test your understanding of can change delta U in an adiabatic closed system through different phrasings of the question. Because it's adiabatic, you know that heat cannot change the internal energy of the system. As ...

Vivian Nguyen

Hello,

Can anyone simplify or clarify section 8.7 in the textbook regarding the definitions of translational, vibrational, and rotational energies and the following equations? It was confusing, and any sort of overview would be really helpful!

Thank you for your time :)

Vivian Nguyen

Yes, sublimation occurs when the phase change goes directly from solid to gas. It occurs in the right conditions where the pressure is low enough below the triple point on a phase change diagram. http://www.kentchemistry.com/images/links/matter/Phase.gif However, this is all I can remember from high...

Vivian Nguyen

I thought heat capacity was an extensive property?

Vivian Nguyen

Heat capacity is an extensive property because it depends on the amount of the substance. Meanwhile, specific heat capacity is an intensive property because it does not matter the amount of substance present. For example in lecture, the heat capacity was 49 kj/c while the specific heat capacity is j...

Vivian Nguyen

Yes! There can only be one sigma bond between atoms

Vivian Nguyen

If an increase in temperature leads to an increase in the equilibrium constant K then it should be an endothermic reaction because to increase K that means that more products are made. ( K = [product]/[reactants]) Endothermic reactions need heat to form product, so it'll produce more product with an...

Vivian Nguyen

pKw =log Kw

Vivian Nguyen

You're not mathematically incompetent! Stay positive before finals :) Here's what the ice chart should look like _____Ni (CO)4_____4CO I____1.0___________0 C___X/4__________4(X/4) E ___1 - X/4_______X Kc = X^4 / (1 - X/4) Because the equilibrium concentration of CO is X, it means that the change in ...

Vivian Nguyen

The higher the Ka the stronger the acid. Think about the calculation to get the equilibrium constant - [Products]/[Reactants]. As a result, the reaction would favor a more complete dissociation of the weak acid, thus giving it a stronger ability to donate a proton (strong acid). pKa is the opposite ...

Vivian Nguyen

Hello, Could anyone further explain the answer to question 115 in chapter twelve regarding how using acetic acid as a solvent changes the solute's behavior as a strong or weak base? Are there rules in general to see how different solvents will affect whether the solute is a strong/weak acid/base? Th...

Vivian Nguyen

Ionic character refers to the concepts we talked about in chapter 4. It specifically corrects the covalent bonding model since the electrons aren't shared between the atoms equally unless the molecule is nonpolar. This occurs as a result of the differing electronegativities (electron pulling power)....

Vivian Nguyen

Hello,

Only the exceptions will have the electron configuration with 4s1. The exceptions are the elements in group 6 and group 11, which does include Cu and Cr.

Vivian Nguyen

This is briefly covered in Fundamentals J.3 if you want a better explanation, but from what I understand, you should first start with the complete ionic equation. This features everything in the chemical formula, with the aqueous compounds broken up into their ions. Whatever is on both the product a...

Vivian Nguyen

I think you can use either, just as long as you stay consistent with all the reactants and products. Likewise if you're calculating anything using the ideal gas law, PV = nRT make sure to use the gas constant R with either atm or bars to match the rest of your problem. Both constants are on the form...

Vivian Nguyen

Hello, The lone pair makes the bond angle less than it would've been because the bond angles are approximated with the consideration that each area of electron density is through a bonded pair. The smaller angle results from the fact that the lone pair is more repelling, so it pushes the atoms bonde...

Vivian Nguyen

From the shape of AX2E3, you can see that it is linear. http://homepage.smc.edu/scholefield_michelle/chem11/handouts/VSEPR%20Theory%20and%20the%20Shapes%20of%20Molecules.pdf The lone pairs do not distort the shape, it is still straight and not bended in any way like t-shaped or see-saw shapes. The b...

Vivian Nguyen

The reactants and products should be in the same phase when calculating the equilibrium constant. In the case you described, yes they should all be gaseous when calculating Kp. But you can also calculate Kc using concentrations.

Vivian Nguyen

Cyanido is the new naming system while cyano is the old one. I'm pretty sure either will be accepted/expected on a test. It's useful to refer to the pdf that's on Dr. Lavelle's website for chem14A as a reference sheet while going through the homework problems. https://lavelle.chem.ucla.edu/wp-conten...

Vivian Nguyen

During my discussion section, our TA said that both naming styles can be used /accepted. Knowing the charge of the polyatomic ions will be necessary to find the oxidation state and write the formula, so yes?

Vivian Nguyen

The lewis structure looks like this :https://en.wikipedia.org/wiki/Chloryl#/media/File:Chloryl-cation-2D-A.png As for the shape it is bent, but the electron arrangement is trigonal planar. The shape is bent because only the positions of the atoms are considered for the shape of the molecule, even th...

Vivian Nguyen

A non polar bond occurs when the electrons are equally shared while a polar bond occurs when the electrons are unequally shared due to differences in electronegativity. For example, H2 would be nonpolar because the atoms have the electronegativity. Meanwhile, OH is polar because oxygen is much more ...

Vivian Nguyen

Diffraction patterns are made by things with wave-like properties such as light, water, electrons, neutrons etc. It occurs because the waves interact with each other and it creates patterns of high and low intensity through constructive and destructive interference. Figure 1.19 on page 15 in the tex...

Vivian Nguyen

Is there a specific problem you can refer too? From the molar mass you can calculate the mass of an atom using Avogadros number. So you would take (molar mass/ 1 mol)× (1 mol/ 6.022x10^23 atoms) which would give you the mass per atom of that element.

Simply divide the molar mass by 6.022x10^23

Vivian Nguyen

Hello, If by valence shell configuration you mean electron configuration then the elements in group 5 will have a configuration consisting of first the previous noble gas in brackets, then any f-orbitals filled, d-orbitals, then s-orbitals. For example, the electron configuration for Vanadium is [Ar...

Vivian Nguyen

Hello, Zeff is the Effective Nuclear Charge. Nuclear charge describes the positive charge of the protons in the nucleus of the atom. In many-electron systems, the nuclear charge is less than what it is supposed to be based on the protons because of the electron interactions. For example, the inner s...

Vivian Nguyen

Hello, carbon has the higher electron affinity because it has 2 unpaired electrons and an open orbital. Meanwhile, nitrogen has an unpaired electron in each of the p-orbitals, so adding another electron would be more difficult because it will be repulsed by the electrons already in the orbitals. As ...

Vivian Nguyen

Hello, Electron affinity is the energy change that occurs when an additional electron attaches to an atom. It's describing how likely an atom will accept an electron. The more positive the electron affinity, the more likely the atom will accept the electron because it will release energy, and not ta...

Vivian Nguyen

Hello, The Px,Py, and Pz would go on their respective axes on the Cartesian Coordinate System which has an x,y,and z-axis. There would be an orbital on each axis. How it looks is what your regular x and y-axis is represented with arrows up and down, but there is an additional z-axis that points outw...

Vivian Nguyen

Hello, for me I have N/A on Weekly Online Discussion as well.

The only thing I have inputted is my Test 1 Grade. . . kinda worried that my homework also says 0/40 even though I do turn in homework. Sorry, I'm not sure when the grades will be uploaded though.

Vivian Nguyen

"Quantum" means "the smallest possible discrete unit of any physical property", so how I understand it is how measurements are restricted to certain packets/quantities. For example, Dr.Lavelle used water buckets to illustrate the point. Each bucket represents the smallest discret...

Vivian Nguyen

Hello, Yes, m (mass of an electron) is a given that you can find on a formula sheet or just look up online. It is 9.10938356 × 10-31 kg. I'm not sure what you meant by integrating the KE equations, but you should use the equations c=\lambda v , and E(of electron) - threshold energy = Kinetic Energy....

Vivian Nguyen

Charlotte, I don't think you would need to know what color it is... I haven't run into any practice problems that asked for what color the wavelength is. But I'm sure it's nice to be familiar with some common wavelengths such as the range for visible light, range for UV light, etc

Vivian Nguyen

Hello Ashley, The work function is the energy necessary to eject an electron off of a specific type of metal (Copper, Aluminum, Zinc, etc...they all have different work functions). The work function can also be called the threshold energy and can also be signified with the greek letter phi \Phi . In...

Vivian Nguyen

Hello! Although my understanding is a bit rough, the photoelectric experiment is different from what you were describing. The photoelectric experiments exposed the particle model of light since electrons would not be ejected unless the waves had a short wavelength/high frequency. The photoelectric e...

Vivian Nguyen

Hi Catherine!

I had my discussion section today, and my TA collected only four total homework problems from what we have gone over so far. So I turned in four answered homework problems not four for each section... Hope that makes sense!

Vivian Nguyen

Hello Kyra, For G9 they're asking you for the mass of silver nitrate needed to prepare that 500. mL of 0.179 M silver nitrate. You're going to want to use the other formula where Molarity = moles of solute (n) / volume of solution (v) . In the question you're given the molarity (0.179 mol/L) and the...

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