CHEMISTRY COMMUNITY

Miya Lopez 1I

"Homogeneous reactions are chemical reactions in which the reactants and products are in the same phase, while heterogeneous reactions have reactants in two or more phases. Reactions that take place on the surface of a catalyst of a different phase are also heterogeneous. A reaction between two...

Miya Lopez 1I

I don't know the answer and am confused on those as well so I'm going to go to the review of Test 2 in Haines 39 at 11 am. I'm sure the TA will go over the answers and explain it there.

Miya Lopez 1I

Are we expected to know whether a reaction is fast or slow in order to use the pre-equilibrium approach? For example, in lecture today for the pre-equilibrium approach, step 1 was a fast bimolecular dimerization and step 2 was a slow bimolecular reaction.

Miya Lopez 1I

Average rate is an approximation and therefore isn't very accurate. I think most problems will want us to find instantaneous rates because they are more accurate

Miya Lopez 1I

Unique rate of reaction looks like -\frac{1}{C}*\frac{\Delta \left \lfloor R1 \right \rfloor}{\Delta t} and instantaneous reaction has the form \lim_{x\rightarrow 0} \frac{\Delta \left [ concentration \right ]}{dt} or \frac{d\left [ concentration \right ]}{dt} the instantaneous rate is more accurate.

Miya Lopez 1I

How will we know when to use the pre-equilibrium approach? Will we always use this approach instead of the other two ways?

Miya Lopez 1I

The final will include all material from the entire quarter including what he goes over on Wednesday. Friday is review of past exam questions.

Miya Lopez 1I

In the solutions manual for the 6th edition 14.13, it states that "Pt is necessary when both oxidized and reduced species are in the same solution" and that it is necessary for "gas/ion electrode reactions"

Miya Lopez 1I

Hi, I had to miss a couple of Friday lectures :( Does anyone have Friday week 6 and week 7 lecture notes they would be willing to share?
Thank you!

Miya Lopez 1I

A reducing agent is a substance that is oxidized, which means it loses electrons.

Miya Lopez 1I

Since a redox reaction is a reduction/oxidation reaction, I thought oxygen had to be present but when I searched it up it says that "Oxygen does not have to be present in a reaction for it to be a redox-reaction. Oxidation is the loss of electrons." https://simple.wikipedia.org/wiki/Oxidat...

Miya Lopez 1I

When you change the log of Q to the log of K, you know that the reaction has reached equilibrium. I also am not sure how we determine which way the reaction will proceed.

Miya Lopez 1I

When a chemical reaction is at equilibrium, the Gibbs free energy is, indeed, equal to zero, but that doesn't mean that the Gibbs free energy under standard conditions is (the little circle to the top right is what you're most likely missing)... Can you explain more about what the standard conditio...

Miya Lopez 1I

When a reaction is at equilibrium, no more work can be done and the Gibbs free energy or delta G is zero.

Miya Lopez 1I

When do we know when to use the Vant Hoff equation?

Miya Lopez 1I

When the reaction is at equilibrium the Gibbs Free energy will be zero

Miya Lopez 1I

SydBenedict2H wrote:Will he ask us any acid base questions, or is he only asking Gibbs and electrochemistry?

I don't think we'll be tested on acid base questions since it was on the midterm already. It'll just be Gibbs free energy and up to what we learned in class today (but not including it)

Miya Lopez 1I

Miya Lopez 1I

I'm confused about this diagram as well, but maybe it is just assumed Cl- will be a separate component?

Miya Lopez 1I

Valentine's Song for Dr. Lavelle - 2/11/2019

ips-D357FBBF-7982-4763-B872-B32942F794F7.mp4 [ 5.88 MiB | Viewed 123691 times ]

Miya Lopez 1I

The variable that represents heat capacity is I think just "C", please correct me if I'm wrong.

Miya Lopez 1I

Why is it that the phase change for water from a liquid to a gas than from a solid to a liquid has more energy? I think when water changes from a liquid to a gas there is more energy because the particles need to be moving faster as a gas and the all bonds in the liquid need to be broken for it to ...

Miya Lopez 1I

How could the volume change in an isolated system? Would the system just expand on its own?

Miya Lopez 1I

Rachel-Weisz3C wrote:I think for pressure we use atm and for volume it should be Liters/milliliters, depending on the problem provides.

Is the SI unit for pressure Pascal? Should we be using the SI unit or just atm?

Miya Lopez 1I

Did you divide the concentrations by the volume of 10 L? Also, there is a coefficient of 3 for H₂, so you would need to raise the concentration of H₂ to the 3rd power.

Miya Lopez 1I

I'm not sure if I'm correct but to get the change row in the ICE table, isn't it always going to be either -x or +x? I haven't encountered a problem where there are coefficients in front of it. But I am also confused on this topic.

Miya Lopez 1I

You don't include liquids in your equilibrium expressions because they occur in such large amounts that they are considered the solvents of the chemical reaction. Any reaction that occurs using a liquid will not provide a large enough change to that liquids concentration so as to require us to incl...

Miya Lopez 1I

A weak acid does not fully dissociate in water and therefore, would require an equilibrium equation. A strong acid fully dissociates in water and so it would be written as just a forward reaction. You just have to memorize the strong acids and every other acid is a weak acid. The strong acids are H...

Miya Lopez 1I

Also, what does it mean to be "completely ionized"?
In class Dr. Lavelle stated that "Ba(OH)₂ (aq) is a strong base, essentially completely ionized."

Miya Lopez 1I

Can someone explain to me what percentage ionization means? In the example Dr. Lavelle did in class today, he asked what is the pH and percentage ionization of acetic acid in 0.10 M Ch₃COOH?

Miya Lopez 1I

In the example Dr. Lavelle did in class today with kA to find the pH, can someone help explain to me how he was able to approximate it to $\frac{x^{2}}{0.10}$ ?

Miya Lopez 1I

How can you tell if you have a weak/strong acid or base?

Miya Lopez 1I

On the final, are we supposed to memorize/be able to recognize all of the ligands?

Miya Lopez 1I

I believe it is the opposite on the other side of the reaction. Attached is a picture of my worksheet from discussion. So from the image, I think HCl is a Bronsted acid and its conjugate base is Cl - . H 2 O is a Bronsted Base in this reaction and its conjugate acid is H 3 O + I'm not sure if I am e...

Miya Lopez 1I

When finding the molar mass of Fe₂, you would look on the periodic table to see the molar mass of just Fe which is 55.845, and multiply it by 2 to get 111.69 g.mol-1 of Fe₂.

Miya Lopez 1I

But if you have more lone pairs, they would push the other bonds/molecules even further away from them correct? Thank you:)

Miya Lopez 1I

I believe if they give you the molecular formula and the AXE formula you could determine the shape. Say if you were given H2O: AX2E2... then you know there are 2 bonding atoms and 2 lone pairs. Then once you draw the molecule out you could figure out its shape.

Miya Lopez 1I

If you had a molecule with three different lewis structures (resonance) and they had formal charges each with multiple zeros, would you pick the lewis structure with the most zeros/lowest formal charge to be the most stable lewis structure of that molecule?

Miya Lopez 1I

Could someone please explain to me how we know that we are supposed to use oxygen for this problem? Am I missing something in the question where it says to use oxygen, or is it because it's a certain type of ion?

Thank you:)

Miya Lopez 1I

When I added up the total amount of valence e- I should have, I got 30 valence e-. In the solutions manual, they started with NH2 first, but in my lewis structure I started with H2C first. I still have the same amount of total valence e-'s as the lewis structure in the solutions manual. Does it matt...

Miya Lopez 1I

I think what determines the bond angles is that each atom has to be equally spaced from one another. The exact numbers are calculated experimentally, so we don't have to know them.

Miya Lopez 1I

I'm not sure if this is correct, but I think part b is asking if the wavelength is too small to be detected. So you would just have to see if your final answer is a very very small number.

Miya Lopez 1I

I think you would use the line only when it is bonding with something else, so it wouldn't be a lone pair.

Miya Lopez 1I

r is the distance between the atoms or molecules, and in the textbook on page 193 it states that "It turns out that the potential energy varies as the sixth power of the distance between the molecules... Doubling the separation of polar molecules reduces the strength of the interaction by a fac...

Miya Lopez 1I

When atoms are combining covalently, meaning that they are sharing electrons, they want to get a full outer orbital of 8 electrons and become stable.

Miya Lopez 1I

I'm not sure if this is correct, but what I understand resonance to be is when you can draw lewis structures of atoms bonding in different, yet equivalent ways. With the example in lecture of NO3-, we can draw it with a double bond connecting an O and the N on the left side, right side, or from the ...

Miya Lopez 1I

Lecture on Monday covered part of chapter 3. We talked about covalent bonds, octet rule, how to draw lewis structures, and resonance.

Miya Lopez 1I

When it says an electron in the s-orbital can penetrate to the nucleus of an atom, penetration is describing how close an electron can get to the nucleus. On this website, https://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Quantum_Mechanics/10%3A_Multi-electron_Atoms/Multi-Electron_...

Miya Lopez 1I

If you are given the electron configuration of an element, you can determine the number of unpaired electrons by drawing out the orbital diagram. Then when you fill in the levels, you can see which subshells do not have paired electrons. I found this video helpful when I was stuck on this too: https...

Miya Lopez 1I

Just to clarify, this means that for any element with an electron configuration that has both s and d orbitals, the d orbital would come before the s and followed by p. But for elements without the d orbital it would be the s orbital first. Correct me if I am wrong. And also s orbitals have higher ...

Miya Lopez 1I

When l=2, m can be -2, -1, 0, 1, 2 which corresponds to 5 orbitals.

I got this from the chart we wrote in lecture on 4/25.

Hope this helps :)

Miya Lopez 1I

In class when the professor gave an example to find the orbitals for Bromine, he used shorthand and wrote [Ar] instead of repeating the same orbitals. I believe he said when we use shorthand to use the elements that are noble gases (group 18), but I am not sure exactly why that is the case. When you...

Miya Lopez 1I

I'm confused about the concept of photons versus energy. are photons the energy unit and therefore the more photons present the more electrons released? or are photons different from energy? I think photons *have* energy, but photons are not the energy unit (?). In the textbook it says, "It is...

Miya Lopez 1I

I'm not sure if everyone's tests are in the same order but my Q4 uses Phenanthrene. I wrote a balanced equation for the combustion of Phenanthrene (C14H10). So first I wrote C14H10 + O2 ---> CO2 + H20 Then I wrote the elements in a column and how much the elements had on each side of the equation, a...

Miya Lopez 1I

I don't have any fun/easy ways to memorize the formulas, but I believe Professor Lavelle said that all formulas will be given to us on tests/exams. We just have to know how to apply them.

Miya Lopez 1I

Increasing the wavelength decreases the kinetic energy of ejected electrons because when you have E=hv, and you substitute in the frequency (v) as c/(lambda) you get.. E= h * c/(lambda). So when you increase the wavelength, lambda, it makes the fraction c/(lambda) a smaller number overall which mean...

Miya Lopez 1I

DET stands for the detector that detects the kinetic energy of the ejected electron.

Miya Lopez 1I

When a question asks you to find how many molecules there are of something, you would use Avogadro's number in your calculations. For example in E.29 (c) "E.29 A chemist measured out 8.61 g of copper(II) chloride tetrahydrate, CuCl2*4H2O. (a) How many moles of CuCl24H2O were measured out? (b) H...

Miya Lopez 1I

The Geiger-Marsden experiment showed the nuclear model of an atom. Because some of positively charged alpha particles deflected more than 90 degrees and some bounced straight back, this suggested that the alpha particle was repelled by the positive charge of a nucleus. Protons and neutrons in the nu...

Miya Lopez 1I

Subscripts must never be changed because that would change the entire formula. If you have a fraction like 33/2 for one coefficient, you can just multiply the whole equation by 2 in this case to get whole numbers (which is preferable).

Miya Lopez 1I

Emely Reyna 1F wrote:You should look at the constants worksheet that value is given.

I was confused about where the book got this number too. So for all electrons, their mass will always be the same?

Miya Lopez 1I

This might still be guessing and checking, but when I balance equations I write down each element in a column. Then, I write how many there are on the left side of the equation to the left of the element & how many there are on the right side of the equation to the right of the element. Then whe...

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