CHEMISTRY COMMUNITY

Manu Vohra 1L

Should we know how to integrate the differential rate laws for the final exam?

Manu Vohra 1L

A catalyst is a molecule that is used up in a reaction and then re-created. I usually use this fact to help differentiate the catalyst from the intermediate (which is created then consumed by the rxn).

Manu Vohra 1L

Yes, he is but it will probably not be posted before tonight or tomorrow as I am sure he has his own finals too.

Manu Vohra 1L

Usually, it is bar or atm.

Manu Vohra 1L

Yes, the Van't Hoff equation would be needed in this case. Essentially you use this equation when you are given a K value for a specific temperature (K₁ at T₁) and use it to find the K value at another temperature (K₂ at T₂).

Manu Vohra 1L

^ order for the aqueous ions does not matter as long as they are on the appropriate side (anode or cathode).

Manu Vohra 1L

I think anything from the second half of electrochem or kinetics is acceptable.

Manu Vohra 1L

This problem would not require the Van't Hoff equation. An instance where you would need to use the Van't Hoff equation would be if you were looking to find a K value at a given temperature T₂ (you would have to be given K at another temperature as well to use as K₁ and T₁ in the equation).

Manu Vohra 1L

For cell diagrams it usually doesn't matter which aqueous species comes first, however, you do want to make sure of a few things: --the electrodes are always on the ends --cathode is always on the right and and anode always on the left. --aqueous ions (H+ and OH- included) are always closest to salt...

Manu Vohra 1L

Builidng off of the above reponse, just make sure that all aqueous ions are closest to the salt bridge. Also note that if a particular half reaction inlcudes H+ or OH- in it when balanced, you must also include that in the cell diagram on the respective side (anode or cathode depending on which half...

Manu Vohra 1L

^Lyndon's for sure. Not sure I can recommend any of the others since I didn't go to them....

Manu Vohra 1L

I think it covers 4J + the end of chapter problems, 5G, and 5J for sure for the 7th edition. I am not entirely sure about which electrochemistry sections will be covered though.

Manu Vohra 1L

You would use this equation when you are trying to find out how a K value would change if you increased the temperature of a reaction (you would need to be given another K value at a lower or higher temp which is why there is K1/K2 and T1/T2).

Manu Vohra 1L

We rarely need to use this equation but since professor Lavelle did mention it in class, it may be a good idea to know anyways.

Manu Vohra 1L

Why does steam at 100^oC burn more than water at 100^oC?

Manu Vohra 1L

Why is the entropy of surroundings 0 for an isothermal irreversible free expansion? (From Figure 4I.6 in 7th edition textbook)

Manu Vohra 1L

In the textbook the most common unit used for enthalpy is kJ/mol.

Manu Vohra 1L

since the system is isolated, no matter or energy can be exchanged with the surroundings. Therefore, after 100 years the amount of energy in the system (the internal energy, U) will remain constant at 100kJ. Remember that DeltaU=0 for all isolated systems.

Manu Vohra 1L

101.325 J = 1 atm(L)

Manu Vohra 1L

If you read the section before you start answering the questions, you should be able to do most of the homework by following the format of the examples given. Dr. Lavelle is going a bit out of order for this unit so I would pick something we've already covered (like Hess's Law) and start with that.

Manu Vohra 1L

When a bond is broken it does release energy, but in order to break that bond, usually some amount of energy is needed. The amount released by breaking the bond tends to be more than what is needed to initiate the breaking of that bond.

Manu Vohra 1L

The equation we use is :
A reversible process is a process whose direction can be "reversed" by inducing infinitesimal changes to some property of the system via its surroundings.

Manu Vohra 1L

However, always make sure to double check your approximation and ensure that change in x is less than 5% of the inital concentration!

Manu Vohra 1L

There really isn't much to it. Just know that the K values decrease significantly after each deprotonation so for most acids we only consider the 1st deprotonation (H 2 SO 4 is the only excpetion according to the textbook where the first and second deportonations must be considered and two ice table...

Manu Vohra 1L

The higher the constant Ksp, the greater the solubility. Think about this conceptually. Something that has a high Ksp favors the products so it must be very soluble or dissolvable...

Manu Vohra 1L

When using an ICE table, the book stated that we can assume that a change in concentration, x, is negligible if it is less than 5% of the initial concentration of a particular substance. It also stated that one could tell by looking at how small the K value is, but it did not specifiy a particular v...

Manu Vohra 1L

One of the bullets on Outline 1 states that we should be able to simplify cubic equations (for ICE tables). Do we need to know how to do this as none of the textbook or module questions required us to work with cubic functions and they were also not covered during lecture?

Manu Vohra 1L

Expect all of Equilibrium and Acids and Bases to be on it. Professor Lavelle will make an in-class announcement about what the test will cover, probably this Friday. He also posts his announcements on his website so keep watching that too for more info!

Manu Vohra 1L

You can turn in any 7 of the homework questions that are listed in Lavelle's syllabus for credit every week.

Manu Vohra 1L

My roomates were both in the 20 series and the material they covered seemed more or less the same as what I covered in the 14 series with Lavelle. However, they did go more in depth than we did. The one thing we did cover that they did not cover at all in the 20 series would be acids and bases (unde...

Manu Vohra 1L

The 14 series is very similar to AP Chemistry so if you took that in high school you will be fine. The 20 series just tends to go more in-depth on certain topics but the material is more or less the same as the 14 series.

Manu Vohra 1L

Electron withdrawing ability is essentially referring to the ability of a bonded atom to pull the oxygen's electrons towards itself in order to minimize the likelihood that the conjugate base will just reform the acid (If oxygen's electrons are being pulled away and towards this other bonded atom th...

Manu Vohra 1L

Also, remember that water is amphoteric as well!

Manu Vohra 1L

I am not sure. From what I know those are the only two exceptions to the rule so I would just remember them just in case.

Manu Vohra 1L

^ It is just another term for the strength of the dipole. A value can be assigned to magnitude using the formula Lavelle gave us during lecture, but we do not need to know how to calculate it. He just gave us that formula so we can gain a better understanding conceptually.

Manu Vohra 1L

I think the final is on the entire course. Professor Lavelle said he will be telling us the details about the final during lecture on Friday (11/30/18).

Manu Vohra 1L

single electrons found as radicals occupy an unhybridized p-orbital. That said, the single electron is still counted as a region of electron density so I think it is still considered when determining hybridization.

Manu Vohra 1L

Hydrogen bonding results in higher melting and boiling points since it is the strongest type of intermolecular force (other than ionic bonding).

Manu Vohra 1L

Try Khan Academy! That is my go-to for any confusing topics.

Manu Vohra 1L

In addition to the above reply, remember that a single unpaired electron (found in radicals) counts as a single region of electron density (basically a single unpaired electron is treated as if it were a normal lone pair).

Manu Vohra 1L

There will not be anymore audio visual modules for the rest of the quarter. There may be some for 14B next quarter though!

Manu Vohra 1L

Regardless of whether the bond is single, double, or triple, it is still one region of electron density. Therefore, there are no changes made to the VSEPR model.

Manu Vohra 1L

The arrangement is dependent only on the number of regions of electron density whereas the molecular geometry has to take into account the number of bonded electrons vs. the number of lone pairs and how they interact among each other (lone pairs force bonded atoms closer together and therefore creat...

Manu Vohra 1L

The ability of a cation to distort an anion is known as its polarization power . Smaller, more positive cations pull electrons more strongly so these cations are said to have a strong polarization power. Polarizability is essentially the ability of the anion to pull in those electrons. Smaller negat...

Manu Vohra 1L

It is best to choose the atom with the lowest ionization energy because as ionization energy decreases, you are more likely to find an atom that wants to share its electrons (get rid of them in a way) than hold on to them as lone pairs.

Manu Vohra 1L

I think anything that we have covered within the last week is acceptable.

Manu Vohra 1L

According to professor Lavelle it will be 8 questions with multiple subparts. It should be quite similar in difficulty to test 2 according to my TA. My TA also said that we should have plenty of time to complete it since it will be just a bit longer than test 2 even though we will have almost triple...

Manu Vohra 1L

I think they are using values the values shown in Figures 1F.4 and 1F.6 on pages 54-55. We would not need those values on a test. We are just required to know the basic trends of atomic radii.

Manu Vohra 1L

According to the textbook, [Ar] 4s²3d¹⁰4p⁵ is the correct way to write the electron configuration of Br.

Manu Vohra 1L

From what I know, Professor Lavelle only created the modules for specific topics that his students have struggled with in the past. I guess people seem to have a relatively good understanding of the topics covered after the quantum world unit.

Manu Vohra 1L

Not 100% sure but I would think that is all we will have time for. I am sure professor Lavelle will be making an in-class announcement as well as online announcement very soon in regards to what will be covered on the midterm.

Manu Vohra 1L

According to the test schedule on Professor Lavelle's website, test 3 will be administered starting Tuesday November 27 in discussion section (the week after Thanksgiving).

Manu Vohra 1L

There is no equation to solve this. During the video module, professor Lavelle states that one photon can only dislodge one electron (assuming it has a high enough energy to do so). Therefore, if 1 million photons hit a metal surface, the absolute maximum number of electrons that could be ejected wo...

Manu Vohra 1L

From what I have heard, there will not be any more Audio-Visual Modules this quarter. Professor Lavelle only created the modules for the topics he found his students to struggle with most (Quantum World) and high school review material.

Manu Vohra 1L

According to Professor Lavelle's in-class announcement on Friday 10/19, test #2 will cover everything on the outline except Section 1F (Periodic Trends) which we did not yet cover in class.

Manu Vohra 1L

It should be the lowest number of significant figures out of the values given to you in the problem. So for example, if I am given two values, one with 3 significant figures and one with 2 significant figures in the problem, my final answer should have 2 significant figures, regardless of any outsid...

Manu Vohra 1L

Yes, there are cases when the empirical and molecular formulas are the same. This happens when the molar mass of the calculated empirical formula matches the molar mass given to you for the molecular formula.

Manu Vohra 1L

Hello, I am also taking the first test this Thursday. My plan is to study up for the test and worry about homework for chapter 1 later. The homework due this week can be from either outline one or outline two so personally I would prefer to hold off on working a new topic until I completely master t...

Manu Vohra 1L

I am not entirely sure myself. Given this is a college chemistry course, I would think professor Lavelle would like us to know all of the naming categories you mentioned. That said, I would think the test would focus on naming things like ionic compounds (ex: cobalt (II) chloride) and covalent compo...

Manu Vohra 1L

There is no set cutoff. Multiple factors come into play when deciding whether a reaction is 'efficient' or not including the time needed for the reaction to occur, the cost of the materials involved, and the percent yield. Therefore, every reaction's efficiency will have to be gauged individually.

Manu Vohra 1L

When I had to essentially memorize them for AP Chem in high school, I paid close attention to the prefixes and suffixes because they usually have a pattern associated with them. For example, polyatomic ions ending with 'ate' have one more oxygen atom than polyatomic ions ending with the suffix 'ite'...

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