CHEMISTRY COMMUNITY

Matthew ILG 1L

I'm really going to miss Dr. Lavelle. I'm really bummed that we won't be able to say goodbye and thank you to him in class. I just want to say thank you to Dr. Lavelle for the last two quarters of chemistry and my first experiences in a college classroom. I had a truly great experience with him as a...

Matthew ILG 1L

Is there a diffference in which equation is used when a problem asks to find the "rate of decomposition" of a molecule vs when it asks you to find the rate of composition of a molecule?

Matthew ILG 1L

Looking back through my notes, I realize I have several different equations for each order rxn and I am not sure which one to use or which is most common when asked to simply find the rate of decomposition of something. Would someone be willing to clarify the basic equation for each order rxn please...

Matthew ILG 1L

Is there a due date for the final? The email did not say anything about when the final will be due.

Matthew ILG 1L

I'm really going to miss Dr. Lavelle. I'm really bummed that we won't be able to say goodbye and thank you to him in class. I just want to say thank you to Dr. Lavelle for the last two quarters of chemistry and my first experiences in a college classroom. I had a truly great experience with him as a...

Matthew ILG 1L

We have yet to receive any official word from the chem department but hopefully we will receive an email soon about discussion sessions, as well as the review sessions and final.

Matthew ILG 1L

Yeah we have not received any official word on the situation from the chem department or Dr. Lavelle, so I am not sure what the situation is for the final or the review sessions. At least we finished learning all the material already.

Matthew ILG 1L

I was curious about this too and whether or not we simply needed 100 posts by the end of this quarter. I believe I had more than 50 last quarter but was not sure if I would still need 50 more posts this quarter or just the remainder to 100.

Matthew ILG 1L

I believe we are still waiting on specific news and updates for chemistry and from Dr. Lavelle.

Matthew ILG 1L

The final will be cumulative, and I believe that only one or two problems will be from the homework, as with most of his other midterms and finals.

Matthew ILG 1L

There have not been any announcements made yet by Dr. Lavelle but the letter from Chancellor Block said that there would be more updates from professors in the coming days.

Matthew ILG 1L

In today's lecture(3/9/20) Dr. Lavelle gave an example of how Nitric Oxide catalyses the conversion of oxygen to ozone in lower atmosphere.
He stated that NO(g) is a catalyst. However, is O2(g) also a catalyst?
It is not formed at any point during the process, so I assume it is not an intermediate.

Matthew ILG 1L

5G and 5J are the only sections from thermo that were not included on the midterm

Matthew ILG 1L

I'm almost certain that this is an error in the textbook; I've done that same problem twice and I've gotten your answer twice. You may want to see Prof. Lavelle's updated solutions manual errors on his website to see if this is one of the errors. But I can assure you that your work is correct. Than...

Matthew ILG 1L

Will we lose points on the test or final if we forget to include the degree sign?

Matthew ILG 1L

Test 1 only had 7 or 8 I thought. Does that mean that test two is going to be longer?

Matthew ILG 1L

I believe that we only need to know the final equation at the end of the derivation. We only derive the formula in class to understand where the equation comes from. But I do not think we will be asked to derive any equations or formulas on any test or exam.

Matthew ILG 1L

I was just wondering how applicable the things you learned in 14A and 14B were to you when you were doing your medical internship.

Matthew ILG 1L

You know that K decreases as temperature increases. This means that the reaction is exothermic. Because of this, the reactants are favored, and increasing the temperature will result in a shift to the reactant side. More ammonia will NOT be formed, because this is a product. You do not need an ICE ...

Matthew ILG 1L

I have tried part A several times but I keep coming up with K=1.096. How does the book manage to get 1.0 x 10^80. Does it have something to do with the 2 in front of H20 in the balanced equation?
The only Standard Gibbs free energy of formation given by the appendix is -228.57 for H2O I believe.

Matthew ILG 1L

Wait sorry I just realized that you use the deltaG°=-RTlnK.

Matthew ILG 1L

On textbook problem 5.G.19, it asks to calculate the standard Gibbs free energy for the reaction i2(g) <--> 2i(g), where K=6.8 at 1200.K The problem does not give us any partial pressures, so I was wondering what formula or equation should be used, or if there is a way to find the partial pressure u...

Matthew ILG 1L

The hw problems you should do to review are 5G and 5J, as well as 6K through 6O

Matthew ILG 1L

You are able to use either the log or ln, and I believe Dr. Lavelle provided an equation using each. However, he also stated that log is often preferred by scientists because pH also uses log.

Matthew ILG 1L

I know that test 2 will cover the second page of thermodynamics, but I was wondering which hw problems related to that second page?
Are 4i and 4J included in that, or is it only 5G and 5J problems?

Matthew ILG 1L

A reduction is spontaneous when the standard reduction potential is positive.

Matthew ILG 1L

A salt bridge is a laboratory device used to connect the oxidation and reduction half-cells of a galvanic cell(a type of electrochemical cell). It maintains electrical neutrality within the internal circuit, preventing the cell from rapidly running its reaction to equilibrium.

Matthew ILG 1L

Thank you Dr. Lavelle for always doing your best to make chemistry fun, from the comics on slides to the music before or after lecture, to the little notes spaced throughout the midterm and final that always bring a smile to my face. Thank you.

Matthew ILG 1L

No additional material! Just the second page of outline 4 (thermodynamics, focus 5) and outline 5 (electrochemistry).

Matthew ILG 1L

Is the change in enthalpy supposed to be much larger for part b than it is for part a?

Matthew ILG 1L

I am on problem 4.c.3 in the book, and the example 4.c.1 is very similar to it. However, in the example, it says that Cv=5/2R, and that Cp=7/2R because in the book Cp=Cv+R.
On our equation sheet, it says that Cp=5/2R. I am confused as to which ratio is correct for Cp and Cv when converting to R.

Matthew ILG 1L

On this same problem, why don't we use the molarity or volume of either of the compounds that are given to us in the problem? Why do we just multiply C(cal) by delta T. Hello, I believe we do this because the relationship q= -qcal is already established. It is simpler to find qcal with the informat...

Matthew ILG 1L

Will the conversion of 1atm=760 Torr be given to us at all? I have yet to find that on the equations sheet from test one. I could be looking in all the wrong places though.

Matthew ILG 1L

There are occasionally a few true or false or fill in the blank questions thrown in to the test, but the rest is all free response.

Matthew ILG 1L

I was just on this problem and luckily found this post. Are we supposed to know that 1atm is equivalent to 760 torr or is that somewhere on the equation sheet? Also how do we convert from L*atm to kJ?

Matthew ILG 1L

I believe that the mass and moles can both be used because the two can be converted back an forth, given the correct and necessary information. They both work, similar to how ceclius and kelvin both work at times. It can be changed to moles or to grams, but we do not need to because the equation wor...

Matthew ILG 1L

Thank you both very much. That is very helpful.

Matthew ILG 1L

On this same problem, why don't we use the molarity or volume of either of the compounds that are given to us in the problem? Why do we just multiply C(cal) by delta T.

Matthew ILG 1L

A reversible reaction is basically when the reactants form products that, in turn, react together to give the reactants back. It is shown by the two way arrows usually.

Matthew ILG 1L

Extensive properties, such as mass and volume, depend on the amount of matter being measured. Intensive properties, such as density and color, do not depend on the amount of the substance present

Matthew ILG 1L

ΔS total =ΔS system +ΔS surrounding So if the ΔS total =0, then ΔS system = -ΔS surrounding They will not always be equal and opposite, but that is typically when this relationship will be important. Also, you could solve for ΔS system and ΔS surrounding and add if the question is asking for the ΔS...

Matthew ILG 1L

The rule of less moles only applies when you are dealing with gases. If the substances in the rxn are not gases, then I do not believe the rule applies.

Matthew ILG 1L

In a irreversible reaction, the reactants react to form the products, which cannot revert back into reactants. In reversible reactions, as the reactants react with other reactants to form products, the products are reacting with other products to form reactants. Combustion is an example of an irreve...

Matthew ILG 1L

Mariana Fuentes 1L wrote:Does that mean that Ka and pKa are kind of opposite?

Yes exactly!! The smaller the value of Ka, the larger the value of pKa, the weaker the acid.

Matthew ILG 1L

I'm going through and doing problems from each section of the book to prepare for the midterm. Does anyone have any especially good problems they would suggest doing in preparation for the midterm? Can be from any section we have covered. Thank you

Matthew ILG 1L

I believe that Dr. Lavelle said we can ignore x when K<10^-3.

Matthew ILG 1L

The third law acts similar to a limit function in calculus:
As the temperature of the system approaches absolute zero, the entropy of the system approaches zero.

Matthew ILG 1L

Isolated systems are completely sealed and closed off. Imagine a test tube with a lid on it, then wrapped completely in a "puff jacket" as Dr. Lavelle said in his in class example from a few weeks ago. It does not interact with its environment at all.

Matthew ILG 1L

Does anybody know if we will be learning new material for the entirety of Friday's class, or will part of it be review and example problems for the midterm?

Matthew ILG 1L

If you are referring to K value vs Q value:
When Q>K, the rxn will shift to the left, creating more reactants
When Q<K, the rxn will shift to the right, creating more products

Matthew ILG 1L

U = q - w is used when there is heat added to the system (q). H = U + PV is under constant pressure and constant temperature.

Matthew ILG 1L

I may be wrong, but I believe the Boltzmann equation is still used for positional entropy.

Matthew ILG 1L

We needed to know the conversion from celcius to kelvin on the last test, so I assume that on the midterm and other tests we will need to have it memorized as well. However, I do not believe we need to use the exact conversion value of 273.15, but rather we are bale to use 273.

Matthew ILG 1L

Water is one heat capacity you should memorize. Other than that, the heat capacity of different elements is usually given in the specific problem.

Matthew ILG 1L

Dr. Lavelle gave a good example today in lecture. He said a closed system in a closed system, energy can still exchange with surrounding, but matter is not exchanged (i.e a sealed beaker of water. the beaker does not insulate) In a isolated system, nothing exchanged with the surroundings. It is as i...

Matthew ILG 1L

Lewis acids and bases are defined in terms of being able to accept or donate electron pairs, while Bronsted Lowry acids and bases are defined in terms of being able to accept or donate hydrogen ions ( H+ )

Matthew ILG 1L

Thank you! I still have yet to pick mine up as well.

Matthew ILG 1L

"In chemistry, the convention is that anything going out of the system is negative and anything coming into the system is positive. If your system is a gas in a piston, work is being done on the system when it is being compressed, so the work done on the system is positive, and the work done by...

Matthew ILG 1L

On question 6.A.7, it asks us to write the name of each acid based on the molecular drawing (HClO3 and HNO3).
Is there a list of acid names we are expected to memorize and know, or is there a way to know the names of these acids based on the formula and atoms within it.

Matthew ILG 1L

You usually add the 2 i front of the sp2 when you are describing the hybridization of a bond. If you are just describing the hybridization of an individual molecule, I don't believe that you need the 2 in front.

Matthew ILG 1L

If you determine the coordination number you can determine how many molecules bond to it, if you find this out you can find the molecular shape. I agree with this. the coordination number helps you determine the shape. Some common ones are: CN=6 is Octahedral CN=4 is tetrahedral or in the case of c...

Matthew ILG 1L

The Ta's and Ua's have said that either is acceptable as well. Which ever naming convention is easiest for you to remember.

Matthew ILG 1L

In addition to this, a weak acid leads to a strong conjugate base. And vise versa, a strong acid leads to a weak conjugate base.

Matthew ILG 1L

I found a chem community post from 2011 that said this:
"They are actually the same ligand, but the the first (cyano) is an older naming convention. Cyanido is the IUPAC preferred name for the ligand".
It also says that both forms are acceptable.

Matthew ILG 1L

Coordination compounds and acid and base structures are the newest material, but I'm pretty sure that if you do older problems as a way to review for the final your TA will accept that as well. But it may be better to be safe and just turn in problems from the coordination compounds and acid and bas...

Matthew ILG 1L

I'm sure he will also show the locations on a slide in class on Wednesday or Friday, like he did for the midterm. He showed a quick glimpse of it in class today as well, and I believe A-L last names are in CS50, though I'm not sure where M-Z last names are.

Matthew ILG 1L

I believe that the stronger the acid, the weaker the bond, and therefore the easier it is for that bond to break and for the acid to completely dissociate in water. So to answer your question, what sets certain acids apart as "stronger" and varying levels of dissociating completely is the ...

Matthew ILG 1L

Will we be required to know and memorize the latin names of elements for the final? A video I watched kept using the latin names, such as cobalt being cobaltate and platinum being platinate when naming their coordinate compounds. Will a list of latin anmes of elements be given on the final or do we ...

Matthew ILG 1L

I have heard that the discussion posts have been graded both ways in the past. Some years they grade on a week to week basis and other years they simply check your total number of posts at the very end. It is good to try and stay up to date, but if you fall behind, talking with your TA is never a ba...

Matthew ILG 1L

You will also need to know unit conversions I believe, such as grams to kilograms or meters to nanometers.

Matthew ILG 1L

Will we be learning new material throughout the entirety of this week (December 2-6) for the final? Or will the last Friday of class be a review day for our final?

Matthew ILG 1L

In addition to the review sessions, are there any specific videos or chemistry youtubers you would suggest watching who are good at teaching the more conceptual things?

Matthew ILG 1L

The strength of an acid depends on two things: The strength of the A-H bond, and the stability of the resulting anion. Bond strength is related to the length of the bond, and because Iodine has a much larger atomic radius than Fluorine, HI has a much longer, and therefore weaker, bond. The hydrogen ...

Matthew ILG 1L

It sounds like you are doing fine in the class. I would say that reading over some of the textbook and attending the workshops are very helpful in reviewing and applying what we learned in lecture. When reading over the textbook do you suggest taking notes? I have tried to read it and it just gets ...

Matthew ILG 1L

The Bronsted definition: an acid is a proton (H+ ion) donor, and a base is a proton acceptor
The Lewis definition: an acid is an electron acceptor, and a base is an electron donor.

Matthew ILG 1L

Yes, you coun't the number of lone pairs and hydrogens and you should get 11 bonding sites. You may get 12 but my TA said that the Hydrogen that is on the most far right that is bonded to carbon cannot form a hydrogen bond because hydrogens need to bond to N O or F (or small molecules..) and since ...

Matthew ILG 1L

For this question, you had to be able to identify that all the single bonds had a sigma bond in it and that all the double bonds that a sigma bond and a pi bond in it. When counting the number of hydrogen bonding sites you need to include the H-bonds already present and the lone pairs on N,O, or F....

Matthew ILG 1L

The way i remember is: Sigma=Single. The double S helps me out. Also sigma bonds are every bond in a structure.

Matthew ILG 1L

In addition to the difference between acids and bases, there is also a difference between organic acids and bases vs inorganic acids and bases. Acids containing carbon are known as organic acids. Bases containing carbon are known as organic bases. Acids that do NOT contain carbon are known as inorga...

Matthew ILG 1L

Acids containing carbon are known as organic acids. Bases containing carbon are known as organic bases. Acids that do NOT contain carbon are known as inorganic acids or mineral acids. Bases that do NOT contain carbon are known as inorganic bases.

Matthew ILG 1L

What topics should we expect to show up on test #2? From what I've heard, Test 2 will cover material up until Friday's lecture. Based on this, questions on Test 2 can appear from any material up until VSEPR. This includes, but is not limited to: 1. Review of high school chemistry 2. Quantum 3. Chem...

Matthew ILG 1L

So the final is cumulative, but Test #2 is just information from after the midterm?

Matthew ILG 1L

We won't have to draw VSEPR models, but we will most likely have to draw lewis structures and be able to label the VSEPR information.

Matthew ILG 1L

When labeling the bonds in a trigonal pyramidal model are we allowed to say that it is 109.5 degrees or do we have to specify that it is slightly less than that?

Matthew ILG 1L

I assume we will need to know how to do Lewis Structures, which was taught before the midterm, in order to label VSEPR models. But other than that I am not sure how much we will need to know or study from before the midterm.

Matthew ILG 1L

If "arrangement" is referring to the Lewis Structure and "shape" is referring to VSEPR model, then the arrangement is a 2-dimensional view of the molecular configuration, while the shape is a 3-dimensional model that has more specific angles.

Matthew ILG 1L

I don't believe that electronegativity and atomic radius are directly related. However, their trends are opposite, with the atomic radius increasing down and to the left and the electronegativity increasing up and to the right. It is a case of correlation without causation I believe.

Matthew ILG 1L

The syllabus says that only pens are allowed on tests. I have always used pencils for homework and other classes because I always am erasing things. But with a pen I have just started putting a large "x" over whatever I would normally erase.

Matthew ILG 1L

What type of calculator are you using? Also if you are rounding during intermediate values during the equation process that may be a reason that you are ending with a rounded value.

Matthew ILG 1L

The trends, such as electronegativity, atomic radius, and ionization energy, are typically very straight forward and have little to no exceptions.

Matthew ILG 1L

8 valence electrons is the limit for an element to hold in a given shell. If there are more than 8, then a new shell is formed.

Matthew ILG 1L

The way I learned in high school, the elements in third period and below are typically allowed to break the octet rule.

Matthew ILG 1L

Bonds lengths are measured in angstroms, the stronger the bond, the shorter the lengths. The length will be given to us I believe, as was the case in Wednesday's lecture when the Dr. Lavelle stated in a slide "Observed N--O bond length in (NO3)- = 1.24 Angstroms. "

Matthew ILG 1L

For week 5, I was still doing some hw from the "quantum world" section. The problems seem to still be relevant with the notes, although I did do half of my problems on "chemical bonds" as well.

Matthew ILG 1L

The reasoning for the octet rule that I learned in high school is that atoms "want" to be like the noble gases (He, Ne, Ar, Kr, Xe, Rn) and have 8 electrons in their outer shell, because electrons are most stable with a full outer shell.

Matthew ILG 1L

An easy way I like to remember that double bonds are shorter and stronger than single bonds is I think of them as sticks. Longer, skinnier sticks are easier to break i.e. weaker bond. The shorter and wider the stick, or in our case, the bond (triple bond), the stronger it is.

Matthew ILG 1L

The Lewis Structure should typically be symmetrical, with the singular element in the center.

Matthew ILG 1L

I know the problem you're referring to. Its 1.B.5. You have to convert the 140.511keV to eV by multiplying it by 10^3, and then multiply the eV by 1.6022x10^-19J to find the J.

Matthew ILG 1L

I have found in the past that drawing orbitals actually helps me understand the orbital levels better than just looking at it quantitatively. But there are others who would not benefit from drawing circles in a chemistry class.

Matthew ILG 1L

Having the equation sheet on the tests and quizzes, I would think that it is not too important to know how to derive the equations. There are many equations that are extremely complicated and time consuming to prove as well. I think that if Dr. Lavelle has proved the equation on the board during a l...

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