CHEMISTRY COMMUNITY

Kishan Shah 2G

The questions would have to say isothermal irreversible, so you would use the deltaS=nRln(V2/V1) formula. The delta S obtained is the delta S of the system. For a irreversible system, the graph is a sharp vertical dip, which means the surroundings do not have time to react to this change, so the del...

Kishan Shah 2G

Yeah same with me. I am usually really focused before finals week but there is a lot going on in terms of panic and new news. I try and get through some work but it seems like there are constant distractions every few minutes.

Kishan Shah 2G

You would have to be given the constant A, the rate constant, and the temperature to solve for activation energy.

Kishan Shah 2G

I don't think they bruincast the review session. However, they have a worksheet that they usually go through and they post it on chemistry community and then they will post the answers sometime after the review session. So if you absolutely can't make it you can still review the content they covered.

Kishan Shah 2G

yes, and he said he will teach pre-equilibrium approach to us in todays lecture!

Kishan Shah 2G

Last quarter the final was around 8 questions which a few parts to each one. It roughly covered each topic we had learned. However, it did not take 3 hours to finish. As Brian said, I had a lot of time to check my work before I turned it in.

Kishan Shah 2G

I don't remember there being a question where you had to utilize solubility rules. I think for concentration cells there was a HW problem that said if you change one of the ions in your salt bridge what would happen, and I think you were chagning NO3- to Cl- and if PbCl2 forms its insoluble so the s...

Kishan Shah 2G

You can use whichever units you would like but, as Brian said, make sure the units match up in all of your terms before solving.

Kishan Shah 2G

Yes there are multiple ways of expressing the equation. The first one is the linearized form and thats the one that Lavelle put on the Kinetics syllabus. I prefer to use that one since its easy to graph and see the linear line.

Kishan Shah 2G

Reduction occurs at the cathode and oxidation occurs at the anode.

Kishan Shah 2G

Since we know that this is in acidic solution. We also know that Chromium is being reduced, we can conclude that hydrogen ions will be in our reactants and water will be in our products. Also the electrons will be on the reactants side. After we determine what our products and reactants are, we basi...

Kishan Shah 2G

Yes, that is correct. No coefficients in your cell diagram. Use platinum in instances when you have no solids in your redox reactions.

Kishan Shah 2G

I'm not sure. I have only seen Carbon(graphite) and Platinum. I would stick with platinum just to be safe.

Kishan Shah 2G

It is basically the difference in potentials that gives rise to an electrical current. I'm not sure about the second part of your question though.

Kishan Shah 2G

Usually you can do the hw on material that he has taught within the past week of your discussion time.

Kishan Shah 2G

Second page of the thermodynamics outline(outline 4), and the all of outline 5. We will begin to learn kinetics but it will not be on the test.

Kishan Shah 2G

Hmm. I am not having that problem. Maybe try using a different web browser. I am also not sure how to post images on chemistry community.

Kishan Shah 2G

Yeah thats another good way. I may just end up using it!

Kishan Shah 2G

We will begin learning kinetics on Friday, but it will not be on the test.

Kishan Shah 2G

I agree with those above. I also thing its smart to go about and create a little study guide as you move through the text, lecture notes, and homework problems, outlining which situations in which to use certain equations and rules and exceptions. Repetition of the problems is key as the more proble...

Kishan Shah 2G

There is no other reason, other than the fact that it helps to visualize and see what is being oxidized and reduced.

Kishan Shah 2G

There is no other reason, other than the fact that it helps to visualize and see what is being oxidized and reduced.

Kishan Shah 2G

I think it is definitely manageable, however I do know that 14BL is a lot of calculations and it takes time. So if you think that learning OCHEM along with doing chemistry labs is too much then split it up.

Kishan Shah 2G

The best way to determine when to use which instead of memorizing them is to look at the units to see which units you are working with and what you want to end up with.

Kishan Shah 2G

Yes, you would just need to plug in 0 degrees celsius and 1 atm.

Kishan Shah 2G

Basically, Cv represents the heat capacity at constant volume, so a bomb calorimeter per say. Cp represents heat capacity at constant pressure, so an irreversible expansion. Cv is 3/2R and Cp is 5/2R

Kishan Shah 2G

This is a good question. When I was doing my calculations I used the same value for both but my calculations could be wrong. Does anyone know?

Kishan Shah 2G

Constant volume means there is no work done. At constant pressures, q is equal to delta H and work is -PdeltaV.

Kishan Shah 2G

What does AAP stand for?

Kishan Shah 2G

Personally, you can go under "your posts" tab and check the date on which you posted. This is the most definite way to check if you have completed the required number of posts in the right time period.

Kishan Shah 2G

In my opinon. The most applicable scenario in which we would use our knowledge about closed, isolated, and open systems in when assessing whether there are changes in heat and work. For example since a bomb calorimeter is an isolated system there is no work done on the system.

Kishan Shah 2G

Exactly what was said above. Dr. Lavelle just used those in derivations and to explain concepts to us. We don't actually need to solve problems using them.

Kishan Shah 2G

A negative delta G value or a positive detla S universe (total) value.

Kishan Shah 2G

Dr. Lavelle didn't lecture on any topics. He rather went over past exam questions in preparation for our midterm.

Kishan Shah 2G

You can reverse the sign of enthalpy change when doing Hess's law and you are trying to determine the overall reaction by manipulating the equations.

Kishan Shah 2G

I think the problem he did in his lecture was a good example. You have to identify the number of orientations the molecule can be in. Lets say its 3. Then you raise this number to the power of how many molecules of it there are. That is your W (degeneracy) in the boltzmann equation.

Kishan Shah 2G

Has Dr. Lavelle taught this yet?

Kishan Shah 2G

Basically work is represented by "w". negative work means that the system has lost energy since it has itself done work. positive work means that the system has gained energy because something else has done work on the system.

Kishan Shah 2G

I attended lyndon's review session earlier today, and he said he will be posting the worksheet later this week. He usually comes and announces it in lecture. I'm assuming he will do this either on Wednesday or Friday.

Kishan Shah 2G

The flat lines on a heating curve represent the deltaH(fusion) or the deltaH(vaporization) depending on where the horizontal line is. The increasing diagonal lines are representing the q=mcAT as we are heating the substance with a certain heat capacity.

Kishan Shah 2G

An isolated system is something where matter and energy cannot enter or leave the system. A closed system is where only energy, but not matter, can enter or leave the system. And an open system is where both matter and energy can enter or leave the system. That being said, an insulated water bottle ...

Kishan Shah 2G

Just took a look and that is right. 4D has Hess's law, and 4E is bond enthalpies, all of which we have covered. 4C may have some problems as well.

Kishan Shah 2G

You could read through the 4A and 4B focuses, but I would wait until he covers it in class. It seems as if he is going out of order for this unit.

Kishan Shah 2G

The way you calculate the enthalpy of these reactions is always (Delta H(Bonds Broken) - DeltaH(Bonds Formed)). So if you break a C-H bond lets just say, but then reform it, they will cancel out according to our equation. That is what is happening in this problem because the Bonds Form release energ...

Kishan Shah 2G

yes, the cutoff is 10^-3.

However, I would advise only to use the short cut when the value is 10^-5 since you don't want to take a chance and have your answer be off by a few digits. On the test I would always check your answer using the quadratic formula if you used the short cut.

Kishan Shah 2G

Yeah I do know that the Hess's Law HW problems are from 4d. Other than that I am also confused on which hw problems we should be doing.

Kishan Shah 2G

A very simple way to convert from concentration to pressure is (Pressure = Concentration * RT)

Kishan Shah 2G

I do not fully understand the scope of your question but I'll answer to the best of my ability. If they ask for final equilibrium concentrations and you begin with a certain amount of reactant, lets say 0.1, then the E section for that reactant would be 0.1-x, so you would plug x back in to find the...

Kishan Shah 2G

If H2 is removed from this chemical reaction. That means that the Q>K and the reaction will shift toward the reactants. Basically the system wants to compensate for the decrease in H2, so it will produce more reactants (H2 and N2) to raise the amount of H2 back so that Q=K

Kishan Shah 2G

In those instances in which you are not given a chemical equation, you need to use the context clues to generate an equation. Usually you will have to come up with the equations yourself only for Acid-Base equilibrium problems, in which the acid or base and water are almost always the reactants and ...

Kishan Shah 2G

As Kyle said, if Q<K then there is more reactants at that instance, so in order to reach equilibrium (Q=K), the reaction needs to proceed toward the products.

Kishan Shah 2G

Changing the volume changes the pressure. This can cause the reaction to lean toward the reactants or products but it does not change the equilibrium constant value.

Kishan Shah 2G

Click on the "Register Alias and Password) link at the top menu bar once you are logged in, and you will be able to change your alias to the new discussion section you are in

Kishan Shah 2G

Increasing pressure by inserting an inert gas will not change the way the reaction leans. Only increasing pressure by reducing volume will affect the reactant quotient which will change the direction that the reaction favors.

Kishan Shah 2G

I would recommend you read the textbook, complete all the HW problems, revisit your lecture notes, and browse Chemistry Community. If you do these things well you will be prepared for the test.

Kishan Shah 2G

In the context of equilibrium, you use this equation to convert from pressure to concentration. So if you want to calculated K(p) and you are given concentration values, you can use PV=nRT to convert to partial pressure values for that reactant or product. The same applies for converting from pressu...

Kishan Shah 2G

Yes, the concentration change of solids and liquids is insignificant. If you think about it, if they do not affect the concentrations of reactants/products, then they serve no purpose in the equilibrium constant.

Kishan Shah 2G

Q and K are calculated using the same rules and formula. However Q is used when you are given initial concentration/pressure values, and K is used when you are given equilibrium concentration/pressure values. You can compare Q and K to determine in which direction the reaction will proceed.

Kishan Shah 2G

Basically solids and liquids have a constant concentration. There may be very tiny changes in volume of them but its not enough to affect our calculations. The activity of solids and liquids at equilibrium is 1, so therefore it doesn't affect equilibrium concentrations.

Kishan Shah 2G

Threshold is 10^-4

Kishan Shah 2G

How can you identify when to calculate a reactant quotient vs an equilibrium constant. Also, are the rules for calculating them the same (ex: do you omit solids and liquids for reactant quotient as well?)

Kishan Shah 2G

This equation can be broken down into two smaller equation. By looking at the chart it becomes evident of what those two equations are. Then identify K values at the correct temperature for these reactions and multiply K values together for the overall K for the reaction.

Kishan Shah 2G

Always use variables in your change row. the coefficient for your change variable corresponds to the coefficient in the chemical equation. Use a negative sign to indicate using up of reactants and a positive sign to indicate production of products.

Kishan Shah 2G

Yes. The molecule needs to be polar in order to for it to have dipole dipole interactions since the dipole on one molecule can form an IMF with the dipole on the other molecule.

Kishan Shah 2G

They have the same trend but they mean different things. Electronegativity refers to the amount of pull that an atom can have on an outside electron because it wants the electron. Ionization energy means the amount of energy it takes to remove one electron from an atom.

Kishan Shah 2G

The Cl atoms don't directly attach to the DNA. The Cl atoms are replaced by nitrogen atoms when the cisplatin binds to guanine on the DNA. This is now going into too much depth. Just know its general function.

Kishan Shah 2G

Different resonance structures may have different formal charges for the atoms that are double bonded in one and are single bonded in the other. Just look at the overall charge of the molecule and make sure your formal charges add up.

Kishan Shah 2G

Because the conjugate base of HClO4, which is ClO4 is more stable than the conjugate base of H3PO4, so HClO4 is more likely to disassociate more in solution as H+ ions and ClO4- anions. Eventhough it is polyprotic, to my knowledge it really has no effect on acidity strength. Here is a formal explana...

Kishan Shah 2G

When it absorbs a hydrogen atom, then it absorbs energy so the energy change is positive meaning it gained energy.

Kishan Shah 2G

SO3 is basic, not acidic. Acidic oxides are oxides that reacts with water to form a solution of a Bronsted acid. SO3 is an example of an acidic oxide because when it reacts with water, it forms H2SO4. SO3 + H20 --> H2SO4. Since H2SO4 is an acid, SO3 is an acidic oxide. It is also useful to not that...

Kishan Shah 2G

Na[Fe(OH2)2(C2O4)2]

Kishan Shah 2G

The TA's will decide when to give back Test 2. The final will cover everything since day 1 of class.

Kishan Shah 2G

Nope! Lavelle only posts video modules for quantum and fundamentals.

Kishan Shah 2G

Try not to get too caught up in the wordiness of the questions. You need to break everything down so you have just moles of whatever atom/compound you want to find the molarity of and the volume of the solution. Then divide the number of moles by the number of liters to get the concentration.

Kishan Shah 2G

Hydrogen Bonds and pi ponds really have nothing to do with each other in my knowledge.

Kishan Shah 2G

Dr. Lavelle provided his own chart. I think it is linked above in one of the other replies!

Kishan Shah 2G

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.

Kishan Shah 2G

@Leila: The shape of AX2E is bent. The bond angles are 120 degrees. For AX2E2 it is still bent, but the bond angles are 109.5 degrees since the two lone pairs push the two atoms further away from them therefore decreasing the angle.

Kishan Shah 2G

I think you mean to say "induced-dipole induced-dipole." Yes this is the weakest form of interaction since it is synonymous with LDF and Van der Waals forces. So technically it is present to some extent in all molecules. Contrary, "Dipole-Induced-Dipole" is an interaction between...

Kishan Shah 2G

The easiest way to explain ion-dipole interaction, is the salt in water example. Lets take NaCl for example. The sodium has a positive charge and the chlorine has a negative charge. So the water molecules will surround the the NaCl ion in such an orientation that the positive hydrogen atom in water ...

Kishan Shah 2G

I think the general idea behind pi and sigma bonds that we need to know is determining how many of each there are in a large molecule of some sort. So the basic rule of a single bond having 1 sigma bond, a double bond having 1 sigma and 1 pi bond, and a triple bond having 1 sigma and 2 pi bonds is u...

Kishan Shah 2G

Can someone explain more in depth why CH2Cl2 is polar?

Kishan Shah 2G

What Camellia said is correct. However, yesterday I came across the idea that HCl has a stronger bond than HBr since the bond length in HCl is shorter and stronger since Cl has a smaller atomic radii than Br does. How do you know which reasoning to use?

Kishan Shah 2G

To my knowledge Test 2 will only contain information from the end of Chemical Bonds outline and from the Molecular Shape and Structure outline. This is also a good question to ask your TA's

Kishan Shah 2G

That is probably a good question to ask our TAs as I am also wondering the same thing.

Kishan Shah 2G

The class is based of points. The max points is 500. The first test was 50 points, the midterm was 120 points, the HW problems are 50 points, and then the rest is consituted by Chem Community participation, Test 2, and the Final. Your final grade will be determined by the amount of points you earned...

Kishan Shah 2G

The best course of action would probably be to talk to your TA in the next discussion section or reach out to them via email.

Kishan Shah 2G

I do not think our scores will be posted online until the next few days. However, we received our physical test grades back after class from our TA's today.

Kishan Shah 2G

Yes, under the chem14A tab on the website, on the bottom right corner these is a link that says midterms solutions.

Kishan Shah 2G

3F and latter sections from the Chemical Bonds Outline, and all the sections from the Molecular Shape and Structure Outlines will appear on the test.

Kishan Shah 2G

The high electronegative atoms will be the only ones strong enough to pull away the electron from hydrogen to form the H-bond.

Kishan Shah 2G

According to Dr. Lavelle, we should receive them after lecture on Wednesday

Kishan Shah 2G

Sure! That would be great

Kishan Shah 2G

Read the textbook in order to fill in gaps in your knowledge from the lecture. Once you think you know the information, then attempt the HW problems to get an accurate representation of how well you know the material.

Kishan Shah 2G

An easy way is to count the number of lone electrons, not lone pairs, and add that the number of bonds( so a single bond would be one bond, a double would be two bonds). Then subtract this value from the number of valence electrons for that element.

Kishan Shah 2G

This is due to the fact that the electrons are delocalized. Therefore, the bonds in the structure are a blend of single and double bonds, or in another words they have single and double bond character. Therefore the bond lengths are the same.

Kishan Shah 2G

This is due to the fact that the electrons are delocalized. Therefore, the bonds in the structure are a blend of single and double bonds, or in another words they have single and double bond character. Therefore the bond lengths are the same.

Kishan Shah 2G

This weeks HW will be on chemical bonds

Kishan Shah 2G

Br would be in the center will 3 single bonds to Flourines. Draw in 3 lone pairs for each flourine to complete the octet for them, and add 2 lone pairs onto the Br in the center. In this case, Br is capable is having more than an octet.

Kishan Shah 2G

I had the same question. I emailed my TA and am awaiting a response.

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