CHEMISTRY COMMUNITY

Gurvardaan Bal1L

If you refer to Dr. Lavelles outlines for each topic on his website, they give questions you can answer and conceptual problems that give you a good idea of what to study and how much to study in preparation for the final.

Gurvardaan Bal1L

If I remember correctly, the book literally just mentioned it as an exception and then moved on past it so I don't think we'd be able to know.

Gurvardaan Bal1L

I don't think you will have to know anything about that seeing as how it was not covered in 14b. But if you want to know, a nucleophile is reactant that seeks out centers of positive charge in a molecule. :)

Gurvardaan Bal1L

I don't think they would be any different, K and Q are basically the same thing just that K is at equilibrium and Q is at a particular time in a reaction. The formula for that would be the concentrations of products multiplied against each other(each raised to the power of their respective coefficie...

Gurvardaan Bal1L

You're right in how you state the first theorem, but the fact of the matter is that it applies if you do nothing to the system. Basically, if you leave an isolated system alone for 5 second and come back 5 minutes later, the energy is still the same because it is isolated.If you were to change the v...

Gurvardaan Bal1L

In this case when you double the amount of A you double the reaction rate so that is not squaring. It would be squaring if you doubled the concentration of A and then the reaction rate quadrupled, or if you tripled the concentration and the rate increased by a factor of 9. Based off this you would b...

Gurvardaan Bal1L

Right and I understand that, but there are examples of problems in the book where products are a factor as in section 15.3 page 621. So what I'm asking is can the rate law be applied to reverse reactions using the product concentration or maybe halfway points in the reaction process?

Gurvardaan Bal1L

For stopped flow technique, you are basically mixing solutions of reactants together and observing their reaction over a course of a millisecond using spectroscopy to measure it. The stopping syringe, at least to my understanding, would prevent anymore reactant from being added into the reaction cha...

Gurvardaan Bal1L

Do rate laws always take the initial rate into account, seeing as how we only are interested in the concentrations of the reactants? Or is this just a format to get the rate of the forward reaction, and you could also write a rate law for the reverse of a reaction?

Gurvardaan Bal1L

From what I understand from today's lecture, k is the normal rate constant for a reaction, let's say for rate = k[A] N [B] M [C] L . However, if [B] 0 and [C] 0 >> [A] 0 , we can say that rate = k'[A] N , and that the reaction is a pseudo-first order reaction. Comparing the two, we can see differen...

Gurvardaan Bal1L

Yes, since past those problems its past 15.6 which is not covered.

Gurvardaan Bal1L

Nicole Jacobs 1C wrote:How do you tell if the reaction is controlled by thermodynamics? by kinetics?

Kinetics is the rate/speed of the reaction, while thermodynamics is how favorable the reaction is to occur.

Gurvardaan Bal1L

Why is the reaction with the higher standard potential considered to be at the cathode? Is this always how we should approach assigning rxns to different electrodes?

Gurvardaan Bal1L

Its based off what they tell you, if they say that each electrode is made of platinum then you would need it on both sides, if not then you would put it on whatever electrode they say uses platinum.

Gurvardaan Bal1L

I'm a little confused as to why the hydrogen electrode is found to be the cathode in the example between the hydrogen and zinc electrodes. I thought the cathode is where reduction takes place, and although I understand that because of the negative standard potential the hydrogen electrode is the cat...

Gurvardaan Bal1L

Why does container A have more entropy than container B and C? I thought that larger/more complex molecules are supposed to have higher entropy, which seems to be contradicted here.

Gurvardaan Bal1L

When you are looking at a reaction, what is the best way to determine whether entropy increases/decreases? I understand that if there are only gas molecules/elements you would would look at the net change in the number of moles, but what should you do for reactions that have components in multiple p...

Gurvardaan Bal1L

For the midterm what are some of the formulas that we will be expected to know how to derive? Will any of these formulas not be on the formula sheet?

Gurvardaan Bal1L

Naana Boateng 1I wrote:What is the difference between Gibbs free energy and enthalpy ?

Another thing to note about Gibbs free energy is it is the free energy available to do only non expansion work, not just any other type of work.

Gurvardaan Bal1L

What do you need to know about the third law of thermodynamics A good way to think about this is, as temperature decreases we get to a more solid/organized state, such water in liquid form to solid form as ice. As we do that, we are decreasing entropy because the molecules are obviously moving less...

Gurvardaan Bal1L

I'm confused about how the Clausius inequality does not contradict the idea that entropy is a state function. How can deltaS = qrev/T =qirrev/T due to the fact that it is a state function but then the Clausius Inequality states that deltaS > qirrev/T? Thanks for the help! if you read the paragraph ...

Gurvardaan Bal1L

When determining how stable a compound is, does a more negative standard Gibbs free energy of formation refer to the more stable compound? Say if you had two compounds, one that is more negative than the other. Would we classify the more negative compound as "more stable"?

Gurvardaan Bal1L

What exactly is residual entropy and how is it related to the Boltzmann equation?

Gurvardaan Bal1L

For problem 9.13, why is R used instead of heat capacity for the entropy equation regarding temperature change?

Gurvardaan Bal1L

Maria1E wrote:Are we supposed to know how to use the formula 3/2RT for Test 1?

I believe not because Prof. Lavelle only mentioned no calculations for work and internal energy, and that formula is for internal molar energy for an ideal gas.

Gurvardaan Bal1L

Does isothermal expansion always have a delta U = zero or is it only true for ideal gases?

Gurvardaan Bal1L

For part b on example 8.6(on page 281) why is delta U equal to q using the heat capacity at constant volume? I thought that at constant pressure the change in internal energy is equal to the change in enthalpy, so I'm confused as to why we are measuring q using the heat capacity at constant pressure...

Gurvardaan Bal1L

Hyein Cha 1K wrote:how is the unit of pressure kg/(m*s^2)?

Kg/(m*s^2) is simply a conversion from atmospheres. 1 atm = 10332 kg/(m*s^2), so this is basically just another way of expressing pressure in different units.

Gurvardaan Bal1L

For 8.45 part b, why can we use the standard reaction enthalpy to calculate the heat absorbed when the textbook explicitly states that carbon is not in its pure form? I thought that by definition, standard reaction enthalpy means that this is the enthalpy for when reactants in their standard states...

Gurvardaan Bal1L

What is the difference between these two? Standard heat of combustion is the change in enthalpy of a substance when it undergoes complete combustion with oxygen, while standard heat of formation is the change in enthalpy when 1 mole of a compound or substance in its standard state is formed from it...

Gurvardaan Bal1L

Hi! I always forget the difference between endothermic and exothermic reactions. Does anyway have an easy way to remember them? Thanks! (Claire Woolson Dis. 1K) Endo- is the root for within/inside, so this would be taking heat in. Exo- is the root for outside, so this would be releasing heat. Hope ...

Gurvardaan Bal1L

Expansion work is when you perform work(which is when you achieve motion against an opposing force), the changes the volume. A good example of this would be gas in a combustion chamber. As the gas pushes up the piston, there is now more volume in the combustion chamber, which is expansion. The formu...

Gurvardaan Bal1L

What exactly is bulk matter and how is it defined? Would it be anything larger than an atom( e.g. molecules)?

Gurvardaan Bal1L

What are superacids and superbases? How can we tell whether an acid or base is one and what are their conventional uses?

Gurvardaan Bal1L

Do we not include water in the acidity/basicity constants because it is a pure liquid or because it is in excess? I heard both from different people and wanted to know which is correct or if both are correct.

Gurvardaan Bal1L

Why do you multiply the mole fractions by 0.1 bar? I understand doing that for X2, but for 2X why wouldn't it be 0.2 bar(seeing as the coefficient is now doubled so the pressure would be too)?

Gurvardaan Bal1L

Depends on the solvent. Based off what I found not all solvents are liquid so I'm guessing the answer would be sometimes, as it depends on the phase that the solvent in question is in.

Gurvardaan Bal1L

I understand that there are two different forms of the equilibrium constant equations and that they are calculated with molarity and partial pressure(respectively), but is there any difference as to how they are interpreted? Today in lecture Professor Lavelle talked a little bit about this with the ...

Gurvardaan Bal1L

Based off what the syllabus says and the sections in the book, I would do up to problem 63 for the chapter 11 HW, the problems after that are from past section 11.8. It would probably be helpful for someone to ask to make sure this is correct though.

Gurvardaan Bal1L

Possibly. I would say to make sure to know why and how the orbitals are formed, because that could be a possible conceptual question. You should know why electrons choose to be alone versus in pairs, how hybridized orbitals increase options for bonding, etc. As long as you have a good grasp for how ...

Gurvardaan Bal1L

If there are multiple regions of electron density (Say 5) and you have one lone pair of electrons, the shape would then be a seesaw. How do you know what the angles are for the bonds in the molecule? I know the lone pair would have some effect on the angle of the bond but I'm not really sure how to ...

Gurvardaan Bal1L

altaing wrote:Will dipole moments be on the midterm?

Unsure if they will be tested in any particular way, but you should definitely know what they are on a conceptual basis.

Gurvardaan Bal1L

Why don't quadruple bonds occur very often? Quadruple bonds seem to make sense by the Lewis structure point of view, but when studied in an experimental level you'll see that it is difficult/impossible for quadruple bonds to occur because it would require the orbitals to point in certain directions...

Gurvardaan Bal1L

A) When you're are given the n and l to find the total number of possible electrons you determine the possible ml values and and multiply the number of possible ml values by 2. ml is l, l-1,...-l. n=2; l=1 so the subshell is p. This means that ml can be -1,0,1 and 2 electrons can fill each of those...

Gurvardaan Bal1L

Yes, you would do this.

Gurvardaan Bal1L

1.55) If an absorption occurs in the infrared spectrum at 3600 cm^-1, what is the frequency of the radiation that corresponds to that absorption? I understand that we need to use E = (v/c), and I understand how to the get the right answer once you convert the speed of light to meters. But I'm wonde...

Gurvardaan Bal1L

I am also struggling with this problem. How would you know to use the equation E=v/c? And why is an absorption, with units in cm, considered energy? If you read the problem fully, it tells you that in infrared spectrophotometry energy is expressed in terms of v/c, which is where E = v/c comes from....

Gurvardaan Bal1L

If you go on the chem 14a page and scroll down to course materials, its right underneath the section with the information about the TA's, its close to the top of the page.

Gurvardaan Bal1L

Another form of the Rydberg equation you can use is:

Frequency = R( (1/(n1)^2) - (1/(n2)^2) )

You would get 1/4 and 1/16 because when you put in the energy levels for n1 and n2(which would be 2 and 4), and then using the Rydberg constant you could then proceed to solve the problem.

Gurvardaan Bal1L

Will we be expected to know conversion factors from units such as miles to meters or ounces to grams on the test in our discussion section or will such numbers be supplied to us?

Gurvardaan Bal1L

What part of the EMS is the light used for photoelectric experiments typically from? This was a question from the post-module assessment on photoelectric effect.

Gurvardaan Bal1L

What does answer choice D mean when it says the energy of the radiation increases? Does energy have anything to do with frequency or amplitude/intensity of the wave? What D means is that the energy of the oscillations of the electric and magnetic field is increasing. These oscillations all transfer...

Gurvardaan Bal1L

If your told one wave of light has higher energy than another do you assume that the amplitude is higher, the frequency is higher, both, or can it not be determined? If you are told this, you can assume that the amplitude is larger, but you cannot assume that the frequency is also higher. Frequency...

Gurvardaan Bal1L

The answer to this problem is (c) due to how electrical fields are directly related to the frequency. If you go to page 4, on the third paragraph directly before the definition of 1 Hertz, the book talks about how the passing of an light ray by an electron pushes the electrical field of an electron ...

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