CHEMISTRY COMMUNITY

Lasya Gudipudi 1A

The equilibrium constant is equal to the forward reaction rate constant divided by the reverse reaction rate constant.

Lasya Gudipudi 1A

How can you tell whether a reaction is exothermic or endothermic based on activation energies for the forward and the reverse reaction, such as the homework problem 15.65 in the sixth edition?

Lasya Gudipudi 1A

I am having the same issue too. Here is my work:

Lasya Gudipudi 1A

Products are not included in the rate law because it looks at the initial concentrations when there are no products formed.

Lasya Gudipudi 1A

The activation energy is the amount of energy required to go from the reactants to the transition state. So, if activation energy increases that results in more energy required, which causes for a slower reaction. A slower reaction means a higher reaction rate.

Lasya Gudipudi 1A

Yeah, my TA emailed us and said that if you put that photosynthesis is non-spontaneous, he would give us our points back.

Lasya Gudipudi 1A

Pt(s) is generally used whenever a solid is not given to write the cell diagram for both the anode and the cathode.

Lasya Gudipudi 1A

You use H+ and H20 to balance half reactions in an acidic solution. H20 is used to balance the oxygen atoms while H+ is used to balance the hydrogen ions. It is easier to balance oxygen first, so that you know how many H+ ions you need to balance the equation.

Lasya Gudipudi 1A

I believe we get them during discussion this week.

Lasya Gudipudi 1A

Yeah, I was told the test will include everything from Gibbs Free energy till last Friday's lecture.

Lasya Gudipudi 1A

Yeah, I always do all the homework problems to get prepared for the exams. Also, I try to do some of the worksheets that the UAs post on here.

Lasya Gudipudi 1A

I don't think it will include concepts for Monday's lecture, but it will definitely include gibbs free energy.

Lasya Gudipudi 1A

Yeah, I just used the equation for constant pressure of an ideal gas to solve for the heat capacity of nitrogen gas.

Lasya Gudipudi 1A

When work is being done on the system, w is positive, and when work is being done by the system w is negative.

Lasya Gudipudi 1A

There are different types of heat capacities. C refers to heat capacity when there is no constant pressure or volume. C_p refers to the heat capacity when it is an ideal gas at constant pressure while C_v is the heat capacity of an ideal gas at constant volume.

Lasya Gudipudi 1A

He hasn't uploaded it on here yet, but he will make it sometime this weekend and will go over it during his review session on Monday 7pm-10pm in Franz 1178.

Lasya Gudipudi 1A

The midterm will cover all the topics we talked about in lecture until Friday (2/8/18). It is helpful to go over the objectives on his outlines for concepts on the midterm.

Lasya Gudipudi 1A

The first one is used when the external pressure is not constant, which is reversible expansion, and the other equation is used when the external pressure is constant, which is irreversible expansion.

Lasya Gudipudi 1A

To play it safe, I would just convert to atmospheres anytime you are asked for pressure.

Lasya Gudipudi 1A

Work is the energy required to complete a certain reaction in terms of chemistry.

Lasya Gudipudi 1A

Will the Peer Learning Sessions continue with the week's content, content for Week 5, or will they be backtracking in order to help with Midterm review?

I think it will be content from Week 4 and a little bit of Week 5 depending on which day you go. I feel like most will be review for the midterm.

Lasya Gudipudi 1A

If you are given the pKa, you would have to use the ICE table to find the concentration of [H3O+] at equilibrium and then take the -log of that value to find pH.

Lasya Gudipudi 1A

It is atmospheres, which is the same thing as atm.

Lasya Gudipudi 1A

No, he said if you ever miss a lecture, just get the notes from someone.

Lasya Gudipudi 1A

The equilibrium constant only changes when temperature changes. Anything else will not cause the ratio of products and reactant to change.

Lasya Gudipudi 1A

K only changes when the ratio of products and reactants change, but when concentrations change, the ratio stays the same. Therefore, K stays the same.

Lasya Gudipudi 1A

R is always a constant, so it will always be given. I think we may use the ideal gas law to convert from K_c to K_p or to find concentration when given pressure.

Lasya Gudipudi 1A

Use the information in Table 11.2 to determine the value of K at 300 K for the reaction 2 BrCl(g) + H2(g) <--> Br2(g) + 2 HCl(g). So for this textbook question, you have to go to table 11.2 where it tells you the equilibrium constants at different temperatures for two separate equations. If you mul...

Lasya Gudipudi 1A

K_eq is used to represent either K_c or K_p, but I don't think you will be marked down if you use K_eq all of the time. However, just to be safe I would use K_c when dealing with molarity and K_p when using partial pressure.

Lasya Gudipudi 1A

It doesn't really matter if you use parentheses or brackets when solving for K in terms of calculation. But to find K c , you use concentrations, so it is more appropriate to use brackets to represent molarity while when finding K p , you use partial pressure which is represented with parentheses. T...

Lasya Gudipudi 1A

In the sixth edition of the textbook, table J.1 lists the strong acids and bases in water, so it would be helpful to memorize these. Strong acids include HBr, HCl, HI, HNO 3 , HClO 4 , HClO 3 , H 2 SO 4 . Strong bases include group 1 hydroxides, alkaline earth metal hydroxides, such as Ca(OH) 2 , Sr...

Lasya Gudipudi 1A

Yes, the Rydberg's equation only applies to hydrogen, and we will only be required to know how to calculate energy levels for Hydrogen atoms.

Lasya Gudipudi 1A

Why is CO₃^2- monodentate and bidentate?

Lasya Gudipudi 1A

Yeah in lecture, he stated that strong acids and bases are completely ionized in water and weak acids and weak bases are not. So, for the scope of this class, you can say 100% dissociated.

Lasya Gudipudi 1A

Yeah, you will need to know how to name compounds because in a lot of the homework problems, the name is given instead of the molecular formula. He usually says that the final will be similar to the homework problems.

Lasya Gudipudi 1A

If the final asks for the intermolecular forces in a molecule, can we always write that London forces are present or are there cases where they are not? I believe Lavelle said that London Dispersion Forces are always present in between molecules that are close to each regardless of whether they are...

Lasya Gudipudi 1A

It also helps to determine the VSEPR formula or the steric number of the molecule and then determine the hybridization from there.

Lasya Gudipudi 1A

So in this molecule, all the borons have a formal charge of -1 and all the nitrogens have a formal charge of +1. Therefore, the molecule would have a net charge of zero.

Lasya Gudipudi 1A

Since it is a polyatomic species, you would look at the individual molecular compounds to determine the shape. For each C, the 3 Hs and the Be are arranged symmetrically, around the C. So, the shape about the carbons would be tetrahedral. However, since the question is asking for the hybridization o...

Lasya Gudipudi 1A

Also, in the example we did in class with XeF 4 , this is a square planar because it has 4 bonding pairs plus 2 lone pairs while a tetrahedral only has 4 bonding pairs, such as CH 4 . XeF4 has 6 regions of electron density while CH4 has 4 regions of electron density, which can also play a role in th...

Lasya Gudipudi 1A

Yes. In the example we did in class with the sulfite ion, the bond angles are expected to be 109.5 degrees because they are arranged tetrahedrally, but the bond angles are actually 106 degrees due to the extra lone pair on the sulfur atom.

Lasya Gudipudi 1A

MaiaRodriguezChoi3E wrote:Does anyone know of any resources similar to the audio visuals for the other topics this quarter? Do people find Khan academy helpful, or crash course videos?

I find Kahn Academy pretty helpful for understanding the general topics and if I need more specifics I will refer back to the textbook.

Lasya Gudipudi 1A

Lattice energy is used in ionic compounds to describe the bond strength. It is the amount of energy required to separate a mole of an ionic solid into the gaseous form of its ions. For example, the lattice energy of NaCl is the energy released when gaseous Na+ and Cl– ions come together to form a la...

Lasya Gudipudi 1A

I agree that the formal charge should be close to 0 on the central atom and if there are any charges they should be on the outer elements. It is also important to look at electronegativity, but the least electronegative element is more likely to be the central atom, so this follows the pattern that ...

Lasya Gudipudi 1A

Any element on or below period 3 of the periodic table can have an expanded octet because these elements have d orbitals that can hold more electrons.

Lasya Gudipudi 1A

I believe that questions about the properties of bonds will not appear on the midterm because professor Lavelle said that midterm material that will appear on the test will be up to what we covered in lecture on Wednesday.

Lasya Gudipudi 1A

The change in uncertainty in momentum is inversely proportional to the uncertainty in its wavelength. Yes, you have to use De Broglie because wavelength equals h/momentum, so if momentum decreases, then wavelength increase and vice versa.

Lasya Gudipudi 1A

In the sixth edition, question 57 on chapter 3 asks to draw the lewis structure of hydrogen sulfite ion (HSO3^-). How do you know that hydrogen is not bonded to sulfur and instead it is bonded to oxygen because I found a way that all the formal charges are 0 expect for an oxygen when hydrogen is bon...

Lasya Gudipudi 1A

The 4s orbital is filled before the 3d orbitals because the 4s subshell is lower in energy compared to 3d.

Lasya Gudipudi 1A

The work function specifically refers to the minimum amount of energy required to eject an electron, and the threshold energy refers to the frequency that light has to reach to eject an electron. However, when calculating using the equation, they are the same thing, which is why Professor Lavelle us...

Lasya Gudipudi 1A

So, to add up the electrons of a compound, you need to first count the number of valence electrons for each atom. In SO4^2-, Sulfur has 6 valence electrons and Oxygen has 6 valence electrons. But there is 4 oxygens, so the total number of electrons of oxygen is 24e-. You add the 24e- of oxygen with ...

Lasya Gudipudi 1A

To fill in the activities section for this question, you had to correspond each event with the type of wave it uses. So, for example, reading is visible light and suntan is UV. Then, you compare the wavelengths you calculated in nanometers and list the events from largest to shortest wavelength. For...

Lasya Gudipudi 1A

My TA said that the main topics covered on this test are photoelectric effect, De Broglie wavelength, Heisenberg uncertainty, Atomic spectra, and quantum numbers.

Lasya Gudipudi 1A

I believe there will be questions on quantum numbers, but I don't think there will be anything on electron configuration since he hasn't gone over that yet. Dr. Lavelle also said on Friday that the Friday lecture will be the last topics covered on test 2.

Lasya Gudipudi 1A

I remember that I came across a question that listed no numbers, so I was told to use 4 significant figures. The answer in the book also listed 4 sig figs, so I would use 4 sig figs if no numbers were given.

Lasya Gudipudi 1A

I think it will be only on quantum world, so you should understand everything listed under outline 2.

Lasya Gudipudi 1A

Personally, I tend to be as accurate as possible on every step to get the closest I can to the correct answer, then I will round to the amount of significant figures. Sometimes,I am still a bit of by about .1 or .2, but most of the time it is pretty accurate.

Lasya Gudipudi 1A

The number of significant figures that the answer should have is determined by what is given in the question and not what has been calculated. Therefore, since the molar mass of 84 is the only number that is given, then the answer should have 2 significant figures because 84 has 2 sig figs. If there...

Lasya Gudipudi 1A

So, I got the same ratio as you did, but instead of multiplying by 3, I multiplied by 5 to get 5:5:12. By multiplying by 3, the H would be 7.14 and you need whole numbers. Therefore, the answer is C5H12O5.

Lasya Gudipudi 1A

On the homework for E.9 on the sixth edition, there was a compound called magnesium sulfate heptahydrate, which is MgSO4, but they didn't provide the actual formula. For the first test, do we have to know how to name compounds? If so, how do we do that?

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