CHEMISTRY COMMUNITY

Adrian Lim 1G

How would we know that I2 is not conductive?

Adrian Lim 1G

I think usually the signs for delta s in the surroundings and system depend on the reaction itself. I believe the surroundings and the system would essentially be the opposites of each other. As stated above, delta s is basically q/T, so we could determine signs from heat either absorbed or released.

Adrian Lim 1G

I would know the different graphs; however, if you were to know the different parts of the equation, graphing it shouldn't be too hard but it would probably be wise to know the graphs of the different reactions.

Adrian Lim 1G

Also, for that question, do you know where the 1.8 from k'/k comes from and the -0.59 comes from at the end? When I plug in my numbers I end up getting something like 1.06 for k'/k, so my numbers are off.

Adrian Lim 1G

For that equation, do you know if it would matter if we switched k and k' as long as the corresponding temperatures are the same? Would you end up getting the same result?

Adrian Lim 1G

I'm not too sure why for step 1, it is just written as Cl instead of Cl-. It might be due to balancing charge, but the solutions manual says that the intermediate is the chloride ION, so I would just stick to Cl-

Adrian Lim 1G

I would first look for the intermediate(s), which is produced and then used up to get the overall reaction. As for the diagrams, I just went from left to right of the molecule, but I don't think it would hurt too much to have the compound written in a slightly different form as long as everything is...

Adrian Lim 1G

I don't think it will include the slow and fast reactions.

Adrian Lim 1G

Why can we use the mass in this instead of concentration in this problem?

Adrian Lim 1G

For the most part, it would be easier to see the changes if you had the rate of reaction and the corresponding orders. From there, you could just plug in new concentrations to see what kind of effect it would have on the overall rate.

Adrian Lim 1G

Does anyone know which homework problem 15.6 would go up to?

Adrian Lim 1G

Because C is independent of the rate, we consider it as zero order. Therefore, we would not include it in our rate of reaction equation

Adrian Lim 1G

Because C is essentially zero order, it would be best to leave it off. If you leave it in the rate law, you would need an exponent of a 0 essentially indicating that it is independent of rate. Otherwise, you would probably be marked off for leaving it in.

Adrian Lim 1G

We usually want the rate to be a positive number because it might seem unusual for a rate to be a negative number. Thus, when we calculate the rate of a reactant, we usually add the negative sign in front of the change of concentration over change in time. This is because the change in concentration...

Adrian Lim 1G

Yes, you should have units to see which units you need for k. Also, it is wise to always make sure to include units; even if it isn't necessary, it's nice to double check certain terms and values.

Adrian Lim 1G

The rate of N2 would be 1/3 times the rate of H2

Adrian Lim 1G

I think the answer in the solutions manual shows the rate of reaction of NO2 in this specific reaction, so it doesn't divide by 2 for part a

Adrian Lim 1G

For that same question, what do they mean when they ask for the unique rate of reaction?

Adrian Lim 1G

I also do not understand why we would need deltaG values to calculate the potential of a half-reaction

Adrian Lim 1G

Isn't I2 a solid though?

Adrian Lim 1G

You would not need to multiply E by the factor, but if you were to switch the equation, the E would change sign.

Adrian Lim 1G

I believe it would be better to flip the anode because in a redox reaction, we would add up the two half-reactions, so some terms would need to balance out on both sides.

Adrian Lim 1G

I also think that for the test, it would just be given to us in a chart or some form

Adrian Lim 1G

Just think of the opposites, so the oxidizing agent is reduced, while the reducing agent is being oxidized!

Adrian Lim 1G

We changed the final temperature during review in order to reflect the fact that the final conditions were exactly the same as the initial conditions

Adrian Lim 1G

I believe for reduction of pressure from 8 atm to 1 atm, work would just be 0 because according to w = -Pdeltav, since volume doesn't change, work would just be 0. This step should be done separate from the volume change, however, which can be given by w = -nRTln(V2/V1).

Adrian Lim 1G

I believe if the process is isothermal, meaning there is no change in temperature, then the reversible system would have a delta U = 0.

Adrian Lim 1G

So would the signs be the same for entropy as well?

Adrian Lim 1G

I would memorize the equation, but it should be pretty simple to derive just in case you forget on the test.

Adrian Lim 1G

delta G = (-604.03 - 392.36) + 1128.8 = 130.41 kj/mol
lnk = - 130410/(8.314*298.15) = -52.61
k = e^(-52.61)
k = 1.419 * 10^-23
k = 1 * 10^-23
Hopefully this helps!

Adrian Lim 1G

Just as Andres stated, we assume the temperature is 25C because it is in standard state. However, when you plug T into the equations, make sure the temperature is in Kelvin because the unit of R is given in Kelvin

Adrian Lim 1G

For 11.83, we need to find both delta H and delta S in order to use the formula delta G = delta H - T delta S to find delta G. We are not given the delta G, so we would need to find this. Once you find delta G, you can just use the formula delta G = -RTlnK to find K, the equilibrium constant.

Adrian Lim 1G

Yes, I think the heat capacity will usually be given to you.

Adrian Lim 1G

I think it would be best to use 273.15 and then for the final answer just truncate if necessary for the number of sig figs.

Adrian Lim 1G

I believe the equation can be used for ideal gases

Adrian Lim 1G

Yes, I believe most of the time, the questions will tell you whether or not it's an ideal gas.

Adrian Lim 1G

I think it also depends on the information that you're given. Depending on that information, you can determine which equation to use.

Adrian Lim 1G

I believe the signs in the solutions manual are referring to the system itself

Adrian Lim 1G

The units are J/K, but if you forget, it could be helpful to write out the units and then see which cancel and what you're left with.

Adrian Lim 1G

What would the c value be in delta S=n*C*ln(t2/t1)?

Adrian Lim 1G

So the signs would be in reference to the system?

Adrian Lim 1G

What if there were a change in pressure?

Adrian Lim 1G

Yes it did! Thank you!

Adrian Lim 1G

The delta H given is for 1 mole of reaction or 3 moles of H2. However, the question is asking for the change for the production of only one mole. Thus, you would have to take the given delta H and divide it by 3

Adrian Lim 1G

I also thought that there would be a C=O double bond formed. Can anyone please clarify?

Adrian Lim 1G

On his website, he also said under announcements that there will be no questions on isothermal or reversible expansion on test 1.

Adrian Lim 1G

For 8.17, the solutions manual says delta E is 0 when change is occurring at a constant temperature. is deltaE just the same as deltaU?

Adrian Lim 1G

Also, the problem says that the surroundings is a cooling system, which means that the surroundings will absorb the heat from the system. Thus, because the system is losing heat, the q in relation to the system would be negative.

Adrian Lim 1G

In the solutions manual, why is ln (v2/v1) stated as ln (2.4/1.2)? Where does the 2.4 come from?

Adrian Lim 1G

Why do we need to multiply the distance, d, to 1L/1000cm^3 to find delta V?

Adrian Lim 1G

I believe Dr. Lavelle posted the formula sheet similar to what we would be receiving on the test.

Adrian Lim 1G

Just to clarify, R is the ideal gas constant and its units are given per mole. Thus, when you are using this for q = mcdeltat, make sure the m is amount given in moles so the moles with the c would cancel.

Adrian Lim 1G

Like the reply above stated, it's just a different way to calculate work. We can use - delta n R T if we know the net change in moles of the equation in order to find the work.

Adrian Lim 1G

R is essentially the gas constant, which is 8.314 J * K^-1 * mol^-1. When we use this constant to find heat (q) with the equation q = m * c * delta t, we need to make sure the m is in moles because the unit of the constant is given per mole.

Adrian Lim 1G

Both would probably be acceptable, but it may be best to stick to whatever Dr. Lavelle prefers to use in lecture.

Adrian Lim 1G

Yes, I don't think he covered the initial homework problems yet, which is probably why he is allowing us to turn in both week 1 and week 2 homework problems during week 2 of discussion.

Adrian Lim 1G

So would heat be a path function?

Adrian Lim 1G

If there is a net dipole moment, then the molecule is essentially polar. If the dipole moments cancel, this makes the molecule nonpolar.

Adrian Lim 1G

We should probably know the common strong and weak acids and bases, but otherwise there are ways we could determine the strength, such as a the presence of higher electronegative elements to offset charge or the length of the bonds.

Adrian Lim 1G

Also, to look at what kind of dentate it would be, you could look for nitrogen. Usually, nitrogen would have a lone pair of elections that would want to form a bond. Also, you could look for atoms that have a negative charge, for those are the ones that would want to form bonds. Otherwise, it would ...

Adrian Lim 1G

Using lone pairs may also help to write the VESPR type, which can help with naming of the shape. For example, if you had one lone pair on the central atom and three bonded atoms, the VSEPR would be AX3E, and as a result, you can tell the shape from this.

Adrian Lim 1G

Do you know if Dr. Lavelle has a chart of all the shapes and bond angles of the different shapes? Also, some angles are a bit confusing, as some may say approximately less than 109, whereas a solution may be more accurate, such as 107.5. Should we know the exact numbers?

Adrian Lim 1G

For the electron arrangement, you can essentially look at the number of electron densities around the central atom, whereas for the actual shape, you need to just look at the number of atoms surrounding the central atom. However, you need to also be aware of any lone pair electrons, which could resu...

Adrian Lim 1G

Should we just memorize the names the old way instead of the new naming system?

Adrian Lim 1G

Where does the roman numeral III come from? Does it stem from the charge of the chromium?

Adrian Lim 1G

This is because at times, lone pairs may result in more repulsion, thus creating a different bond angle.

Adrian Lim 1G

Is there a difference between the electron arrangement and the shape of a molecule? How do the electron pairs impact the electron arrangement and how do the electron pairs impact the shape of a molecule?

Adrian Lim 1G

H20 has a bent structure, so the dipole moments that move towards the more electronegative oxygen do not cancel out, making H20 polar. However, in CO2, the structure is linear, meaning the dipole moments would end up cancelling out each other, making it non polar.

Adrian Lim 1G

To reiterate, the spin number is +1/2 and -1/2; however, we will not be able to determine which is which at certain times depending on how one draws the spin of the electrons in the orbitals.

Adrian Lim 1G

Does anyone know if we're expected to list all the possible resonance structures wherever applicable on the midterm?

Thanks

Adrian Lim 1G

What if the electron configuration were 3d^3 4s^2? Would electrons be removed from the s-orbital or the d-orbital?

Adrian Lim 1G

Also, I believe you can look at the different spins on the electron to tell whether it is in an excited state or ground state

Adrian Lim 1G

Hi I just had a follow up question about the second part. Why isn't the electron configuration for Tungsten [Xe] 4f^145 d^5 6s^1? I remember Dr. Lavelle talking about exceptions during a lecture, and one of them included chromium, which would want to have a half full d^5 orbital. Why doesn't Tungste...

Adrian Lim 1G

Jenny, I do not think that chapter 3 would be included in test 3; just 1.6 to the end of Chapter 2

Adrian Lim 1G

Should we convert all the units to meters or picometers before doing this problem?

Adrian Lim 1G

What is the importance of h/4pi? Where does the 4pi come from?

Adrian Lim 1G

I would just remember that visible light is between 400 nm (violet) and 700 nm (red)

Adrian Lim 1G

Just to clarify, do you multiply or divide avogadro's number?

Adrian Lim 1G

It would depend on the problem as all the replies above have stated, but it may be a good idea to see the units of the values that the problem gave and just be consistent with that.

Adrian Lim 1G

Should we know the approximate numbers of the different wavelengths?

Adrian Lim 1G

Planck's constant is a set number for the constant h. It is used in formulas, such as E = hv. It will be given to you on the formula sheet. Just to reiterate the above reply, don't get it confused with p. p stands for momentum and is equal to the mass * velocity.

Adrian Lim 1G

Hi,
Does anyone know why the answer the question 29 part b on the photoelectric post-module is not B? They tell us the work function for sodium is 150.6 kj/mol and then asks us how much energy is required to remove an electron from the sodium atom. Wouldn't that just be 150600 J or 1.506 * 10^5?

Adrian Lim 1G

Just to clarify the above response - the energy of the incoming photon - work function = energy of the electron being ejected. Also remember that photons work in packets, meaning one photon needs to have a sufficient amount of energy to eject one electron, also known as the work function. One photon...

Adrian Lim 1G

Yeah since you will probably get the value of the constant on the formula sheet, I would just use the value given. Otherwise, just follow the rounding necessary based off the given values.

Adrian Lim 1G

Hi,
Are you talking about part a with Na, Al, and F? After dividing all three by the smallest, I got 5.9, so I would assume you could round to 6.

Adrian Lim 1G

You have to use the molar mass of CuSO4 5H20 because the question is asking you to find the mass of the whole compound, including the 5H20.

Adrian Lim 1G

I also don't understand the problem very well. Do you think it'll be mentioned in the test on Friday?

Adrian Lim 1G

I believe it is okay to leave it in pm as long as you label your units. However, in chemistry, if you were to convert the pm to meters, it would probably be best to write your answer in scientific notation, considering the fact that a picometer is extremely small in comparison to a meter.

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