CHEMISTRY COMMUNITY

Kyra LeRoy 1E

For the final, do we need to know how to balance redox equations in basic conditions? Or should we just focus on acidic?

Thanks!

Kyra LeRoy 1E

Do we need to be able to use/apply the pseudo-first- or pseudo-second-order rate laws for the final?

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Kyra LeRoy 1E

Did anyone do question 9.20? I want to check my answers. :)

Thanks!

Kyra LeRoy 1E

When using experimental data, answers will not always be exact. However, they should be close enough to where you can assume 1.9 or 2.1 is 2, but not assuming the answer is 2 if you have, for example, 2.5.

Kyra LeRoy 1E

Also if anyone does 15.20 could you post your answers here?

Thanks!

Kyra LeRoy 1E

Did anyone do 15.18? If you did, can you post your answers here? I want to check if I got them right.

Thanks!

Kyra LeRoy 1E

On a test, I'm sure they'd still give you the points as long as all of the conversions match up (as long as it doesn't ask for a specific unit). My TA said if the question doesn't ask specifically for moles, then you can leave it in mmol if you are not confident that your conversions will be correct!

Kyra LeRoy 1E

For product to form, there must be something taken from the reactant. Therefore, you take the initial concentration of A and subtract the concentration that has been used to create B at time t.

Kyra LeRoy 1E

Do we need to know how to derive all of the differential/integral rate laws for the upcoming test?

Thanks!

Kyra LeRoy 1E

Is H20(l) never included in cell diagrams?
If so, are H20(g) and H20(s) included?
Also, are there any other molecules that will never be included in a cell diagram?

Thanks!

Kyra LeRoy 1E

When writing out the cell diagrams, how do we know when to put Pt(s) on it? And if its applicable, will it be on both sides? Or is it possible to have Pt(s) just on one side?

Thanks!

Kyra LeRoy 1E

For the half-equations Ag+(aq) + e- -> Ag(s) (cathode) and Ag(s) + Br-(aq) -> AgBr(s) + e- (anode) the cell diagram in the solutions says Ag(s)|AgBr(s)|Br-(aq)||Ag+(aq)|Ag(s) Why are the Ag(s) and AgBr(s) in the left half separated by a vertical line instead of a comma, even though they are in the s...

Kyra LeRoy 1E

Can someone walk me through writing the half-equations and balanced equation for this problem?

Pt(s)|O2(g)|H+(aq)||OH-(aq)|O2(g)|Pt(s)

Kyra LeRoy 1E

For all of the answers, I got my answers in Joules, but the solutions manual answers are in J/mol. Is there a reason for this, & will there be a difference between the two on the test?

Kyra LeRoy 1E

A follow up: I'm not sure if we went over the 2.303RT/F in class but I was watching videos on the Nernst equation & it talked about this.

I think it may just be a conversion factor if you want to use log instead of ln.

Kyra LeRoy 1E

Can someone explain where the 2.303 comes from in the Nernst Equation when
(2.303RT)/F = .059 V
so
E°= - (.0592)/n log(Q)

& why does this use log instead of ln?

Thanks!

Kyra LeRoy 1E

Can someone explain in which situations we use Cv and Cp? I think I remember my TA saying with entropy Cv is actually used when the volume and temperature are changing, but I don't know if I heard that correctly, since last chapter we used it when the volume was constant.

Kyra LeRoy 1E

In the solutions manual, it uses 1 mol of nitrogen gas in calculations. How do we know that there is 1 mol? Is this just something we assume if not given a molar amount?

Kyra LeRoy 1E

I just wanted to double check if my train of thought was correct on this one:

Is the heat negative on the 800K reservoir because the process is taking heat from that reservoir and giving it to the 200K reservoir?
If not, why is it negative?

Thanks!

Kyra LeRoy 1E

It takes heat to change the phase, so basically if you have ice and put it in water, it is first going to take the heat away from the water to melt the ice, and THEN the water will lose more heat to in turn heat up the "ice water." Therefore you add the heat required to melt and the heat t...

Kyra LeRoy 1E

You'll know to do a phase change when it hits the temperature for fusion or vaporization. I think normally these questions will have to do with ice/water because the melting point is 0 degrees Celsius and boiling is 100 degrees, and so its a pretty straightforward/easy one to remember. If it is ice ...

Kyra LeRoy 1E

On tests, are we going to need to know all of the steps that Dr. Lavelle went over in class, or do we just need to know the final form of the equations?

Thanks!

Kyra LeRoy 1E

Did you set the negative q of copper to the positive q of water? The copper is losing heat so you have to account for that by putting -q.

Kyra LeRoy 1E

In a simple form, you write out the reactions for combustion for those given enthalpies (add + O2 to all of them, reactants will be CO2 & H2O, except for with H2, then all you get as a product is H20). Then you just proceed as normal by multiplying/adding the equations together to cancel things ...

Kyra LeRoy 1E

Because getting from Celsius to Kelvin is just adding 273.15, the difference between T2 and T1 in Celsius is going to be just the same as between T2 and T1 in Kelvin. For example: If the initial temp is 20 degrees Celsius, that is 293.15 K. If the final temp is 40 degrees Celsius, that is 313.15 K. ...

Kyra LeRoy 1E

Can someone explain more in-depth the difference between ΔU & ΔH? I have a general understanding, but I’d like to have a more solid knowledge for the test. (for ex: in which circumstances do we use which one?)

Thanks!

Kyra LeRoy 1E

Do we need to memorize common enthalpies for elements that are not on the constants/equations sheet or will they be provided on the exam?

Kyra LeRoy 1E

How do we know if a substance is in its standard state? I know its the most stable form, but is there a way to tell if it is in that form? Or do we just have to memorize the standard states for common substances?

Thanks!

Kyra LeRoy 1E

Is there a certain time we should use joules vs using kilojoules (& vice versa)?

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Kyra LeRoy 1E

When you set the heat in ice and water equal to each other, why is there a negative sign in front of heat(water)?

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Kyra LeRoy 1E

Do we still get the paper with all of the constants & equations on it for tests in this class?

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Kyra LeRoy 1E

For question 45, the question asks about a pattern that can be drawn from the strengths. The answer says "aryl amines<ammonia<alkylamines" and "methyl<ethyl<etc." Where do these come from?

Thanks!

Kyra LeRoy 1E

100 kPa=1 bar, so to go from 1kPa you multiply each by 1/100 bar.

Kyra LeRoy 1E

If there are more moles of reactant, then an increase in pressure and decrease in volume makes the equation shift to the right. If there are more moles of product, increased pressure and decreased volume will mean a shift to the right. However, make sure you note that if pressure is increased becaus...

Kyra LeRoy 1E

Nonpolar; there is no difference in electronegativity between the atoms since they are all the same element.

Kyra LeRoy 1E

For part C, it asks whether Cl2 or F2 is more thermodynamically stable relative to its atoms at 1000. K. How exactly do we figure out which is more stable?

I got that the concentration for each is:
Cl2 .001 mol/L
Cl 1.1x10^-5 mol/L
F2 8x10^-4 mol/L
F 3.2x10^-4 mol/L

Thanks!

Kyra LeRoy 1E

In 17.31, when you add an element before or after the complex in brackets, how do you know how much of it to add?
For example, on A the answer for potassium hexacyanidochromate (III)
K3[Cr(CN)6]
How do you know that there are 3 potassium?

Thanks!

Kyra LeRoy 1E

Can someone explain the answer to this question to me? It asks: "Do you expect the bond angle between two hybrid orbitals to increase or decrease as the s-character of the hybrids is increased?" The correct answer is increase. Also, what exactly do they mean by "s-character"? Tha...

Kyra LeRoy 1E

For the upcoming test, the shapes/angles are just something to know by memory, correct? Also, does anyone know if there are there specific ones we need to have memorized or just all of them that are mentioned in the textbook?

Thanks!

Kyra LeRoy 1E

In general, the central element should not be negative, and the outer should not be positive. As long as that is followed, you just want to have the lowest overall charge & for the most part try not to have any charges on a single element above +1 or below -1.

Kyra LeRoy 1E

For the most part, electron affinity increases going upwards and to the right. There are a few exceptions (like nitrogen, for example), so the trend is not always exact. If you look at the 3rd photo on this website, it shows the EA's of each element with a corresponding color that makes some of the ...

Kyra LeRoy 1E

The 4s energy level is higher than 3d (and 5s higher than 4d, etc.), and you remove electrons from the highest energy level first, therefore you remove from the 4s first. You remove from the higher energy levels so that the ion is more stable.

Kyra LeRoy 1E

It goes from 1s to 2p in the question, and as you go down the periodic table it increases. In this case the increase downwards must be greater than the decrease to the right.

Kyra LeRoy 1E

Electron affinity is the energy released when an electron is added to a gas phase atom, so when it attaches, energy is is given off.When EA is negative, there is no excess energy to give off and actually more must be provided to attach it, and therefore EA is considered low. High electron affinity w...

Kyra LeRoy 1E

What exactly is the significance of the Px Py and Pz for the P-orbitals? Do we ever need to write these when writing electron configurations?

Thanks!

Kyra LeRoy 1E

There are 2(l)+1 orbitals in a subshell of quantum number l. So for D, when l=3, 2(3)+1=7

Kyra LeRoy 1E

When you have
E(photon)=1.66x10^-17 +(1/2)mv^2
why do they plug in (3.6x10^6) as v in the solution manual, when the given value in the problem is 3.6x10^3?

Thanks!

Kyra LeRoy 1E

It may be important to remember that the Lyman is UV & Balmer is visible, because I noticed that in one textbook problem it says "in the UV region" but never says Lyman or n1=1, but the problem solution requires you to recognize that UV means n1=1. However, I can't see the other two be...

Kyra LeRoy 1E

Just chapter 1. We haven't covered anything from chapter 2 in class yet.

Kyra LeRoy 1E

According to my TA, we don't need to know the exact wavelengths that go with each, but we do need to know which series n=1=1, n1=2, etc. go with.

Kyra LeRoy 1E

I don't believe so, its just the mathematical way to solve it because of the exponent on (1/2) being a variable. If there was another way I'd imagine it would be pretty complicated!

Kyra LeRoy 1E

So for question G9 I'm using the formula M(I) x V(I) = M(F) x V(F)
I got
M(I)=.179mol/L
V(I)=.5L

but I can't figure out M2 and V2? or am I possibly mixing up which ones are the initial and which are final?
This might actually turn out to be simple, but I'm stuck! Help!

Thanks :)

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