CHEMISTRY COMMUNITY

camrynpatterson3C

But all the good ones Argon. /:

camrynpatterson3C

Periodically.

camrynpatterson3C

Question 4 about the droplets assumes that the number of moles is 4. How do we know this??

camrynpatterson3C

Would the reaction of I- and I3- be an oxidation reaction or a reduction reaction? How would it be either, since both the charges are -1?

camrynpatterson3C

For this homework problem, since we're trying to find the std Gibbs free energy of another step in the reaction that has a K 10x bigger than the first K, shouldn't we just be able to find K1 from deltaG=-RTlnK, then plug that number in times 10 to find the free energy of the next step in the reactio...

camrynpatterson3C

Is the change in internal energy for irreversible expansion always 0? If so, why? And are there any other times that the change in internal energy will always be 0?

camrynpatterson3C

Homework question 15.95 part D asks how many intermediates must form in the reaction, when given the reaction profile with 3 steps. How do we know the answer to this is 2?

camrynpatterson3C

Part A of 15.67 asks by what factor the rates of reaction increase when given two Ea's at a certain temperature. Why does the answer involve putting the rates of the catalyzed and uncatalyzed reactions in a ratio?

camrynpatterson3C

On the test constants and equations sheet, it doesn't specify which equations are for first, second, and zero reactions. Do we just need to memorize which is which or will it be specified?

camrynpatterson3C

Are general rate laws always equal to k[A]n[B]m[C]l?

camrynpatterson3C

When you flip an equation, such as what we have to do for the half reactions in some parts of 14.11, does the sign of E standard not change??

camrynpatterson3C

Should we balance the full redox reaction chemical equation before separating it into the reduction and oxidation reactions, or balance when they're separated? Does it matter?

camrynpatterson3C

Why is it that the change in internal energy for the isothermal expansion of an ideal gas is always 0? I know q will be 0 because it's isothermal, but isn't there still work being done if it's expanding or compressing?

camrynpatterson3C

How do we find deltaS(vap) when the temperature isn't set at the boiling point?

camrynpatterson3C

I'm still unsure as to exactly what Gibbs free energy is. I know it's expressed in terms of the difference between enthalpy and entropy, but is that all we can say about it? Is there nothing specific, like how enthalpy is heat and entropy is "disorder"?

camrynpatterson3C

For this problem, I understand that we have to add the entropy changes when the temperature changes and when the volume changes. However, I thought the equation for the entropy change when there's a temperature change was deltaS=nCpln(V2/V1), and not deltaS=nRln(V2/V1) like the solutions manual has ...

camrynpatterson3C

In lecture, Lavelle said "in a thermodynamic analysis, systems are often approximated as reversible". Doe this mean that any system we're calculating something for, we can assume that and can use the equation q(rev)=-w?

camrynpatterson3C

I somehow keep getting the answer wrong to this when I try to find Tf. I thought I just set the two q=mcdeltaT equations together, but I'm getting a wrong answer. Any ideas?

camrynpatterson3C

For part b, the solutions manual uses the equation w=-nRTln(V2-V1) for reversible expansion. I'm confused on what this is and where it comes from. Can someone help me please?

camrynpatterson3C

Work, at constant pressure, is equal to -PdeltaV.
The change in internal energy of a system is equal to q + w. Therefore, deltaU is equal to q + (-PdeltaV).
At constant pressure, q is equal to deltaH.
So, deltaU = deltaH + (-PdeltaV).

Hope that helps a little.

camrynpatterson3C

Also, I realized there are problems on the homework such as 8.47 and 8.53 that deal with delta U, although the question as a whole is about reaction enthalpies. Are we not expected to do problems like that on this test either?

camrynpatterson3C

Hi,
Lavelle said that problems relating to work and internal energy won't be on Test 1. I was wondering what this meant in terms of what homework problems are relevant. Is it everything from 8.29 on that is still for this test, and just not 8.1-8.27?

camrynpatterson3C

What equation is part C using to find delta H? And is delta H referring to the reaction enthalpy?

camrynpatterson3C

What formula are we supposed to use to find the heat changes of the ice cube and the water? And why do we set the equations equal to each other?

camrynpatterson3C

I wasn't even sure how to begin this question. I see, though, that the solutions manual uses C(p,m) = 5/2(R) and C (V,m) = 3/2(R). Those equations are in the book yet I don't remember Lavelle mentioning them. So, how does this correlate to what we've learned in lecture? Or do we just need to know it...

camrynpatterson3C

how do you calculate the pH of an acid base reaction?

camrynpatterson3C

If the pKb for a weak base ends up being 3.24 (as in 12.57b), how come it is still considered a base? Isn't a value that low considered to be for an acid instead?

camrynpatterson3C

Will we be tested on the biological compounds Professor Lavelle has mentioned? For example, do we need to to know the specifics about the pophyrin ligand and how it has to deal with hemoglobin?

camrynpatterson3C

Adding on to this, for pressure specifically, are bars and atms interchangeable? If not, what is the conversion between them?

camrynpatterson3C

How do we know if a complex has a negative or positive charge? For example, tetracyanonickelate(II) has a formula of [Ni(CN)4]2-. But, how do we know that to write in the formula the 2- charge?

camrynpatterson3C

I know the roman numerals in a compound is the oxidation number for the metal, but I don't know exactly what an oxidation number means or how to find it. Am I crazy, or did Lavelle not teach that? So, how do we find the oxidation number of a compound? Also, when given the oxidation number in the nam...

camrynpatterson3C

Is there any other way to predict bond angles than having to write out the full Lewis structure, then determine what shape it is, then determine the angles? I feel like there must be a shorter way since some questions ask you to "predict" them.

camrynpatterson3C

The solutions manual calls certain shapes "angular", yet I don't know what that is. I thought maybe it was the same thing as bent, but I'm not sure. For example, question 4.5 (a), the correct answer is angular, when I thought it was linear. So what does angular mean?

camrynpatterson3C

This question asks to write the Lewis Structures for ammonium chloride, potassium phosphide, and sodium hypochlorite, but it doesn't give their formulas. Are we supposed to know how to write these? Like ammonium chloride is NH4Cl, etc. Or is he always going to give us their formulas to use?

camrynpatterson3C

Does a large dipole moment between two atoms mean that the electronegativities of the two atoms are greatly different, so the bond has high ionic character?
I'm slightly confused on the relationship between dipole moments and electronegativity... Clarification would be great, thank you!

camrynpatterson3C

Technically, all bonds between atoms of different elements are polar to some extent. Ions are nonpolar. A molecule is considered polar if the electronegativity, or the electron pulling power, in one element is higher than the other's.

camrynpatterson3C

I found a discrepancy between the periodic table I've been looking at and the one in the book. The one in the book uses La and Ac as the first elements in the d orbitals instead of the first ones in the f orbitals. I will use the book's from now on, but why is there this difference between periodic ...

camrynpatterson3C

Why is the electron configuration for Silver, [Kr]4d^10 5s^1, instead of [Kr]4d^9 5s^2? Also, why is the electron configuration for Tungsten, [Xe]4f^14 5d^4 6s^2, instead of [Xe]4f^14 5d^3 6s^2? And for this, do we always have to write the f orbital in the configuration if the element is in row 6 or...

camrynpatterson3C

1.57 says: Lines in the Balmer series of the hydrogen spectrum are observed at 656.3, 486.1, 434.0, and 410.2nm. What is the wavelength of the next line in the series? The solutions manual uses the v=R(1/n2^2 - 1/n1^2) equation, but since Professor Lavelle taught us the E=-hR/n^2 equation, I figured...

camrynpatterson3C

Hi guys!
Does anyone know if we will have to be able to identify what kind of radiation something is based on its wavelength, on the test?
For example, #44 on the Atomic Spectra Post-Module Assessment.

camrynpatterson3C

Basically, as Mia said, use the Lyman series in the Rydberg equation when n1 is 1, and the Balmer series when n1 is 2. I don't believe that the Balmer series with n1=2 means that the electrons are starting in their ground state, or else it would be equal to 1. I believe the Balmer series applies whe...

camrynpatterson3C

This question confused me at first, but I noticed in the solutions manual that they converted keV to Joules. Does anyone know if this is something we need to know how to do, because we never learned it.

camrynpatterson3C

First of all, I don't think we know how to set up a net ionic equation yet. But does anyone know how?
Also, where did the NaOH come from?? I don't even see it in the net ionic equation in the solutions manual, but then they start using it in part b.

camrynpatterson3C

To find the concentration of NH4NO3 first, do we use just 1 liter or 4, since 3 was added?

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