reenigne

Thanks!

So...I'm looking @ a homework problem that asks to rank the standard molar entropy (from lowest to highest) of CH4, CF4, CCl4.

Naively, I would have ranked them as CCl4, CF4, CH4 (CH4 having the highest value) because I picture the larger chlorine atoms surrounding the carbon as having less freedom of movement (they're more likely to bang into each other).

But I have it backwards.

Is there some intuitive explanation for why CCl4 has a greater molar entropy than CH4?

TY!

I'm not sure if this is the correct place to ask, but I would like to find a web-forum where people discuss medical aspects about short stature. I've Googled-around and found this site (http://www.dailystrength.org/c/Short-Stature/forum), but I'm looking for something a little more medically-oriented.

Does anyone know of a forum like this?

Just in case anyone has any thoughts, here's the short version of why I'm asking.

• My son was involved in a serious car accident at 5 years of age (multiple skull fractures, jaw fractures, etc.)

• At the time of the accident, he was probably around the 30th percentile for height.

• He is 12 yo now and has gradually slipped in height percen

If you look at an Aufbau subshell diagram like this one (http://f.tqn.com/y/chemistry/1/S/j/g/econfiguration.jpg), it indicates that the 4f subshell has lower energy than the 5d subshell.

So, naively, I would expect that lanthanum's ground state electronic configuration would be [Xe]4f^1 6s^2 , but according to wikipedia, Lanthanum has no 4f subshell electrons--instead it contains 1 electron in 5d. The next element (Cerium) does not continue to add electrons in the 5d subshell. Rather, Cerium shifts to the 4f subshell.

Is there an intuitive explanation for why Lanthanum's 5d gets 1 electron before we start filling in the f subshell?

Thank you!

If I look at the Lewis structure, the molecule seems symmetrical to me. The molecule is "bent" around the internal oxygen atoms, but still it seems as though the symmetry is maintained, so my guess would be that the dipoles of the polar bonds H-O cancel out and the molecule would be NON-polar, but everything on the google suggests it's polar (along with the fact that it mixes w/ water pretty easily).

IS there a simple GEOMETRIC explanation for the molecule's polarity?

Hopefully, the question is clear.

But, as an example, the C-C single bond is listed as having a length of 154pm. How was this actually determined back in the olden days?

Would it still be determined like that in the present day? Are there new methods? Can it be done by crystallography?

I guess that's a small handful of questions.

Thanks for any info!

edit: not a homework question. Just curious.

I've seen this posted everywhere on the internet, but without an explanation. Basically, they say that (after a log transformation) you don't count the digit(s) to the left of the decimal point when reporting your answer.

I think I kinda sorta get it, but I'd like a more rigorous explanation (or at least affirmation that I'm thinking about this correctly).

e.g. if you had 2 different H3O+ concentrations:

• 2 x 10^(-2)M
• 3 x 10^(-3)M

the log of each would be

• -1.698
• -1.523

Since the coefficients of the original molar concentrations are different, then the log transformation should be reported using enough digits so that you can distinguish between them as well.

i.e. if you on

Hi,

From what I understand the IUPAC name for this (http://www.chemspider.com/Chemical-Structure.24059.html) molecule is 2,5-dichlorohexane.

Is there a reason for adding the prefix "di" in front of the chloro? I know it's there because there are 2 chlorine substitutions on the hexane backbone, but doesn't the fact that there are two numbers (2 and 5) render the "di" redundant? In other words, what information does the "di" add that the 2,5 does not?

Thanks!

Hi,

I'm wondering if anyone can provide a simple mechanistic explanation for why many/most? salts in water increases w/ increasing temp.

Maybe NaCl is a reasonable example to discuss here.

I suppose changing entropy of the salt and the water molecules plays some factor, but I'm not sure exactly what's going on.

Thanks for any info!

I'm doing a % yield lab, where I mix specific amounts of BaCl2 & Na2SO4 to make insoluble BaSO4 + NaCl. This all makes sense.

However, there's a portion of the lab where we add concentrated HCl to the mixture. I'm not sure what the purpose of the HCl is here. My guess is that it drives the reaction in some way (increases yield), but mechanistically I don't know why.

Any ideas why?

Thanks!

Edit for clarity.

• mix Na2SO4 + BaCl2
• add small amount of concentrated HCl
• boil (also not 100% certain of the purpose of the boiling steps)...are we simply maximizing ionization of the salts and maximizing the collisions/formation of insoluble BaSO4?
• cool
• aspirate liquid
• add wate

Hi,

I'm sure this is silly, but why can't I write the lewis structure for phosphate like this (http://imgur.com/RquxtEf).

If I understand correctly, the total charge as drawn is still -3 (phosphorus is +1 and each oxygen is -1).

Obviously, the correct structure gives P 10 valence electrons (double bond to one of the oxygens), but how do you know when this is the true structure and the image that I provided is not accurate?

Thanks!

So, I understand how you can determine the formula for a material if you know the empirical formula and the molar mass of the pure material, but I'm wondering if anyone can provide some examples of how molar mass of pure materials might be determined in real life.

I can see using the ideal gas law equation to do it. Are there accessible examples where it's done for a solid or a liquid?

TYVM