CHEMISTRY COMMUNITY

powerberry

So basically a high activation energy means kinetic control, and the opposite means thermodynamic control? What is the basis behind this naming?

powerberry

When an hydrogen is removed to make the substance a cation, you can use the ending '-ylium,' I believe.

powerberry

Thanks. I just went along and wrote both and then put the average in parentheses.

powerberry

When I minimize the structure for the first time I get 2.1746 kcal/mol, but if I continue to minimize, it goes to 2.1733. Should I use 2.173, 2.174, 2.175 for this answer?

powerberry

When I used Chem3D to calculate the CCH angle for cyclobutane, there were several values between 112 degrees and 115 degrees but more of them were toward the 115 degree side. What value should I write?

powerberry

Hello, on the worksheet it says that we should round to the nearest degree for the Calculated geometries and bond angles section for number 7.

However, the beginning tells us to round to the nearest 3 decimal places. What should we do?

powerberry

Things with more molar mass will have a higher entropy. Each molecule can be in 5 states, but CF4 is larger than say CHF3.

powerberry

It should read 96485.3 C/mol. It's a typo.

powerberry

The equation they use is the same equation as the ln equation but with the constants converted to match a log value. Either one can be used to find the right answer.

powerberry

W is degeneracy, the number of positions a given molecule can be in, usually given by the number of possible positions of a molecule to the power, such as 2^3 for 3HBr(g). Kb is the Boltzmann Constant which can be found in the formula sheet.

powerberry

A higher cell potential = a higher tendency to be reduced. Something that is more easily reduced is a stronger oxidating agent.

powerberry

I think the most popular is platinum...I haven't seen carbon, but the electrode should first be whatever metal is in the equation and if none exist, then you can use platinum.

powerberry

Technically log(x) and ln(x) are the same thing with a different base, so I would assume so.

powerberry

Remember that the Enaught is always the reduction voltage, so when you subtract the anode from the cathode, you're not rearranging the equations to make sure that the electrons balance on both sides. This may a be a little bit confusing so I prefer just writing the half equations and adding/subtract...

powerberry

The anode should be on the left and the cathode on the right.

powerberry

You can set your own values for initial volume and final volume.

Vi = 1 L
Vf = 3 L

Then use the equation delta S = R ln(Vf/Vi)

powerberry

Benzene should be pretty easy to remember, since it is a model molecule for learning about resonance. I'm not too sure about methanol though.

I think that the table given says the names of certain molecules, so you will probably be fine without having memorized every possible organic molecule.

powerberry

I think that is just unnecessary information. You can use just the value of delta H = -5471 and multiply it with the rest of the equation and it will still yield the same result.

powerberry

Thank you. I think the answer book may have just put the negative inside the parenthesis for that one part instead of outside then.

powerberry

For 7.55, the answer says 23.9x10^3 kJ/L. Even though I got this answer, I'm just wondering why the answer book didn't use standard scientific notation for this answer.

Thanks in advance!

powerberry

Just a quick question. For the water's specific heat capacity, when do you know when to use -4.184 as opposed to 4.184? (Positive or negative)

Thanks!

powerberry

You cannot use the overall equation because the ability of H2CO3 to lose one electron and then the other differs, and that is shown by the differing Ka values.

powerberry

Whenever something is aqueous, water is implied.

powerberry

You must find out how many grams are produced of C, H, and Cl to find the mass of O in the original sample.

Then you calculate the # of moles of C, H, Cl, and O to find the empirical formula for the compound, and multiply by the appropriate amount to match the molecular mass.

powerberry

You have to find out the molecular formula (real formula as it exists) of the substance, which can only be found by knowing the empirical formula and multiplying by the appropriate amount to reach a molar mass that they give you.

powerberry

I think this might be because 1.8x10^(-5) is an approximation in itself.

powerberry

In terms of bond length, the bonds will be the average of all the bonds in the resonance structures. For example, in nitrite (NO2-), the resonance structures are... [::O=N-O:::] <-> [:::O-N=O::] with a lone pair on the nitrogen. However, this does not mean that there exists two forms of nitrite, wit...

powerberry

Also, Ka3 becomes really small because the molecule itself becomes more negative as protons are removed, so it holds on to its remaining protons strongly.

powerberry

I got Kb=4.8x10^-4 as well. Should just be a typo.

powerberry

Our blood contains carbonic acid H2CO3, which has the reactions... H+ + HCO3- <-> H2CO3 <-> H2O + CO2 As CO2 is released by our body through breathing, Le Chatelier's principle will make sure that more CO2 is produced, thus lowering the amount of H+ in our system. This is why you must breathe harder...

powerberry

I think this is just a typo. It should be F2^(2-) > F2^(-) > F2 > F2^(+) with F2^(2-) demonstrating the longest bond.

powerberry

What part are you confused about? This just says the question.

Ka2 means the second equilibrium constant for the reaction after one H+ has been removed. Hopefully this sets you on the right track!

powerberry

[HA] would only equal [H3O+] if all of HA dissociates in the reaction HA+H2O->H3O+ + A-. However, HA is a weak acid, so this is not the case.

powerberry

Would checking to see if our estimation is valid just replugging the numbers back in to find the K?

powerberry

On this part of the question, the Kb is only 3.6 x 10^-4, yet the answer key approximates the 0.25M - x as 0.25M. Shouldn't this only be done when the K value is <10^-5?

Thanks.

powerberry

Chem_Mod, thanks for letting me know!

powerberry

Possibly :D But I think the fact that the world 'basin' and 'base' are so similar might be just a coincidence. Though it is a good mnemonic device.

powerberry

It doesn't work for b-d because those don't fully dissociate (they're not all strong acids). You have to use the PKa to find the concentration of H3O+ and then use that to calculate the pH.

powerberry

Question 2: When do products dissociate more? Do they only dissociate more if the products are strong acids/bases (i.e. sometimes conjugates of weak acids/bases) or if the products are aqueous salts? When you have a reaction that produces a strong acid/base, those will definitely dissociate. Otherw...

powerberry

Question 1: I know that the SO2 is the lewis acid and the H2O is the lewis base; however, is SO2 also a bronsted acid?? Does it make a difference if it is aqueous or not because if it is aqueous, it will dissociate further into SO3^2- + 2 H3O+ To dissociate means it is aqueous. In 2H2O + H2SO3 --> ...

powerberry

I did a quick search about the etymology of the word base and here is what I found! http://h2g2.com/dna/h2g2/alabaster/A708257"onclick="window.open(this.href);return false; Bases were identified and categorised as the substances which are neutralising acids. For that reason, the progress in the char...

powerberry

You must know that diethylenetriamine is a tridentate. There are two of them, which makes 6 areas of electron density.

6 areas of electron density = octahedral.

powerberry

Do you mean the oxidation number for the metal cation within the coordination complex? This is determined by knowing the charge of the entire coordination complex as well as the charge of each individual polyatomic ion that makes up the coordination compound. For example, if you were given Diamminet...

powerberry

What's the difference between Q and K if they are calculated the same way? When do you know which one to use? K is the equilibrium constant which will indicate the direction of the reaction at equilibrium only. Q, however, is a constant that indicates the direction of a reaction at any given concen...

powerberry

Usually there will be a positive x that is too large to subtract from one of the partial pressures, so you choose the other one.

powerberry

Generally. The pKa essentially tells you how much of the acid will actually dissociate. If the pKa is low, then more of the acid will dissociate, representative of a stronger acid.

At the halfway equivalence point, pH = pKa.

powerberry

What part are you confused about?

powerberry

I would start with Lavelle's chart and then read other things for supplemental information. For the atoms that are not halides or oxygen, you just have to imagine them with an -ide ending, which you would replace with -o. For example, Nitrogen -> ion form: Nitr ide -> coordination compound form: Nit...

powerberry

When are there 2 carbonates, you say -dicarbonato-.

You only use bis- when there is already a di- or tri- in the molecule itself, such as ethylenediamine. To denote two of those, you would say bisethylenediamine to avoid confusion.

powerberry

I would just start with knowing the ones that are on the homework problems about coordination compounds, as those are most likely to be on the quiz.

powerberry

You would use the quadratic formula but instead of simple integers, you'll have numbers like 1.1x10^-3, etc to put in for a, b, and c.

However, Lavelle said that if K is something to the 10^-5 or smaller, then the x's can be justifiably be eliminated from the problem for simplicity.

powerberry

It seems that the metals whose names are not derived from Latin do not change, such as cobalt and nickel.

powerberry

It depends on how many times they bond to the central metal atom. A monodentate only bonds once, etc.

I'm pretty sure tetradentates and pentadentates exist, even if they are not so common. I don't think anything over 6 bonds can exist, though.

powerberry

Usually, square planar complexes are with d8 configured transition metals, with a couple of exceptions. Otherwise, it's mostly tetrahedral.

powerberry

I'm assuming that the bis-, tris-, etc prefixes have precedence over the others.

powerberry

Yeah, that appears to be the case.

powerberry

It depends. You can write H2O for simplicity, but sometimes it is better to write OH2 to indicate that the oxygen is the one binding to the metal of the ligand, rather than hydrogen.

powerberry

If the overall ligand charge is negative, the metal in the ligand will probably be positive so it will change to metal-ate, which some exceptions such as cobalt and nickel that just stay the way they are.

For your chloride question, if it is a Cl- inside the ligand, it will definitely be chloro-.

powerberry

When it is outside the ligand it forms a bond ionic in character. When naming these bonds, you don't put the prefixes for number, such as in Magnesium Chloride, MgCl 2 . However, you would mention the number if the bond were more covalent in nature, such as Oxygen Dichloride, OCl 2 . Hope this helped!

powerberry

There's a list in the course reader; I would definitely take a look at those for sure. As for the others, I'm not sure if knowing them is required but they would be useful anyway, so why not?

powerberry

Yes, but keep in mind that if they ask for specific elements, not all of these orbitals may be filled.

powerberry

A bracket indicates that the charge is present somewhere in the molecule. In the molecule you mentioned, the negative charge is most likely on that oxygen which has a negative formal charge, so they put it there. But, you can still draw brackets around the whole thing and mark it as -1. Edit: Simpli...

powerberry

I think it's arbitrary, but just to demonstrate that there are many possible orbitals above the structure that are unfilled. (While lithium can have a p orbital, hydrogen cannot.) However, electrons do not fill already existing orbitals, they form the orbitals when they are at that energy state.

powerberry

How would you write the bond composition for triple bond? The second pi bond would use another one of the p orbitals at a different axis. You may want to specify that they are different axes using pi(O2px) and pi(O2py) for instance. Also, in the hybridization of lone pairs, do you list the principa...

powerberry

It is a combustion reaction so carbon dioxide and water must be released. The only thing left is nitrogen, which comes diatomically, so N2 would be the third product.

powerberry

Yes essentially. The number of different mls represent the number of orbitals.

powerberry

It depends what you want to do. For example, if you need to find the Joules per photon, you would use Avogadro's number in stoichiometry to find the joules per photon.

powerberry

I think it's just a precaution to let people know it's at about room temperature and not under any abnormal conditions, so it is irrelevant to what we are finding here.

powerberry

They're bonded to hydrogen and the atoms next to them. Even if you didn't know that, you would assume there are lone pairs which make up a sp3 hybridization.

powerberry

I'm not sure about the reasoning, but here is a link that I found that shows an HF molecular orbital.
http://www.science.uwaterloo.ca/~cchieh ... hetro.html

powerberry

I think we do. The hybridization of the lone pairs is just the hybridization of the atom. For example, that oxygen has a double bond and 2 lone pairs. Therefore the lone pairs are Osp2, since they are not bonded to any other atom.

powerberry

I don't think we'll be asked to draw in the lines, but we may possibly have to understand why certain energy levels for electrons are lower.

I think we'll be fine as long as we can demonstrate we know the concept.

powerberry

I don't think so. Transition metals tend to lose their s-shell electrons and retain their d's.

powerberry

I believe Lavelle said that either is acceptable. In the course reader, it's in the shortened form.

powerberry

One of the things I encountered on the homework was NH3 which is trigonal pyramidal with a tetrahedral arrangement. I know the actual angle is about 107 degrees, but for these kind of questions, would <109.5 degrees be acceptable?

powerberry

Are you asking why it can't be 0? I think it's because it's filled in the order of -1, 0, then 1, which means that 0 can never be filled last. If you are just asking about why those numbers would be chosen, it is because the p orbital has 3 orientations, so the numbers -1, 0, and 1 correspond to the...

powerberry

I was a little confused by this as well. Chem_Mod, please help.

powerberry

The wavelength (lambda) equals Planck's constant divided by momentum. Momentum is denoted p and can become mass times velocity. So you have lambda = h/p lambda = h/mv Rearrange by multiply v to the top and dividing lambda to the bottom v = h/m*lambda Then you can enter your numbers to find the veloc...

powerberry

I think it's just showing that the energy you need to eject an electron is the same as the ionization energy (as it should be because that is the definition!) Basically, the "energy to eject an electron," "ionization energy," and "work function" more or less refer to E(...

powerberry

There are several techniques you can use to balance equations. First is the cross-over method that generally works when you have different amounts of the same element on both sides in molecules. (e.g. NH3 and H2). The 3 from NH3 will become the multiple of H2 and vice versa for 2NH3 and 3H2. These c...

powerberry

I'm not sure what you mean here. The hybridization of an atom, more or less, describes the bonds that it is making. For example, the Carbon in Methane (CH4) is sp3 hybridized because of its four bonds.

powerberry

That's not a yellow rabbit; that's Pikachu!

http://images1.wikia.nocookie.net/__cb2 ... ikachu.png

powerberry

What do you mean by the VSEPR formula? If you're talking about hybridization, each unpaired electron counts as one area of electron density, I believe.

powerberry

It also affects the symmetry of specific molecules. For example, NH3 is tetrahedral shaped and would be nonpolar if it were trigonal polar with H on all sides, but the lone pair does not allow the symmetry, turning it into a non-symmetrical tetrahedral arrangement.

powerberry

504047082 wrote:Are there any structures that are usually polar/non-polar? Are there any quick rules of thumb we should know that would help us quickly figure out the polarity?

Not really structures, but shapes that are symmetrical (that have the same atoms on each side as well) are generally nonpolar.

powerberry

I think the carbon in question has a triple bond with the nitrogen, since the answer key says that nitrogen has only 1 lone pair. This would create a linear arrangement for the CCN:

powerberry

Probably not, for now. I think the important thing is probably to understand the concepts behind the exceptions that we learned.

powerberry

I'm not too sure about the properties of radicals and their formal charges, but my theory is that since oxygen is more electronegative than chlorine, ClO exists without a balanced formal charge.

powerberry

Looks like an error to me. Carbon cannot have an expanded octet.

powerberry

In a molecule that is a tetrahedral arrangement, there is no "across from" for the chlorines. No matter where you put the chlorines, they will be next to another chlorine.

powerberry

D-block elements usually have a +2 charge because their valence electrons are just the s-orbital electrons.

powerberry

I think there may be a mathematical way, but there would be too many combinations to memorize with all the different groups of elements, etc. Generally, we'll probably be asked to draw resonance for something that just has 2 or 3 different structures.

powerberry

Even if the difference isn't very great, there will still be a small, however slight, dipole moment on some of these molecules. Generally, non-symmetric linear molecules, or tetrahedral molecules that have 3 of the same terminal atoms and 1 different one will be polar.

powerberry

Electrons are typically removed from the valence shells, which are the highest s and p orbitals. Also, Hund's rule still applies here, but backwards. Electrons will be removed from their orbitals until all of them are unpaired, and then the unpaired ones will be removed.

powerberry

Usually, brackets go around Lewis structures that have an overall charge. The simplest would be something like [H]+ [::F::]- as a Lewis structure.

powerberry

That is correct. Double and triple bonds all count as one area of electron density.

powerberry

It is more important to satisfy octets rather than the formal charge, I believe.

For N2O, I have :N:::N:O::: so that oxygen has a formal charge of -1 and nitrogen has a formal charge of +1, which makes sense because oxygen has higher electronegativity. This way an octet can be filled

powerberry

Some questions ask for the geometry of a specific molecule. If the molecule is SF4, which shows a seesaw shape and a trigonal bipyramidal arrangement, what should we write for the geometry when asked? (My TA said we should write both but specify which is which)

powerberry

Edit: My answer was incorrect.

powerberry

Is there a particular reason that one is preferable toward the other? For instance, when would we use g/mol rather than g*mol^-1 and vice versa?

Search found 108 matches