CHEMISTRY COMMUNITY

Ria Nawathe 1C

I see a small upwards pointing arrow in the lower right corner of each reply, but I'm not sure if students can click on it.

Ria Nawathe 1C

Like the previous answer stated I think it's an issue with the textbook problem and not your conceptual understanding, because you're approaching it correctly! My textbook also had 2HD(g) <--> H2(g) + D2(g).

Ria Nawathe 1C

Yes, I believe so! Everything that's posted on the Chem 14B class website is what's offered.

Ria Nawathe 1C

I think you're using the wrong K. I used K=160 for H2 + I2 <---> 2HI @ 500K and I got 2.1 * 10^-5 M. Hope this helps!

Ria Nawathe 1C

It is possible to have large Kc values with the Kc expression being cubic. The cubic nature of the expression depends on what information is given in the problem. However, I don't think we'll get problems like this on any exams just because as you said it does get more complicated to solve since we ...

Ria Nawathe 1C

Hi! For this problem, the first thing you should do is create an ICE table based on the graph. The graph tells you the initial concentrations of A (about 28 M), B (0 M), and C (0 M), and it also shows you the equilibrium concentrations of A (about 18 M), B (5 M), and C (10 M). Based on the differenc...

Ria Nawathe 1C

The correct answer is A, equilibrium constants are useful because they are one number that gives us information about the relative concentrations of reactant and product. K is the ratio of the equilibrium concentrations of products to the reactants raised to their respective stoichiometric coefficie...

Ria Nawathe 1C

You're correct, C is false! At equilibrium, the forward and reverse reactions do still occur, just at the same rate.

Ria Nawathe 1C

When will TAs officially be assigned? My discussion section is tomorrow but I don't see who my TA is on myUCLA.

Ria Nawathe 1C

I also think this might be an error in the solutions. Prof Lavelle mentioned in one of the module videos that one of the situations in which there would be no change is if the pressure was increased by adding an inert gas (which doesn't affect the volume and therefore the concentration), but in this...

Ria Nawathe 1C

Hi! Like the previous response stated, a negative delta H indicates an exothermic reaction, as heat is being released/lost from the reaction system. You would consider the heat that is released to be a product of the reaction. Therefore, if temperature is increased, you are essentially increasing a ...

Ria Nawathe 1C

^^ Yeah we only did conceptual stuff, we don't need to know how to calculate the exact probability. However, it might be helpful to know how many nodes (areas with 0 probability of electron density) each subshell in an atom has. The total number of nodes in a subshell = n-1, # of angular nodes = l, ...

Ria Nawathe 1C

Yes, those are correct! The number of orbitals in a subshell is equal to the number of possible ml values for the specific value of l. For 4p, l = 1 so ml = -1, 0, 1; therefore 4p has 3 orbitals.

Ria Nawathe 1C

A conjugate acid is the resulting species when a base accepts a proton, and a conjugate base is the species that results when an acid gives off a proton. For example, the conjugate acid of the base NH3 is NH4+, as NH3 + H+ --> NH4+. The conjugate base of H2SO4 is HSO4-, since H2SO4 donating a proton...

Ria Nawathe 1C

By relative orientations I think they mean the relative arrangement of the hybrid orbitals. For sp3, each of the 4 hybrid orbitals points to one corner of a tetrahedron. For sp2, each hybrid orbital points to a corner of an equilateral triangle. Hope this helps!

Ria Nawathe 1C

I agree with the previous answer, the heme complex + the hystidine protein make up myoglobin.

Ria Nawathe 1C

Yeah I think you have to meet with your TA to go over your midterm!

Ria Nawathe 1C

The textbook has a set of rules in Focus 9C.1 (Toolbox 9C.1) for writing the formulas and naming the compounds! For writing the formula, the textbook says to write the chemical symbol of the central metal atom first and then write the symbols of the ligands in alphabetical order. For different ligan...

Ria Nawathe 1C

You would place a lone pair on the equatorial vs axial plane based on which position would limit the number of 90 degree interactions with the other atoms in the molecule, since these interactions are unfavorable.

Ria Nawathe 1C

Just a heads up, the textbook uses the -ido convention but the Sapling HW uses o!

Ria Nawathe 1C

Hi! I had trouble with this one too, but the book has a helpful list of rules in Focus 9C.1 for naming coordination compounds/complexes. First, everything enclosed by the brackets is part of the complex ion. The complex ion has an overall charge of +1, as Cl is -1 and the whole coordination compound...

Ria Nawathe 1C

So I have no clue, so I tried to research what it might be, and I'm getting conflicting answers, one of which says that it's simply perpendicular to each other (normal to each other), and the other of which says they are standardized to one another. The first definition makes the most sense to me, ...

Ria Nawathe 1C

What does it mean for hybrid orbitals to be normalized vs unnormalized?

Ria Nawathe 1C

I don’t think you can assume that any molecule with a central atom that has lone pairs is polar. For example, XeF2 is non polar, and it has 3 lone pairs on the central atom. The lone pairs are arranged at 120 degrees to each other and the F-Xe-F bond angle is 180 degrees, so there is a 0 net dipole ...

Ria Nawathe 1C

I don't think there will be discussions on Thursday or Friday, but I'm not sure if students in those discussions will have to make it up.

Ria Nawathe 1C

Just to add on, an unpaired electron on a radical like NO2 is also considered to be a region of electron density.

Ria Nawathe 1C

Dr. Lavelle mentioned that the energy of the hybrid orbitals is the average of the energies of the atomic orbitals used.

Ria Nawathe 1C

FionaHunter21 wrote:Are there dipole moments between all atoms with a difference in electronegativity or just the polar bonds?

I believe all bonded atoms with a difference in electronegativity exhibit a dipole, but the magnitude/strength of the dipole is given by mu = |q|*d (charge * distance between the atoms).

Ria Nawathe 1C

I agree with the previous answer, Dr. Lavelle mentioned in one of his lectures that the unpaired electron in radicals like NO2 is considered a region of electron density.

Ria Nawathe 1C

The effective nuclear charge refers to the protons/nucleus of an atom, not the electrons. In terms of periodic trends, the effective nuclear charge increases as you go across a period because the atomic number increases and electrons are being added to the same energy level. It decreases down a grou...

Ria Nawathe 1C

Cations, molecules with electron deficient central atoms (like BF3), and molecules with polar double bonds (like CO2) tend to be lewis acids since they are more likely to accept an electron pair. Anions and molecules with lone pairs (like H2O) tend to be lewis bases since they have electrons to dona...

Ria Nawathe 1C

A dipole moment is a partial positive charge and partial negative charge within a molecule, though the molecule is as a whole electrically neutral. For example, the hydrogens in H2O have a partial positive charge and the oxygen has a partial negative charge due to the electronegativity difference be...

Ria Nawathe 1C

To add on, in terms of periodic trends polarizability tends to increase as you go down a group because the atomic radius and the number of electrons increase.

Ria Nawathe 1C

For anions, polarizability increases as you go down a group since the atomic radius and number of electrons increases and the effective nuclear charge decreases. In general, the larger the radius and the more electrons an atom has, the more polarizable. For polarizing power, the smaller the atomic r...

Ria Nawathe 1C

London dispersion forces are induced dipole-induced-dipole interactions. Basically, when non-polar molecules collide their electron densities are shifted, forming a temporary delta negative and delta positive side. This induces the neighboring molecule to form a temporary dipole as well and produces...

Ria Nawathe 1C

I believe Professor Lavelle mentioned it's the energy per mole of the given interaction. For example, if there was 1 mole of Na+ and Cl- interactions, the amount of energy released due to the ion-ion interactions would be 250 kJ.

Ria Nawathe 1C

An example of a molecule with a permanent dipole is H2O; the difference in electronegativity between the O and Hs causes the electrons to be pulled towards O, creating a permanent delta negative and delta positive side. Temporary dipoles occur when molecules that are otherwise non-polar, like N2, co...

Ria Nawathe 1C

I think the electrons on the anion are referred to as polarizable and the cation as polarizing and not the other way around because the protons in the nucleus of the cation don't "move" due to the attractive force they experience from the electrons of the anion. It is the electrons that ar...

Ria Nawathe 1C

In terms of thermodynamics, if you think about the molecule/compound as a system, anything that increases the energy of the system, for example putting in energy to break bonds, makes delta E positive. When energy is released, delta E is negative. The intermolecular/interionic interactions have nega...

Ria Nawathe 1C

For non-resonance structures, electrons are localized.

Ria Nawathe 1C

I believe angular is 2 atoms bonded to the central atom with 1 lone pair, and bent is 2 atoms bonded to the central atom with 2 lone pairs.

Ria Nawathe 1C

Will the final also be multiple choice?

Ria Nawathe 1C

Here is the textbook's explanation for why it increases stability (it's in Focus 2B): "As well as delocalizing electrons over the atoms, resonance also lowers the energy below that of any single contributing structure and helps to stabilize the molecule. This lowering of energy occurs for quant...

Ria Nawathe 1C

The angular momentum quantum number l, which tells us about the subshells in each shell, is determined by the principle quantum number (n=3 in this case). For n=3, l can be 0...n-1 which is 0, 1, and 2, corresponding to s, p, and d.

Ria Nawathe 1C

Delocalized electrons are electrons that do not "belong" to a particular atom or are not associated with a specific bond in the molecule. Here is the textbook's explanation for why it increases stability (it's in Focus 2B): "As well as delocalizing electrons over the atoms, resonance ...

Ria Nawathe 1C

Within a particular energy level (n), all electrons with the same angular momentum quantum number (l) are in the same sub-shell, and all electrons with the same n, l, and ml (magnetic quantum number) are in the same orbital.

Hope this helps!

Ria Nawathe 1C

What is the difference between radial and angular nodes, and how many do each of the orbitals (s, p, d, f) have?

Ria Nawathe 1C

He drew 3 up-spin electrons first because according to Hund's Rule, electrons occupy empty orbitals in the same sub-shell before pairing up. As for why the up-spin electrons are drawn first, I think it just has to do with convention.

Ria Nawathe 1C

If you think about EM radiation as a wave of oscillating electric and magnetic fields that are perpendicular to each other, the frequency is related to how the electric field changes, or oscillates, with time. The greater the frequency, the faster the field changes/oscillates. The smaller the freque...

Ria Nawathe 1C

Within a particular energy level (n), all electrons with the same angular momentum quantum number (l) are in the same sub-shell, and all electrons with the same n, l, and ml (magnetic quantum number) are in the same orbital. Here's an explanation with a helpful graphic: https://chemistry.stackexchan...

Ria Nawathe 1C

That's what I heard too, some of the TAs said it was all multiple choice.

Ria Nawathe 1C

Delta v should be 10 m/s. I believe this is an error in the book's solution. Here's a full list of errors in the solution manual:

https://lavelle.chem.ucla.edu/wp-conten ... rs_7Ed.pdf

Ria Nawathe 1C

As the previous answer stated, the equation is E = hv. The photoelectric effect demonstrated that light exhibits properties of particles and also demonstrated the relationship between energy and frequency of photons.

Ria Nawathe 1C

^^ Thanks!

Ria Nawathe 1C

The circular standing wave model is just a math model that was developed to reconcile electrons having wave-like properties and having quantized energy states. In this model, each stable circular standing wave (with whole number wavelengths) around the nucleus represents an energy level (n=1, 2, 3.....

Ria Nawathe 1C

Does anyone know if we'll also be given the wavelengths corresponding to the different regions of the EM spectrum, or will we need to just know it?

Ria Nawathe 1C

They're not mandatory but they are helpful, and the videos are pretty short so it won't take too much time to check them out!

Ria Nawathe 1C

How do you identify which energy level is n1 and which is n2 for frequency = R(1/(n1)^2 - 1/(n2)^2)? Is n1 always the initial energy level and n2 always the final energy level?

Ria Nawathe 1C

Why do spectral lines in the same series (Balmer series, Lyman series, etc.) always represent transitions ending with the same final energy level?

Ria Nawathe 1C

According to the particle model of light, the intensity of light is proportional to the number of photons, which translates into how bright the light is. Intensity is not related to wavelength.

Ria Nawathe 1C

Yes, I think that's the rule we're expected to follow. On the Chem 14A website, Professor Lavelle posted "Everything you want to know about Sig Fig" under the Course Materials header, and the 2nd page summarizes rules for rounding, which include the nearest even number rule. https://lavell...

Ria Nawathe 1C

I don't think there is a way to submit the problems. I think as long as you have 1 attempt for each question, you're fine.

Ria Nawathe 1C

For dilution, you start with a solution of a certain concentration and just add solvent to decrease the concentration. The only thing that's changing is total volume of the solution, the moles of solute always stays the same.

Ria Nawathe 1C

Typically when you need to convert moles of something into atoms or molecules, you would use Avogadro's #. Ex: 0.50 mol C * (6.022E23 atoms C / 1mol C) = 3.0E23 atoms C

Ria Nawathe 1C

You would use the first method and directly divide the moles of KCl by the final volume since the moles of solute remain constant through the process, as a previous answer mentioned. In terms of when to use the M1V1 = M2V2 equation, you would typically use it for problems where you have to calculate...

Ria Nawathe 1C

Are molar masses considered measured values or defined constants?

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