CHEMISTRY COMMUNITY

Kristen Kim 2K

The assumption for delta G standard is that the temperature is at 25 degrees C or 298 K.

Kristen Kim 2K

The cell diagram is structured so that it indicates the anode is on the left of the salt bridge (||) and the cathode is on the right side.

Kristen Kim 2K

In the half reactions, F2(g) is being reduced, so this is the cathode, and HF(aq) is being oxidized, so this is the anode.

Kristen Kim 2K

The formula you can use for the reactant rate is R = -delta[R]/delta t. When you plug in the values for the change in [R], the value is negative. But since that value is also being multiplied by the negative in front of the equation, the overall answer will be positive. Since the rate of O2 is just ...

Kristen Kim 2K

The constant k in the differential rate law depends on temperature and activation energy.
RATE = k[R]^n

Kristen Kim 2K

K = 0 then delta G = 0
K < 1 then delta G > 0
K > 1 then delta G < 0

Kristen Kim 2K

Is the cell reaction spontaneous if E is positive and nonspontaneous if E is negative?

Kristen Kim 2K

How do we find the half reactions? Some of them are straightforward, but others are really vague and it's difficult to pinpoint which compound to use.

Kristen Kim 2K

How do we know what to write for the reduction/oxidation half reactions from a full reaction? Do we just look up the compound in the appendix and see which reaction matches?

Kristen Kim 2K

Why does reaction free energy depend on pressure and K?

Kristen Kim 2K

An intensive property just means it doesn't depend on the amount of matter. The voltage difference is the same regardless of how many times the reaction occurs. I think it would be similar to something like delta H fusion/vaporization; it's a set value for that reaction at those certain conditions.

Kristen Kim 2K

In chemical equilibrium, the question will probably be asking about if the reaction stated is at equilibrium or not, and if not, then to explain why. (Q = K means equilibrium, Q not = K means not at equilibrium). It also might ask about the relationship between the amount of reactants or products, w...

Kristen Kim 2K

For delta G and delta H, the values for the most stable form of that element will be 0. Delta S will most likely still be a value greater than 0, unless it is a perfect crystal.

Kristen Kim 2K

For this problem, there are two variables that are changing: volume and temperature. In order to find total entropy, you need to solve for two equations and add the two together to get the total value. We can use delta S = nRln(V2/V1) for the change in volume and delta S = nRln(T2/T1) for the change...

Kristen Kim 2K

A salt bridge keeps the solutions of both anodes and cathodes neutral by basically providing opposite charges. This is so that electron transfer will continue. If the salt bridge isn't there, there will be a buildup of electrical charge on one side and the transfer of electrons will stop.

Kristen Kim 2K

The standard values for Gibbs free energy for both of these compounds are in Appendix 2A. We can plug in these values into the products minus reactants formula for Gibbs free energy. Depending on if the delta G is positive or negative, we can determine if the forward or reverse reaction is more stab...

Kristen Kim 2K

Container A has a greater number of particles than the other containers. Therefore, the entropy change is greater. In comparing monatomic with diatomic, there will be more of the monatomic particles because it needs twice as many particles to equal one diatomic particle.

Kristen Kim 2K

Yes. The units cancel out when dividing products by reactants.

Kristen Kim 2K

This will be on the constants and equations sheet.

Kristen Kim 2K

Yes, the solution says "Assume ideal behavior and 1 mol N2 gas."

Kristen Kim 2K

I would just use atm for everything, especially because R constant units are (L*atm)/(K mol).

Kristen Kim 2K

What is the general formula for solving for reaction enthalpies? I'm having a hard time solving for problems where it asks to "calculate the heat absorbed."

Kristen Kim 2K

The first law of thermodynamics states that energy is neither created nor destroyed, therefore the overall amount of heat (q) needs to be the same. system + surroundings = universe In heat transfer, if one substance X is losing heat to another substance Y, then substance Y must be gaining the heat t...

Kristen Kim 2K

The same heat (q) with a lower temperature will yield a greater change in entropy. If the temperature is higher, there will be a smaller change in entropy for the same q value. Since delta S = q/T, if q is the same for two temperatures, the higher temperature means a greater denominator, therefore i...

Kristen Kim 2K

I think it will be given on the constants sheet on the exam. But it won't hurt to remember that Cv = (3/2)R and Cp = (5/2)R.

Kristen Kim 2K

Yes. The definition of expansion work is "the work arising from a change in the volume of a system." The formula for expansion work is given by w = -(Pex)(delta V), where Pex is a constant external pressure.

Kristen Kim 2K

If the system is isothermal, that means that the system and surroundings do not exchange matter or energy between each other. This is the case for a reversible expansion because the temperature must be constant in order for the volume to fluctuate so that the pressure is kept constant.

Kristen Kim 2K

Degeneracy is the number of ways of achieving a given energy state, and can be found by relation of the Boltzmann equation.

Kristen Kim 2K

Something with a high heat capacity means that it would require a lot of heat to increase in temperature, which might make it a good insulator but a bad conductor of heat. Conversely, something with a low heat capacity means that it doesn't take much heat to increase the temperature, which might mak...

Kristen Kim 2K

We were given the formula q = (g)(Csp)(delta T), so we can just rearrange the variables to get Csp = q / (g * delta T). We would need to know q (energy), the mass of the substance (g), and the change in temperature (delta T).

Kristen Kim 2K

Heat capacity just refers to how much heat is needed to raise the temperature of some substance by 1 degree C. Molar heat capacity is how much heat is needed to raise the temperature of 1 mole of that substance by 1 degree C.

Kristen Kim 2K

We know that the formula for percent deprotonation, or percent ionization, is [H+]/[HA] times 100. in this problem, we are trying to find [H+] in order to plug it into the pH formula. The percent deprotonation and the concentration of [HA] (which is in this case benzoic acid) are given to us. 2.4% a...

Kristen Kim 2K

If PCl5 is aqueous, I would use [PCl5], and if PCl5 is gaseous, use P PCl5. Unless they specify to find partial pressure, I would just use the concentration notation.

Kristen Kim 2K

It depends on which direction the reaction proceeds. If there are some amount of both products and reactants, you can check to see if Q is larger or smaller than K to determine which way the equilibrium is shifting.

Kristen Kim 2K

This only applies if the change in composition (x) is less than 5% of the initial value. Usually if Ka is less than 10^-3, I would disregard the x.

Kristen Kim 2K

After you do the ICE box method and find the equilibrium concentrations, you divide the equilibrium concentration of the conjugate acid or base by the initial concentration of the acid or base given and multiply that by 100. For example, if the chemical reaction was CH3COOH + H2O --> CH3COO- + H3O+,...

Kristen Kim 2K

Use Kp when the reactants and products are gaseous, and use Kc when the reactants and products are aqueous.

Kristen Kim 2K

I would say to use Qp when the reactants and products are in gaseous state, and use Qc when the reactants and products are in aqueous state.

Kristen Kim 2K

The values in between mean that neither the reactants or products are favored.

Kristen Kim 2K

Most likely they will be given. Referring back to Chem 14A, we know the concentration of a strong acid or base because it is completely ionized. For weak acids and bases, we will learn how to use ICE tables to calculate them.

Kristen Kim 2K

The Roman numeral in the parentheses is the oxidation number of the transition metal. The sum of all charges inside the brackets must add up to the charge on the overall coordination compound. For this specific problem, you are trying to find out the oxidation number of the transition metal. To find...

Kristen Kim 2K

The Roman numeral in the parentheses indicates the oxidation number of the transition metal in the coordination sphere, so that would mean Cobalt has a charge of +3. This would mean that there would need to be 3 Br to offset this positive charge, since Br has a charge of -1.

Kristen Kim 2K

The more electronegative atom stabilizes O- by withdrawing electron density. For example, comparing Cl - O and Br - O, Cl pulls the O- closer than Br does. This makes the oxoacid more likely to lose H+.

Kristen Kim 2K

Yes, since we've finished molecular shape and structure. We can technically do our homework problems based on any of the chapters, but it would be wise to focus on outlines 3, 4, and 5 because of the upcoming test this week.

Kristen Kim 2K

Dissociation energy is the energy required to break a bond. Bond multiplicity refers to how many bonds are between two atoms, and as the number of bonds increase, the dissociation energy also increases because it takes more energy to break multiple bonds. As atomic radius increases, dissociation ene...

Kristen Kim 2K

The outline on the class website says we need to know how to identify and draw them, as well as explain their characteristics and how they form coordinate covalent bonds.

Kristen Kim 2K

Degenerate refers to orbitals with the same energy. For example, 2p would have three degenerate orbitals, 2px 2py 2pz, because they are in the same n=2 energy level.

Kristen Kim 2K

Sigma bonds interact end to end, while pi bonds overlap side by side. Every bond contains one sigma bond. For example, a single bond would be one sigma bond. A double bond would be one sigma bond, one pi bond. A triple bond would be one sigma bond, two pi bonds.

Kristen Kim 2K

Yes, the number of bonds do not matter when looking at the regions of electron density.

Kristen Kim 2K

It depends on if we are ahead of the material by that day.

Kristen Kim 2K

Polarizing power refers to the ability of cations to cause distortions in an anion. Polarizability could be seen as the opposite end, where it describes the ability of an anion to have their electrons become distorted by a cation.

Kristen Kim 2K

I think you should make sure the octets are filled first before you go on to check formal charges.

Kristen Kim 2K

He used the example of an Na+ ion and Cl- ion being bonded by a transfer of electrons. Even though this is technically an ionic bond, some of the negative charge from the Cl- ion is pulled toward the positive charge of the Na+ ion, and this happens in the bonding region. This is the "covalent&q...

Kristen Kim 2K

After drawing the basic Lewis structure for a compound and calculating formal charges, how do you know when to add a double bond and how many of them to add?

Kristen Kim 2K

Can someone explain the reasons behind the trends we see in the periodic table?
- Atomic radius
- Ionization energy
- Electronegativity
How do they relate to shielding effect and number of electrons or protons?

Kristen Kim 2K

You would use [Xe], since that is the preceding inert gas in relation to Tl.

Kristen Kim 2K

Write the Lewis structure of ONF.
Why are there two electrons on top of the N in the Lewis structure?

Kristen Kim 2K

I think the experimentally observed lengths will just be given, but they are basically going to be in between the single bond and double bond lengths because the actual length should be an average of the lengths from the resonance structures.

Kristen Kim 2K

Can someone explain the relationship between Rydberg's equation and Bohr frequency condition?

Kristen Kim 2K

λ=h/p is the de Broglie wavelength equation. This is used to find the wavelength that is emitted by any moving particle since everything technically has wavelike properties, whether they are detectable or not. λ=hc/E is the equation to find quantum energy of a photon, from the photoelectric effect. ...

Kristen Kim 2K

Does a higher frequency of light mean higher kinetic energy of ejected electrons?

Kristen Kim 2K

Many people sell the physical copy of the solutions manual online, such as on the Facebook UCLA Free/For Sale group or the Textbook Buy/Sell group. Amazon also seems to be selling new/used copies.

Kristen Kim 2K

E = hν (h=6.626 x 10^34 Js)
c = λν (c=3.00 x 10^8 m/s)
E(photon) - E(energy to remove e-) = E (excess) = EK(e-) = (mv^2)/2
E(n) = -(hR)/(n^2) (R = 3.29 x 10^15 s^-1)
λ = h/p
∆p ∆x ≥ h/4pi

I might be missing a few but most of these are on Outline 2 that is posted on the class website.

Kristen Kim 2K

Professor Lavelle mentioned that wavelengths up to 10^-18 m would be detectable.

Kristen Kim 2K

Basically the photoelectric effect is when light (UV) is shined onto a metal surface, electrons in the metal surface become excited and they get emitted. Scientists did an experiment on this thinking that the more intense the light, the more electrons will be emitted. But they were proved wrong beca...

Kristen Kim 2K

I think doing the practice problems are the most helpful since you're practicing how to solve questions that might essentially be asking the same question but just with a completely different wording. Also, I would think that really taking time to understand the concepts rather than memorizing them ...

Kristen Kim 2K

In the ultraviolet spectrum of atomic hydrogen, a line is observed at 102.6 nm. Determine the values of n for the initial and final energy levels of the electron during the emission of energy that leads to this spectral line. I understood that I had to kind of work backwards and start with convertin...

Kristen Kim 2K

The subscript indicates what kind of compound it is, so if the subscripts are changed, the actual compound would change as well. For example, if we want to indicate there are two molecules of formaldehyde, we would write 2(CH2O) instead of C6H12O6 (subscripts multiplied by 2), which would then indic...

Kristen Kim 2K

Systematic error refers to a lack of accuracy, while random error corresponds to a lack of precision. So if there is a large systematic error, the results would be similar to each other, but would be far off from the true value. If there is a large random error, the average of the results might be c...

Kristen Kim 2K

On the grading portion of the syllabus, it says that we gets 3 points a week for the weekly online discussion, so that means we just have to either post or reply to a post to get those points?

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