CHEMISTRY COMMUNITY

KeyaV1C

Jasmine 2C wrote:
KeyaV1C wrote:I don’t think it is. I saw the Thursday one floating around here but not the Tuesday one. Did you have any specific questions on the Tuesday test?

I wanted to know the answer for Question 4

KeyaV1C

I had a question about the answer to question 3 part a. Wouldn't the order of rxn with respect to HgCl2 and C204 ^2- be 1 and 1 because when the concentrations double, the rates also double? Thanks! I had the same question but I think the rate with respect to C2O4 is second order and with respect t...

KeyaV1C

I don’t think it is. I saw the Thursday one floating around here but not the Tuesday one. Did you have any specific questions on the Tuesday test?

KeyaV1C

All the equations on the sheet are given to us. Plus the exam is open book so I don’t think you need to know any calc for the final

KeyaV1C

Kinetics describes the pathway of reactions, with an emphasis on the activation energy that signifies the energy difference between the free energy of reactants and the transition state. Kinetic analysis is about the speed or rate of reaction, using experimental techniques to observe reactant &...

KeyaV1C

When water goes from gas to liquid it is undergoing a phase change and therefore requires a lot more energy than just a temperature change. When steam hits your skin, energy will be released as it undergoes a phase change. This energy release causes a much worse burn than if the same amount of boili...

KeyaV1C

Clara Cho 2K wrote:Do you think we will still meet for discussion?

I don’t think so

KeyaV1C

EMurphy_2L wrote:oh also when can you just neglect elements? like 6L.9) KMnO4 and FeCl are involved in the reaction but just MnO4 and Fe are written in the redox reaction and cell diagram????

I’m not too sure but I think you can ignore elements when their oxidation states don’t change during the reaction

KeyaV1C

For part c you have to split up the half reactions in order to calculate the overall standard cell potential
[Cl2 + 2e --> 2Cl-] + [2H+ --> H2 + 2e] = Cl2 + 2H —> 2 HCl

For part d you have to reverse the sign on the cell potential in order to get the correct reaction

KeyaV1C

R -> gas constant = 8.314 J/(mol*K)
T -> temperature in kelvin
F -> faradays constant = 96,485 C/mol
n -> number of electrons transferred

KeyaV1C

A concentration cell is a cell that is has two half-cells with the same electrodes, but with different concentrations. The voltage difference is created by electron transfer from the cell with the lower concentration to the cell with the higher concentration. An example for this could be a cell wher...

KeyaV1C

Ghadir Seder 1G wrote:so something is neither oxidized or reduced when its in the same oxidation state in both the reactants and products?

Yeah if the oxidation states are the same, the element is neither reduced nor oxidized

KeyaV1C

Yeah generally a negative delta G -> spontaneous reaction therefore the cell does work

KeyaV1C

I think we’ll get our tests back during discussion

KeyaV1C

I think it’s M/s - mols*L^-1*s^-1

KeyaV1C

The cell potential of a galvanic cell is always positive

KeyaV1C

In general, short reaction times favor kinetic control while longer reaction times favor thermodynamic control

KeyaV1C

Metals with small ionization energies and low electro-negativities tend to be good reducing agents

KeyaV1C

The product is always in the cathode end

KeyaV1C

I think the posts get checked every Sunday

KeyaV1C

Since Gibbs free energy is a measure of energy available to do work, when the reaction is at equilibrium, no more work is being done and therefore delta G is 0.

KeyaV1C

I’m not too sure if I understand your question, but when you’re balancing redox reactions when you’re given individual reactions, you need to make sure the electrons cancel out.

KeyaV1C

I got -27 kJ/mol as my answer.

KeyaV1C

All elements in their standard states will have 0 as their standard Gibbs free energy of formation.

KeyaV1C

This is what the graph in the solution section of the book looks like

KeyaV1C

I don’t think so

KeyaV1C

This is a useful link: https://courses.lumenlearning.com/cheminter/chapter/calculating-ph-of-salt-solutions/ When you are given a problem with a salt in water, the salt dissociates. Ex. NaF + H20 -> Na+ + HF + OH - Since the Na+ is a stable ion and doesn't contribute to the pH, you can set up an ice...

KeyaV1C

This equation allows you to tell whether a reaction is spontaneous or not deepening on given entropy and enthalpy values. You can also calculate temperatures for which the reaction is spontaneous.

KeyaV1C

Nonlinear molecules have 3 rotational degrees from the 3 axes of rotation. Since there is symmetry about only one axis, linear molecules have 2 rotational degrees. The degrees of freedom contribute to the heat capacity.

KeyaV1C

I just emailed them to you!

KeyaV1C

Increasing the number of molecules in a system can increase the number of microstates, since there are more possible arrangements of the molecules. Increasing the volume can also increase the number of positions where each molecule can be, which would increase the number of microstates. I don’t thin...

KeyaV1C

Non-expansion work is one way of knowing that the pressure is constant

KeyaV1C

In a closed system, the matter within the system is constant, however, energy can be transferred from the system to its surroundings and vice versa. In an isolated system, neither matter nor energy can be transferred between the system and its surroundings.

KeyaV1C

You have to set up an ICE table with the concentrations given to you

KeyaV1C

I don’t think so. I would just do some of the intro thermochemistry problems to be on the safe side.

KeyaV1C

Irreversible expansion occurs against a constant external pressure so the equation is just w= - P* Δ V. Reversible expansion has a pressure that keeps changing so then the equation is w= -nRT ln(V2/V1)

KeyaV1C

Expansion work is pressure-volume work whereas non-expansion work is anything else such as electrical, frictional, etc. For example, biological instances of non-expansion work include muscle contraction and nerve impulses.

KeyaV1C

I think Delta H = Delta U when there is no work being done, implying that the volume is constant.

KeyaV1C

When water goes from gas to liquid it undergoes a phase change which requires a lot more energy than just a temperature change. When steam hits your skin, a lot of energy will be released as it condenses. This energy causes a much worse burn than if the same amount of boiling water were to hit your ...

KeyaV1C

When the reactant is removed, the equilibrium shifts to make more reactant in order to make up for the loss.

KeyaV1C

[Concentration of deprotonated species] / [Initial concentration of original species] * 100%

KeyaV1C

When K is really small, the value of x tends to be really small as well, barely changing the concentration of the reactants.

KeyaV1C

Endothermic and exothermic refer to transfer of heat (q) or changes in enthalpy ΔRH. The classifications endergonic and exergonic refer to changes in free energy.

KeyaV1C

yeah it is

KeyaV1C

Yes it does. Increasing the pressure of a reaction by decreasing volume favors the side of the reaction with less mols of gas. If you increase pressure by adding an inert gas, it doesn’t change the concentration of reactants or products.

KeyaV1C

In autoprotolysis a proton is transferred between two identical molecules, one of which releases a proton which is accepted by the other molecule. Ex. H20 + H20 -> h30+ + OH-

KeyaV1C

you would increase the yield by removing products from the reaction

KeyaV1C

1 bar is 0.986923 atm. The unit you use depends on the R value you use so that the units cancel out

KeyaV1C

We don't include solids and liquids in equilibrium constants because they don't affect the reaction reaching equilibrium. Equilibrium constants depend on the pressure of gases and concentrations of aqueous solutions in the reaction.

KeyaV1C

Chemical equilibrium is the state in which the forward reaction rate and the reverse reaction rate are equal. At equilibrium, the concentrations of the reactants and the products do not change. This implies that the concentrations of products and reactants don’t have to be equal at equilibrium.

KeyaV1C

The sure brackets around the compound just indicate that you’re writing the concentration of the compound => [] = concentration. You use p to calculate kp only when the compounds in the reaction are gases.

KeyaV1C

The primary difference between K and Q is that K describes a reaction at equilibrium, whereas Q describes a reaction that is not at equilibrium.

KeyaV1C

If the K value is 1 then the concentrations of products and reactants in the rxn are equal. If the K value is larger than 10^3 then the equilibrium sits at the right and the reaction favors the products more.

KeyaV1C

The CH3 group has electron donating properties, making it less electron withdrawing than the H attached to the carboxyl group in formic acid. That’s why formic acid is slightly stronger than CH3COOH

KeyaV1C

They should yield the same answer.

KeyaV1C

Since no particles can travel faster than the speed of light, it makes no sense that a particle with mass (ie. electron) would be able to travel faster than the speed of light.

KeyaV1C

The solutions are posted on the website:https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14A/Midterm_ans.pdf "The electron configuration of Mg is 1s2 2s2 2p6 3s2. Mg2+ 1s2 2s2 2p6 Highest energy level is 2p for all five electrons. Principle quantum number, n = 2 (also called shell)...

KeyaV1C

Just that it is a method where a solution of known concentration is used to determine the concentration of an unknown solution.

KeyaV1C

Absorption is usually negative and emission is positive

KeyaV1C

Sulfato is usually monodentate, but there are less common examples when it can be bidentate

KeyaV1C

I’m pretty sure all we need to know about isomers is that the double bonds on the molecule prevent the isomers from rotating between cis and trans geometry and that they are held in place because the pi bond prevents rotation.

KeyaV1C

If the conjugate base is more stable, the compound it corresponds to is more acidic. If you look at the conjugate bases for formic acid and acetic acid, both conjugate bases are stabilized by resonance, and electronegativity. The main difference is that there's a CH3 group instead of an H adjacent t...

KeyaV1C

An oxoacid is a compound whose molecule contains at least one hydroxy group bonded to an atom that is doubly bonded to at least one oxygen atom. Ex. Carboxylic acids, sulfuric acid, nitric acid, and phosphoric acid.

KeyaV1C

That sounds about right. I’m pretty sure the only naming we need to know is for coordination compounds

KeyaV1C

When a ligand has a prefix (di-, tri-, tetra-) you need to use bis- and tris. Ex. [Pt(H2NCH2CH2NH2)2Cl2]Cl2 -> dichlorobis(ethylenediamine)platinum(IV) chloride

KeyaV1C

pK is just the negative log of a constant. pKa is the negative log of the acid dissociation constant/ Ka value. pKb is the negative log of the base dissociation constant/ Kb value.

KeyaV1C

I think it’s okay to leave out the 2 because in all the homework problems, the solutions were always written without the energy level

KeyaV1C

On the syllabus he said "This class does not use a curve," so I don’t think he'll adjust the grades.

KeyaV1C

I think that’s for 14B. For A we don’t really have to do much with Acids and Bases other than calculate pH or identify compounds as acidic and basic

KeyaV1C

When an acid and a base react, the compound formed by the cation of the base and the anion of the acid is a salt

KeyaV1C

Generally, metal oxides are basic and non-metallic oxides form acids. You can characterize whether compounds are acidic or basic by looking at the location of the atoms on the periodic table.

KeyaV1C

You can tell by the location of the atoms on the periodic table. Be, Al, Ga, Sn, Pb, and Sb form amphoteric compounds. Anything to the left of them on the period table forms bases, and anything to the right forms acids.

KeyaV1C

If it helps you can also think of it in terms of protons or hydrogen atoms. For example if you have HCl in gas phase, it is a relatively stable molecule, but if you look at HCl in its aqueous phase, it loses the H atom and forms a Cl- ion. HCl (aq) + H2O(liquid) -> Cl-(aq) + H3O+(aq). HCl is an acid...

KeyaV1C

Yes Bronstead and Lewis definitions are just different definitions for the same thing. If a molecule loses a proton (generally H atom) it gains a lone pair.

KeyaV1C

I think the topics will probably be evenly distributed

KeyaV1C

The carboxyl group is a weak organic acid therefore making the compound acidic

KeyaV1C

I don’t think we have to memorize the exact number. Saying >109.5 on the exam should be fine.

KeyaV1C

I attached the Lewis structure below. The dipole moments don’t cancel therefore it’s a polar molecule.

KeyaV1C

NaCl could be one example — the + charged sodium cation is attracted to the - charged chloride anion.

KeyaV1C

They prefer the equatorial position

KeyaV1C

If you look at the structures of the molecules you can see that CH4 and CCl4 don’t have dipole moments. So the molecules for which the interactions would be important are b, c, and d.

KeyaV1C

Water and DNA base pairing are common examples of hydrogen bonds.

KeyaV1C

I don’t think it should matter since it’s the atom positions that are used to determine the name of the VSEPR shape.

KeyaV1C

On the 14A website there is an equation sheet posted. I’m pretty sure we will be getting the equations from that sheet.

KeyaV1C

Here’s how I did it:

KeyaV1C

It is more polar because there is a greater difference in electronegativity between the C-O bond than the B-O bond.

KeyaV1C

I didn’t draw out all the resonance structures, but you would just change the location of the double bonds in order to draw all of them out.

KeyaV1C

Nitrogen has a lower ionization energy than oxygen because of the way the shells are filled. It is one of the two exceptions to the ionization energy trend.

KeyaV1C

Because of the way the shells in N and O are filled, O has a lower ionization energy than nitrogen. This happens because it’s more preferable to have a half filled shell in O than only 2 e- in N. I’m pretty sure they said that B and O are the only two exceptions to the trend.

KeyaV1C

I don’t think we went over these concepts in class

KeyaV1C

I don’t think we need to know the details for how they are related, but usually the forces between molecules determine the physical properties of liquids and solids. In solids the intermolecular force is high, in liquids it is medium, and in gasses it is low.

KeyaV1C

If a compound is made from a metal and a non-metal, its bonding will usually be ionic and if it’s made from two non-metals, its bonding should be covalent

KeyaV1C

A) N=3, L=1 corresponds with 3p => 3 orbitals
B) corresponds with 5d, ml= -1 => 1 orbital (even though d has 5 orbitals only one of them has ml=-1)
C) 2p, ml=0 => 1 orbital
D) n=2 (is the actual question in the book) => s or p => 1+3 = 4 orbitals

Hope that helps!

KeyaV1C

I don’t think we need to know it in too much detail. I’m pretty sure we only need to know it in the context of the quantum numbers that correspond to a solution for a wave function.

KeyaV1C

Here’s what I have in my notes: Schrodinger's wave function equation -> Uses a wave function to describe position of e- in an atom -> Ψ: height of wave at position (x, y, z) -> Ψ^2: represents probability of finding an e- / electron density distribution H(Hamiltonian)Ψ = E(energy)Ψ ↳ operate a chang...

KeyaV1C

1m = 1,650,763.73 wavelengths of radiation.
1 wavelength: 1m/1,650,763.73 = 6.06*10^-7 = 605 nm

KeyaV1C

When two troughs interact/ two crests interact, it leads to a larger total amplitude, implying constructive interference. It’s destructive when the crest of one wave interacts with the trough of another.

KeyaV1C

It’s probably a good idea to remember how to derive it especially since it’s a pretty short derivation. λ=h/p and p=mv so λ=h/mv

KeyaV1C

I’m pretty sure in class Dr. Lavelle said that we do not need to memorize nomenclature for now. I would suggest looking up the names of the chemicals in order to find out their molecular formula, and then try balancing the equations from there.

KeyaV1C

On the Chem 14A class website there’s a link that has everything in detail you need to know about sig figs:
https://lavelle.chem.ucla.edu/wp-conten ... OUT_SF.pdf

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