CHEMISTRY COMMUNITY

TarynD_1I

https://users.stlcc.edu/gkrishnan/rateunits.htm
here is a helpful link to organize which units go with each order of reaction!

TarynD_1I

You'd use concentration of products over reactants for gaseous and aqueous, not liquid and solid.

TarynD_1I

It would be anode concentration over cathode concentration.

TarynD_1I

I believe that the pseudo rate law is essentially increasing all but one of the reactant concentrations, making them basically constant. This makes small changes in the small concentration significant by isolating it.

TarynD_1I

Lavelle is doing the exam through CCLE, so printing out and scanning isn't needed, since it will all be online

TarynD_1I

PranaviKolla2B wrote:Does the Arrhenius equation simply tell us the effect of temperature on the rate constant?

Yes, the Arrhenius equation is used to measure/calculate what happens to the rate constant (and the rate of the reaction) when a change in temperature occurs.

TarynD_1I

If using the equation E(cell) = E(cathode) - E(anode) and using reduction values found in the appendix or on the sheet he will give us on the test, then I'm pretty sure that there is no need to flip the anode cell potential value when accounting for oxidation. In this case you would not need to chan...

TarynD_1I

At a higher temperature, it is more likely that moving particles will collide with each other with enough energy to surpass the activation energy barrier. Therefore, the reaction will be faster.

TarynD_1I

You could also check your grades on myucla regularly, since the TA's might input test 2 grades prior to discussion session

TarynD_1I

molecularity according to the textbook is the number of reactant molecules, atoms, or ions that take part in a specific elementary reaction.

TarynD_1I

a salt bridge allows the electrons to go from the cathode to the anode to prevent charge buildup

TarynD_1I

The electrochemical series is Chapter 6M.2 and basically lays out the relative strengths of oxidizing and reducing agents.

TarynD_1I

I believe we use the Nernst equation to find the cell potential at any point in a reaction

TarynD_1I

there are no big review sessions by the TA's and UA's but office hours and the step up/workshop sessions in young and covel are very helpful

TarynD_1I

First order reactions has a linear rate and depends on one concentration

TarynD_1I

My TA explained that cell diagrams look like this:

s | g | aq || aq | g | s

and the electrons go left to right (from the anode to the cathode)

TarynD_1I

I think we use Van't Hoff when trying to calculate how K is affected by a change in temperature

TarynD_1I

chari_maya 3B wrote:If it is alkaline, why would you balance it first acidically?

You would have to balance the hydrogens with H+ first in order to balance out the charges, and then cancel the extra protons with OH-

TarynD_1I

Balancing acidic and alkaline reactions are mostly the same, but balancing alkaline reactions have an additional step. in a basic reaction, after balancing the reaction with protons (H+), you have to also balance out the protons with OH-.

TarynD_1I

My TA explained that cell diagrams look like:

s | g | aq || aq | g | s

where | indicates a phase change and || is a salt bridge

also, the anode is on the left of the salt bridge and cathode is on the right of the salt bridge

TarynD_1I

Isolated: does not exchange matter or energy with surroundings
Closed: can exchange energy with surroundings, but not mass

TarynD_1I

I'm pretty sure it's not cumulative, it probably will be on material from after the midterm, but he'll definitely confirm the topics closer to the test.

TarynD_1I

How can you differentiate when to use -nRlnV2/V1 versus using -PV? I feel like I always get mixed up when I should use which equation. Any tips for knowing which one to use when? https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=160&t=58744&p=221113&hilit=helpful&sid=b6cc45c218434...

TarynD_1I

isochoric: constant volume

isobaric: constant pressure

isothermic: constant temperature

TarynD_1I

for b, pentene has more entropy than cyclopentane because cyclopentane is a rigid ring that is not that flexible, while pentene is more flexible (thus having more entropy).

TarynD_1I

ashwathinair wrote:Sometimes I post multiple times on the same thread - is this counted as separate posts or as just one?

I think it would count as multiple posts, but for a definite answer I'd ask your TA since they give the credit at the end of the quarter.

TarynD_1I

You use specific heat capacity when trying to find the heat required to raise the temperature of one gram of a substance by 1 degree Celsius.
Molar heat capacity is used to find heat required to raise the temperature of one mole of the substance.

TarynD_1I

qp is equal to delta h when a system is at constant pressure, so no nonexpansion work is being done.

TarynD_1I

From what I remember from 14a,
Strong acids include: HCl, HNO3, H2SO4, HBr, HI, HClO4
Strong bases are mostly bases that include OH in the chemical formula (ex: NaOH, KOH)

TarynD_1I

Use Cv when the system is at a constant volume, and Cp when the system is at a constant pressure, I'm pretty sure it'll either be stated in the problem or will be able to be inferred by other info.

TarynD_1I

State functions can be added or subtracted, which allows us to calculate changes in values of the system

TarynD_1I

a regular calorimeter is thermally insulated, while the bomb calorimeter is an insulated container completely immersed in a metal box of water. in addition, a constant pressure calorimeter is used to calculate change in enthalpy, while a bomb calorimeter (constant volume) is used to calculate the ch...

TarynD_1I

i'm pretty sure that Dr. Lavelle does not have any past exams in the test bank, but going to the midterm review sessions that he has set up help drastically with understanding concepts or for practicing problems.

TarynD_1I

you would divide the x amount (found using ice table) by the original concentration and multiply by 100. If this percentage is less than 5%, then the approximation is valid.

TarynD_1I

During reversible reactions, products and reactants are always being made (going back and forth), while in irreversible reactions products can't revert back to what it was as a reactant. I also think that during reversible reactions, the system stays at equilibrium, and during irreversible reactions...

TarynD_1I

Heat is not a state function because it is dependent on the path of the reaction, while enthalpy is a state function because it does not depend on the path of the system but is dependent on initial and end results.

TarynD_1I

Delta h is change in enthalpy, while delta u is the change within the internal energy of the system.

TarynD_1I

The gas constant depends on which measurement that the question uses (J, atm, bar, or torr usually) and it will be on the equations sheet.

TarynD_1I

Work is not a state function because it depends on the path from the initial to final states of the reaction. Heat is not a state function because it depends on the paths of each individual state.

TarynD_1I

Internal energy is a state function I believe because it is independent of the path of the process in question. It has different values at each different state of the system.

TarynD_1I

Think of heat in a endothermic reaction as a reactant (need heat to reaction to proceed) and in a exothermic reaction as a product (reaction produces heat). For exothermic, if K decreases when temperature increases, the reaction shifts to the left, and if K increases when temperature decreases, the ...

TarynD_1I

When referring to Bronsted acids and bases, we refer to proton donors (acids) and proton acceptors (bases).
Lewis acids and bases are electron pair acceptors (acids) and electron pair donors (bases).

TarynD_1I

K is the equilibrium constant of an reaction that is already at equilibrium, while Q (reaction quotient) is used when the reaction is not already at equilibrium. Q is also used to show in which direction the reaction shifts (for example, when K>Q, then the reaction shifts to the right).

TarynD_1I

Solids and liquids are not used in calculating an equilibrium constant, only gasses and aqueous solutions are considered. This is because the activity of the pure solids and liquids are considered to be 1, so it would not affect the equilibrium equation (their concentrations do not change throughout...

TarynD_1I

the equivalence point shows where the amount of titrant neutralizes the analyte solution.

TarynD_1I

We use the reaction quotient Q when the reaction is not in equilibrium, to figure out which way the reaction shifts. Use K when the reaction is at equilibrium.

TarynD_1I

You would use Le Chatelier's Principle when the physical parameters of a reaction changes (including temperature, concentration, and pressure). Le Chatelier's basically tells us what happens to the reaction as these changes occur (i.e. if the reaction shifts to the right or the left).

TarynD_1I

when calculating for K, the calculation expression is in a ratio, and all of the units cancel each other out. K therefore also has no units.

TarynD_1I

Water is not accounted for when calculating for K because it does not affect the equilibrium of the reaction. Pure solids and pure liquids usually do not affect K and are not included in its calculation expression.

TarynD_1I

Chatelier's Principle is, as Professor Lavelle said in class, chemical reactions adjusting to minimize the effect of change. This change usually refers to changing physical parameters of temperature, pressure, or concentration.

TarynD_1I

Respiratory acidosis is a surplus of carbon dioxide in the bloodstream, and since CO2 is acidic, it lowers the pH of blood to be acidic. This happens when a person is suffocating, or not breathing out the CO2 they produce. Therefore, acidosis may be deadly because the pH of blood should not be acidi...

TarynD_1I

Acids that contain oxygen are under the "oxoacid" group, which means that the more oxygen atoms that are present, the more acidic the compound is (because of high electronegativity). When comparing two oxoacids, the molecule with a larger number of oxygen atoms would be more acidic. I'm no...

TarynD_1I

Period 3 elements and lower can have an expanded octet because it is able to utilize its d-orbital to also hold electrons.

TarynD_1I

I believe that if a molecule has resonance, it has a lower pka, and thus making it more acidic.

TarynD_1I

Lyndon gave us this list during his last workshop session:

Strong acids: HCl, HBr, HI, HNO3, H2SO4, HClO4

Strong bases: LiOH, NaOH, KOH, RbOH, ScOH, Ca(OH)2, Sr(OH)2, Ba(OH)2

TarynD_1I

How does water act as both a Bronsted acid and a base?

TarynD_1I

Electron affinity is the likelihood of an atom gaining an electron. Since Nitrogen's 2p shell is has 3 up-spin electrons, making it half full, it would not want to take on another electron because it would make the atom less stable. Half full and completely full subshells are more stable than partia...

TarynD_1I

A polydentate ligand has to have more than 2 lewis base sites, for example having more than 2 donor electron pairs that bind to the central atom.

TarynD_1I

I think water is considered to be a constant in the equilibrium constant formula (it is considered to be 1) because it shouldn't affect the equilibrium of the reactants.

TarynD_1I

kA is the acid dissociation constant, and larger values for kA means that the acid is stronger and dissociates better, while smaller values for kA means that the acid is weaker and does not dissociate as well.

TarynD_1I

Hydrogen is not very electronegative. In terms of periodic trends, electronegativity goes up as you go up a group as period numbers increase (towards fluorine).

TarynD_1I

Why does NO2 have a higher boiling point than N2O? I am confused because NO2 is a radical. NO2 has a higher boiling point because it is more polarizable, which means it has stronger van der waals forces. Since NO2 has more electrons than N2O, it is bigger and more polarizable. I don't think it has ...

TarynD_1I

From what I understand, the geometry is counting up all the areas of electron density, while the shape involves how the areas of electron density from the lone pairs affects the overall shape of the molecule. For example, H20 would have a tetrahedral geometry (because it would have 4 areas of electr...

TarynD_1I

I think SO2 would have a higher boiling point because it has more electrons than O3, therefore making it more polarizable. Since it is more polarizable, it has stronger van der waals forces, which take more energy to break, causing SO2 to have a higher boiling point.

TarynD_1I

If an element is in the third period or lower, it can have an expanded octet because it can utilize d-orbitals.

TarynD_1I

You should probably know which types of bonds are stronger than others, because the stronger the bond, the higher the melting/boiling point. For example, ion-ion being the strongest bond and induced dipole-induced dipole being the weakest.

TarynD_1I

You would calculate the difference in electronegativity between the atoms. Polar molecules usually also have a dipole moment, or a difference in partial charges within the molecule.

TarynD_1I

What exactly is polarizability and how are we supposed to apply it? Like, what is its purpose because I'm kind of confused? Polarizability is how an electron cloud is distorted by an outside electric field. The bigger the atomic radius of an atom, the more polarizable it is because the positive nuc...

TarynD_1I

A dipole moment happens when there is a separation of partial charges within a molecule, which happens when there is a big difference in electronegativity. For example, in H20, there is a dipole moment pointing towards oxygen because oxygen has a much higher electronegativity than hydrogen.

TarynD_1I

E=hv is used to find the energy of a photon using Planck's constant and frequency of light.
E=pc is used to find the energy of a photon using the speed of light and the momentum of a photon. I'm pretty sure we only use E=pc when momentum of the photon is provided.

TarynD_1I

You can tell by the difference in electronegativity I think. If one atom in a molecule has a high electronegativity and another atom in the molecule has a low electronegativity, then there is a dipole moment. So basically one side is more positive and one side is more negative. The dipole moment is ...

TarynD_1I

You use de Broglie's equation to find the wavelength of a particle that has resting mass (not light/photons).

TarynD_1I

Lavelle does not expect us to draw the hybrid I think, because he didn't show it in class. So it's preferred that you draw all of the different resonance structures.

TarynD_1I

I'm pretty sure you'd multiply by 2 to account for both -5 and +5

TarynD_1I

You would use de Broglie's to find the wavelength (or describe wave properties) of an object that has resting mass (not light), and you would use E=hv to find the energy of a photon (light).

TarynD_1I

In the review session today on bonding/structures, he told us to either draw all of the resonance structures (and state that there is a hybrid), or to draw the actual hybrid of the structures

TarynD_1I

Yes, because a half filled or a completely filled configuration is more stable than a partially filled.

TarynD_1I

The H is the Hamiltonian which is just an operator that acts on the ψ. The ψ describes the system mathematically and E is energy. In the review, the problem that was used as an example basically just gave you the H and you had to plug it into the equation and not solve. I think we just have to know...

TarynD_1I

Usually, the electron affinity trend is that EA increases from left to right across the groups, but noble gasses (He, Ne, Ar, etc) have lower EA than the rest of the group.

TarynD_1I

Can someone please help walk me through how to draw the lowest energy Lewis Structure for N2O with N as the central atom? (12c on the dino nuggets midterm practice). I was a little confused when they explained it in the review session. Thanks!

TarynD_1I

I don't believe that we have to separate px, py, and pz when writing electron configurations. I think Lavelle does it in class to show that each is a different orientation, but when writing configurations on hw or on tests, I haven't been splitting them up.

TarynD_1I

Electron affinity is when an atom (in the gaseous phase) takes on an electron to form an anion (a negative ion). Basically, a neutral charged atom gains an electron, and the electron's negative charge makes the atom's net charge negative. Also, the prompt will probably tell you if the atom is gaseou...

TarynD_1I

Anions are bigger than their parent atoms because there is more negative electronic charge than positive charge, so there is more electron repulsion. Cations are smaller than their parent atoms because the bigger positive charge from the nucleus makes the attraction of the electrons stronger, thus s...

TarynD_1I

I was advised that the best way to study is by reading the chapters in the book and by doing all of the suggested problems on the syllabus

TarynD_1I

E=hv is the equation used to solve for the energy of a particle of light, which is a photon.

TarynD_1I

I'm pretty sure we use E=hv to find the energy of a photon

TarynD_1I

Lavelle explained in class that since photons do not have mass (because light doesn't have mass), so they obtain all of their energy from their momentum. So, instead of calculating momentum (p) by multiplying velocity by resting mass, the photon's momentum will probably be given to you in the questi...

TarynD_1I

the uncertainty value is 0.2 because the actual value would lie between 2.34 - 2.36.

TarynD_1I

I think that you use E = pc when mass is not considered (maybe like a photon, because Lavelle said in class that photons do not have mass, but they have momentum).

TarynD_1I

this past test i don't think that the graders took off if you had the wrong amount of significant digits, my TA said he wasn't taking off for sig figs this test

TarynD_1I

I was recommended to keep as many digits as possible until the very end. This last test, our TA told us that he wasn't placing a heavy emphasis on sig figs so we shouldn't worry about it, but they might start counting it in the future.

TarynD_1I

According to the Hill System, you're supposed to put C carbon first, then Hydrogen, then all the other elements in alphabetical order. But if there is no Carbon the formula, then all the elements are written in alphabetical order.

TarynD_1I

the amount of points that each question was worth was put on the test but they do give partial credit if you did the right work but got the wrong answer

TarynD_1I

Usually for the homework problems, when asking for molecular or empirical formulas, the mass percentage composition or the amount in grams of each element is listed out in the order that the resulting compound will be in.

TarynD_1I

You should multiply all coefficients to make them whole integers, especially if the question is asking for a molecular or empirical formula.

TarynD_1I

10^3 = 1000 while 10^-3= 0.001

When you see a negative, it just means to move the decimal to the left, while a positive exponent means to move the decimal to the right

TarynD_1I

Professor Lavelle also has a link on his website (https://lavelle.chem.ucla.edu/wp-conten ... OUT_SF.pdf) that is really helpful for figuring out sig figs :)

TarynD_1I

For a couple of the examples given in my discussion last week where we were practicing writing out and balancing chemical equations, we weren't given states of matter, but for those questions, it was easier to use context clues to figure it out. It might be a little harder to figure out which reacta...

TarynD_1I

I'm pretty sure that hand-written homework from the textbook is collected at your discussion (except this week) and chemistry community posts are due on Sundays.

TarynD_1I

Just making sure: when writing out combustion reactions, it's implied that we add oxygen as a reagent and CO2 and H20 as products, right?

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