CHEMISTRY COMMUNITY

Nare Nazaryan 1F

They'll be given but it's up to you to figure out which is for what order and how to use them exactly.

Nare Nazaryan 1F

Since rate constants depend on concentration (which is positive), they are always positive.

Nare Nazaryan 1F

If reactant energy is higher than the product energy, the reaction is exothermic and the opposite for endothermic.

Nare Nazaryan 1F

I think the slow step is the one that determines the rate law for the overall reaction.

Nare Nazaryan 1F

PranaviKolla2B wrote:What else are the functions of catalysts, besides lowering the activation energy?

They speed up a reaction by reducing the activation energy or changing the reaction mechanism.

Nare Nazaryan 1F

Use it to find activation energy or the reaction constant from temperature change.

Nare Nazaryan 1F

Mol per liter per time (in seconds).

Nare Nazaryan 1F

It is not in the rate law because it was formed then used and does not appear in the overall reaction.

Nare Nazaryan 1F

Google says that "a reaction which is not first-order reaction naturally but made first order by increasing or decreasing the concentration of one or the other reactant is known as pseudo first order reaction."

Nare Nazaryan 1F

Are you referencing kinetics vs thermodymanics? If so, I am not sure how that would be formatted.

Nare Nazaryan 1F

Lyndon's review sessions (especially for the midterm and final) and the textbook problems are the most helpful.

Nare Nazaryan 1F

That's right, we don't include zero-order reactions.

Nare Nazaryan 1F

The slope of the tangent line is the same as the derivative, so you can just take the derivative.

Nare Nazaryan 1F

005162520 wrote:What do you mean by large activation energy barrier ? If it has a large activation energy barrier does that mean the reaction takes longer ?

Yes, it takes much longer since it is a lot slower (and usually we don't see diamond rings for example turning to graphite)

Nare Nazaryan 1F

For favorability, thermodynamics comes in handy; however, kinetics tells you the speed of the reaction not favorability.

Nare Nazaryan 1F

Mol/(Liter*second); moles per liter per second

Nare Nazaryan 1F

It represents the charge (coulombs) of 1 mole of electrons.

Nare Nazaryan 1F

If you are referring to R (since n is the number if moles) then we use 8.134 because it has Joules and moles.

Nare Nazaryan 1F

Half reactions are the reduction and oxidation processes that occur in a redox reaction, which we break up to make easier to solve.

Nare Nazaryan 1F

Just like in equilibrium, changing the concentrations will change the direction the rxn is favored, so we apply Le Chatelier's principle.

Nare Nazaryan 1F

Standard condition is 1M solution at 1 atm, with temperature of 273.15 K.

Nare Nazaryan 1F

I think the whole purpose is that it helps separate the oxidation and reduction.

Nare Nazaryan 1F

I think we should know the ones in groups 1,2,16,17 and any common ones we talk about.

Nare Nazaryan 1F

Ions are charged particles, so they cannot have a zero charge.

Nare Nazaryan 1F

Oxidation refers to losing electrons, while reduction means gaining electrons. You can tell by comparing the oxidation numbers of the products and reactants.

Nare Nazaryan 1F

I think it is fine to assume that. Some compounds with oxygen or hydrogen might make it so that the oxygen/hydrogen's oxidation state is different, but I don't think we will discuss it in this course (I'm not 100% sure though).

Nare Nazaryan 1F

When you have q[v], it means that volume is constant (v=0), so if you plug that into the deltaU equation, your work will also be 0 since it's based on volume (w=-PdeltaV) and therefore, you get deltaU=q. On the other hand, when you are doing q[p], that means your pressure is constant (p=0) and there...

Nare Nazaryan 1F

The way I remember the difference is that extensive properties can be divided by the amount of the substance (e.g. heat capacity divided by mass) to become intensive properties (specific heat capacity as a result of heat capacity/mass).

Nare Nazaryan 1F

Because matter cannot transfer if it is sealed, but heat can (which is what a closed system is).

Nare Nazaryan 1F

Yes, it is always the same as on every test/midterm/final.

Nare Nazaryan 1F

Natalie Benitez 1E wrote:How would we know on the exam if something is reversible or irreversible ?

I believe it is reversible if the pressure is not constant and if the internal and external pressure are the same.

Nare Nazaryan 1F

It is when the volume increases/expands.

Nare Nazaryan 1F

It's basically conservation of energy (the universe is a closed system, therefore energy transfers but does not get lost).

Nare Nazaryan 1F

Delta H is positive when ice turns to liquid (applying heat to change from solid to liquid).

Nare Nazaryan 1F

Delta U= q (aka heat) + w (aka work).

Nare Nazaryan 1F

An isolated system is completely closed off from its surroundings and cannot exchange matter or energy with its surroundings. A closed system is closed off from its surroundings and cannot exchange matter, but can exchange energy with its surroundings. Isolated system: a thermos flask. Closed system...

Nare Nazaryan 1F

Work (and heat) are not state functions. Work is proportional to the distance an object is moved, which depends on the path used to go from the initial to the final state (therefore not a state function). Usually doing things that require force and distance are considered as doing "work."

Nare Nazaryan 1F

I don't think it's necessary to draw them, but it will probably be helpful; otherwise, the values of the bond enthalpies should be given somewhere.

Nare Nazaryan 1F

Hess' law states that the change of enthalpy in a chemical reaction is independent of the pathway between the initial and final states (enthalpy is a state function and you can add enthalpies to get the total enthalpy).

Nare Nazaryan 1F

I believe those values will probably be given to us based on examples from class.

Nare Nazaryan 1F

It just means that, since enthalpy is a state property, different enthalpies can be added together.

Nare Nazaryan 1F

It predicts what would happen if a parameter changed and how the reaction would adjust to fixing that change in parameter.

Nare Nazaryan 1F

X was ignored because 0.10 is less than 10^-3, which means it is so small that it would not make a difference to decrease by X; therefore, you only use the 0.10 (think of Dr.Lavelle's example of the million dollars minus $10).

Nare Nazaryan 1F

Yes, it is the same because when Q is less than K, there are more reactants than products so the reaction needs to form more products to reach equilibrium.

Nare Nazaryan 1F

We use the quadratic equation when equating the values we got from the ICE table (products/reactants) to the given equilibrium constant K, and if X is not smaller than 10^-3.

Nare Nazaryan 1F

Because it's a liquid and because it's in excess (as a solvent), it is not included.

Nare Nazaryan 1F

It is when all the reactants and products are in the same phase (e.g. gas).

Nare Nazaryan 1F

I think both are fine since they will both be recent topics; I'm saying this because I took Lavelle for 14A and our TAs were OK with it.

Nare Nazaryan 1F

I believe it will be all of "chemical equilibrium" and whatever we get to for "acids and bases" since those are the material for the first two weeks.

Nare Nazaryan 1F

The P stands for pressure, the V for volume, the n for number of moles, the R is the gas constant, and T is temperature.

Nare Nazaryan 1F

Yes, solving for Q is the same thing as solving for K in terms of calculations (just that the reaction might not have reached equilibrium yet).

Nare Nazaryan 1F

Polyprotics have more protons to donate.

Nare Nazaryan 1F

He said that the conjugate base (anion) of a weak acid will raise the pH of a solution by removing protons from the water and generate -OH.

Nare Nazaryan 1F

It is most likely cumulative, so anything we have learned can be on it.

Nare Nazaryan 1F

Bronsted acids have to donate their hydrogen atom/proton; therefore, NH3 can't be a bronsted acid.

Nare Nazaryan 1F

Potassium acetate is produced:

CH3CO2H(aq)+K^+(aq)+OH^-(aq)-->K^+(aq)+CH3CO2^-(aq)+H2O(l)

Nare Nazaryan 1F

EDTA is ethylene-diamine-tetra-acetate, and it binds/chelates with cations (metals) in the blood to get rid of them.

Nare Nazaryan 1F

Cisplatin is very common for chemotherapy.

Nare Nazaryan 1F

You just need to take the sum of all the oxidation numbers and then subtract the overall charge from that to get the charge/oxidation number of the transition metal.

Nare Nazaryan 1F

Yes, CO2 would be an acid in this case.

Nare Nazaryan 1F

There are many times where anxiety plays a huge factor in a students' performance on an exam, but there are solutions such as studying ahead of time and not cramming for a test, as well as getting enough rest.

Nare Nazaryan 1F

It would be the ligand name (alphabetically), then cation.

Nare Nazaryan 1F

A ligand is a molecule attached to a metal (in biology, usually attached to protein/enzyme).

Nare Nazaryan 1F

Cis means the electronegative atoms are on the same side (e.g. two chlorines), which trans is when they're on opposite sides. Cisplatin works because Guanine can displace two chlorines from one side, vs. two chlorines on opposite sides (trans).

Nare Nazaryan 1F

The oxidation number/state is the charge that cation/anion has. For example, chlorine's oxidation state would be -1 (chloride).

Nare Nazaryan 1F

I think we can do it on one sheet of paper and label it week 9 and 10.

Nare Nazaryan 1F

Van der Waals and London interactions are used interchangeably, and refer to induced-dipole induced-dipole interactions. They are the weakest intermolecular force.

Nare Nazaryan 1F

Yes, the difference in electronegativity should be about 0.5 to be considered polar. Shape also plays a role in terms of the possibility of dipole moments canceling.

Nare Nazaryan 1F

I believe it is always tetrahedral when 4 bonds surround the central atom, however, lone pairs could also play a role and change the shape.

Nare Nazaryan 1F

It should cover material after the midterm (plus the very last slide he did before the midterm about the different interactions). So I believe that would be last Friday's lecture, today's lecture, and probably this Friday's lecture (I'm not sure about next Monday's). Topics would include dipoles, in...

Nare Nazaryan 1F

H2O would be bent, with oxygen in the center and one hydrogen on the lower left of oxygen and the other on the lower right. This is due to the polarity of water, with the hydrogen atoms having partial positive charge and the dipole arrows being directed toward the oxygen (partial negative charge). O...

Nare Nazaryan 1F

If the compound is neutral, you would need all the formal charges to be zero. However, if it has a net charge then one or more atoms might have a negative or positive charge. You want the most electronegative atoms to have a negative charge (oxygen for example), and typically the central atom needs ...

Nare Nazaryan 1F

Electronegativity increases as you go across a period and up a group, with flourine being the most electronegative atom (same trend as ionization energy and electron affinity).

Nare Nazaryan 1F

Hydrogen bonds are very strong, therefore it is difficult to break them. This means it takes a higher melting point to break the bonds.

Nare Nazaryan 1F

I agree with the above statement. I'd also like to note that hydrogen bonding occurs with the atoms flourine, nitrogen, and oxygen (electronegative atom that would bond with the hydrogen of a different molecule).

Nare Nazaryan 1F

Polarity depends on electronegativity. The difference of electronegativty between the two atoms signifies whether they will have a positive or negative partial charge.

Nare Nazaryan 1F

905289082 wrote:What is the pattern on the periodic table that we're supposed to memorize for determining electronegativity?

Electronegativity increases as you move up and across the periodic table.

Nare Nazaryan 1F

When the formal charge is 0, that means that the number of bonds of the atom are balanced with its lone pairs. So yes, it does mean that it is more stable.

Nare Nazaryan 1F

I believe it is possible, but for now all we need to know is that double bonds are shorter and also stronger than single bonds

Nare Nazaryan 1F

It is pretty much the polarity between atoms, indicated with an arrow pointing toward the negative delta direction.

Nare Nazaryan 1F

I think we need to know dipole moments for the midterm, but just not the very last slide he was going over with the specifics.

Nare Nazaryan 1F

As far as we have learned, covalent bonds are only made between nonmetals. However, I did some research and discovered an example of a covalent bond between a metal and nonmetal. Aluminium is a metal but it can bond covalently with chlorine to form aluminium chloride during high temperatures. Alumin...

Nare Nazaryan 1F

We don't need to know how to find bond lengths; it would be given (in angstroms). Conceptually, we need to know that double bonds are shorter than single bonds.

Nare Nazaryan 1F

It's easier for Gallium to lose three electrons to become an octet like Argon, than to gain five electrons to become an octet like Krypton.

Nare Nazaryan 1F

Cations are positively charged ions since they lose electrons. Anions are negatively charged since they gain electrons. They're important because they help the element form octets.

Nare Nazaryan 1F

I think anything we have covered up until the midterm could possibly be on it. You can also ask Dr. Lavelle just to be sure.

Nare Nazaryan 1F

It can be a little tricky, but it all depends on what is given. If you are given frequency and need to find wavelength, for example, you can use c=wavelength*frequency and just adjust the equation to what you're trying to solve. Some problems will ask you for an answer after you go through a few dif...

Nare Nazaryan 1F

You use E=hv when finding the energy of a photon. In this case, h is Planck's constant and v is frequency.

Nare Nazaryan 1F

For this week, the five problems we do have to all come from the "Quantum World." I don't think it matters whether we do more problems from section A or B (etc) than other sections in that unit.

Nare Nazaryan 1F

I'm not positive how much longer we're going to be in this unit, but I have a feeling it might also be next week too, since Professor Lavelle mentioned that this is a lengthy unit. Especially compared to the other topics, this seems more complex.

Nare Nazaryan 1F

The midterm and final are going to be outside of class hours. The midterm is scheduled for November 6 from 6-8 pm, and the final is on December 8 from 11:30am-2:30pm. I am not sure where the midterm will be, though.

Nare Nazaryan 1F

I think that if you post Sunday of week one, it will be counted as week one. The "week" probably starts on Mondays.

Nare Nazaryan 1F

Increasing intensity doesn't lead to electrons being emitted, because increasing the intensity only increases the number of photons instead of the energy that each photon has. So in the photoelectric experiment, it's best to see light in terms of photons, since the energy of photons is what helps em...

Nare Nazaryan 1F

I would suggest doing the homework problems so that you get a good range of possible test questions and develop fundamental/conceptual skills to solve problems. You can also look at the lecture notes and online modules, as well as go to peer learning sessions and office hours.

Nare Nazaryan 1F

HI! Thank you so much for taking time out of your already busy schedule to answer our questions. I'm not sure if someone asked this already, but in terms of medical school, I've always wondered how I'd be able to balance that with family, especially because my ultimate career goal is to become a neu...

Nare Nazaryan 1F

Showing work, even if your final answer is incorrect, will always give you partial credit which is important since the tests are 50 points (roughly 7 points/problem if its 7 questions).

Nare Nazaryan 1F

When balancing equations, you want to add stoichiometric coefficients to change the number of MOLES of the compound, not the molecules.

Nare Nazaryan 1F

Yes, combustion (and oxidation) involve a compound reacting with oxygen (O2) and producing a certain amount of carbon dioxide (CO2) and water (H2O).

Nare Nazaryan 1F

I'm sure we will be given the periodic table and the molecular formulas for compounds (if not asked to find the molecular formula). I am not sure about a formula sheet, but I would definitely recommend memorizing Avogadro's constant since I noticed that we had to use it in a lot of questions from se...

Nare Nazaryan 1F

I don't think there is a faster way, even though that would make things so much easier. Maybe in the future we will learn a simpler way? I wish I could be of more help.

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