CHEMISTRY COMMUNITY

Diana_Diep2I

Does the value of k affect the rate of a reaction? Like if k is large, does it mean that the rate of reaction is faster?

Diana_Diep2I

Are you talking about the pre-equilibrium approach? But yes you can ignore the reverse reaction. If you're talking about the pre-equilibrium approach, then for the fast step before the slow one, the reverse must be taken into account.

Diana_Diep2I

It is easier to use only the concentrations of the reactants rather than both reactants and products. The reaction may go to equilibrium and it is harder to measure the rates of both R and P.

Diana_Diep2I

On Lyndon's review worksheet, how would we use the preequilibrium approach to figure out k[A][E]?

Diana_Diep2I

It also speeds up the rate of the reverse reaction and because a catalyst only affects speed, it does not affect enthalpy.

Diana_Diep2I

Why does k have to be in [M]/s?

Diana_Diep2I

Does anyone know how the Chemistry 14B Final will be given now that classes have gone online? Are all the review sessions cancelled/online now? Will the grading scheme for the course remain the same?

Diana_Diep2I

The exponent in an overall rate is not the same as the exponent in the elementary step right? What is the difference?

Diana_Diep2I

When you find the ratio between Rate 1 and Rate 4, you will see that [C] will be in zeroth order. That means that now the differential rate law is k[A][B]. Now, when finding the orders of A and B, you don't need to take into account [C] because the reaction does not depend on the concentration of [C].

Diana_Diep2I

How come the answer key says to choose the reduction reaction with the highest standard reduction potential and to choose the oxidation reaction with the lowest reduction potential and then proceeds to do the opposite?

Diana_Diep2I

When do we add things like NO3 in the half-reaction and when do we not add it? How do we know to add OH- in the reaction?

Diana_Diep2I

These inert electrodes are there because there are no conducting solids for the H2 reaction and the Cl2 reaction. Add them when you don't have a conducting solid. For example, when Fe3+ gets reduced to Fe2+, both still are in aqueous solution. However, you need a conducting solid like Pt(s) that all...

Diana_Diep2I

Why is there a KOH in the answer?

Diana_Diep2I

Yeah unfortunately there is no given reaction for Au3+(aq) + 2e-, but there is a reaction for Au3+ +3e- --> Au. So you work with what you have. You still want to end up with some form of the given reaction in the problem. How do you combine the appendix reactions to give you the same Au+(aq) --> Au(...

Diana_Diep2I

The objective is to make the cell potential positive so that the cell can do work. If it is negative, the cell is unable to do work and the reaction is unfavorable. Hence, try to combine your values in a way so that you get a positive value. This is for galvanic cells. Electrolytic cells have negati...

Diana_Diep2I

Why is water used in this problem? They said that SO4- doesn't oxidize and I am wondering why?

Diana_Diep2I

Can I assume that 2Hg has no charge while Hg2 has a 2+ charge?

Diana_Diep2I

How do we know that 2Cl- is being oxidized to Cl2 rather than Cl2 being reduced to 2Cl-?

Diana_Diep2I

Is there a guideline for translating cell diagrams to redox reactions? For example, in 6N3c, the book switches the anode and the cathode so that the anode reaction is on the right and the cathode reaction is on the left.

Diana_Diep2I

In the 6N3 c) problem, the book combines pressure and concentration in the Q expression. I know that they cancel out the units of pressure, but I still don't understand?

Diana_Diep2I

I think you're looking at the wrong problem for the answer.

Diana_Diep2I

When do we use log and when do we use ln when using the Nernst equation? Or does it not matter?

Diana_Diep2I

What is the difference between 2Hg^2+ and Hg2^2+? Does one reduce to the other?

Diana_Diep2I

There are two reactions involving oxygen in basic and acidic solution. How do I determine which one is the anode and which one is the cathode?

Diana_Diep2I

I think a nonspontaneous reaction requires an external input of energy, like charging a battery. And if it's dead then yes I don't think any reaction happens unless you add that external energy.

Diana_Diep2I

Sorry, I forgot the positive ion. If it's a salt bridge, something like NaCl will be inside. So if Cl- moves to the side that is being oxidized, Na+ would move to the side that is being reduced.

Diana_Diep2I

It allows ions to flow between the solutions so as to keep both of the solutions in the cells neutral. For example, if Zn is being oxidized to Zn2+, ions like Cl- will flow through the salt bridge to keep the Zn side from becoming too positive.

Diana_Diep2I

If Hg is being oxidized in Hg2Cl2, do we write Hg --> 1/2Hg2 or 2Hg -- Hg2? Do I include the Cl2?

Diana_Diep2I

If the cell diagram has all single lines, how can we determine where the porous disk so as to determine reductions and oxidations?

Diana_Diep2I

I think it is because the system isn't pushing/expanding any pressure from the outside

Diana_Diep2I

To add to the previous post, in an irreversible reaction, delta S is 0 because the surroundings is basically a vacuum. So yes, there is no opposing force

Diana_Diep2I

Yes, because the temperature is larger in the denominator, the fraction would be smaller compared to if the temperature was smaller. This is also why a certain amount of heat has more effect on the entropy when the temperature is lower.

Diana_Diep2I

It is the only entropy that is left after you take out all types of entropy like thermal entropy. When you reduce the temperature and try to get to 0 Kelvin, the molecules would not be in motion. The only entropy that would be left is the positional entropy. One molecule could be in multiple orienta...

Diana_Diep2I

What is the difference in entropy when it comes to a reversible reaction? Irreversible? Do we calculate it the same way using the deltaS=nRln(V2/V1)?

Diana_Diep2I

Two systems can transfer different amounts of heat and do different amounts of work and still arrive at the same deltaU.

Diana_Diep2I

This problem requires the two S equations. The answer key uses R for change in volume AND change in temperature. When do we use C and when do we use R?

Diana_Diep2I

The Δ G value in the table will be a bit off compared to if you were to actually calculate it using the values of ΔH and ΔS in Δ G = Δ H − T Δ S

Diana_Diep2I

When do we use C and when do we use R?

Diana_Diep2I

You use the same format as volume, but this time you put P1 above P2 because of Boyle's Law. P1V1=P2V2, so P1/P2=V2/V1. This makes sense because pressure decreases when volume increases. You could expect the entropy to increase.

Diana_Diep2I

Wait, sorry the book uses R in 4F11, but 4F12 tests the same concept

Diana_Diep2I

When do we use nCvln(T2/T1) and when do we use nRln(T2/T1)? In this problem the book uses R instead of C and I was wondering when we should use either of them?

Diana_Diep2I

How come the answer for this problem is -312 kJ/mol instead of 312 kJ/mol? I used the third method to find the answer, and I got 312. How did the book get a negative answer?

Diana_Diep2I

It is the number of states to the power of the number of particles.

Diana_Diep2I

The answer key uses the reversible isothermic equation to answer part b, but we didn't learn that in lecture? Are we supposed to know it for the midterm?

Diana_Diep2I

Why is qp=∆H and not qv?

Diana_Diep2I

Will we be using the integral equation? When will we use w=-P∆V and when will we use the integral? What is the difference between them? Is it because in the integral, external pressure may not be constant?

Diana_Diep2I

What is the clear difference between reversible and irreversible expansion? I am confused about the role external pressure plays on both of these.

Diana_Diep2I

The answer key gives 6.01 kJ/mol as one of the values. Where did they get it?

Diana_Diep2I

What is the difference between q and delta H?

Diana_Diep2I

No we don't. Dr. Lavelle said that polyprotic acids required multiple steps for each time the acid donates a proton.

Diana_Diep2I

Ka should be in a table in the book. This problem tests 14A material. You're supposed to know that Al3+ can serve as a metal cation that can have multiple bonds (coordination compounds)

Diana_Diep2I

You can check the percent protonation to see if it's less than 5%. You can also check the Ka/Kb value. if the value is less than 10^-3, you can almost safely approximate.

Diana_Diep2I

Use the ICE box for when the problem asks for something like the pH or pOH of a weak acid/base and you have to find the concentration of the H3O+/OH-. Or, when the problem asks for the equilibrium compositions of the reaction. Then you'd have to find the concentrations for the reactants using the IC...

Diana_Diep2I

Can someone explain the difference between the third and fourth flask in this problem?

Diana_Diep2I

If [H3O+] < 10^-7, then the solution is considered neutral because we know that autoprotolysis generates 10^-7 M H3O+

Diana_Diep2I

You get a negative pH when the concentration provided is greater than 1

Diana_Diep2I

I'm not exactly sure what kind of calculations you are talking about You would have to use an ICE chart, with Ka and Kb. The problem would most likely ask for the pH/pOH and the concentrations of H3O+/OH-.

Diana_Diep2I

Can someone explain why endothermic reactions favor product formation while exothermic reactions favor reactant formation? I don't understand how the graphs and delta H relate to the concept when explaining product/reactant formation.

Diana_Diep2I

Yeah, I was wondering if K would just equal to the total pressure (7.68) bar? Since solids and liquids are not included in the constant expression?

Diana_Diep2I

Create an ICE chart for the reaction Cl2-->2Cl (it's in the table 5G2). You will find the equilibrium compositions of Cl2 and Cl using the given Kc at 1000 K. Do the same thing for F2. Compare the concentrations you find between Cl2 and Cl/F2 and F. If the concentration of the reactant is greater th...

Diana_Diep2I

I think we get that when the pH scale exceeds 14. This usually occurs when the molarity or concentration of H3O+ or OH- is greater than 1.

Diana_Diep2I

The proper explanation was the comparison of Q to K, where the concentration doubled due to the volume being halved. When the concentration doubled and we found Q(this is before we wait for the system to return to equilibrium), we found that Q<K. And when Q<K, the reaction shifts to the right.

Diana_Diep2I

I think because it's on the products side, removing one of the products would increase the production of both compounds (NO and SO3)?

Diana_Diep2I

Q is for when the reaction isn't at equilibrium. K is for when the reaction is at equilibrium.

Diana_Diep2I

There technically isn't a concentration for a solid b/c it doesn't make sense. We're measuring the change in concentration of compounds in K. As for pure liquids, the concentration isn't changed much. The change is negligible it's practically 0. So if we put something like the concentration of water...

Diana_Diep2I

Do we include H2O in the gas phase? I know we don't include it in the liquid phase but I am unsure about gas.

Diana_Diep2I

Like the post above me said, the reaction favors the reactants if K is small. The reactants are more stable. If K is big, the reaction favors the products and the products are more stable.

Diana_Diep2I

If you draw the tetrahedral lewis structure in its actual shape, you would see that they would not cancel due to the vectors pointing upwards or downwards. The structure does not have bond angles of 90º. There would be a net dipole going up or down. For example, CH2Cl2 would still be polar and like ...

Diana_Diep2I

I'm not sure if it has what I'm asking. I'm asking if having different atoms surrounding the central atom affects the bond angles?

Diana_Diep2I

What would the bond angle of COH3 be? I know that it is a tetrahedral structure, but would the bond angle be any different due to the oxygen atom?

Diana_Diep2I

Are oxides of main group elements considered bases? Or do they have to react with water to form bases/acids? For example, Na2O has to react with H2O to form NaOH. Is Na2O considered a base? Or is it the NaOH?

Diana_Diep2I

Sorry I forgot to mention that you should look for the strong conjugate acids/bases that come from weak acids/bases. Like for example in a) NH4Br, Br- is a weak conjugate base of the strong acid HBr so it doesn't affect the pH and you shouldn't pay attention to that. NH4+ on the other hand, is a str...

Diana_Diep2I

In c), F- is the anion of a weak acid (HF). In lecture today we learned that the conjugate base of a weak acid will raise the pH of the solution by removing protons from water to generate OH-. As a result, the pH will be >7. e) Al3+ is the transition metal that is hydrated and has strong e- withdraw...

Diana_Diep2I

In problem 2F16, it asks if the N2px orbital participates in hybridization for NH2+ and NH2- if the 2px orbital is lying perpendicular to the plane of the molecule. I am not quite sure as to how to answer this question. How do I know if a particular orbital participates in a hybridization?

Diana_Diep2I

It is ethylene-diamine-tetra-acetate and it removes metals from the blood by chelating or binding to cations, aka metals. It has six binding sites(2 amino-nitrogen atoms and 4 carboxylic groups)

Diana_Diep2I

There really is no difference between the two as both are water, but it is most likely to show that it is oxygen that binds to the complex and not the hydrogen. The formula OH2 gives a more accurate depiction of the structure just like how Dr. Lavelle reversed NH3 and H3N during lecture.

Diana_Diep2I

The order in which you put your ligands does not matter, but the naming process matters because then you have to take into account alphabetical order.

Diana_Diep2I

6 because en has two binding sites. Because it is a bidentate and there are two of them, it binds at four sites. Add the four to the two Cl sites and you get 6.

Diana_Diep2I

What is the difference between Bronsted and Lewis acids and bases?

Diana_Diep2I

How come bisoxalato comes before diaqua in the name? For reference, the name of the complex is sodium bisoxalato(diaqua)ferrate(III). I thought we were supposed to ignore the greek prefixes and only pay attention to the ligand itself?

Diana_Diep2I

Which structure has stronger IMFs? SiF4 or Si2F2?

Diana_Diep2I

doesn't the strength of london disperson forces take priority over dipole-dipole forces when determining which compound has a higher boiling point? Not really. You have to first compare IMF strength before comparing different London dispersion force factors like size or number of electrons. In this...

Diana_Diep2I

Which interaction is stronger than the other? Hydrogen bonds or ion-dipole interactions?

Diana_Diep2I

Question 2E30b asks which molecule has the largest dipole moment and I am conflicted between 1 and 3. Can someone help? Thanks!

Diana_Diep2I

Yes. The phrase "like dissolves like" basically means that polar molecules dissolve in polar molecules, or anything with a charge basically. Because Cl- ion has a negative charge, it will be hydrated. But something like C6H6 cannot dissolve in water or polar substances because it is a nonp...

Diana_Diep2I

Yes they are considered a special dipole-dipole interaction. For example, (HF interacting with NH). However, it is considered stronger than other dipole-dipole interactions.

Diana_Diep2I

When do we look at size and when do we look at electronegativity difference when it comes to checking to see which molecule has the higher boiling point? For example, H2S vs H2Se or SiH4 vs SiF4. Do I look at the electronegativity or the size/polarizability of the molecule?

Diana_Diep2I

Can someone explain to me what exactly potential energy is between interacting molecules?

Diana_Diep2I

to rephrase: How can I tell when a molecule has a dipole moment?

Diana_Diep2I

How can we tell if a molecule is polar or nonpolar? For example: CH2Cl2. How would I be able to find the forces that occur between that molecule besides London forces?

Diana_Diep2I

I get what the post above is saying, but what does "extent of hydration" mean? Is it like how many H2O molecules the ion attracts?

Diana_Diep2I

The "increase in mass" actually refers to the increase in C and H atoms because an increase in mass means an increase in the number of electrons. So actually it does not have much to do with the actual mass but rather the increase in the number of electrons when you add C and H. This cause...

Diana_Diep2I

In addition to the post above me, this gives rise to intermolecular interactions. The partial charges on the molecules can induce dipoles on other molecules.

Diana_Diep2I

I know in lecture that Dr. Lavelle said that London interactions and dipole-induced dipoles were similar and interchanged, but the book says that London forces are between nonpolar molecules while dipole-induced dipoles were between a polar molecule and a nonpolar molecule. Which is it?

Diana_Diep2I

It uses both of its hydrogens to form hydrogen bonds with other water molecules but keep in mind that these are not actual bonds. They are interactions between the oxygen atom and the hydrogen atom.

Diana_Diep2I

Emily_4B wrote:Do you guys know if we’ll get the midterm back or be able to look at it in office hours to review this question?

I was told that we would get our midterm back next Wednesday during lecture.

Diana_Diep2I

605110118 wrote:What is the difference between pi and sigma?

sigma is all single bonds and pi is the second bond in a double bond

Diana_Diep2I

VioletKo3F wrote:What's the equation for the formal charge?

V-(L+S/2) where V is for valence electrons, L is for number of lone electrons, and S is for number of shared electrons.

Diana_Diep2I

To add to the replies above, a large anion is usually polarizable because the outer electrons are further from the nucleus and are more likely to feel less of an effective nuclear charge. Meanwhile, a small cation has more polarizing power because of its stronger nuclear charge.

Diana_Diep2I

How would a double bond help stabilize a structure? In most cases, it would help reduce the formal charge of the atom to 0. For example, oxygen with a single bond and 3 lone pairs has a formal charge of -1. But if you change its bond to a double bond with two lone pairs, it will have a formal charg...

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