CHEMISTRY COMMUNITY

Kathryn 1F

Yes! I'm pretty sure, because it would be hard to cancel them out due to intermdiates.

for eg, take
A+catalyst-->B (fast)
B-->C + catalyst (slow)

you could cancel out for B, but then your expression would be in terms of the catalyst

Kathryn 1F

LorenzoDuvergne3I wrote:From what I've seen, you cancel everything out that appears on both sides. Is B supposed to be the enzyme?

Yeah lol. We talked about it in a step up I went to today, but I don't think its been covered in class yet

Kathryn 1F

When determining rate laws for multi step reactions, I know we have to cancel out the intermediates. However, if there is an enzyme involved
like for
A+B-->C
C-->D+B

I know we'd have to cancel for C, but would we have to for B?

Thanks!

Kathryn 1F

When we have a reaction, does the stoichiometric coefficients of the reactants or products affect the rate law? How can we tell?

Kathryn 1F

I think he was referring to an enzyme catalysed reaction, not the enzyme itself. We assume that the reactants are saturated with respect to the enzyme, so the enzymes are already working at full potential. Adding more reactant is not going to make the enzyme work faster

Kathryn 1F

I think for k in the rate constant you do have units, which vary depending on which order it is. But I don't think K (at equilibrium) does

Kathryn 1F

How is kinetics different from thermodynamic? won't they both still tell which direction the reaction will proceed?

Kathryn 1F

algebraically, [NO]= 2[O2] does mean that O2 increases half as fast, because this shows that NO increases 2 times as fast as O2.

Another way you can think of it is (1/2)[NO]=[O2]

Kathryn 1F

So because E^o is an intensive property (does not change with amount of substance), you can't add 2 together for different reactions like you could with gibbs. This is why we have to convert to gibbs first, then add to get delta G total, then convert back to E^o total. This is separate from adding t...

Kathryn 1F

In class we had E(nought)=0.77V for Fe3+ + e- = Fe2+
When we multiplied the eqn by 2 to get 2Fe3+ + 2e- = 2Fe2+, we kept E(nought)=0.77V.

Why is this? Why didn't we multiply .77 by 2?

Kathryn 1F

What is E (and E(nought))? In my notes I have E(nought) meaning "Standard Reaction Potential"--but I don't understand what that means, conceptually. Also, what is it used for in a battery?

Kathryn 1F

I am confused. how does the salt bridge not just dissolve in the aqueous solutions on either side of the cell, making it useless?

Kathryn 1F

I think they're from 9.51 onwards

Kathryn 1F

I just worked through this one and thought to note,
because of log rules S=kbln(W^Na) is the same as S=Na*kbln(W)
It made calculating it a lot easier!

Kathryn 1F

The question is:
If SO2F2 adopts a positionally disordered arrangement in its crystal form, what might its residual molar entropy be?

How would you so this? I assume use the formula S=kln(W) but I don't know how to find W in this case

Kathryn 1F

Can an isothermal reaction be irreversible? Or is that only for reversible reactions?

Kathryn 1F

when using $w=-P\Delta V$ , I always get the answer in L*atm. How do you convert it to J?

Kathryn 1F

So which one does more work? I think it would be reversible bc of the curve, but I'm not entirely sure why

Kathryn 1F

Today in lecture we derived the entropy equations and related $\Delta S=k_{b}ln(V2/V1)$ to $q/T=nRln(V2/V1)$ .
What is the relationship between nR and kb?

Kathryn 1F

The question gives enthalpies of formation in kJ/mol, but then asks for the enthalpy density (enthalpy released per liter). How would I find this? I am given the density of TNT in g/cm^3, but idk how i would use that

Kathryn 1F

Rami_Z_AbuQubo_2K wrote:When pressure is constant, q becomes q_p and this is equal to $\Delta h$ .

Why is this? How does keeping the pressure constant equal to enthalpy? Thanks!

Kathryn 1F

it's supposed to be an isolated system, so the chamber is insulated and the reaction happens inside, with no change of volume. Heat is measured before and after the reaction to find out how much energy was released

Kathryn 1F

I think CP is higher because then you also have to do work to change the volume?

Kathryn 1F

1 cubic metre is 1000L, so I think you can just convert between the two

Kathryn 1F

I am confused on the difference between Standard Reaction Enthalpy and Standard Enthalpy of Formation and how they are connected to each other. They seem to be defining the same thing which is enthalpy when all the elements are in the standard state?

Kathryn 1F

The ones mentioned in class were all the group 1 ions (like Na+, K+), as well as Cl-. I think its because they are already pretty stable how they are, so they aren't gonna interact with the water to change the pH

Kathryn 1F

in 14A we had to recognize strong acids/bases, but I think because we know about the Ka and Kb values this quarter we could use them instead.

Kathryn 1F

Generally, a strong acid has Ka > 10^-3, and a weak acid has Ka < 10^-3.
a strong base has Kb > 10^-3, and a weak base has Kb < 10^-3.

Also, I think in class Lavelle mentioned that organic acids (like acetic acid) are generally weak acids.

Kathryn 1F

the equation is just the reaction of hno2 with water. We could use a separate one to describe the salt dissociating, but we can just infer that no2- will be there from the salt, too. Thats why for the "I" in the ICE table we put .150M NO2-, instead of 0 like we had been doing previously fo...

Kathryn 1F

Adding an inert gas wouldn't affect the equilibrium because the concentrations of the reactant and product would remain the same, meaning there would be no change in the equation. But if the volume changes, how is there not a change in the concentration if the concentration is affected by volume? T...

Kathryn 1F

In class friday, Lavelle talked about a "quick" way to tell which way the reaction shifts when the volume decreases based on how many moles of gas there will be? Can someone please explain this? Does it have to do with balancing equations? In class he referred to the example N2 + 3H2 -> 2NH3

Kathryn 1F

In class I noticed we don't have any units for K. Are there none? why?

Kathryn 1F

The textbook says SO3 is an acid (6th edition 12.17), and i understand that the sulfur can accept electrons, but why can't the oxygens donate their lone pairs, making it amphoteric?

Kathryn 1F

Can someone explain 41d - how many atoms in thymine could form a hydrogen bond. The answer is 4 but I only see 2--on either oxygen. Where are the other 2?

Kathryn 1F

For #31, would it also be correct to put NO2 in the complex or does it have to be ONO? I would say it has to be ONO, nitrito, because if you write NO2 that can be mistaken with nitro. Which seem similar but are not because the central atom for each differentiates. I think we should specify ONO-, bu...

Kathryn 1F

Ashita Tanwar 3H wrote:Can there be multiple rings around the same central atom?

Yes, like having 3 bidentates around one metal.
For example, you can have 3 (en) ligands around a Co, with each forming its own ring around the Co.

Kathryn 1F

not sure about the first one, but in one of the review sessions the TA said that chlorido and chloro meant the same thing.

Kathryn 1F

In class, Lavelle mentioned that pi bonds form with non hybrid orbitals (the example was with C2H4).
Do pi bonds only form with non hybrid orbitals? Why?

Kathryn 1F

So the way I think of it is, AX3E2 has 5 regions of electron density, so have the trigonal bipyramidal structure in mind (AX5). The axial bonds are 90 from each planar bond, and each planar bond is 120 from each other. To get AX3E2, we want to replace lone pairs for bonds that are furthest from the ...

Kathryn 1F

So a molecule has dipole moments if one atom is more electronegative than the other. we write (delta)+ next to the less electronegative atom, because the electrons are being pulled away (eg in the case of H2O, H has (delta)+) we write (delta)- next to the more electronegative atom, because the elect...

Kathryn 1F

Also when can we know that bond angles are less than what they usually are? Like I remember in lecture Lavelle said a bond angle was 106.5 degrees. I think the one he was talking about was SO_3^2- (sulfite). By drawing the lewis structure, we see that the central atom, S, has 4 regions of electron ...

Kathryn 1F

Because P has a lower ionization energy. O and Cl have roughly the same, so they all go around the outside

Kathryn 1F

I think it is sufficient to say that because of the resonance,
120pm<the N-O bond lengths<140pm.
The resonance causes the bond lengths to be longer than a double bond, but shorter than a single bond.

Kathryn 1F

I was also confused as to whether all molecules have hybridized orbitals...I think the answer is yes, if they can. Like I assume H-H doesn't as H only has the s orbital. But from what I gather its generally necessary, at least for the central atom, so that it can bond? I think its mostly key to dete...

Kathryn 1F

just realized this question's already been discussed, my bad

Kathryn 1F

so i'm pretty sure the silver halides are a type of salt, because they are ionic compounds. Also, I think the polarizability is how readily an anion will have a distorted electron shell (a higher polarizability means a greater covalent character). So AlF is the most soluble in water because F has th...

Kathryn 1F

Does hybridization affect bond angles? I think Lavelle mentioned it in class on Monday, but I'm still confused about why hybridization relates to angles.

Kathryn 1F

How would we draw the most stable Lewis structure for NO3-?
The midterm asked why the bond lengths were the same for this structure, which suggests that they were all single or double bonds, but I can't make it work with the octets?

Kathryn 1F

It is negative because energy is released when a bond is formed. Therefore, I think that the negative energy does imply attraction when talking about bonds because 2 atoms are forming a bond, so they're attracted to each other.

Kathryn 1F

Can someone clarify the equation $E=\frac{\alpha 1 *\alpha 2}{r^6}$

Specifically, what is meant by $\frac{1}{r^6}$ being a strong dependence?
We talked about it during Wednesday's lecture.

Kathryn 1F

The reason H2O has a much higher boiling or melting point than H2S isn't down to the individual atoms, but how they interact with each other. Hydrogen bonds will generally form between molecules when the H is bonded to an N, O, or F, such as in H2O. They are weaker than covalent bonds but are still ...

Kathryn 1F

H and He are exceptions because they only have the 1s orbitals, so a max of 2 electrons. Therefore, it is impossible for them to form an octet. B is an exception because it only has 3 valence electrons, so generally only forms 3 bonds (for 6 electrons), such as in BF3. However, it can form 4 bonds, ...

Kathryn 1F

Do you mean like if the value is given like "the velocity is 10 +- 1 m/s"? in this case, the indeterminacy in velocity is 2, as the velocity could be between 9 and 11. So you would take the +-1 * 2.

If it says "the indeterminacy is (delta)2", then you can take that as is

Kathryn 1F

I think the brackets just symbolize that the molecule has a charge, like if something were []-, then the lewis structure would have an extra electron. I hope this answers your question!

Kathryn 1F

Because uncert.p*uncert.x=h/4π, in order to maintain equilibrium, the uncertainties in p and x are inversely proportional. As in, if the uncertainty of p increases, the uncertainty of x decreases.

Kathryn 1F

Hi! For your first example, the whole 5p1 is removed because that represents just one electron. One electron must be removed to have a charge of +1. The opposite is true for the second example as you need 3 extra electrons

Kathryn 1F

Hi! Because to form a positive charge, 2 electronsust be removed. They are removed from the highest energy states, in this case 4s and the last 3d

Kathryn 1F

They represent which axis the orbital goes around, or which mathematical function is used to form it. In the case of px, the orbital goes about the x axis with the nodal plane on the zy plane.

Kathryn 1F

In class today (Lecture 3), Lavelle said that an electron could not have the configuration (1,1,0). I am confused, why not?

Kathryn 1F

Hi!
I think that the x, y, and z is because are for p because there are 3 types of p orbitals (px, py, and pz), which we talked about on wednesday i think? So i assume for d orbitals we would call them z^2, x^2-y^2, xy, yz, and zx, which correspond to the d orbitals.

Kathryn 1F

10^-38m is not measurable simply because it is too small for us to accurately measure at this time. In class, Lavelle said that the threshold for what we could measure was around 10^-13 or 10^15m, which is still very small. For reference, the diameter of an atom is around 1 angstrom, or 10^-10m.

Kathryn 1F

It is generally more accurate to round answers only at the end, or even to manipulate/combine equations so that you only have to do one calculation to get your final answer. If you have to do multiple calculations, it is good to note extra digits in the intermediate steps so that you don't have roun...

Kathryn 1F

Hello! In equations when you use metric units, people use kilograms instead of grams, just because kg is the standard SI unit for mass, so its what equations are based on. This is pretty conventional but its because most things we would weigh in the classical sense, like everyday objects, are better...

Kathryn 1F

Hi! The units of molarity are moles per litre, which can also be written as mol/L or mol*L^-1, because raising a number to a negative power places it on the denominator. This can be figured out using the equation M=(Moles of solute)/(Liters of solution), with the units being moles/l You can also fig...

Kathryn 1F

I thought it might of been because of conservation of mass. We can't create nor destroy mass so adding it would be like creating mass? I think that's the original issue with unbalanced eqns, that there is unequal mass/numbers of elements on both sides, so by balancing them, you make it equal. in th...

Kathryn 1F

Hi!
I think because singular oxygen atoms are not a proper "product" of the equation, you can't just add them on to make the equation balanced. Even though it may appear balanced, they have changed the equation when you only need to change the ratios, making the eqn incorrect.

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