CHEMISTRY COMMUNITY

Justin Lai 1C

I think the class is graded.

Justin Lai 1C

What do you do with a dead chemist?
Barium

Justin Lai 1C

Yes, need both deltaH fusion and deltaH for warming up liquid water to final temp.

Justin Lai 1C

Yeah was confused about that as well. Don't you need two unknown variables for a function?

Justin Lai 1C

I think that this equation can be used for different temperatures and also different Ea as well.

Justin Lai 1C

Only isothermal reactions have u = 0 so q = -w. T being 0 does not always mean that q = 0. Isothermal reaction is when T = 0. This is because as work may be done by or done on the system, there is a supply or removal of heat from the system so that T = 0 and that the internal energy of the system re...

Justin Lai 1C

Making bad chemistry jokes because all the good ones Argon

Justin Lai 1C

What is the chemical formula for "coffee"?
CoFe2

Justin Lai 1C

I think NO has resonance meaning that there has multiple possible structures. So there are more possible structures for NO than for BF3 which is why there is more residual entropy.

Justin Lai 1C

Things to look for when comparing entropy. The following will usually have higher entropy:
Gases in larger volume>smaller volume
Gases>liquids>solids
Larger mass>smaller mass
Greater complexity>less complex

Justin Lai 1C

I'm pretty sure that we don't have to.

Justin Lai 1C

Yes, you should draw out the lewis structures. If you do, you will see that NO is non-symmetric and has resonance. BF3 is symmetric and only has one configuration, so NO should have greater residual entropy.

Justin Lai 1C

What do we have to know about the Sn2 organic reaction substitution nucleophile 2? I get that an atom is replaced by another, but what is the nucleophile?

Justin Lai 1C

If the problem asks for calculating the number of microstates for one mole, make sure you use Avogadro's number for the number of atoms as the power.

Justin Lai 1C

For the activated complex model, I think we need to know how to identify the slowest step (rate determinant step), which will be the highest peak. Additionally, to know the position of the atoms in a reaction as it progresses, like if the transition state will have atoms closer to the position that ...

Justin Lai 1C

I think we need to know the 3 concepts
(1) molecules must collide
(2) must collide with sufficient energy to break bonds-overcome energy barrier or activation energy
(3) must collide in the correct orientation

Justin Lai 1C

I don't think the second step would be considered to be in equilibrium. If the first step is the slow step, the second step would just proceed normally. The rate is determined by the slow step so just the first. The reason why when the second step is slower, that the first step is considered to be i...

Justin Lai 1C

The main difference is that catalysts occur in the beginning and the end of the reaction. They may both be cancelled out, but catalysts occur in the beginning and may be consumed in one of the elementary steps, but in the end the catalyst will reform as it was in the beginning. An intermediate will ...

Justin Lai 1C

It says in the lecture notes that the rate law for each elementary step follows directly from molecularity, which is the number of species. Because of that, we can determine that an elementary step with a first order rate law is unimolecular meaning one species, a second order rate law is bimolecula...

Justin Lai 1C

I think that the equation is lnk = -Ea/RT + lnA with the negative sign.

Justin Lai 1C

Also know that there in a graph with lnk and 1/T as its axes, the slope will be linear and will equal -Ea/R.

Justin Lai 1C

The catalyst usually appears in the beginning of the reaction and the end of the reaction. So if it is consumed, it will reappear in the end. The intermediate does not appear in the beginning or the end of the reaction-it is both formed and consumed in the middle of the reaction.

Justin Lai 1C

When we use the (change in concentration)/(change in time) equation does that mean that it is 1st order?

Justin Lai 1C

Also for kinetics specifically make sure you know that the units for a rate constant can vary depending on the order of the equation. The rate should be in mol/L*s so you can determine the rate constant from there depending on the order. Or we might have to get the order of a reaction when we are gi...

Justin Lai 1C

Today in lecture, Dr. Lavelle said that for amines each atom that the N is bonded to could be replaced with a CH3, so it was drawn a single N with a lone pair and three CH3 groups. But in my notes it shows a that the functional group has a NH2. Does the N not have to be bonded to two H atoms?

Justin Lai 1C

Will we be required to draw the functional groups?

Justin Lai 1C

Sorry, the equation is k = k'/([B initial]m [C initial]l)

Justin Lai 1C

There is also an equation if you are solving for k' for rate = k [A] [C], k = k'/[initial B]m [initial C]l[/b] when [B] and [C] are in surplus,

Justin Lai 1C

Because Eo is an intensive property, voltage difference is the same and does not depend on how many times the reaction occurs.

Justin Lai 1C

The anode has the element that is most likely oxidized while the cathode has the element that is reduced. The half-reaction with the element that is most likely reduced has a higher standard potential (more V) so it forms the cathode. The half-reaction with the element that is less likely reduced ha...

Justin Lai 1C

Is the hydrogen proton concentration the same as the conjugate base concentration for an acid?

Justin Lai 1C

Stronger acids tend to have a greater percent ionization because its conjugate base will tend to stay in that form and be more stable.

Justin Lai 1C

Yes, strong bases have very stable conjugate acids because the strength of a base can be measured in how likely the conjugate acid is to stay an acid. This is because a strong base completely dissociates

Justin Lai 1C

Yes, amphiprotic compounds are included in amphoteric compounds because they can act as an acid or base. Amphiprotic compounds act as acids or bases by either donating or receiving protons.

Justin Lai 1C

Q is the formula for concentration of products/reactants at any time. K is the ratio of products to reactants at equilibrium and they use the same formulas

Justin Lai 1C

The solvent is the material that contains the solute and concentration change in the solvent is assumed to be negligible, so it is not included in the chemical equilibrium expressions

Justin Lai 1C

I think a good way to look at it is also remembering the regions of electron density. Sp2 has three regions of electron density so it is trigonal planar. Sp has two regions of electron density so it is linear

Justin Lai 1C

Doesn't sp^2 hybridization have three regions of electron density?

Justin Lai 1C

Yes pretty sure there is axial and equatorial plane. Lone pairs start occupying axial planes to make square pyramidal and square planar.

Justin Lai 1C

After figuring out how many bonding areas there are, you still need to distinguish from atoms and lone pairs. Can't just rely on geometric shape to find bond angles because lone pairs affect the angles but only atoms are used to name the shape

Justin Lai 1C

Also important to note that the most stable structures are those that have lower energy. Atoms form bonds in order to reach a state of lower energy which is why it takes energy to break bonds.

Justin Lai 1C

It is also really rare to have a formal charge of -2 in a stable lewis structure, so if the formal charge ends up being -2, try reducing the formal charge by adding bonds or drawing them a different way.

Justin Lai 1C

Does the first electron to enter an orbital always have an upwards magnetic spin?

Justin Lai 1C

It's also interesting because s has a magnetic quantum number of 0. And there's only one orbital for s because it is the orbital with symmetrical e- density. However p would have magnetic quantum numbers of -1, 0, and 1 because it has orbitals in the orientation of xy, yz. xz that line up on those n...

Justin Lai 1C

Why do electrons fill up the 4s shells before the 3d shells in Potassium and Scandium if 3d is lower energy?

Justin Lai 1C

I think that the more electronegative an atom is, the more easy it is to attract electrons. This goes up in a diagonal trend, so increase as group goes to the right and as period goes up, disregarding noble gases. The atomic radius will increase as group goes to the left and period goes down. There ...

Justin Lai 1C

Frequency should always be positive so the negative sign is used when the change between initial and final is negative

Justin Lai 1C

I'm pretty sure all equations that we need on the test will be provided on the equations sheet. It is negative because some people switch the n1 with the n2 and to keep frequency as a positive number, they use the negative sign.

Justin Lai 1C

Yes I think it's just a guideline to follow to make it easier. I think when he says balance first the element that appears the least, he means the amount of times in the equation, not the number of moles.

Justin Lai 1C

Hi, when there are numerous instances in a problem when multiplication/division is needed, can we just find the final answer and do the sig fig in the end after all the multiplication? Also, is a problem with both addition and multiplication different because you have to recount the sig figs after ...

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