CHEMISTRY COMMUNITY

SydBenedict2H

The only one that isn't -k is is 2nd-order, which is just k (+k).

SydBenedict2H

All are given except you might want to know different forms for 1st-order.

SydBenedict2H

Can you have it be moles per mL per second? Or per day?

SydBenedict2H

Just remember that if you use the overall net equation for E you leave the signs and if you're adding up form had reactions etc. you have already flipped the sign so just add.

SydBenedict2H

I think you want to balance the atoms, charge, and number of electrons all because its still a half reaction until you put it all together for the final reaction.

SydBenedict2H

So -0.1 has more oxidizing power than -0.02, with any positive value having the strongest oxidizing power compared to these two.

SydBenedict2H

Just remember that for acidic conditions you are adding H2O to whichever side needs to balance Oxygens and H+'s typically to the other. You do the same thing with basic solutions but with OH- and H2O

SydBenedict2H

I understand factually that an oxidizing agent is whatever is being reduced and a reducing agent is whatever is being oxidized. However I'm having trouble what exactly this means more conceptually. Anyone have a way to explain it that might help?

SydBenedict2H

How do you know which reaction is being oxidized and which is being reduced in a question where you are only given a the final reaction? Whichever reactant has a value that is becoming less positive, as more electrons 'reduces' the number, (+7 to +5 etc.) is being reduced. Whichever reactant is get...

SydBenedict2H

Why is it that for only the first order it isn't dependent on the initial concentration?

SydBenedict2H

I thought on Monday he said first order rate laws would always have a linear slope? -k?

SydBenedict2H

How do we know when to use each rate law? Will we have to be able to recognize it or will the question tell us?

SydBenedict2H

Check the textbook, it should be in there!

SydBenedict2H

It should mirror the homework so if you've been seeing that type of problem in the textbook then its likely that it could appear.

SydBenedict2H

On Monday Professor Lavelle said that we could tell when the 1st order rate law is being used because the slope would be linear, yet today for the 2nd and 0 order rate laws, those slopes were linear as well. Did i miss something?

SydBenedict2H

How can we tell when each rate law is supposed to be used? Is it related to what the variable on the y-axis is?

SydBenedict2H

Will he ask us any acid base questions, or is he only asking Gibbs and electrochemistry?

SydBenedict2H

If they mention internal energy then they are referring to delta U and you should use its associated equations.

SydBenedict2H

So basically what matters is if energy is being put into a system vs. is being "taken out of" a system.

SydBenedict2H

So does this mean we aren't going to have to use the integral formula to calculate anything on tests?

SydBenedict2H

The heat of the surroundings would not be able to effect the isolated system so regardless of the surrounding heat, it doesn't matter. It will not effect the system and would not matter for calculations/the problem at large.

SydBenedict2H

If its ever in bar, thats more or less equivalent to atm.

SydBenedict2H

If these two were not equal, then they would be attempting to reach a state of equilibrium (being equal). So if you had a closed system with a certain pressure on the inside and a different pressure on the outside, and you suddenly removed whatever was making the system closed rather than open, the ...

SydBenedict2H

With this free expansion, would the pressure and volume both be positive for the work equation? I get confused as to if the P is always negative or not.

SydBenedict2H

Can someone explain the last example he did on Friday? Im a little confused still as to how/why NO2- was 0.15 and H3O+ was still 0

SydBenedict2H

So you can only calculate K when you already know its at equilibrium?

SydBenedict2H

How exactly does one actually test the 5% rule (if x less than 5% of initial concentration then the approximation is valid)? He always says it in lecture but hasn't actually done the math and I need to see things like that before i fully grasp them regardless of how basic i know it is.

SydBenedict2H

and furthermore, if you switch the concentrations from all being 0.1 to all being 0.2, is it still at equilibrium as all the values increased proportionally?

SydBenedict2H

In class on 1/11/19 we did an example where we calculated K with initial concentrations at eq. being 0.1, 0.1, and 0.1. We got 100 for the K value. We then said that if P doubles (V halves) then the new initial concentration wold be 0.2, 0.2, and 0.2. We calculated the Q value for this and got 25. C...

SydBenedict2H

For P (partial pressure), bar and atm are used almost interchangeably as their values are apparently quite similar.

SydBenedict2H

K calculates the equilibrium constant (either with partial pressure P or concentration n/v) whereas Q can be use anytime and is useful in its comparison to a K value. Whether it is greater than or less than the reactions K value, dictates which direction the reaction is going and if there are more p...

SydBenedict2H

So 1 bar is roughly equivalent to 1 atm? The same holding true for, lets say, 6 bar and 6 atm?

SydBenedict2H

Why are all the Carbon atoms in 4.93 SP^3 hybridized? Don't they only have 3 regions of electron density each?

SydBenedict2H

Double and triple bonds count as single regions of electron density correct? Im trying to explain them to my friend and she's convinced they count as 2 and 3 respectively.

SydBenedict2H

HF will have greater polarity than HCL, which will in turn have greater polarity than HBR, which is more polar than HI. It corresponds directly with electronegativity as the stronger the electronegativity of an atom, the more it pulls an electron, and thus the more polar the molecule becomes.

SydBenedict2H

When it goes down a period does it get to 3SP^3 ever? We only did examples in class that were in the second period so I'm a tad confused.

SydBenedict2H

This is why when doing VSEPR if there is a linear molecule (2 bonds) and you add a lone pair it becomes bent. The repulsion from the lone pair is so strong that the bonds move closer towards each other to be away from the lone pair.

SydBenedict2H

They bond with things that have a partial negative charge as they have a partial positive charge. They will form hydrogen bonds with N, O, and F (if they have partial negative charges, which they should). H bonding holds DNA together and gives whatever it makes up higher melting and boiling points.

SydBenedict2H

To learn these I just made a chart, or you can write down the one posted above as it can be super helpful, and then put it all into flashcards on quilt. I studied that until i had it memorized, then, doing a bunch of problems switches the memorization from route to actual understanding.

SydBenedict2H

Also, regarding this, Yes, and they also count when determine electron arrangement. It is important however, to remember that lone pairs do not count when naming the shape. The lone pairs DO count when naming the shape in some instances as it can help you know what shape it is. If its just 3 bonds a...

SydBenedict2H

So for hybridization we count all bonding pairs and all lone pairs to get all the regions of electron density? Do we ever only count the bonding pairs?

SydBenedict2H

Is 2SP^3 always equivalent to SP^3, or just sometimes? Its when its on that level correct? All of the examples we did in class were the 2SP^3 so I'm slightly confused as to how it works for molecules above period 2.

SydBenedict2H

What if the molecule is polar and doesn't have hydrogen bonding?

SydBenedict2H

Im having trouble being able to easily identify when a bond is a sigma bond vs. when its a pi bond. Does anyone have any quick and easy tips? I feel like its super simple and im just way over complicating it.

SydBenedict2H

If you didn't get your midterm after lecture last week, go to your TA and they should have it. When your TA graded it they did a pretty good job of explaining what you got wrong and can explain why you got things wrong.

SydBenedict2H

Are you referring to the [] compound's we covered in class on Monday? The coordinated compounds/bonds?

SydBenedict2H

So the shorter the bond,the stronger it also is?

SydBenedict2H

Anytime two atoms of the same type are bonded together it must be a covalent bond correct? Like in Disulfide bonds?

SydBenedict2H

On the same question, based on the reply, what is the V we use to solve for v? Its the velocity of the electron right? I feel like im just missing something super obvious here...

SydBenedict2H

They compared it to a fingerprint, an ID of sorts. Based upon the specific wavelength that is emitted/absorbed, an object (whatever it may be) can be identified.

SydBenedict2H

If the energy of the light (photons) is higher than the work function (the little symbol that looks kind of like the green lantern symbol) then its met the "threshold" and can eject an electron. The difference between the work function (threshold) and the energy from the light equates to w...

SydBenedict2H

This relates to the uncertainty regarding electrons. The more we know concerning an electrons position, the less we know about its momentum and vice versa. The two things exhibit an inverse relationship toward each other. My TA made it seem like we more so had to undderstand the concepts than we had...

SydBenedict2H

Honestly as long as you know the order and which is shortest and which is longest, you should be ok. I would try to learn the rough values of each differing type, but beyond that I think you should be fine.

SydBenedict2H

Im not sure if I've missed an obvious explanation but i'm slightly confused as to what is covered and when. I know last Monday we started chapters 1 and 2, however i'm not sure if we finished the chapters and now have new chapters assigned, or if we are still doing those chapters. Will the homework ...

SydBenedict2H

Does it matter if you use 2.99x10^8 or 3.00x10^8? or are they close enough that the difference is indiscernible?

SydBenedict2H

Im slightly confused as to why Kg is the standard SI unit for mass when all of the mole conversions and problems weve been doing thus far have been in grams?

SydBenedict2H

And do we also need to have memorized at what values each differing type of light starts and ends?

SydBenedict2H

Is the sulfide being referred to in question E.15 the metal that is mentioned in the question? I was confused where the Sulfide suddenly came from?

SydBenedict2H

Typically I do it by trial and error as wel (more or less logic-ing it out) but you can do the method from that one example he did where he got 13/2 (6.5) then multiply both side by 2

SydBenedict2H

How do you know which order they should go in though?

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