CHEMISTRY COMMUNITY

Ethan Breaux 2F

so if I'm understanding this correctly... zero orders are just equal to the constant (k). how would we write them in the k[A][B]^2 thing or would be leave them out?

Ethan Breaux 2F

always use the units that the question initially gives you unless stated otherwise. so yeah convert everything to one type of unit. and don't forget conversions between kJ and J (unrelated sidenote)

Ethan Breaux 2F

first you solve for k then you use the formula to solve for t and you get t = (1/[A]t - 1/[A]o)/k to solve for t in which [A]t can be replaced by (1/16)[A]o , (1/4)[A]o , and (1/5)[A]o which gives you something like for 1/16th : t = (16/[A]o - 1/[A]o)/k

Ethan Breaux 2F

you have to get the formula for t from the second rate equation which causes you to get t = (1/[A]t - 1/[A]o)/k and in this case you can replace [A]t with (1/16) x [A]o causing the equation to be t = (16/[A]o - 1/[A]o)/k and you just plug stuff in :)

Ethan Breaux 2F

Khan academy has a great video on it but yeah like they said you have to do it as if it were in acidic then you add the HO-

Ethan Breaux 2F

I generally add the OH- after I balance it using acidic solution then just convert the H+ to OH- (Khan academy has a good video on this) and you only really use H2O to balance oxygen you don't always need to add it.

Ethan Breaux 2F

don't forget that oxygen is always 2- and hydrogen is always 1+ thats usually how you calculate it then its just dependent on if you do the addition/subtraction correctly.

Ethan Breaux 2F

deltaU = 0 doesn't mean theres no heat just that theres no difference in the amount of heat in the beginning compared to the end (no change). Just like said above its just a way to tell you to use q = -w since q+w = 0

Ethan Breaux 2F

yea basically if Celsius is changed by 1 decree then so is Kelvin since its just addition

Ethan Breaux 2F

because it holds more energy since it has the heat energy of boiling water + the heat energy required for the phase change

Ethan Breaux 2F

they're used in those K = [Products]/[Reactants] problems to calculate solubility

Ethan Breaux 2F

don't forget if the x value is very small (i.e. less than 10^-3) you can ignore the x when subtracting it from another value!

Ethan Breaux 2F

Does anyone know if midterms have ever been graded on a curve?

Ethan Breaux 2F

delta G = delta H - T x delta S

Like someone above said if you plug in numbers to the equation it'll make pretty good sense.
Most of this stuff will be dependent on temperature.

Ethan Breaux 2F

are there ever curves?

Ethan Breaux 2F

They'll usually just say constant temp or isothermal which is pretty much the same thing.

Ethan Breaux 2F

Cp = Constant Pressure
Cv = Constant Volume

Ethan Breaux 2F

its defined by state functions which makes it a state function

Ethan Breaux 2F

Gibbs Free energy and electrochemistry for test 2

Ethan Breaux 2F

What's the purpose of using Ideal Gases when they are theoretical? And whats the basic difference between ideal gases and real gases?

Ethan Breaux 2F

On a test or midterm will we be told if the system is Isothermal?

Ethan Breaux 2F

everything above^^^ and you can check the 5% rule by taking the value you plug into the -log for pH and dividing it by the original starting concentration of whatever weak acid was used in the problem (usually a given) then you multiply it by 100%

Ethan Breaux 2F

The post-module assignment just had it that:

K > 1 means that there are more products at equilibrium (lies to the right)
K < 1 means that there are more reactants at equilibrium (lies to the left)
K = 1 means neither are favored.

Ethan Breaux 2F

I know that when doing the ICE box you don't count Cl, Na, or H2O but are there any other elements that we just inherently disregard?

Ethan Breaux 2F

I don't have the 6th edition but I don't see how you could have calculated it so that the initial concentration of a reactant = the value of x... reevaluate how you got the x value. (most problems made you do like x^2/some number)

Ethan Breaux 2F

Don't forget to use c = n/V and that at equilibrium 40% of hydrogen is left.

Ethan Breaux 2F

Calculate the pH of 0.15 M H2SO4 (aq) at 25 Celsius (Ka2 = 1.2 x 10^-2)

Could someone explain the concept of Ka2 and why we ignore the second ionization?

Ethan Breaux 2F

Pretty sure (aq) just means its like surround by water or in water. The problems are also solved basically the same way and there is a chart with values and like info on Al^3+ and how it equals Al(H20)6^3+ (I think that that would be given to us)

Ethan Breaux 2F

Will we have to memorize certain Ka/Kb values or will that be given or just not show up at all?

Ethan Breaux 2F

Can someone give a good/simple explanation of deprotonation is and how to use the percentage in problems?

Ethan Breaux 2F

Its a non polar molecule so I don't think it really matters

Ethan Breaux 2F

Is water then polyprotic?

Ethan Breaux 2F

Can someone explain how to find Coordinate numbers? They're just the bonds right?

Ethan Breaux 2F

Maybe I'm just reading this wrong but are you referring to see saw?

Ethan Breaux 2F

Is VSEPR Notation also referred to as VSEPR Formula?

Ethan Breaux 2F

Knowing the polarity of the element also helps show its ability to form dipole dipole (idk how relevant that is but hey just trying to contribute)

Ethan Breaux 2F

Ion bond > H bond > dipole dipole > dipole induced > induced induced

Ethan Breaux 2F

Yea its because of the lone pairs and I'm pretty sure the formal charge equation proves that.

Ethan Breaux 2F

Just use formal charge formula FC = Valence - [lone pair electrons - (shared electrons/2)]

Ethan Breaux 2F

Hybrid orbitals are interactions of orbitals in the same atom while molecular orbitals are between two different atoms.

Ethan Breaux 2F

They are caused by relative EN due to the fact that electrons move and it is also how Geckos walk on walls and stuff! (Fun fact)

Ethan Breaux 2F

Actually thats incorrect. Covalent radii is half the distance between the two nuclei. It isn't the sum of the two radii at all. When the two atoms bond the like kinda mesh together so yea its just half the distance between not the sum.

Ethan Breaux 2F

Also it's important to know that lone pairs have stronger repelling forces than bond pairs.

Ethan Breaux 2F

When was this discussed in lecture?

Ethan Breaux 2F

Sorry didn't mean to repost question. As a note to any moderators: the site would work better if we could still see what we are replying to while we are replying.

Ethan Breaux 2F

What is the interaction potential energy telling us? What do we use it to determine? Does it have anything to do with whether their is a dipole moment and how strong that dipole moment is? I thought it meant just the energy that is added to the total energy during a reaction. I'm also pretty sure it...

Ethan Breaux 2F

If the bond can go anywhere then might as well draw the arrows I don't think it would ever hurt you.

Ethan Breaux 2F

In all honesty, the octet rule is pretty worthless after the few elements in the 2nd row that it applies to. We just pretend that it continues but hardly anyone knows anything about any element after the 3rd row.

Ethan Breaux 2F

It also shows where electrons are and how they interact.

Ethan Breaux 2F

How does it come with the textbook? I didn't see it.

Ethan Breaux 2F

Does anyone know the name of the site he keeps saying to use?

Ethan Breaux 2F

So would the answer be [Ar]3d6?

Ethan Breaux 2F

Hey so I was wondering if there are any studying resources that are similar to the modules since there are no more of those to use. Thank you! (Also I am not sure where to post this question)

Ethan Breaux 2F

Why is there a negative in the equation (En = -hR/n^2) when we just put the positive value whenever a questions asks us to find the frequency or wavelength? Is there any scenario in which we would put the negative value as the answer?

Ethan Breaux 2F

Does anyone know when more models will be uploaded to the Chem14A website? I felt this is the best place to ask since I am "uncertain" and Heisenberg Indeterminacy is the last module topic.

Ethan Breaux 2F

So as we know the Lyman series is n=1, the Balmer series is n=2, and so on and so on. My question is whether or not we will need to know all the series after these two or will we just be given n = 4?

Ethan Breaux 2F

How come on the EM spectrum "Microwaves" are said to have wavelengths between 1mm and 10cm but actual physical Microwaves can have wavelengths up to 1m? Do Microwaves not use "Microwaves"?

Ethan Breaux 2F

Well the formation of rainbows required pretty specific stuff like there has to be rain and sun and the sunshine needs to be going through at a certain angle in respect to whoever is looking at it and obviously there has to be water droplets in the air and again no clouds. Its more common to see rai...

Ethan Breaux 2F

I think you should write out the entire question haha I don't remember that happening but maybe I'm in a different lecture or missed it or something haha

Ethan Breaux 2F

Well a black body is an object that "absorbs all radiation falling on it, at all wavelengths," and you can calculate the emissions with Planck's Law but I don't think we're really doing many of those calculations. I hope that kinda helped haha

Ethan Breaux 2F

yeah I was confused too but I guess since avogradro is a constant the ratios for the moles are the same as the ratios for the atoms since they're all being multiplied by the same thing.

Ethan Breaux 2F

No we don't need to know them yet but its good practice to figure out the meaning of compound names because they'll be needed in the future

Ethan Breaux 2F

I would instead treat 9.77 as 9.75 and multiply the ratio by 4 so you end up with C 5 : H 39 : O 22 (its more accurate this way). Just look to see if decimals can be rounded to .25 .5 or .75 cuz those are easy numbers to work with.

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