CHEMISTRY COMMUNITY

emwoodc

intermediates are not included in the overall reaction

emwoodc

i believe the stopped flow technique is used when there is a tiny amount of reactant used. it allows you to find the rate of a reaction in milliseconds with small amounts of reactants. However, I'm not 100% sure why this is related to the zero-order reaction.

emwoodc

the k value is always positive!

emwoodc

catalysts do not appear in the overall reactions. think about it as something that is not a part of the chemical reaction but is just used to speed up the reaction.

emwoodc

it doesn't have anything to do with derivatives! I thought that in the beginning too.

emwoodc

the zero order rate law is independent of the reaction concentration.

emwoodc

water is not included so i don't think it would even appear in the rate law! I say don't worry too much about it.

emwoodc

They would not be able to replace each other.

emwoodc

Namita Shyam 3G wrote:Is knowing the units important for the exam? Will we need to memorize this?

Units are always good to memorize for the exam! maybe it will help you to match different diagrams to the right order?

emwoodc

i believe the average rate of change in reactants is always negative to indicate how the concentration is decreasing as it's changing.

emwoodc

in terms of thermodynamics, gibbs free energy is used to calculate work performed in a thermodynamic system under a constant pressure and constant temperature!

emwoodc

a first order graph has a -k slope!

emwoodc

you would have to know which graphs would relate to which order! I suggest you just familiarize yourself with which graph represents which order and you should be good for the final.

emwoodc

We should familiarize ourselves with the graph but I don't think we would be required to graph in the final since it is multiple choice!

emwoodc

the slope is -k for first order reactions and also zero order reactions,

emwoodc

dilution usually decreases all of the cell potential :)

emwoodc

When K < 1, the reaction is not spontaneous, which makes delta G >0, but when K >1, the reaction is spontaneous which means delta G is less than zero

emwoodc

n is the number of electrons that are transferred for that specific question.

emwoodc

The units for delta G are almost always kj

emwoodc

yes you are correct! a dead battery implies a E of 0 which also means that the delta G is zero

emwoodc

You don't have to worry about the coefficients! They aren't used in the calculations

emwoodc

if you break the reaction down, we can see that the the substances that loses electrons is the one being oxidized and that is the reducing agent!

emwoodc

Yes! you are correct :). When E cells are positive, the reaction is spontaneous.

emwoodc

a salt bridge was used to connect to oxidation and reduction half-cells of a voltaic cell! it helps maintain neutrality with electricity.

emwoodc

so the second part of the sentence is just offering an another method to balance the equation!

emwoodc

Internal energy is the energy associated with the random motion of molecules within the system!

emwoodc

heat = negative when the system is doing work and you are losing heat!

emwoodc

try to identify the units first when deciding which R to use. All the units are provided on the equations sheet so I wouldn't worry too much about memorizing them! As I solved more problems I realized I could figure out which R to use by the equation I am using and what answer I need to provide.

emwoodc

This means that when there is constant pressure AND constant volume, delta H (enthalpy) equals delta U

emwoodc

I saw this on a saplings hint and I was lost too! but I did some research and found that Cp-Cv=R!. I'm not sure if it'll come up later but Cp/Cv ratio is also called the heat capacity ratio.

emwoodc

you would have to draw out the Lewis structure and see if they are linear or not. Atom is pretty self-explanatory.

emwoodc

Delta U or E is equal to q only when work =0 but I believe the common instance we see delta U equal q is when there is constant volume. I wouldn't worry about it too much.

emwoodc

Delta U is the change in internal energy of a system. it's equal to the net heat transferred in and out of the system .

emwoodc

The second law of thermodynamics states that entropy always increases for a spontaneous process. I'm not exactly sure why but I believe it's because heat flowing into a surrounding would cause the motion of the molecules to increase? this would eventually increase entropy.

emwoodc

The universe is said to be an isolated system! I believe Professor Lavelle mentioned it briefly during lecture.

emwoodc

Q refers to the energy transfer due to thermal reactions and enthalpy is the total heat content. They are not exchangeable.

emwoodc

So calorimeters are used to measure the heat capacity of materials and this is measured by trapping the heat released from a chemical reaction.

emwoodc

you use -x when the reaction is going towards the products and you use +x when the reaction is going towards the reactants

emwoodc

Do we have a section for acids and bases?

emwoodc

when forming the ICE table it's important to remember that we don't include anything in the solid and liquid form! we definitely include it when it's a gas or aqueous. So for H2O, we would include it if it was a gas!

emwoodc

We use ICE boxes when we have an unknown concentration!

emwoodc

You are correct! K is found at equilibrium and Q is found at any time of the reaction!

emwoodc

the total pressure of a reaction is the sum of all the partial pressures in a reaction.

emwoodc

if the reaction is endothermic it will favor the product formation and if the reaction is exothermic the reaction will favor the reactant formation.

emwoodc

The inverse Kc is for the inverse reaction ! :)

emwoodc

the concentration of solids and liquids do not change! so when we calculate concentration they're omitted!

emwoodc

Dr. Lavelle said that bar is technically the correct unit but since atm is so close to bar you can use atm!

emwoodc

P: pressure
V: volume
n: moles
R: constant
T: temperature

emwoodc

you could yes.

emwoodc

The Gas constant R is always given on the equations sheet and is constant so dw about memorizing it.

emwoodc

It would be Kelvin! Dr. Lavelle mentioned it during class.

emwoodc

VESPR model is what we name all the models that are in 3D, gives us a more in-depth look at how the molecule is arranged in real life.

emwoodc

a bent shape can have either one or two lone pairs

emwoodc

in the VSEPR model, you can see that it is not the same.

emwoodc

it would be linear

emwoodc

<90 and <120

emwoodc

you will probably get your score in discussion

emwoodc

overlapping of bonds equal double and triple bonds.

emwoodc

the reason why these bond angels are less comes from the lone pairs that are pressing the angles down. the only way it would be greater is possibly from removing those lone pairs maybe?

emwoodc

hybridization should be the same for every element.

emwoodc

a double bond would be a sigma and pi bond

emwoodc

you count the number of bonds there are. for example, a single bond is a sigma bond, a double bond is sigma and pi, and a triple bond is sigma and two pi.

emwoodc

when you have double and triple bonds, the orbitals are overlapping side by side and this side by side overlap is called pi bonds. Everything overlapping is called pi bonds so the ones that are no overlapping, which only happens once is called sigma bonds.

emwoodc

so the single bonds are sigma bonds, the double bonds are sigma bonds and pi bonds, and triple bonds are one sigma bonds and two pi bonds

emwoodc

not yet, but later yes.

emwoodc

Xenon has an empty d orbital which allows it to have extended electrons.

emwoodc

where did you learn that oxygen can only have double bonds

emwoodc

defining them is not very necessary but knowing what it means should be helpful.

emwoodc

they're the same

emwoodc

a biradical is an even compound with two radical centers; however, we didn't really talk about it in class so we shouldn't have to know much about it.

emwoodc

elements beyond the 3rd period have extra room to take the extra electrons in! which allows it to be expanded

emwoodc

at the point where we are at the lecture, no

emwoodc

the strength and length changes when it is a double or triple bond so when you use it you should think about it

emwoodc

yes, lavelle specified in class that the atom with the lowest ionization energy should be at the center

emwoodc

calculate formal charge

emwoodc

everything after the midterm is covered!

emwoodc

as long as the topic is still on the topic discussed we should be turning in homework according to it,

emwoodc

EMR is the speed of light so we typically use it

emwoodc

you use conversion factors!

emwoodc

you can't go wrong with always answer using grams and converting early on wouldn't hurt.

emwoodc

for review I don't know if you took AP Chem or not but my AP chem review books gave me a lot of review questions.

emwoodc

emwoodc

I heard most of the test questions are similar to the ones in the homework so if you find the topic and compare solutions it'll be easy to figure out how to solve the problem! if not, going to office hours won't hurt.

emwoodc

Everyone is getting their tests back in their discussions this week so it should be okay to talk about them freely

emwoodc

it's 5 posts every week and the week ends with sunday night.

emwoodc

click on your own username and you should be able to find all your responses and new topics

emwoodc

If we are not done with Quantum Topic 1 by the end of week three, do we just keep turning in questions from that section? just new problems?

emwoodc

TA said we will be getting the equation sheet we got for every test.

emwoodc

Im not entirely sure what the R means in the equation. It throws me off

emwoodc

lamda is the upside down v with a little edge at the top and it symbolizes wavelength and the v is frequency

emwoodc

i personally did the first 5 questions that were on the homework list and I got full credit

emwoodc

if you round throughout the problem there's a chance that your measurements will be off and the answer will be off

emwoodc

when adding or subtracting you use the number with the least sig figs and match the answer to it

emwoodc

Yes, if you round the sig figs too early in the problem, it could produce an answer that's one or two numbers off

emwoodc

Most of them are mentioned but the one that gets me the most is the rule where if there is a decimal point the zeros after it always counts

emwoodc

according to the rounding rule, it should be 64%

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