CHEMISTRY COMMUNITY

Dang Lam

Yes, catalyst can appear in the overall rate law, intermediates are the ones that cannot appear in the overall rate law

Dang Lam

can someone explain to me why K=k/k'?

Dang Lam

yes we will

Dang Lam

Wayland Leung wrote:Why do we not include any intermediates in the overall rate law when the intermediates are a part of the slow step?

From my understanding, we don't include the intermediate in the rate equation because we cancel the it out when we combined the elementary equations to get the overall equation.

Dang Lam

When we're solving for the order of a reactant in an equation, we usually go about by finding the experiments in the table in which that reactant's concentration changes and where the other reactants are held constant. However, if one of the reactants is independent of the rate, how does this affec...

Dang Lam

Yes you can look at the data and tell the order of the reactant but Dr.Lavelle requires some sort of work or explanation in order to receive full credit. You can use the ratio of concentration to rate to show work.

Dang Lam

If all of the stoichiometric coefficients were different, the unique rate can still be the same using any of them to calculate it because we are multiplying the (change in concentration/change in time) by 1/coefficient. This therefore allows us to calculate the unique rate using any of the species ...

Dang Lam

Chem_Mod wrote:This is to show that the first step is the most important overall for determining reaction rate, as it is slower than the second, making it rate-limiting.

so which reaction (slow or fast) should we use to write our rate law?

Dang Lam

yes because for oth order, the rate law is written as:
rate = k[A]^0
which is equal to rate = k
since the unit for rate = mol/l*s, the unit for k is therefore mol/l*s

Dang Lam

For example 15.2 in the textbook, how did they determine the order of H3O+? Like I am confused with the method they were using with fc and ln. Can someone please explain? Thank you

Dang Lam

You flip the sign of deltaG because the deltaG given is for the formation of Tl3+. The question asks for the standard potential of the Tl3+ /Tl couple, which when written like that indicates that Tl3+ is the reactant and Tl is the product, making it the flipped version of the formation of Tl3+. Tha...

Dang Lam

Anode is the one being oxidized. Oxidizing agent is a substance that has the ability to make other substances oxidized, meaning this substance causes the other substances to lose electron.

Dang Lam

the cathode half reaction is :
2Hg2+ + 2e- --> Hg2 2+
we know Hg2+ is a cathode because it is being reduced (oxidation number decreased from the given equation)

Dang Lam

How do we know when to include an inert conductor into our cell diagram?

Dang Lam

for part a, why did we have to flip the sign of delta G to negative instead of keeping it positive like given? Also how did they come up with the equation for part a?

Dang Lam

how do you know if delta u =0 though? is it because there is no change is temperature? since deltaU = 3/2 R deltaT, and since deltaT = 0, deltaU is therefore =0 as well?

Dang Lam

I have seen some problems in which W also sometimes is calculated using Avogadro's number. When would this be the case instead of doing 2^molecules in the system? When you have n moles. Using a similar example I did in class: 4 moles of CO would have a residual entropy of: S = k ln W where W = 2 4 ...

Dang Lam

to elaborate on that, given that enthalpy is a state function, we don't care about the path taken. Regardless, we will get the same answer if we take the final state - initial state. Therefore, this idea allows us to calculate enthalpy of h2o vaporization through multiple steps.

Dang Lam

can you elaborate on why entropy increases when molecules are broken down please?

Dang Lam

Yes, Cp is use for ideal gas only!!!

Dang Lam

there's an error in the solution manual. You should be using Cv :)

Dang Lam

Calculate the standard entropy of vaporization of water at 85 C, given that its standard entropy of vaporization at 100. C is 109.0 J K 1 mol 1 and the molar heat capacities at constant pressure of liquid water and water vapor are 75.3 J K 1 mol 1 and 33.6 J K 1 mol 1, respectively, in this range. C...

Dang Lam

Can someone explain why entropy of a "perfect crystal" is 0 (S=0)?

Dang Lam

Yes, Dr.Lavelle actually went over all the cases in which delta G can be both positive and negative

Dang Lam

simple words: set delta G=0 to find the Temperature (T) that will make delta G equal 0. Given that, we know that if we increase T, delta G will be smaller and smaller. So anything Temperature that is > then the T you found will give delta G a negative number

Dang Lam

yes, sub1 would require less heat to raise the temperature than sub2

Dang Lam

so does this mean that delta Hf is similar to delta Hrxn?

Dang Lam

it depends on the specific heat capacity. based on your equation, q=mc*deltaT, you would calculate q using the mass (m) of the substance

Dang Lam

No you cannot because there is no volume change.

Dang Lam

i don't think it has to do with specific heat.

Dang Lam

I believe it has to do with the increase in molecular motion and disorder.

Dang Lam

Is delta Hf the same as delta Hrxn?

Dang Lam

I think you should focus mostly on deltaH

Dang Lam

Because you are breaking the bonds, meaning energy is required and that mean positive value

Dang Lam

Yes, I was very confused when trying to do the homework when I started with number 3 and was completely lost

Dang Lam

yes! remember AXE?
A = central atom
X = bonded atom
E = bonded lone pairs

Dang Lam

although there are other alternative ways to figure out coordination number, I personally think it is easier to draw the lewis structure to avoid careless mistakes

Dang Lam

yes, because we are dealing with equilibrium reactions.

Dang Lam

Yes, I think you should study that in case

Dang Lam

Can someone explain the formation of the ideal gas law formula?

Dang Lam

Is there a different way to draw this structure or that is the only one. Also I noticed that the way the formula is written matched with the drawing so is that like a hint on how to draw a lewis structure for a molecule?

Dang Lam

What is the differences between Kp and Kc? Can someone help?

Dang Lam

Can you please explain why we can put Be in the middle? thanks

Dang Lam

A = central atom
X= an atom bonds to A
E= lone pair on A

Dang Lam

It has to do with electronegative. A nonpolar bond is a bond arises when the electronegativities of two atom are the same, aka the dipole moment = 0, or they cancels each other out. Polar bond is the opposite of that

Dang Lam

Clarification: So when you have a double bond, the first bond would be consider sigma bond and the second one would be pi bond? For tripple bond, the first one would be sigma and the other two would be pi?

Dang Lam

Can someone show me how to draw the lewis structure for N2O? How do you figure out which structure has the lowest energy?

Dang Lam

Are we going to get tested on nodes for test 3?

Dang Lam

-Ionization Energy = Energy needed to remove an e-
-Election Affinity = Energy released when an e- is being added
They have the same trend because it takes a lot of energy to remove/add an e- to a stable atom, aka in this case the noble gas.

Dang Lam

Does anyone know when does the "f-orbital"start and can you give an example? thanks

Dang Lam

You can use both equation because one of them is just the derived equation of the other. However, it is better to use the equation E=-hR/n^2 to find the energy of each "n" level then find the ∆E by subtracting the Einitial from the Efinal. From there you can find the wavelength using E=hv....

Dang Lam

The question asks "What is common to the lines within a series (lyman/balmer,etc..) that makes grouping them logical?

Dang Lam

I prefer to use 2.998x10^8 because it gives a more accurate and precise answer. It's like when we calculated the moles in the previous chapter, we carried all the decimal points until the final answer then we rounded it. But if you feel more comfortable using 3.00x10^8 then it should be fine too. :)

Dang Lam

What I would do is that I would write down all the digits in the first calculation and carry them all the way down to the final answer. Then I round it

Dang Lam

Usually, I skim through the equation and do a quick calculation from each side (reactant and product).

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