CHEMISTRY COMMUNITY

Miranda 1J

When we have a balanced equation and we have to split it into its reduction and its oxidation do we always put the oxygens, waters, etc. in the reduction equation and why?

Miranda 1J

Is Q the conc of the anode over the conc of the cathode? what does it depend on?

Miranda 1J

Will naming organic compounds, not just alkanes, be on the final? Also, in how much detail are we expected to know the functional groups etc.?

Miranda 1J

Although I get the working out, I don't get which equation is being used in part (a) where we're asked to find the rate constant for the reaction given

Miranda 1J

part (c) says: How much time must elapse for the concentration of A to decrease to 15% of its initial concentration? How do we use the 15% in our calculations? I looked at the answers and sort of got what they've done but I'm still a bit confused

Miranda 1J

a) A -> B, given that the concentration of A decreases to one-half its initial value in 1000s determine the rate constant expressed for the rate loss of A ... I feel like this is simpler than the question is making it seem but I'm getting confused, can someone tell me how to go about this?

Miranda 1J

How is it that the slope for both zero and first order reactions is -k but for second order reactions its k?

Miranda 1J

I'm not sure I understand how half-life is related to rate of reaction. Can someone please clarify?
Thanks!

Miranda 1J

Do we need to know how to derive the rate laws in the y=mx+c form or do we only need to know the integrated form of the equation?

Miranda 1J

When we are trying to find the Ecell how do we know which one of the two equations we swap the sign of?

Miranda 1J

I read through the book but I still don't understand how we use the Nernst Equation to find pH. Can someone please explain?

Miranda 1J

I don't get what we need to know about ion-selective electrodes. I don't think they've come up in homework problems either so I'm not sure in how much depth we need to know what they are and how they're used.

Miranda 1J

What’s difference between the two equations for E? (E = E° - (RT/nF)lnQ and E = E° - (.05916 V/n)logQ).

Miranda 1J

In a concentration cell, why does the product concentration need to be lower than the reactants?

Miranda 1J

In how much detail do we need to know the process of electrolysis?

Miranda 1J

How would we interpret a cell diagram such as: Ag(s) ; AgI(s) ; I- (aq) ;; Cl- (aq) ; AgCl(s) ; Ag(s) ?

where ; represents one line and ;; represents two

Miranda 1J

I get that we need to know how to draw a galvanic cell but do we need to distinguish between that and a standard hydrogen electrode? I mean do we need to know how to draw both or just to understand the concept behind the standard hydrogen electrode?

Miranda 1J

Can someone please explain which compound's number of moles we put when using this equation?

Miranda 1J

Can we use the equation DS = q/T for both the surroundings and the system?

Miranda 1J

Which one of the equations shown in lecture is the one we will most likely be asked to use? Will we have to show how to get from one equation to the other?

Miranda 1J

Why is it that at equilibrium we say that DG is equal to zero? Do we have to know why or just that we use that in our calculations?

Miranda 1J

In the book it says "A process is spontaneous if it is accompanied by an increase in the total entropy of the system and the surroundings" I know it sounds stupid but I don't get this, can someone explain what exactly is meant by this?

Miranda 1J

Degeneracy is basically the number of different ways energy can exist and the higher the entropy then the more the ways that energy can exist (proportional).

Miranda 1J

I also read somewhere that it "quantifies the entropy of a system", what exactly does that mean in terms of types of entropy?

Miranda 1J

The question is: A cylinder fitted with a frictionless piston contains 3.00 mol of He gas at P=1.00 atm and is in a large constant -temperature bath at 400 K. The pressure is reversibly increased to 5.00 atm. Find w, q, and U for this process?

Can someone help?!

Miranda 1J

For the test do we need to know how to derive the work equation? I know Dr. Lavelle said work and DU won't be on the test but this seems like a conceptual thing to me so I'm not entirely sure.

Miranda 1J

Can someone please explain when we use Cv and when we use Cp and how we would know which one to use? Also, what's the difference between DH= nCpDT and DH= gCspDT? Does it matter which one we use?

Thanks!

Miranda 1J

you do DH= [(2DHf K2S)+(2DHf H2O)] - [(DHf H2S)+(2DHf KOH)] this should be =[-417.5 kJ/mol + 2(-285.83 kJ/mol)] - [-39.7 kJ/mol + 2(-482.37 kJ/mol)] = +15.28 kJ/mol

Hope that makes sense

Miranda 1J

Can someone please explain this problem to me? I'm super confused! Are we just supposed to use enthalpies of formation and if so what do we do next?

Thanks!

Miranda 1J

DU is the total energy of the system whereas DH is the heat addition to the system at a specific temperature.

Miranda 1J

What is the key thing to look at when determining if a molecule is monodentate, bidentate, etc.?

Miranda 1J

When doing ICE table problems how do we know when to assume that x is 0?

Miranda 1J

So if we have a compound with two ligands, and three of each are attached to the metal (6 bonds in total), would the coordination number be that of each individual ligand (3) or that of both ligands added together (6)?

Miranda 1J

I think what Dr. Lavelle meant by the water being in large excess was that so little of it is ionized at any one time, that its concentration remains virtually unchanged, so essentially just another constant in the equation.

Miranda 1J

Do we only use the reaction quotient, Q, when the reaction only goes in the forward direction?

Miranda 1J

I'm not really sure how to go about this question: The following flasks (page 456) show the dissociation of a diatomic molecule, X2, over time. a) Which flask represents the point in time at which the reaction has reached equilibrium? b) What percentage of the X2 molecules have decomposed at equilib...

Miranda 1J

All bonds contain a sigma bond and double and triple bonds contain a single bond each and 1 & 2 pi bonds respectively. The sigma bond is formed by the head-on overlap of two sp orbitals while the pi bonds are formed by the side-on overlap of the p unhybridized orbitals.

Miranda 1J

You just look at how many electron domains are around the central C. If you have more than 1 C then you look at the hybridization around each one of them separately.

Miranda 1J

You should always put lone pairs as far away from each other as possible. I don't think it matters where you put the first pair as long as the second one is the furthest away it can be.

Miranda 1J

I'm not sure how we would go about these two questions in the book which basically show two shapes and give a bond angle and ask whether there must be, may be, or cannot be one of more lone pairs of electrons on the central atom. If we don't know what the molecule is, how can we determine how many e...

Miranda 1J

you would draw the lewis structure the same way the atoms are presented in the formula

Miranda 1J

Remember that Hydrogen is never the central atom

Miranda 1J

The central atom will always be the one with the lowest electronegativity. When you have carbon compounds, carbon is typically the central atom.

Miranda 1J

P is the subshell and the x,y,z are the orbitals within that subshell.

Miranda 1J

In such cases you would try to find which structure has a formal charge closest to zero, indicating a more stable molecule (0 being the most stable).

Miranda 1J

I think it meant increasing the amount of the same-sized light waves hitting the surface of the metal.

Miranda 1J

That's just a way of writing the short-hand e- configuration. If you're asked to write the full electron configuration then you don't shorten it from the last noble gas before it, you do it all starting from the 1s subshell.

Miranda 1J

I know we haven't discussed this in class yet but I read somewhere on the chemistry page that we should go through the modules and video for this topic during week 2. Does anyone know whether it will be on this week's test or not?

Miranda 1J

I think the Lyman and Balmer series are the only two you should remember, seeing as they were the only two mentioned in lecture. But even for them all you need to know is that for Lyman series (UV) n=1 and for the Balmer series (visible region) n=2.

Miranda 1J

All (complete) combustion questions are the same. For your equation you always start off with what you are burning (in this case butane) and you react it with oxygen. This always gives you carbon dioxide and water as products. If you had an incomplete combustion question then you'd have to add carbo...

Miranda 1J

In a combustion analysis of an unknown compound do we always assume it only contains C, H, O ? How would we know if it contained something else too?

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