CHEMISTRY COMMUNITY

RyanTran2F

What are the standard conditions of a galvanic cell? Is it only that solutes are at 1 mol/L or are there more requirements? Thanks :)

RyanTran2F

Would we need to know where and how to draw the arrows? Thanks :)

RyanTran2F

On questions about electrophilic addition, would we be given the diagrams of the molecules and reaction and then be asked to draw arrows or will we have to do all of this by ourselves? Are there any other types of questions that this technique/method will need to be used in? Thank you :)

RyanTran2F

The question asks if heat is being transferred when "A balloon filled with gas is expanded to a larger volume and lower pressure while maintaining the same temperature." The answer is Yes but I am not too sure how to arrive at this answer. Is it since we need to do work on the system to in...

RyanTran2F

Why is the answer in Part b not 2I + Ar -> I2 + Ar (disregard charges on the molecules)? I understand that Ar is on both sides so they can cancel and we get the answer provided in the Answer Key but then why is it in the rate law and not the elementary step? Thanks :)

RyanTran2F

Hi can someone explain how the answer key got the answer in Part A? I did not quite understand the explanation provided. The question asks, "In the reaction of HBr with the reactive intermediate CH3CH=CHCH2+, at low temperatures the predominant species is CH3CHBrCH=CH2, but at high temperatures...

RyanTran2F

When we find reaction enthalpies based on bond enthalpies, we multiply the enthalpy (kJ/mol) to break a bond by the number of bonds (mol) so why does the answer in the answer key sometimes have units as kj/mol (ex. 8.75)? Would it be acceptable if we just put units as kJ? Thanks :)

RyanTran2F

If the elementary reaction is A + B -> P then the rate of this step is Rate = k[A][B] where each is first order and the overall rate is second order. However, previously in class, we learned that overall reactions can have Rate = k[A]^n [B]^m (and we use initial rates to find the powers), so is the ...

RyanTran2F

When we talk about molecularity, is it ONLY used to describe the number of species in an elementary step or will it ever be used to describe a regular overall reaction? Thanks :)

RyanTran2F

Are we given the elementary reactions or will we have to figure out all the components on our own? Thanks :)

RyanTran2F

Hi just to make sure, is this a correct statement to make: the Differential Rate Law (Rate = -1/a * d[R]/dt = k[R]^n) is related to (and are associated with) the method of initial rates since this method helps us find the n (and other powers if there were more parts to the rate law) and the k? Thank...

RyanTran2F

How do you define emf and why does it represent a maximum value? Is it just the potential difference between the cathode and anode? How do we know if a metal will dissolve (do we just make a redox reaction with the metal at anode or cathode then see if the reaction is spontaneous in that direction)?...

RyanTran2F

Why is O2 included in the cell diagram even though it was not in the overall cell reaction? Thanks :)

RyanTran2F

On Part b, If we know the overall reaction is H+ (aq) + OH- (aq) -> H2O (l) then how did we have O2 and OH- on the anode side of the cell diagram and H+ and O2 on the cathode side? Where did the O2 come from? On Part b, where did we get KOH(aq) in the cell diagram? Thanks :)

RyanTran2F

When writing cell diagrams, does the order matter for things on the same side of the ||? Sometimes the book would write it in the same order as it was in the reaction equation (ex. anode side of || would have Au(s) | Au3+ (aq)), but at other times the order would be switched (anode is still on left ...

RyanTran2F

Yea I think the book also always had the anode on the left and the cathode on the right (similar to how it is in the galvanic cell picture)

RyanTran2F

Galvanic cells often have equal molarities of 2 electrodes but concentration cells have different molarities with the same type of electrode on both sides. About your other 2 questions, I am not too sure but I think this is just another way of using the relationship between chemical and electrical e...

RyanTran2F

And to add on to that, this is true for the concentration cell, not the voltaic cell which we learned previously which usually had equal molarities on both sides and different electrodes.

RyanTran2F

I think in class Dr. Lavelle uses 1 atm instead of 1 bar. Also if you are required to interchange between 2 units of pressure, I think he would give you that information on the Constants and Equations Sheet. I hope that helps :)

RyanTran2F

Will the work and answers to the questions be posted online after the session? It would be great if they could post a pdf of the work and answers or just have pictures of the work they did during the session. Thanks :)

RyanTran2F

If a question asks for the half reactions, do we write it in the order it was given in the equation or always write it as a reduction process (similar to the reaction in the table)? Thanks :)

RyanTran2F

At equilibrium, K can be 1, >1, or <1. If K>1 then products are favored and ΔG is negative (the reaction favors the products). We also learned that a reaction proceeds spontaneously towards equilibrium (which is when ΔG = 0) so then does that mean, based on the equation learned in class, that at equ...

RyanTran2F

Hey, If J/k mol is given for enthalpy, and there is no value of mol that needs to be accounted for, then the entropy would also be in J/k mol. In some cases, such as when calculating standard reaction entropy, and you are given the amount of moles per product or reactant, then the answer would like...

RyanTran2F

Why does the answer key sometimes solve for ΔS and say units is J/K but sometimes J/K mol? When do we add on the "per mole" and will we be marked down if we do not have it? Thanks :)

RyanTran2F

Is ΔU = 0 in Part B because of it is an irreversible pathway? I do not understand how the answer key knew ΔU = 0. Thanks :)

RyanTran2F

The answer key says, "The change in entropy for container A is greater than that for container B or C due to the greater number of particles." Is this saying container A has more particles? If so, how does container A have more particles? Thanks :)

RyanTran2F

So in 9.15 we used ΔH boiling and melting points when the thing we are boiling/melting is at its boiling/melting point. If the thing was not at the correct temperature then we would have to account for the energy needed to get it to the boiling/melting point, the energy to boil/melt it, and the ener...

RyanTran2F

I think they use reversible pathways since, like Salman said, they change very slowly and in small steps. This way we can add up the changes in each step to get the total entropy. Hope that helps :)

RyanTran2F

In Part A it is saying that the molecules are at 0 K (no thermal energy) and are fixed so this is when you only examine the picture in the top left since that is the original (and only) microstate that the system can be in. In Part B, the molecules are able to have different microstates so you would...

RyanTran2F

In lecture on Monday we had a picture of a graph of G and the system is at equilibrium when the slope is 0. What do the rest of the slopes mean? Does a negative slope (to the left of the equilibrium point) mean that the reaction is spontaneous at that point? Thanks :)

RyanTran2F

On #9.1A why did the answer key say ΔS = -qrev/T and then have the answer as a positive value? When do we use a negative sign in the formula? I thought it was when entropy decreases but then on #9.5 the answer key also used a negative in 1 value but not the other? So how do you know if we should mak...

RyanTran2F

So if the external environment was not a vacuum then, to move the piston, there would be work done and this would not be simply due to entropy but because work was done to push the piston against the external pressure? Thanks :)

RyanTran2F

Hi can someone clarify the picture we saw with the piston on Week 3 Friday's lecture? When it says "No work done" pointing from the piston to the right, is it just saying we do not consider the work being done to push the piston? However there IS work being done right (since we have the eq...

RyanTran2F

Are his tests always based only on those sections? Thanks :)

RyanTran2F

#8.25: A constant-volume calorimeter was calibrated by carrying out a reaction known to release 3.50 kJ of heat in 0.200 L of solution in the calorimeter (q = -3.50), resulting in a temperature rise of 7.32 degrees Celsius. In a subsequent experiment, 100.0 mL of 0.200 M HBr(aq) and 100.0 mL of 0.20...

RyanTran2F

Since the step size between Kelvin and Celsius are the same, when we are calculating a heat capacity, are we always allowed to use either Celsius or Kelvin if the question does not specify? Thanks :)

RyanTran2F

There are some material from the book in the sections Dr. Lavelle told us to read that were not covered during lectures (ex. 8.7, 8.9, Box 8.2, and 8.21). Will material from these sections be on Tests/Midterms/Final? Thanks :)

RyanTran2F

Hi. On Tests/Midterms/Final, will we need to know how to derive the formulas we learned (like how he showed us the derivations in class and in the textbook) or will we only need to know how to use them? Thanks :)

RyanTran2F

You can also think of it as multiplying the equation and enthalpy values by a fraction (ex. multiplying by 1/2 is same as dividing by 2) so this is a valid technique

RyanTran2F

In addition to Cam Bear's response, you can see that the question hints at you having to use combustion equation instead of one of the other 2 methods of solving for enthalpy since the book did not tell you to use a specific table or a page in the Appendix. This means you can only use what is given ...

RyanTran2F

I think you should just look at whether or not energy is moving from one place to another. If it is then the system is closed and if not then it is an isolated system.

RyanTran2F

In section 8.12 we learned about supercooling and superheating. Can someone explain why these can happen? How does something pass the freezing point and the boiling point before freezing/boiling (respectively)? Thanks :)

RyanTran2F

I agree with Renee's assumption. In the book in section 8.8, it says that at constant pressure, and with no nonexpansion work ΔH = q. q represents heat, which can be increased by increasing the temperature. So with from equation, we see that with increased temperature, ΔH (enthalpy) will increase as...

RyanTran2F

I agree with Yashaswi's answer. A reversible process is a process that can be reversed as a result of an infinitely small change. If the external pressure is increased one bit, the volume will decrease and vice versa.

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