CHEMISTRY COMMUNITY

Glenda Marshall DIS 3M

Well I feel silly. Thank you so much!

Glenda Marshall DIS 3M

Thank you!

Glenda Marshall DIS 3M

Oh that totally makes sense! Thank you so much and sorry for the typo!

Glenda Marshall DIS 3M

Is there a specific list of common names that we should know for the final? I know different variations of this question have been answered, but all of them have either said that common names and IUPAC will be accepted or referred to ways to name molecules. I understand the rules for common naming f...

Glenda Marshall DIS 3M

Hi!
I am reviewing my notes and I cannot seem to remember why delta H is zero for an irreversible, isothermal expansion. Any help would be appreciated. Thanks!

Glenda Marshall DIS 3M

Homework problem #3.8 in the yellow organic chemistry book says: "Using a Newman Projection, draw the most stable conformation of a hexane looking down the C2-C3 bond. What is this conformation called and give its dihedral angle." I used my model kit to make a chair cyclohexane and it look...

Glenda Marshall DIS 3M

My apologies! Homework problem #14.103 says "which of the following plots would be linear?" and one of the options is "the half-life against [A] for a second order reaction in [A]" I am confused why this is not linear because I thought it would be, but the solutions manual does n...

Glenda Marshall DIS 3M

Why is the graph of the half-life of a second order reaction not linear. Wouldn't the slope be 1/k with the variable being [R]o?

Thanks!

Glenda Marshall DIS 3M

That makes sense, but I am still confused how you know to use

Cu+ + e- ---> Cu Eo =+0.52

as opposed to

Cu2+ + 2e- ---> Cu Eo = +0.34

Because using the lower one would change the answer. Thanks!

Glenda Marshall DIS 3M

In problem 13.25, it asks us to rank the metals given in order of the power of the reducing agent. Part (a) gives us Cu, Zn, Fe, and Cr. I know that the lower the reduction potential the more powerful the reducing agent, but how do we know which reduction potentials to look at to compare their relat...

Glenda Marshall DIS 3M

Hello!
Homework problem #13.17 asks us to

"write the balanced half-reactions for the redox reaction of an acidified solution of potassium permanganate and iron (II) chloride."

How would you know how to write the half reactions when they only give you the reactants? Thanks!

Glenda Marshall DIS 3M

Thank you so much!

Glenda Marshall DIS 3M

Homework problem 4.29 says "draw and label the reaction profile with potential energy as the y-axis for the electrophilic addition reaction of hydrogen bromide, HBr, to propene, CH3CHCH2, producing 2-bromopropane, CH3CHBrCH3" the graph they drew was an exothermic reaction and I am wonderin...

Glenda Marshall DIS 3M

I know that a catalyst reduces the free energy of activation by weakening bonds and thus lowers the standard enthalpy of activation, but how does it raise the standard entropy of activation? The wording the in the book is confusing to me. Thank you!

Glenda Marshall DIS 3M

Hello! On page 79 of the course reader, there is an example of nucleophiles and electrophiles interacting in which there is a polarized Br2 molecule. I thought that we learned in Chem 14A that diatomic molecules cannot be polarized, so I am wondering how this is possible. Thank you!

Glenda Marshall DIS 3M

Hi! On the midterm, question 8 part c) asked how many electrons were transferred in the reaction C6H12O6 + 6O2 ---> 6H2O + 6CO2 The answer is 24 and I understand that each side has a charge of negative 4 so 4 electrons must be involved, but why do they multiply by 6? I can see that the coefficients ...

Glenda Marshall DIS 3M

I am slightly confused how to know where bonds form in organic reaction mechanisms. For example, if we look at the reaction between propene, CH3CHCH2, and hydrogen bromide, HBr, how do you know which carbon the hydrogen bonds with once the sigma bond between H and Br breaks? The answer key shows it ...

Glenda Marshall DIS 3M

Thank you so much!

Glenda Marshall DIS 3M

Thank you Sanmeet! That was super helpful!

Glenda Marshall DIS 3M

In question #14.85 part (b), it asks to write the overall react with the rate law rate=k[I]^2[Ar] (products are I2 and Ar; the role of Ar is to remove energy as the product forms). The reaction they gave was 2I ----> I2 How do we know to exclude the Ar and why would it be a termolecular elementary r...

Glenda Marshall DIS 3M

Can someone please explain how to draw a proposed stucture for an activated complex. Question #14.85 asks us to do this and I don't know where to start. The rate laws they gave are: a) rate=k[CH3CHO] products are CH3 and CHO b) rate=k[I]^2[Ar] products are I2 and Ar, the role of the Ar is to remove ...

Glenda Marshall DIS 3M

Question #14.105 gives the following section mechanism: ClO- + H2O ----> HClO + OH- (fast) HClO + I- ----> HIO + Cl- (slow) HIO + OH- ----> IO- + H2O (fast) and asks for the rate law. By using the pre-equilibrium process, I wrote the rate law as [ClO-][H2O][I-] / [OH-] The solutions manual has the s...

Glenda Marshall DIS 3M

That was so unbelievably helpful! Thank you!

Glenda Marshall DIS 3M

Hello! Problem #14.93 in the textbook says "Raw milk sours in about 4 hours at 28 degrees celsius but in about 48 hours in a fridge at 5 degrees celsius. What is the activation energy for the souring of milk?" When I looked at this problem I knew I had to use the Arrhenius Equation compari...

Glenda Marshall DIS 3M

A question on quiz one said "calculate the entropy when 65.7 g of xenon gas undergoes isothermal expansion from an initial pressure of .50 atm to a final pressure of 1.5 atm. Assume that xenon behaves as an ideal gas." I understand how to do this, but what confused me is that it then asked...

Glenda Marshall DIS 3M

Thanks Niharika! Sometimes I get a little lost in this big chemistry community world and don't see every post!

Glenda Marshall DIS 3M

I remember from thermodynamics that you cannot use both concentrations and parietal pressures when calculating equilibrium constants which is why we always either calculated Kp or Kc. Why can we now use both of them when calculating K and Q for redox reactions? For example, in homework #13.41 the so...

Glenda Marshall DIS 3M

What does it mean to find vapor pressure of a liquid? In problem #10.109 in the homework, part (b) asks "what is the vapor pressure of liquid bromine?" and it does not provide an equation or any other information. It the solutions manual, they solved for K and used that value as the vapor ...

Glenda Marshall DIS 3M

Thank you so much! That was really helpful.

Glenda Marshall DIS 3M

Hi! Can someone please explain homework problem #13.103. The question is: Use data in appendix 2B and the fact that, for the half reaction F2 +2H+ +2e- --> 2HF the standard potential is +3.03 V, to calculate the value of Ka for HF. I don't know how to find the half reactions for this reaction or how...

Glenda Marshall DIS 3M

In homework problem 13.99, the question says that there is a concentration cell with one half cell containing 1.0 M CrCl3 and the other with .001 M CrCl3. It then asks what would happen after adding 100 mL 1.0M NaOH to the cathode if Cr(OH3) is insoluble. The solution says that the NaOH precipitates...

Glenda Marshall DIS 3M

I am wondering why increasing the mass of an electrode in an anode compartment has no effect of the concentration of the anode solution. Wouldn't more metal decompose thus creating a higher molarity solution in the anode compartment?

Thanks!

Glenda Marshall DIS 3M

If given a word problem that only tells you what you start with in a reaction, how do you know what the reduced and oxidized forms of the ions given are? For example homework 13.17 says "Write the balanced half reactions for the redox reaction of an acidified solution of potassium permanganate ...

Glenda Marshall DIS 3M

How do you know the proper equation when H2O, H+, and OH- are involved? For example, in homework problem #13.11 part (d), the following cell diagram is given: Pt l O2 l H+ ll OH- l O2 l Pt In this case, the half reactions are O2 + 2H2O +4e- --> 4 OH- O2 + 4H+ +4e- -->2H2O How would you know that O2 ...

Glenda Marshall DIS 3M

I was wondering if someone can help me understand the process of writing half-reactions from cell diagrams. My main question is if there is particular order that the species are written in. I know that the anode will be to the left of the salt bridge (the double line) and the cathode will be to the ...

Glenda Marshall DIS 3M

I am slightly confused why you want a negative Gibbs Free Energy if Free Energy is the energy available to do work. Wouldn't the more energy you have be better. For example, wouldn't a reaction be more favorable if the products had more free energy than the reactants? In this case the delta G would ...

Glenda Marshall DIS 3M

In this problem, its asks which has a greater change in entropy: 1 mol of an ideal monatomic gas or 1 mol of diatomic molecules that are vibrationally active. Why does the 1 mol of a monatomic gas have a greater change in entropy when the diatomic molecules are more complex? I thought that the more ...

Glenda Marshall DIS 3M

In this homework problem, why did the solution manual write an equation and solve for the delta G? Couldn't they just use the delta G of formation for each of the compounds (like they did in problem 61)? What is the difference between these two problems that suggests different routes of answering th...

Glenda Marshall DIS 3M

For homework problem #8.93, why are the answers in kJ and not kJ/mol. Also, I know Dr. Lavelle talked about this in class, but why is the delta G zero at the boiling point? Thank you!

Glenda Marshall DIS 3M

In example 8.12, it talks about isothermal, free expansion. If the change in entropy of the surroundings is zero because work and change in internal energy are zero, where does the heat that goes into the system come from?

Glenda Marshall DIS 3M

Why is total change in entropy zero for a reversibly expanding gas?

Glenda Marshall DIS 3M

I understand that reversible processes do the most work and that this is what makes them ideal for thermodynamics. I am confused, however, about what makes reversible processes so effective. Why do these processes produce more work than irreversible processes. Thank you!

Glenda Marshall DIS 3M

Yeah that helps a lot! Thank you!

Glenda Marshall DIS 3M

I am very confused by question 7.75. I understand how to use the bond enthalpies to calculate delta H, but why are they subtracting the enthalpy of vaporization?

Glenda Marshall DIS 3M

In homework problem number 15, it says that delta E is zero. What is delta E and how does that help us determine work?

Glenda Marshall DIS 3M

Thank you! That definitely helps! I am still a little confused though because in the solutions manual it says that "heat lost by metal = - heat gained by water. If the water is the surroundings, then why is it negative?

Glenda Marshall DIS 3M

In this problem it says that a piece of copper at 100 degrees celsius is put into water at 22 degrees celsius. I am confused why the copper has a positive "q" value while the water has a negative "q" value. If the water is absorbing heat given off by the copper shouldn't it be th...

Glenda Marshall DIS 3M

When something is path dependent, it means that the method used to reach the final product affects the answer. For example, Dr. Lavelle use the example of two groups climbing a mountain. If one group goes straight up one side, they will exert less energy because they are just powering through and ta...

Glenda Marshall DIS 3M

I 've been told in many review sessions that it is okay to use the Henderson Hasselbalch Equation in a titration when the reaction is in the buffer region. For example: Suppose that 25mL of .10M CH3COOH is titrated with .10M NaOH. What is the pH after the addition of 10mL of .10M NaOH? After finding...

Glenda Marshall DIS 3M

In problem 12.21, I understand that the ratio of CO3 and HCO3 is related by the HH equation. However, in the answer it uses a pKa2 value. I know this value is necessary to solve the problem, so I am curious how I find it without numerical values given in the problem.

Glenda Marshall DIS 3M

Caitlin- The idea of a buffer is that whether you add an acid or a base, the pH will not change and therefore neither H30+ or OH- will be created. The reason you subtract is because, as the NaOH is added, the CH3COOH will give up it's hydrogen to neutralize the OH- in the NaOH. This the concentratio...

Glenda Marshall DIS 3M

In class today, we discussed that when an weak acid and base react, it will yield a salt and water. The conjugate base, however, reacted again with the water to form it's conjugate acid and hydroxide. When solving for the hydroxide concentration, we used the moles of the initial acid to calculate th...

Glenda Marshall DIS 3M

Why is CH3COOH weaker than HCOOH even though it has an extra carbon to help delocalize the charge?

Glenda Marshall DIS 3M

I am confused by part B of this homework problem. If the initial solution is 200 mL of NaOH, why do I only use M1V1=M2V2 once? Shouldn't I use it again with 200mL as V2?

Glenda Marshall DIS 3M

Thank you so much!

Glenda Marshall DIS 3M

I am still super confused on how to do problem 69. Can someone please explain how you can get the volume when you don't know the pressure?

Glenda Marshall DIS 3M

That was an awesome explanation. Thank you so much!

Glenda Marshall DIS 3M

I'm still confused why K changes when temperature changes. Anyone care to explain?

Glenda Marshall DIS 3M

If a molecule has an overall charge, does that automatically make it polar? For example, NH4+?

Glenda Marshall DIS 3M

I am confused about the dipole moments in question 19. Obviously, Fluorine is more electronegative than Sulfur, but how does the lone pair effect the partial charges. Does it make the sulfur more electronegative than Fluorine? And why is the molecule polar?

Glenda Marshall DIS 3M

I've noticed that the terms "angular" and "bent" seemed to be used synonymously. Is there a difference between the two?

Glenda Marshall DIS 3M

I've noticed that the terms "angular" and "bent" seemed to be used synonymously. Is there a difference between the two?

Glenda Marshall DIS 3M

In Chapter 2 problem #101, why is Zinc considered excited?

Glenda Marshall DIS 3M

In question #101 in chapter 2, it gives you a chart that you must fill out. One of the columns requests to know whether the atom is excited or in a ground state. How would you get this information from what is given?

Glenda Marshall DIS 3M

What does it mean for a certain lewis structure to have a "greater contribution" to a resonance hybrid. I know that each possible less structure contributes to the real structure, but how can one contribute more?

Glenda Marshall DIS 3M

Why is phosphorus the first element that can accommodate more than 8 electrons when silicon and aluminum also have a d level?

Glenda Marshall DIS 3M

If we picture an s-orbital as a sphere and an electron can reside anywhere inside the volume of that sphere, then why does the electron only get excited by certain wavelengths of light? I thought electrons couldn't be below or above their levels.

Glenda Marshall DIS 3M

There is a problem on the homework that gives density and percent composition of a compound and then molarity and volume of the final solution. How does the density relate to the information given and how can I use it to solve the problem?

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