Search found 21 matches

by Helen Meng 2J
Fri Mar 11, 2016 2:43 pm
Forum: *Alcohols
Topic: More than one functional group
Replies: 3
Views: 458

Re: More than one functional group

My TA actually said that we should know how to name molecules with two functional groups, or at least be able to recognize it because question 9B on the Winter 2015 practice final asks us to draw the molecules 1,3,4,5,6-pentahydroxy-2-hexanone and 3-hydroxypentanoic acid. These both have two functio...
by Helen Meng 2J
Mon Mar 07, 2016 11:57 am
Forum: *Cyclohexanes (Chair, Boat, Geometric Isomers)
Topic: Chair conformation
Replies: 2
Views: 339

Chair conformation

If for example we were asked to draw the most stable conformation for cyclohexane, would it matter which chair conformation we drew? I know that with substituents there is a difference, but without substituents both are equally stable right?
by Helen Meng 2J
Sat Mar 05, 2016 2:48 am
Forum: Administrative Questions and Class Announcements
Topic: Video Competition
Replies: 66
Views: 23893

Video Competition: Understanding Logarithms and Exponentials

This video was made by Linda Ye and Helen Meng of Lecture 2
by Helen Meng 2J
Sat Feb 27, 2016 6:34 pm
Forum: *Cycloalkenes
Topic: Cycloalkene with multiple double bonds
Replies: 1
Views: 225

Cycloalkene with multiple double bonds

For something that has multiple double bonds, would you use the prefixes of di, tri, etc? For example, number 1.21, the cycloalkene is called 5-methyl-cyclopenta-1,3diene. If the structure were to have three double bonds (like a cyclohexene), would we call it cyclohexa-1,3,5triene for the IUPAC name?
by Helen Meng 2J
Sun Feb 21, 2016 3:14 pm
Forum: *Complex Reaction Coordinate Diagrams
Topic: Entropy
Replies: 2
Views: 493

Re: Entropy

Another way to think of it is that entropy measures the "disorder" of the reaction. If two reactants are being bonded together to form a product, there are fewer total molecules moving around, meaning there is less disorder. This is why gases have higher entropy than solids, since gas mole...
by Helen Meng 2J
Sat Feb 13, 2016 11:24 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Comparing experiments to find order rxn
Replies: 2
Views: 266

Re: Comparing experiments to find order rxn

I think when you are comparing experiments to find the reaction order, you look for when concentrations are held constant. For example, if you have three reactants: A, B and C, and you want to find the reaction order for reactant B, you have to look for two experiments where both reactants A and C h...
by Helen Meng 2J
Mon Feb 01, 2016 9:30 pm
Forum: Balancing Redox Reactions
Topic: Confusion on cathode and anode reactions HW 14.15
Replies: 1
Views: 279

Confusion on cathode and anode reactions HW 14.15

I was doing the homework and came across problem 14.15 (a), which asks us to write the half-reactions and devise a galvanic cell to study the reaction. The equation is AgBr(s) --> Ag+(aq) + Br-(aq), a solubility equilibrium. In the solutions manual, it has these two equations for the anode and catho...
by Helen Meng 2J
Sun Jan 31, 2016 1:55 pm
Forum: Balancing Redox Reactions
Topic: Interface Between Phases
Replies: 1
Views: 240

Interface Between Phases

During lecture on Friday, Dr. Lavelle had a cell diagram "equation" in his course reader that looked something like this: Cu(s) | Cu^2+(aq) || Fe^3+(aq), Fe^2+(ag) | Pt(s) At the bottom of that cell diagram, there are notes that "|" represents the interface between phases and &qu...
by Helen Meng 2J
Sat Jan 23, 2016 12:45 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: What is meant by spontaneous reaction?
Replies: 1
Views: 249

Re: What is meant by spontaneous reaction?

According to the textbook, "a process is spontaneous if it has a tendency to occur without being driven by an external influence". Essentially, I think you are right because a spontaneous process wouldn't need any external influence, including work, to occur.
by Helen Meng 2J
Wed Jan 13, 2016 8:29 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Homework Problem 8.55
Replies: 1
Views: 200

Homework Problem 8.55

I was doing problem 8.55 in the homework, which asks us to calculate the reaction enthalpy for the production of metallic barium. 2 Ba(s) + O2(g) --> 2 BaO(s) delta H = -1107 kJ 2Al(s) + O2(g) --> Al2O3(s) delta H = -1676 kJ And then we need to calculate the reaction enthalpy for this reaction 3 BaO...
by Helen Meng 2J
Fri Jan 08, 2016 8:40 pm
Forum: Phase Changes & Related Calculations
Topic: Exothermic vs. Endothermic
Replies: 8
Views: 1412

Re: Exothermic vs. Endothermic

I believe this would be considered endothermic if we are viewing the ice pack as the system. This is because the ice pack gains energy from the knee in the form of heat. This is similar to the chemical packs Dr. Lavelle was referring to during lecture as well. With a chemical pack, the heat from the...
by Helen Meng 2J
Fri Dec 04, 2015 8:32 pm
Forum: Polyprotic Acids & Bases
Topic: When to use Ka2
Replies: 1
Views: 439

When to use Ka2

When we are calculating pH for polyprotic acids, when we do decide to ignore the second ionization? For example, for number 81 in chapter 12, the solutions manual says to ignore the second ionization because Ka2 << Ka1. How much smaller than Ka1 does Ka2 have to be for us to be able to ignore the se...
by Helen Meng 2J
Sat Nov 28, 2015 10:59 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Buffer Solutions
Replies: 1
Views: 394

Buffer Solutions

Professor Lavelle went over in class that buffer solutions can be calculated using Henderson-Hasselbalch equation. However, this only calculates the pH of the buffer. Will we need to know how to calculate when a buffer runs out? If so, how would we go about doing this? Will we also have to know what...
by Helen Meng 2J
Sat Nov 21, 2015 5:06 pm
Forum: Polyprotic Acids & Bases
Topic: Ka's
Replies: 1
Views: 250

Re: Ka's

I believe Lavelle went over this in his lecture, but it was near the end, so he might have had different amounts of time to cover it for different lectures. In our lecture, he stated that it is harder to lose H+ from a negatively charged ion. For example, if you take the example we went over in clas...
by Helen Meng 2J
Sat Nov 14, 2015 9:23 pm
Forum: Naming
Topic: Naming of Fe(CO)5
Replies: 2
Views: 227

Re: Naming of Fe(CO)5

I think both ways are fine because in Lavelle's green workbook, one of the questions involved Cu, and then the answer said you could use cuprate or copper. If you want reference, it's question number 9 from the Fall 2013 quiz for quiz 3.
by Helen Meng 2J
Sun Nov 08, 2015 5:26 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: How does arrangement affect forming a Chelating Complex?
Replies: 2
Views: 313

How does arrangement affect forming a Chelating Complex?

I'm a bit confused about one of the problems from the homework, number 35 from chapter 17, which asks which of the three lewis structures can form a chelating complex. The solutions manual says that the NH2 from drawing (a) and drawing (c) wouldn't be able to coordinate to the same metal center. Why...
by Helen Meng 2J
Sun Nov 01, 2015 5:09 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Molecular Orbital Diagrams
Replies: 1
Views: 270

Molecular Orbital Diagrams

I'm still a bit confused about MO theory in general, but in particular, I had a question about the diagrams. How do you determine when the sigma 2p is above pi 2p and vice versa? I was at the study session for Professor Lavelle and for two molecules, he had a different ordering for the MO diagrams. ...
by Helen Meng 2J
Sat Oct 24, 2015 2:13 pm
Forum: Hybridization
Topic: 4.39 from Homework
Replies: 1
Views: 275

4.39 from Homework

Could someone explain to me why P4, white phosphorous, has the lewis structure given in the solutions manual? Why does it form a diamond and connect in the middle, as opposed to most lewis structures where there is a central atom connected to other atoms?
by Helen Meng 2J
Sat Oct 24, 2015 2:04 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: When to use Double and Triple Bonds
Replies: 2
Views: 4797

When to use Double and Triple Bonds

When I'm drawing Lewis Structures, sometimes I get confused as to when I need to add a double or triple bond. Are there any tricks to figure out when to use these, or do I just need to practice more until I see more examples of when these bonds come into play? Thanks!
by Helen Meng 2J
Sat Oct 10, 2015 10:25 am
Forum: Properties of Light
Topic: Deriving Rydberg Equation
Replies: 1
Views: 548

Deriving Rydberg Equation

During our discussion on Thursday, our TA mentioned that the R that Professor Lavelle uses is different from the R in the book, so it's best to derive the Rydberg equation instead of memorizing it. He showed us how to do it, but I am still a bit confused. Could someone please elaborate on deriving t...
by Helen Meng 2J
Sat Oct 03, 2015 1:43 am
Forum: Properties of Light
Topic: Manipulating the Rydberg Equation
Replies: 1
Views: 456

Manipulating the Rydberg Equation

In lecture on Wednesday, Professor Lavelle went over the Rydberg equation and said that it only applies for Hydrogen. He also mentioned that there was a way to manipulate it so that it could work for other Hydrogen-like elements. I don't know if anyone already asked this or not, but is this somethin...

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