Search found 39 matches

by Jar-Yee 3L
Tue Mar 08, 2016 11:07 pm
Forum: General Science Questions
Topic: Winter 2011 Final Question 1A
Replies: 1
Views: 621

Winter 2011 Final Question 1A

The question states tht we are using heat from the combustion of methane gas to boil 50.0 mL of water, and asks how many grams of methane are required. For the heat, do we include the heat required to boil the water completely to gaseous form? Or simply to reach the boiling point? Why? The wording s...
by Jar-Yee 3L
Sun Mar 06, 2016 12:04 am
Forum: *Alcohols
Topic: General Question about Functional Groups
Replies: 1
Views: 361

General Question about Functional Groups

Dr. Lavelle mentioned in class that double and triple bonds count as functional groups, right? So when we have both a double/triple bond and another functional group (alcohol, carboxyl, amine, etc) in an organic molecule, which gets priority in numbering?
by Jar-Yee 3L
Sun Feb 28, 2016 6:59 pm
Forum: *Organic Reaction Mechanisms in General
Topic: Activated Complexes v. Transition States
Replies: 1
Views: 751

Activated Complexes v. Transition States

What is the difference between an activated complex and a transition state? Number 15.85 in the textbook asks us to draw the activated complex, and I don't know what that's supposed to mean besides drawing the TS. What's the difference? Is there a difference in drawing them?
by Jar-Yee 3L
Fri Feb 26, 2016 12:50 am
Forum: *Constitutional and Geometric Isomers (cis, Z and trans, E)
Topic: self-test 1.4A
Replies: 1
Views: 412

Re: self-test 1.4A

Not at all. The parent chain consists of 5 carbons (hence pent ane), and the methyl group is attached to the third carbon. No matter from which side you count from, the methyl group will be attached to Carbon number 3. So 3 is the lowest number possible for the methyl substituent group of 3-methylpe...
by Jar-Yee 3L
Sun Feb 21, 2016 10:09 pm
Forum: *Electrophiles
Topic: Identifying an Electrophile/Nucleophile
Replies: 3
Views: 480

Identifying an Electrophile/Nucleophile

I'm confused as to what can be an electrophile/nucleophile. I understand that an electrophile (lacking electrons) could be a cation of some sort or something with a positive charge, but a nucleophile's concept confuses me. Are all nucleophiles atoms? How come bonds can be nucleophiles? And is it pos...
by Jar-Yee 3L
Tue Feb 09, 2016 2:24 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Hogwarts Problem, 2015 Midterm
Replies: 2
Views: 402

Hogwarts Problem, 2015 Midterm

I have a question about the Hogwarts Problem for the midterm. Basically, Ron screws up a spell and blows up his balloon and increases its temperature as well. How come when calculating the change in entropy produced by a temperature change, the molar heat capacity C v is used? The volume changed for...
by Jar-Yee 3L
Sun Feb 07, 2016 2:06 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Does n have units?
Replies: 2
Views: 518

Does n have units?

For the Nernst Equation and the free energy equation of voltaic cells, does n have units of moles? It makes sense for the free energy ΔG=-nFE, because (moles)(Coulombs/moles)(J/Coulombs)= J, but if n didn't have units we would end up with J/moles, which still makes sense. It doesn't make sense when ...
by Jar-Yee 3L
Sat Feb 06, 2016 11:49 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Reaction Quotient Q
Replies: 1
Views: 341

Reaction Quotient Q

I'm wondering how we deal with Q, or [P]p/[R]r for the Nernst Equation.

Occasionally, we have a mix of both partial pressures AND molarities in the reaction quotient.

How do we take into account the discrepancy between units? For example, if one is in Torr and the other is in mol/L.
by Jar-Yee 3L
Thu Feb 04, 2016 10:36 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram Notation
Replies: 2
Views: 367

Re: Cell Diagram Notation

What if the solid isn't a conductor? For example, I2 (s)?
by Jar-Yee 3L
Thu Feb 04, 2016 10:25 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: How to figure out Cathode and Anode Reactions?
Replies: 1
Views: 377

How to figure out Cathode and Anode Reactions?

I realize that reduction occurs at cathodes, and oxidation occurs at the anodes. However, given an entire, unbalanced redox reaction OR a combination of ions in solution, I find it difficult to figure out what equations to use. For example, HW 14.15b: The equation given is H + (aq) + OH - (aq) --> H...
by Jar-Yee 3L
Thu Feb 04, 2016 12:55 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram Notation
Replies: 2
Views: 367

Cell Diagram Notation

Is there a specific way to order the elements, according to their phases of matter? I know that anything to the left of the salt bridge is considered the anode (oxidation) reaction, and everything to the right of it is the cathode reaction (reduction). But within those reactions, sometimes they have...
by Jar-Yee 3L
Sat Jan 30, 2016 9:06 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Clarification on Wording
Replies: 1
Views: 302

Clarification on Wording

When we're asked to calculate "Gibbs free energy" of something, are we looking for G or ΔG?

I'm getting mixed messages with the book, so I'm rather confused.
by Jar-Yee 3L
Sun Jan 24, 2016 10:17 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.91: Calculating Free Energy of a Phase Change
Replies: 1
Views: 402

9.91: Calculating Free Energy of a Phase Change

The question asks us to calculate ΔG for the vaporization of water. ΔG = ΔH - TΔS, so I took the steps to first look up or calculate ΔH and ΔS. I got the ΔS value correct, but in this case I used ΔH vap , while the solutions manual found the ΔH using difference of sums (ΔH f of products - ΔH f of re...
by Jar-Yee 3L
Sun Jan 24, 2016 8:55 pm
Forum: Calculating Work of Expansion
Topic: What is Free Expansion? (9.47)
Replies: 3
Views: 591

Re: What is Free Expansion? (9.47)

Wait, but what's the difference between irreversible expansion and free expansion? The descriptions sound the same to me.
by Jar-Yee 3L
Sun Jan 24, 2016 6:15 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Standard Reaction Entropy vs. Standard Entropy of Formation
Replies: 1
Views: 354

Standard Reaction Entropy vs. Standard Entropy of Formation

Is there a difference to these two?

ΔSrxno vs ΔSfo.

Or is ΔSfo the same thing as ΔSmo?

I'm confused.
by Jar-Yee 3L
Sun Jan 24, 2016 12:03 am
Forum: Calculating Work of Expansion
Topic: What is Free Expansion? (9.47)
Replies: 3
Views: 591

What is Free Expansion? (9.47)

I was doing question 9.47, which asks to find change in entropy for an isothermal reversible expansion, and then an isothermal, irreversible free expansion. I used ΔS = nRln(V f /V i ) for both, which gave me the correct answer. However, when trying to calculate ΔS surr for the irreversible expansio...
by Jar-Yee 3L
Tue Jan 19, 2016 2:01 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.101: Molar Kinetic Energy
Replies: 1
Views: 328

8.101: Molar Kinetic Energy

We're asked to calculate molar kinetic energy of Kr (g) in problem 101, given a certain temperature. I understand that taking the molar heat capacity (J mol -1 K -1 ) and multiplying it by the temperature to get molar KE (J/mol). The solutions guide says that the molar heat capacity is 3R/2. This is...
by Jar-Yee 3L
Fri Jan 15, 2016 2:31 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy of Isothermal Processes
Replies: 2
Views: 423

Entropy of Isothermal Processes

For an ideal gas, ΔU=0 when ΔT=0, evidently because an ideal gas only has kinetic energy, so without heat there would be no change in internal energy. ΔU = 0 = q+w, q = -w. With ΔT = 0, then q = 0. As a result, w = -q = 0 as well. Eventually, a proof with this concept would give us ΔS=nRln(V f /V i ...
by Jar-Yee 3L
Thu Jan 14, 2016 10:17 pm
Forum: Phase Changes & Related Calculations
Topic: Isothermal Reversible Work Calculation Clarifications
Replies: 3
Views: 545

Isothermal Reversible Work Calculation Clarifications

Problem 27b states: "Calculate the work for the process beginning with a gas sample in a piston assembly with T = 305 K, P = 1.79 atm, and V = 4.29 L: ... (b) isothermal, reversible expansion to a final volume of 6.52 L." The equation for isothermal reversible processes with work is w = -n...
by Jar-Yee 3L
Wed Jan 13, 2016 10:21 pm
Forum: Phase Changes & Related Calculations
Topic: Which work equation do I use?
Replies: 3
Views: 508

Re: Which work equation do I use?

Interesting. Does this mean that I shouldn't be looking at the words "reversible" or "irreversible" in such a literal sense? If so, then how should I be looking at it?
by Jar-Yee 3L
Wed Jan 13, 2016 9:54 pm
Forum: Phase Changes & Related Calculations
Topic: Just to be clear...
Replies: 1
Views: 285

Just to be clear...

I'm just having a few problems clarifying the below equation: w = -PΔV We were told in lecture that everything in this equation, with the exception of external pressure, is in respect to the system. w sys = -P ext ΔV sys Does w sys refer to work done by the system? Or work done on the system? Or wor...
by Jar-Yee 3L
Sun Jan 10, 2016 6:08 pm
Forum: Phase Changes & Related Calculations
Topic: Which work equation do I use?
Replies: 3
Views: 508

Which work equation do I use?

In my discussion section, we were given two different equations for work. The first one is for an irreversible process: w = -P ext ΔV The second is for an isothermal reversible: w = -nRTln(v f /v i ) Both use changes in volume, but I don't know when to use one equation or the other. For example, sel...
by Jar-Yee 3L
Sun Jan 10, 2016 5:30 pm
Forum: Phase Changes & Related Calculations
Topic: Start Chapter 8 at 8.11
Replies: 10
Views: 13995

Re: Start Chapter 8 at 8.11

At what number do the section 8.11 problems begin?
by Jar-Yee 3L
Tue Dec 01, 2015 9:32 pm
Forum: Lewis Acids & Bases
Topic: Boron Trifluoride, BF3
Replies: 4
Views: 1490

Re: Boron Trifluoride, BF3

Ah, thanks. How would that affect the pH of the solution?
by Jar-Yee 3L
Tue Dec 01, 2015 9:31 pm
Forum: Polyprotic Acids & Bases
Topic: Finding Ka2 in problem 12.79
Replies: 1
Views: 411

Re: Finding Ka2 in problem 12.79

It's given. All Ka values can be searched up in the index of the textbook.

It's dumb, I know.
by Jar-Yee 3L
Sun Nov 29, 2015 8:28 pm
Forum: Lewis Acids & Bases
Topic: Boron Trifluoride, BF3
Replies: 4
Views: 1490

Re: Boron Trifluoride, BF3

You stated that it would gain an H atom.... Which isn't making sense to me. If BF 3 stripped an H atom off a water molecule, it would technically leave OH - in the solution, and actually raise the pH instead. BF 3 is a Lewis acid. Why would it raise the pH? Do the Lewis definitions of acids and base...
by Jar-Yee 3L
Sun Nov 29, 2015 8:24 pm
Forum: Polyprotic Acids & Bases
Topic: Calculating pH of alanine (HW 12.77)
Replies: 1
Views: 404

Calculating pH of alanine (HW 12.77)

We were asked to calculate the pH of a 3.38 g sample of alanine, NaCH 3 CH(NH 2 )CO 2 , dissolved in 50.0 mL of solution. We were given K a1 and K a2 . I tried doing the ICE table twice and solving for [H 3 O + ] twice, adding them up, and calculating the pH. I got 1.30 (which, I warn you now, is co...
by Jar-Yee 3L
Sun Nov 29, 2015 8:07 pm
Forum: Polyprotic Acids & Bases
Topic: Calculating the pH of a Polyprotic Solution
Replies: 1
Views: 462

Calculating the pH of a Polyprotic Solution

So in HW 12.79, we're asked to find the pH of a .15 M H 2 SO 4 solution. Since sulfuric acid is a strong acid, I assumed maximum ionization/deprotonation/dissociation and just calculated pH with -log[H 3 O + ], and did -log(.15)=.82. However, upon looking at the solutions guide, they started a new I...
by Jar-Yee 3L
Sat Nov 28, 2015 10:11 pm
Forum: Lewis Acids & Bases
Topic: Boron Trifluoride, BF3
Replies: 4
Views: 1490

Boron Trifluoride, BF3

Why is Boron Trifluoride a lewis acid? Until now I always stuck to the Bronsted-Lowry definition of acids and bases, because H + transfer was so much easier. But now I'm stuck with BF 3 , a compound which I cannot see any way to tie in with the Bronsted definitions. The only thing I can think of is ...
by Jar-Yee 3L
Thu Nov 19, 2015 4:19 pm
Forum: Coordinate Covalent Bonds
Topic: Concept of Binding Sites with Oxygen
Replies: 1
Views: 918

Concept of Binding Sites with Oxygen

So I know that some compounds have multiple binding sites, and are hence polydentate. For example, Carbonate (CO 3 2- ) and oxalate (C 2 O 4 2- ) both have oxygen atoms that can act as separate binding sites due to their negative formal charge (and hence attraction to the transition metal cation's p...
by Jar-Yee 3L
Sun Nov 15, 2015 11:39 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Weak vs. Strong Acids/Bases
Replies: 1
Views: 401

Weak vs. Strong Acids/Bases

I apologize ahead of time for the stupid questions... I understand that strong acids dissociate completely, while weak acids don't. (Same with bases) However, I don't understand how to tell a strong acid from a weak one. Is there a certain way to do that? How do I look at the chemical formula of an ...
by Jar-Yee 3L
Thu Nov 12, 2015 3:01 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K with both aqueous solutions and gases
Replies: 1
Views: 359

K with both aqueous solutions and gases

If a homogeneous equilibrium reaction consists of both reactants and products of the (aq) and (g) phases, how will we find the equilibrium constant? I'm wondering because with gases we use (P chemical ) and with aqueous solutions we use [chemical] instead. How do we incorporate both gases and aqueou...
by Jar-Yee 3L
Tue Nov 03, 2015 12:33 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Hydrogen in Molecular Orbitals
Replies: 1
Views: 258

Hydrogen in Molecular Orbitals

When bonding H and F, since the valence shells for each are different, how would we draw a molecular orbital for a single bond between the two?
by Jar-Yee 3L
Sun Oct 25, 2015 11:06 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Extent of Expanded Octets
Replies: 1
Views: 454

Extent of Expanded Octets

I realize that there are exceptions to the octet rule, and that period 3 and higher elements have d-orbitals in the valence shell that can take in extra electrons. But how many more electrons can you accommodate? Is there a set answer for certain elements? This goes back to Ch. 4 homework, question ...
by Jar-Yee 3L
Fri Oct 16, 2015 8:56 pm
Forum: Lewis Structures
Topic: Molecular Shapes
Replies: 1
Views: 285

Re: Molecular Shapes

It's because the world is in 3 dimensions. On paper (since paper is obviously 2-d), it's easier to think of all the atoms lying on a 2-dimensional plane. But the world isn't like that. A third dimension offers way more space for the atoms to move away from each other. Hence, for a tetrahedral struct...
by Jar-Yee 3L
Thu Oct 08, 2015 10:42 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Subshell vs. Orbital
Replies: 1
Views: 594

Subshell vs. Orbital

Okay... I'm really confused on one thing. Is it true that orbitals constitute subshells, which constitute shells? Or is that the wrong way to think about it? Also, when writing in a certain notation: would it be that, say, 3p would be a subshell, and 3p x an orbital? And what would be represented by...
by Jar-Yee 3L
Thu Oct 08, 2015 6:28 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration Notation
Replies: 1
Views: 527

Electron Configuration Notation

Hi all! I had a quick question on writing the notation of certain d-block atoms. I remember that Professor Lavelle suggested we write the orientation of the p orbitals to give the electron configuration notation more of a conceptual meaning. So for example, for a neutral atom of Carbon (6 protons, 6...
by Jar-Yee 3L
Wed Sep 30, 2015 7:04 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: ± vs. Δ
Replies: 4
Views: 1510

± vs. Δ

Hello everyone! In the online modules (and hopefully on Friday), Prof. Lavelle went over that the indeterminacy of a variable (ex. Δv) is equal to the size of the "spread" of the possible values for that variable. For example, if v=10±1 m/s, then the values range from 9 to 11. Hence, the i...
by Jar-Yee 3L
Wed Sep 30, 2015 6:46 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Calculating Frequency of Light Emitted by H atom
Replies: 2
Views: 438

Re: Calculating Frequency of Light Emitted by H atom

You said it yourself! While calculating ΔE, you find that ΔE= -4.09x10^-19 J. A negative value of ΔE simply tells us that there was a drop in the energy level of the electron (from the 4th energy level to the 2nd). Hence, the negative change in energy just tells us that the energy lost 4.09x10^-19 J...

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