Search found 53 matches

Sat Mar 17, 2018 2:31 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.27
Replies: 1
Views: 142

Re: 14.27

you can cancel the F
Sat Mar 17, 2018 12:03 pm
Forum: Phase Changes & Related Calculations
Topic: Reversible Expansions
Replies: 3
Views: 368

Re: Reversible Expansions

In a TA review session he explained that when you have a rev process you are extracting the max work bc you are making such small changes that you can appoximate P-internal = P-external at every instant. PV=nRT. P=nRT/v. substitute w=-nRT/V and integrate w respect to V. this is where you get w = -nR...
Sat Mar 17, 2018 11:58 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 14.93
Replies: 1
Views: 288

Re: 14.93

Sat Mar 17, 2018 11:58 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Concentration cells
Replies: 2
Views: 278

Re: Concentration cells

Sat Mar 17, 2018 11:55 am
Forum: *Nucleophiles
Topic: nucleophile?
Replies: 4
Views: 723

Re: nucleophile?

nucleophiles also usually have a partial - charge like the example from the lecture.
Sat Mar 17, 2018 11:53 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: State functions?
Replies: 9
Views: 666

Re: State functions?

Why are heat and work not state functions? G H and S are all quantities of energy (in the form of heat or disorder) contained within a compound. Work and heat are CHANGES in energy. How you change energy depends on the PATH. your altitude on a mountain = state function = G H S how you got to the to...
Sat Mar 17, 2018 11:48 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Question 14.41
Replies: 6
Views: 524

Re: Question 14.41

You want e- to flow anode to cathode. At the anode Cu(s) > Cu2+ + 2e-. At the cathode Cu2+ + 2e- > Cu(s). So the anode [] is a product and cathode [] is a reactant. Since you want postive E and Q=P/R, so, using the eq, you can see that anode should always have lower [].
Sat Mar 17, 2018 11:42 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram: Porous Disk and Salt Bridge
Replies: 5
Views: 383

Re: Cell Diagram: Porous Disk and Salt Bridge

Sat Mar 17, 2018 11:39 am
Forum: *Nucleophilic Substitution
Topic: Transition States
Replies: 3
Views: 1126

Re: Transition States

I use this:

A---B--C is the transition state since it has a lot of energy, and shows the collision of the particles.
Sat Mar 17, 2018 11:28 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Activation Energy
Replies: 5
Views: 446

Re: Activation Energy

In the question below, each peak is an activation energy of a step in the reaction. The top of each peak represents an activated complex / transition state.
Sat Mar 17, 2018 11:23 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy of Surroundings vs. System
Replies: 2
Views: 304

Re: Entropy of Surroundings vs. System

When you ADD heat, ∆H is +. Ex - adding heat to boil water has +∆H, so ∆S = +∆H/T.
Sat Mar 17, 2018 11:19 am
Forum: Phase Changes & Related Calculations
Topic: Sign for compression vs expansion
Replies: 4
Views: 406

Re: Sign for compression vs expansion

W=-P∆V. ∆V = V_f - V_i.
Sat Mar 17, 2018 11:17 am
Forum: Balancing Redox Reactions
Topic: Ranking elements
Replies: 8
Views: 625

Re: Ranking elements

I like to keep this chart in mind.
Sat Mar 17, 2018 11:14 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Homework 14.17
Replies: 2
Views: 209

Re: Homework 14.17

I attached my work:

I wrote down the potentials for all the possible 1/2 reactions, and found the pair that summed to the most +, since this is a galvanic cell (E>0). Then you just balance and add them. :)
Sat Mar 17, 2018 10:50 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Total entropy change determining spontaneity
Replies: 3
Views: 344

Re: Total entropy change determining spontaneity

Since total entropy of an isolated system must always increase (2nd law) - then ∆S_tot must always be positive. Order cannot come from disorder without an input on energy. For example, think about freezing ice. Liquid > solid is a decrease of energy, but you must put in MORE energy (electrical from ...
Sat Mar 17, 2018 10:44 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: total entropy of the system
Replies: 3
Views: 317

Re: total entropy of the system

Sat Mar 17, 2018 10:43 am
Forum: Biological Examples (*DNA Structural Transitions, etc.)
Topic: 9.69
Replies: 1
Views: 663

Re: 9.69

You get a -dG from the two reactions, and this energy is used to drive the ATP production. It's a transfer of energy between two separate entities, so the heat given off by the two reactions is used to make ATP. Like hot water mixing with cold water, the hot water gives off energy and the cold water...
Thu Mar 15, 2018 8:20 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Gibbs and Activation Energy
Replies: 4
Views: 428

Gibbs and Activation Energy

Hi! Is there a relationship between Gibbs energy and activation energy? Thanks! :)
Wed Mar 14, 2018 12:43 pm
Forum: *Free Energy of Activation vs Activation Energy
Topic: 4.29 Green book
Replies: 3
Views: 1451

Re: 4.29 Green book

this can be seen in the arrhenius equation:

https://www.chemguide.co.uk/physical/basicrates/arrhenius.html
Wed Mar 14, 2018 12:39 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.53
Replies: 3
Views: 375

Re: 8.53

Christy Zhao 1H wrote:How do you know to use the equation $\Delta U=(3/2)nR\Delta T$ ?

Since its in a bomb calorimeter, the volume is held constant, so c=3/2R for an ideal gas.
Wed Mar 14, 2018 12:37 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Is enthalpy a state function?
Replies: 12
Views: 1186

Re: Is enthalpy a state function?

You can think of the enthalpy of formation as the heat stored in the bonds of the molecule, formed from its components.
Mon Mar 05, 2018 12:42 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: rate order vs contribution to overall rate
Replies: 3
Views: 268

Re: rate order vs contribution to overall rate

How does the overall rate indicate these relationships?
Mon Mar 05, 2018 12:41 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 0 order
Replies: 6
Views: 2211

Re: 0 order

How does this graphic representation correlate to the presence of a catalyst?
Mon Mar 05, 2018 12:39 pm
Forum: *Free Energy of Activation vs Activation Energy
Topic: Endergonic and exergonic free energy reaction profiles?
Replies: 2
Views: 1263

Re: Endergonic and exergonic free energy reaction profiles?

I believe these terms are used to refer to the same reactions as exothermic and endothermic.
Wed Feb 28, 2018 12:37 pm
Forum: First Order Reactions
Topic: 15.15
Replies: 4
Views: 292

Re: 15.15

Since the rate increase is linear to reactant concentration increase, it implies it's first order.
Wed Feb 28, 2018 12:36 pm
Forum: First Order Reactions
Topic: Direct Proportions and First Order
Replies: 5
Views: 297

Re: Direct Proportions and First Order

First order indicates that doubling the reactant concentration doubles the rate because rate = k [A]^1
Wed Feb 28, 2018 12:34 pm
Forum: Zero Order Reactions
Topic: Half-life of Zero Order [ENDORSED]
Replies: 4
Views: 329

Re: Half-life of Zero Order[ENDORSED]

I thought we only needed to know half-lives for first-order reactions?
Mon Feb 19, 2018 3:05 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 14.33
Replies: 1
Views: 206

Re: 14.33

∆G is a state function, so you can add them. E_cell is NOT a state function, so you can't simply add them. This is why you have to convert to ∆G and back to E.

viewtopic.php?t=3754
Mon Feb 19, 2018 3:02 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 14.51
Replies: 1
Views: 172

Re: 14.51

I interpreted it as there is a flow of electrons, which, if put into a circuit, would allow for electric work to be used, despite electrons are flowing cathode to the anode.
Mon Feb 19, 2018 2:59 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Problem 14.23 (b)
Replies: 1
Views: 208

Re: Problem 14.23 (b)

Br is the anode since its losing electrons, going from Br- to Br2(l). Br2(l) has an oxidation number of 0, while Br- has an oxidation number of -1. The reverse logic can be used on Hg.
Mon Feb 19, 2018 2:57 pm
Forum: Balancing Redox Reactions
Topic: 14.15c
Replies: 2
Views: 217

Re: 14.15c

Vincent Chiang 1L wrote:The KOH is there as a salt bridge to allow for the flow of ions.

Thank you! How are we supposed to know its KOH? Is this a common convention, like Pt(s)? Thanks!
Sun Feb 18, 2018 1:02 pm
Forum: Balancing Redox Reactions
Topic: 14.15c
Replies: 2
Views: 217

14.15c

Hi! I was wondering why in the solutions manual potassium is included in the final cell diagram? Thanks!
Thu Feb 15, 2018 9:12 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Delta G= Wmax
Replies: 8
Views: 996

Re: Delta G= Wmax

Whats the relationship between free energy and max work - are they equal?
Thu Feb 15, 2018 9:11 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Units for Gibbs Free Energy
Replies: 4
Views: 487

Re: Units for Gibbs Free Energy

When a problem asks for Gibbs Free energy in "kJ" does this mean kJ/mol or just kJ?
Thu Feb 15, 2018 9:10 am
Forum: Balancing Redox Reactions
Topic: Salt Bridges
Replies: 14
Views: 616

Re: Salt Bridges

In a battery, like a AAA battery, what serves as a salt bridge?
Wed Feb 07, 2018 7:03 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.83
Replies: 3
Views: 515

Re: 11.83

This isn't what the solution manual says? Can someone explain how to approach this problem?
Mon Feb 05, 2018 2:23 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge [ENDORSED]
Replies: 4
Views: 801

Re: Salt Bridge[ENDORSED]

What is the porous disk composed of? Does it act differently than the salt bridge in any way?
Mon Feb 05, 2018 2:22 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode and Cathode [ENDORSED]
Replies: 4
Views: 402

Re: Anode and Cathode[ENDORSED]

I may be remembering incorrectly, but in high school, I remember one side being negative and the other positive, is this convention used? If so which side correlates to which sign? Thanks!!
Mon Feb 05, 2018 2:21 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Determining reduction or oxidation
Replies: 4
Views: 761

Re: Determining reduction or oxidation

The ion which is reduced will gain electrons, and its oxidation number will decrease. On the other hand, the ion which is oxidized will lose electrons and its oxidation number will increase.
Thu Feb 01, 2018 2:08 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Regarding the equation deltaS=nCln(Tf/Ti)
Replies: 3
Views: 533

Re: Regarding the equation deltaS=nCln(Tf/Ti)

Also, when do we need to include n, the number of moles, as I see it omitted in some forms of the equations? Thanks!
Thu Feb 01, 2018 2:07 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.11 [ENDORSED]
Replies: 3
Views: 271

Re: 9.11[ENDORSED]

We also use P1/P2 as opposed to V2/V1 since pressure and volume are inversely related. P1V1=P2V2.
Thu Feb 01, 2018 2:06 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: sign of entropy
Replies: 11
Views: 762

Re: sign of entropy

Additionally, during a process of expansion entropy increases as there are more possible states.
Tue Jan 23, 2018 4:38 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: When to use Cv or Cp? to calculate change in Entropy
Replies: 3
Views: 1271

Re: When to use Cv or Cp? to calculate change in Entropy

It depends on the type of system the reaction is being carried out in. If the problem specifies that it is isothermal, use Cp. It it is being carried out in isochoric, use Cv. If it is isobaric, use Cp to calculate q because pressure is not changing and change in volume will be accounted for in cal...
Tue Jan 23, 2018 4:36 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Irreversible vs. Reversible [ENDORSED]
Replies: 10
Views: 826

Re: Irreversible vs. Reversible[ENDORSED]

To clarify: will irreversible expansion be in test #1? I thought Dr. Lavelle said that it would not be tested, but it appears in the assigned homework problems? Thanks!
Tue Jan 23, 2018 4:36 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Irreversible vs. Reversible [ENDORSED]
Replies: 10
Views: 826

Re: Irreversible vs. Reversible[ENDORSED]

To clarify: will irreversible expansion be in test #1? I thought Dr. Lavelle said that it would not be tested, but it appears in the assigned homework problems? Thanks!
Tue Jan 23, 2018 4:32 pm
Forum: Administrative Questions and Class Announcements
Topic: Week 3 Test Topic is endorsed
Replies: 37
Views: 3064

Re: Week 3 Test Topic is endorsed

Will we be tested on memorizing the formulas in section 8.10: A Molecular Interlude: The Origin of the Heat Capacities of Gases? Thanks!
Sun Jan 21, 2018 1:04 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Equipartition theorem and Degrees of Freedom
Replies: 1
Views: 142

Equipartition theorem and Degrees of Freedom

Hi! I was wondering if we need to know the Equipartition theorem and Degrees of Freedom and the formulas for test 1, as I don't remember going over it in class? Thanks!
Tue Jan 16, 2018 7:54 pm
Forum: Phase Changes & Related Calculations
Topic: Steam burning more than water question
Replies: 4
Views: 218

Re: Steam burning more than water question

This can be seen in the phase change diagram, as the long section during which heat is added to change liquid to gas represents a significant amount of energy. This energy, when transferred to a hand, causes a more severe burn.
Tue Jan 16, 2018 7:52 pm
Forum: Phase Changes & Related Calculations
Topic: Types of Systems
Replies: 10
Views: 869

Re: Types of Systems

Is there a type of system which somehow exchanges particles but not heat? Or is this impossible?
Tue Jan 16, 2018 7:50 pm
Forum: Phase Changes & Related Calculations
Topic: Gas Law
Replies: 2
Views: 242

Re: Gas Law

Additionally, it seems, that in the textbook we can usually assume the gas is behaving ideally, unless stated otherwise? Someone correct me if I'm wrong.
Thu Jan 11, 2018 10:15 am
Forum: Phase Changes & Related Calculations
Topic: Exothermic Rxn
Replies: 6
Views: 500

Re: Exothermic Rxn

Is there another way to determine if a reaction can occur spontaneously?
Thu Jan 11, 2018 10:05 am
Forum: Administrative Questions and Class Announcements
Topic: Constants & Equations Sheet
Replies: 3
Views: 227

Re: Constants & Equations Sheet

Is this sheet posted anywhere so we can start working with it? Thanks!
Thu Jan 11, 2018 10:01 am
Forum: Administrative Questions and Class Announcements
Topic: Lecture Outline
Replies: 2
Views: 236

Lecture Outline

Does anyone know if there is a schedule posted anywhere which outlines which sections of the book correspond to each lecture? Thanks :)

Go to advanced search