Search found 16941 matches

by Chem_Mod
Wed Feb 27, 2019 7:14 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: #14.15 a
Replies: 1
Views: 31

Re: #14.15 a

Can you please clarify your question?
by Chem_Mod
Wed Feb 27, 2019 7:13 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L7 and 9
Replies: 2
Views: 40

Re: 6L7 and 9

Can you please copy the text of the question for reference?
by Chem_Mod
Wed Feb 27, 2019 7:13 pm
Forum: Balancing Redox Reactions
Topic: Aq to Aq or S to Aq (14.13d) [ENDORSED]
Replies: 2
Views: 47

Re: Aq to Aq or S to Aq (14.13d) [ENDORSED]

In this case, you will need an electrode to conduct, so Ag(s) is used instead of the aqueous form.
by Chem_Mod
Wed Feb 27, 2019 7:13 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6th edition 14.13 d [ENDORSED]
Replies: 5
Views: 90

Re: 6th edition 14.13 d [ENDORSED]

Can you please post the cell diagram from the book for reference? They are writing it in this manner because they would need to add an electrode, and solid gold can serve as that electrode in the solution.
by Chem_Mod
Wed Feb 27, 2019 7:10 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Problem 14.17- Sixth Edition
Replies: 1
Views: 31

Re: Problem 14.17- Sixth Edition

Notice that the two compounds are ionic, so they will dissociate into their respective metal ions. You can decide which will be the anode half reaction based on which has the higher oxidation potential, and will more want to give up its electrons.
by Chem_Mod
Wed Feb 27, 2019 7:09 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L9
Replies: 1
Views: 33

Re: 6L9

If both the reactants and products for a given half reaction are aqueous metal ions, they are written with the lowest charge closest to the salt bridge and the highest charge closer to the edge of the notation.
by Chem_Mod
Wed Feb 27, 2019 7:09 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.29
Replies: 1
Views: 32

Re: 14.29

If both the reactants and products for a given half reaction are aqueous metal ions, they are written with the lowest charge closest to the salt bridge and the highest charge closer to the edge of the notation.
by Chem_Mod
Wed Feb 27, 2019 7:07 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: platinum [ENDORSED]
Replies: 6
Views: 63

Re: platinum [ENDORSED]

I2 is not a metal, and therefore it cannot act as a conductor. Because of this, you will need platinum.
by Chem_Mod
Wed Feb 27, 2019 7:07 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L. 9
Replies: 1
Views: 41

Re: 6L. 9

In this case, they are giving you two ionic compounds that you know will dissociate in water. Because of this, you should be working strictly with the metal ions for the overall redox reaction. You know that iron will be at the anode because it has a higher oxidation potential than potassium, so it ...
by Chem_Mod
Wed Feb 27, 2019 7:06 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Half Reactions [ENDORSED]
Replies: 1
Views: 31

Re: Half Reactions [ENDORSED]

Because the OH- is already present, you can assume this is a basic reaction. If this were in an acidic reaction, the OH- would interact with H+ to form water, and therefore you would not be able to have OH- present.
by Chem_Mod
Wed Feb 27, 2019 7:04 pm
Forum: Balancing Redox Reactions
Topic: 6.K.3 Part d
Replies: 1
Views: 31

Re: 6.K.3 Part d

Can you please clarify your question?
by Chem_Mod
Wed Feb 27, 2019 6:59 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: question 14.29
Replies: 1
Views: 15

Re: question 14.29

Do you have a specific question in mind? You can always check the initial and final oxidation states of atoms in the compounds if you are given an unbalanced reaction to see which ones are being reduced or oxidized, and are therefore the oxidizing or reducing agents respectively.
by Chem_Mod
Wed Feb 27, 2019 6:58 pm
Forum: Balancing Redox Reactions
Topic: 14.17 6th Edition [ENDORSED]
Replies: 2
Views: 47

Re: 14.17 6th Edition [ENDORSED]

You are exactly right! They are not participating in the reaction, so they do not need to be included.
by Chem_Mod
Wed Feb 27, 2019 6:57 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: help on 14.24 b and c
Replies: 1
Views: 21

Re: help on 14.24 b and c

Try balancing each of the components of the reactants (Hydrogen and Oxygen gas) going to water. For example: O_{2} + 2H^{+} + 2e^{-} \rightarrow H_{2}O For acidic solutions, you should always add water to balance the oxygens, hydrogen ions to balance hydrogens, and then electrons to balance the over...
by Chem_Mod
Wed Feb 27, 2019 6:55 pm
Forum: Balancing Redox Reactions
Topic: 14.1d [ENDORSED]
Replies: 1
Views: 18

Re: 14.1d [ENDORSED]

I assume you mean a 3 in front of C 2 H 5 OH and C 2 H 4 O. You need a 3 to balance the number of electrons. Remember that when you add the oxidation and reduction equations, you must cancel out the electrons (they must be equal on both sides). Because the carbon compound oxidation half reaction onl...
by Chem_Mod
Wed Feb 27, 2019 6:40 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Cell Potential [ENDORSED]
Replies: 2
Views: 30

Re: Standard Cell Potential [ENDORSED]

The above answer is correct. The standard cell potential can be used to tell you the difference in voltage between two electrodes, and this difference is caused by the flow of electrons from one cell to the other. You can also use the standard cell potential to tell you the spontaneity of reaction. ...
by Chem_Mod
Wed Feb 27, 2019 6:32 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.15, part a (6th edition) [ENDORSED]
Replies: 1
Views: 30

Re: 14.15, part a (6th edition) [ENDORSED]

I believe the solutions manual gives the Ag as being solid, not aqueous. In this case, the left side of the equation would have an oxidation number of 0, and the right would have an oxidation number of -1. Remember that this reaction is flipped when you reverse the anode, which would show the loss o...
by Chem_Mod
Wed Feb 27, 2019 6:20 pm
Forum: Balancing Redox Reactions
Topic: 14.13 6th edition [ENDORSED]
Replies: 2
Views: 55

Re: 14.13 6th edition [ENDORSED]

Platinum is used as a conductor in galvanic cells as it is an inert metal that will not participate in the reaction. If you do not have another conducting metal on either side (meaning you need one for the cathode AND one for the anode), you must add Pt. Some examples of common conductors include co...
by Chem_Mod
Wed Feb 27, 2019 6:17 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Given standard reduction potentials [ENDORSED]
Replies: 2
Views: 25

Re: Given standard reduction potentials [ENDORSED]

This is correct. When you flip the equation to represent an oxidation (loss of electrons), you would also flip the sign of the reduction potential. However, keep in mind that if you calculate the E value for the cell at this point, you would add the two equations together, as well as the two E value...
by Chem_Mod
Wed Feb 27, 2019 11:55 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Why does a cathode become negatively charged?
Replies: 1
Views: 35

Re: Why does a cathode become negatively charged?

Well, think of what's happening on the cathode side. Cu2+ is converted to Cu, leading to a decrease in positive charge. Relative to the beginning of the experiment, the cathode side is more negative. This is why positive ions are attracted to the cathode side, as there is a decrease in positive char...
by Chem_Mod
Tue Feb 26, 2019 1:51 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Adding inert metal
Replies: 1
Views: 19

Re: Adding inert metal

For each cell diagram you need a conducting metal as the electrode, if your reduction and oxidation each consist of a solid metal that is going to metal ions then you don't need to add an inert metal electrode because the solid metal will act as either your anode or cathode. If however, you have two...
by Chem_Mod
Tue Feb 26, 2019 1:45 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Liquids as cathode/anode
Replies: 1
Views: 13

Re: Liquids as cathode/anode

Mercury, whose chemical symbol is Hg, is the only metal that is a liquid at room temperature. In general only solid metals are electrodes, but since Hg is a liquid at room temp and is a metal it can conduct electricity as a liquid and should be considered as the electrode. Since this is the only liq...
by Chem_Mod
Tue Feb 26, 2019 1:36 pm
Forum: Van't Hoff Equation
Topic: solving van't hoff equation
Replies: 1
Views: 35

Re: solving van't hoff equation

For the traditional van't hoff equation where lnK=-\frac{\Delta H}{RT} + \frac{\Delta S}{R} obviously R is constant, and assuming we know \Delta H and \Delta S at a given temperature T we can calculate K. If you are referring to the version of the van't hoff equation where you can convert between tw...
by Chem_Mod
Tue Feb 26, 2019 1:17 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 7th Edition 6L.5
Replies: 1
Views: 29

Re: 7th Edition 6L.5

You are correct that I 2 is a solid, however that does not mean it is a conduction solid, ie a metal. I 2 is a solid but it is an insulator and as such would not conduct electricity as an electrode, so you need some other type of electrode to conduct the electrons that are being produced. This is wh...
by Chem_Mod
Tue Feb 26, 2019 1:14 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: test 2
Replies: 6
Views: 83

Re: test 2

You need to know all material covered in class from last week as well as all of the book material that the lectures were from. So this is the outline 5 up to and including the line "Explain the relationship between free energy and cell potential (∆G = - n F E)."
by Chem_Mod
Tue Feb 26, 2019 12:38 pm
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 179
Views: 5645

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Karyn Nguyen 1K wrote:When we balance the equations on worksheet 7, how do we know which side of the reaction to add H2O to?


Usually add H2O to the opposite side you added H+ or OH- in order to balance the number of O and H atoms
by Chem_Mod
Tue Feb 26, 2019 12:37 pm
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 179
Views: 5645

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Karyn Nguyen 1K wrote:For the worksheet 7 (electrochem) question 2, I don't get why the E value would cause C to be false. Can someone explain this to me please?


In order for a spontaneous reaction to occur, total E must be a positive value and when you add up the values for answer choice c, it is negative.
by Chem_Mod
Tue Feb 26, 2019 12:35 pm
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 179
Views: 5645

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Can someone please explain #4 on the electrochem worksheet? I don't understand why the answer is Ag+ not Fe2+ Since you want copper to spontaneously reduce, then you need to check the oxidation values of elements/options given. In order to have a spontaneous reaction with copper reducing, the cell ...
by Chem_Mod
Tue Feb 26, 2019 12:11 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram and Ecell [ENDORSED]
Replies: 6
Views: 1281

Re: Cell Diagram and Ecell [ENDORSED]

Using what I discussed in class, and the example I did in class: ANODE (LEFT) || CATHODE (RIGHT) Cu(s) | Cu 2+ (aq) || Fe 3+ (aq), Fe 2+ (aq) | Pt(s) Put the conducting solids (electrodes) on the outside and aqueous next to the salt bridge. Always include phase in the equation and cell diagram. In a...
by Chem_Mod
Mon Feb 25, 2019 7:42 pm
Forum: Administrative Questions and Class Announcements
Topic: Test 2
Replies: 1
Views: 61

Re: Test 2

Yes. I provide these in all my tests and exams.
by Chem_Mod
Mon Feb 25, 2019 4:38 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: reversing reaction [ENDORSED]
Replies: 3
Views: 47

Re: reversing reaction [ENDORSED]

There are two methods that you can use: 1) E(cell) = E(cathode) - E(anode) E values represent the reduction potential. For your anode, oxidation occurs, so the the total energy of the cell is found by the above equation. 2) Write out all the half reactions, explicitly. You can "reverse" on...
by Chem_Mod
Mon Feb 25, 2019 4:38 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy [ENDORSED]
Replies: 1
Views: 37

Re: Gibbs Free Energy [ENDORSED]

∆G will only equal zero at equilibrium. ∆G˚ is equal to zero in the unusual situation that K (equilibrium constant) is equal to 1 at that temperature. It is unusual because K=1 means that for a simple reaction (R--> P) the concentrations of both the reactant and product are equal. This implies these...
by Chem_Mod
Mon Feb 25, 2019 4:28 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 7th edition, 6M.1 [ENDORSED]
Replies: 1
Views: 63

Re: 7th edition, 6M.1 [ENDORSED]

Since the M electrode is on the left, it is assumed to be the anode for the purpose of measuring the cell potential; therefore, the Cu electrode is the cathode. The M(s)|M+(aq) is probably a typo and should be M(s)|M2+(aq).
by Chem_Mod
Mon Feb 25, 2019 4:22 pm
Forum: Balancing Redox Reactions
Topic: Friday Lecture Example [ENDORSED]
Replies: 2
Views: 45

Re: Friday Lecture Example [ENDORSED]

A solid electrode is required for these half reactions to occur. Platinum was used for the cathode, but an iron electrode could also be used for the cathode.
by Chem_Mod
Mon Feb 25, 2019 4:12 pm
Forum: Biological Examples (*DNA Structural Transitions, etc.)
Topic: Examples for Final [ENDORSED]
Replies: 1
Views: 72

Re: Examples for Final [ENDORSED]

You should be aware of examples in class, but always be aware of how to apply concepts to other examples as well. I noticed you posted this under "Biological examples (DNA Structural Transition, etc.)" which is a topic no longer on the syllabus. Did you mean a different topic? Thermodynami...
by Chem_Mod
Mon Feb 25, 2019 4:11 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibb's Free Energy and Spontaniety [ENDORSED]
Replies: 1
Views: 39

Re: Gibb's Free Energy and Spontaniety [ENDORSED]

Yes, the products are always favored in a spontaneous reaction. You can think of Gibb's free energy representing a balance between the two main thermodynamic forces of enthalpy and entropy. The equation is below: \Delta G = \Delta H - T\Delta S As you can see, the delta G value is dependent on the v...
by Chem_Mod
Mon Feb 25, 2019 4:10 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Max Potential [ENDORSED]
Replies: 1
Views: 31

Re: Max Potential [ENDORSED]

The max potential occurs at initial conditions for the voltaic cell set up. Initially, current flow is high, and slows down over time. We want to calculate the maximum potential, which is the maximum amount of work done, which means we don't want current to have flown yet. So we want the very beginn...
by Chem_Mod
Mon Feb 25, 2019 4:09 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 11.83 6th ed // delta G equation [ENDORSED]
Replies: 1
Views: 41

Re: 11.83 6th ed // delta G equation [ENDORSED]

You are correct; you can use either equation to calculate ∆G° at 25 °C, but just keep in mind that on an exam, you will need to know both methods as you may only be given the information to use one of the methods. For example, you may not be given the enthalpy or you may not be given the individual ...
by Chem_Mod
Mon Feb 25, 2019 4:08 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell diagrams [ENDORSED]
Replies: 1
Views: 41

Re: Cell diagrams [ENDORSED]

The textbook suggests reactant|product for different phases and Ox,Red for the same phase, although the reactant|product convention is not strictly followed in the textbook. Inert metals should be on the outside. Every species in the reaction should be included explicitly or implicitly. For instance...
by Chem_Mod
Mon Feb 25, 2019 4:06 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Porous disk [ENDORSED]
Replies: 1
Views: 24

Re: Porous disk [ENDORSED]

A porous disk just indicates that the solutions are in the same container and allows the two solutions to exchange ions. The function of the porous disk is the same as a salt bridge between two beakers.
by Chem_Mod
Mon Feb 25, 2019 4:04 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cells [ENDORSED]
Replies: 1
Views: 26

Re: Galvanic Cells [ENDORSED]

No, galvanic cells involve a chemical change, so the anode or cathode will always change somehow.
by Chem_Mod
Mon Feb 25, 2019 4:03 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic cells [ENDORSED]
Replies: 1
Views: 28

Re: Galvanic cells [ENDORSED]

Galvanic cells are used to create electric potentials for a variety of uses. Batteries are galvanic cells, so they are actually an extremely common form of chemistry in the real world.
by Chem_Mod
Mon Feb 25, 2019 4:02 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6th Ed. 14.23 [ENDORSED]
Replies: 2
Views: 44

Re: 6th Ed. 14.23 [ENDORSED]

Hg(l) is a pure conductor
by Chem_Mod
Mon Feb 25, 2019 3:57 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 7th 6L.7 / 6th #15 [ENDORSED]
Replies: 1
Views: 45

Re: 7th 6L.7 / 6th #15 [ENDORSED]

You need to come up with two half reactions that sum to the overall reaction. The best way might be to choose one species from the reaction and write down a reduction reaction that includes it. Then subtract (reverse and add) this reduction reaction from the original reaction to get the correspondin...
by Chem_Mod
Mon Feb 25, 2019 3:41 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Maxwell Boltzmann Distribution Curve [ENDORSED]
Replies: 1
Views: 35

Re: Maxwell Boltzmann Distribution Curve [ENDORSED]

It is graphically represented in a plot of speed vs. probability (or fraction).
by Chem_Mod
Mon Feb 25, 2019 3:32 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6th edition page 578 [ENDORSED]
Replies: 1
Views: 27

Re: 6th edition page 578 [ENDORSED]

Zn 2+ (aq) is actually not reduced, it is formed from the oxidation of Zn(s). However, when we measure the standard reduction potential, we assume the species is being reduced by the standard hydrogen electrode and write the reduction reaction on paper. When we report the standard reduction potentia...
by Chem_Mod
Mon Feb 25, 2019 3:12 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: I2 (s)
Replies: 1
Views: 29

Re: I2 (s)

It will produce electricity if you include it in an aqueous half-cell and couple it to another half-reaction with a higher reduction potential. If you meant why won't it conduct electricity, it's because it is not a metallic solid.
by Chem_Mod
Mon Feb 25, 2019 3:03 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Problem question
Replies: 1
Views: 40

Re: Problem question

The solutions manual actually says:
Pt(s)|Fe3+(aq), Fe2+(aq)||H+(aq), MnO4(aq), Mn2+(aq)|Pt(s)
The Pt(s) is necessary because there is no pure conductor involved in the reaction. The H+(aq) is included because the permanganate solution was specified as acidic.
by Chem_Mod
Mon Feb 25, 2019 2:55 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Help on 14.11d
Replies: 1
Views: 34

Re: Help on 14.11d

H+(aq) means there is water in the electrode. Water contains oxygen with a –2 oxidation state. Therefore, the water is being oxidized to O2(g) (oxidation state of 0). Similarly, in the other electrode, O2(g) (oxidation state 0) is being reduced to OH(aq) (oxidation state –2).
by Chem_Mod
Mon Feb 25, 2019 2:47 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6M.1 7th Ed
Replies: 1
Views: 24

Re: 6M.1 7th Ed

A half-cell is neither a cathode nor an anode until it is coupled to another electrode.
by Chem_Mod
Mon Feb 25, 2019 2:45 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.17 6th Edition
Replies: 1
Views: 30

Re: 14.17 6th Edition

Only one of the reduction reactions of permanganate (MnO4) involves acid in the table.
by Chem_Mod
Mon Feb 25, 2019 2:40 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Example 4J.4 in 7th ed textbook
Replies: 1
Views: 28

Re: Example 4J.4 in 7th ed textbook

The activity of pure solids is defined to be exactly 1.
by Chem_Mod
Mon Feb 25, 2019 2:36 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Example 4J.1 in 7th ed textbook
Replies: 1
Views: 29

Re: Example 4J.1 in 7th ed textbook

It states that the solid and liquid phases are in equilibrium at the melting point . This is just the definition of melting point: the temperature at which solid and liquid phases are in equilibrium. We know the melting point of water is 0 °C, so we would expect the reaction to be at equilibrium at ...
by Chem_Mod
Mon Feb 25, 2019 2:32 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Homework Question
Replies: 2
Views: 81

Re: Homework Question

1 x 10–13 is the concentration of OH(aq) at a pH of 1, and 1.0 is [OH] at pH 14.
by Chem_Mod
Mon Feb 25, 2019 2:20 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L.5 part c (7th edition)
Replies: 1
Views: 40

Re: 6L.5 part c (7th edition)

This is a typo. The reactant is Cl2(g) and the product is Cl, so the Cl2(g) should be written first.
by Chem_Mod
Mon Feb 25, 2019 2:13 pm
Forum: Balancing Redox Reactions
Topic: 7th edition 6L.7, Adams, Disc 1A
Replies: 2
Views: 44

Re: 7th edition 6L.7, Adams, Disc 1A

It's the same as writing OH(aq), which of necessity includes a nonspecific cation. KOH(aq) is just more specific.
by Chem_Mod
Mon Feb 25, 2019 2:10 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L3 7th edition
Replies: 1
Views: 11

Re: 6L3 7th edition

Yes; there is an aqueous phase in each electrode, so water could participate.
by Chem_Mod
Mon Feb 25, 2019 2:06 pm
Forum: Balancing Redox Reactions
Topic: Balancing redox reactions
Replies: 2
Views: 35

Re: Balancing redox reactions

Yes, although in some cases it won't matter in which type of solution the reaction occurs.
by Chem_Mod
Mon Feb 25, 2019 2:01 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: standard vs reaction gibbs free energy [ENDORSED]
Replies: 3
Views: 40

Re: standard vs reaction gibbs free energy [ENDORSED]

Yes, except the temperature is not stipulated in standard Gibbs free energy, \Delta G^\circ , just the concentration or pressure of each species. We often report the standard Gibbs free energy change for a reaction, \Delta G_{r}^\circ , though we often just write it as the standard Gibbs free energy...
by Chem_Mod
Mon Feb 25, 2019 12:55 am
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 179
Views: 5645

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Here are the keys to the Gibbs free and electrochem worksheets. As promised, for electrochem, I tried including as much detail as I can to follow through since there was not enough time to go over it. NOTE: For Gibbs free energy worksheet #3a, I made a mistake today in session saying that the condit...
by Chem_Mod
Mon Feb 25, 2019 12:17 am
Forum: Balancing Redox Reactions
Topic: Week 7 worksheet (2E, I, K)
Replies: 4
Views: 403

Re: Week 7 worksheet (2E, I, K)

Correction for 1b: "MnO4- (aq), H+ (aq), Mn2+ (aq) | Pt (s)" will be more accurate answer since H+ is reactant.
by Chem_Mod
Sun Feb 24, 2019 3:34 pm
Forum: Administrative Questions and Class Announcements
Topic: Test 3 Equations
Replies: 1
Views: 37

Re: Test 3 Equations

See all the constants and equations given at my class website: https://lavelle.chem.ucla.edu/wp-conten ... ations.pdf
by Chem_Mod
Sun Feb 24, 2019 1:26 am
Forum: Balancing Redox Reactions
Topic: Week 7 worksheet (2E, I, K)
Replies: 4
Views: 403

Re: Week 7 worksheet (2E, I, K)

Here is worksheet 8 including more electrochem materials :)
by Chem_Mod
Sat Feb 23, 2019 3:26 pm
Forum: Balancing Redox Reactions
Topic: Week 7 worksheet (2E, I, K)
Replies: 4
Views: 403

Week 7 worksheet (2E, I, K)

Hi,

Attached please find the worksheet and discussion notes for week 7.

Best,
Joyce
by Chem_Mod
Fri Feb 22, 2019 6:05 pm
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 179
Views: 5645

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

This week we will go over Gibbs free energy and most of electrochemistry (everything your test will cover). This is two sessions worth of material so please bear with me, see you there!
by Chem_Mod
Thu Feb 21, 2019 11:32 pm
Forum: Van't Hoff Equation
Topic: Overview
Replies: 8
Views: 78

Re: Overview

It gives the equilibrium constant (lnK) as a function of (1/T), by knowing K1, T1, you can calculate K2 at T2
by Chem_Mod
Thu Feb 21, 2019 10:27 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy in cal
Replies: 2
Views: 31

Re: Gibbs Free Energy in cal

If enthalpy and entropy are given in terms of moles, then it would be cal/mole.
by Chem_Mod
Thu Feb 21, 2019 5:27 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Problem 9.89-Sixth Edition
Replies: 1
Views: 40

Re: Problem 9.89-Sixth Edition

Aqueous solutions in Appendix 2A are associated with negative entropies because, they are not necessarily measured in an absolute sense. The values are all measured relative to the entropy of a solution of H+. An aqueous solution have a negative entropy can be thought of forming a solvation shell or...
by Chem_Mod
Thu Feb 21, 2019 5:22 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Problem 4J.15) 7th edition of the textbook
Replies: 1
Views: 23

Re: Problem 4J.15) 7th edition of the textbook

The two numbers you see correspond to two crystal structures that S can form. At room temperature, the rhombic phase is more stable.
by Chem_Mod
Thu Feb 21, 2019 5:15 pm
Forum: Balancing Redox Reactions
Topic: 6K.3 (d), 7th edition
Replies: 1
Views: 36

Re: 6K.3 (d), 7th edition

First, there is a typo, the Cl2 in the product should actually be Cl-. To solve your question, the key is understanding that Cl2 can be both the oxidizing agent and the reducing agent.
by Chem_Mod
Thu Feb 21, 2019 5:01 pm
Forum: Van't Hoff Equation
Topic: Test 2
Replies: 3
Views: 71

Re: Test 2

Yes, but you should realize that gibbs free energy calculation would require you know all the previous material on enthalpy and entropy.
by Chem_Mod
Thu Feb 21, 2019 4:59 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 6th ed 9.65 stability
Replies: 1
Views: 24

Re: 6th ed 9.65 stability

can be used to find the sign of (since T is always positive in this class) instead of using the molar entropies of reactants and products.
by Chem_Mod
Thu Feb 21, 2019 4:54 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Expansion and Non-expansion Work
Replies: 1
Views: 24

Re: Expansion and Non-expansion Work

Expansion work is pressure-volume work, and nonexpansion work is anything else (electrical, friction, motional, etc.)
by Chem_Mod
Thu Feb 21, 2019 10:20 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G of Formation for O2
Replies: 1
Views: 25

Re: Delta G of Formation for O2

The formation of O2 is from the reaction O2-->O2, since the reactant and the product are identical, the deltaG is 0
by Chem_Mod
Thu Feb 21, 2019 10:17 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Pt as an electrode
Replies: 4
Views: 43

Re: Pt as an electrode

Inert electrodes, like the platinum electrode do not participate in the oxidation-reduction reaction and are present so that current can flow through the cell. Platinum or gold generally make good inert electrodes because they are chemically nonreactive.
by Chem_Mod
Tue Feb 19, 2019 4:40 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Test 2
Replies: 2
Views: 40

Re: Test 2

See class announcements online.
by Chem_Mod
Tue Feb 19, 2019 4:39 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Test 2
Replies: 4
Views: 62

Re: Test 2

See class announcements online.
by Chem_Mod
Sat Feb 16, 2019 5:45 pm
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 179
Views: 5645

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Julia Lee wrote:So is there no worksheet for this week?


No worksheet this week! The next session will cover all topics on Test 2.
by Chem_Mod
Sat Feb 16, 2019 11:48 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Test 2
Replies: 1
Views: 43

Re: Test 2

See my class announcement.
by Chem_Mod
Fri Feb 15, 2019 4:46 pm
Forum: Administrative Questions and Class Announcements
Topic: Gibbs Energy Study Guide
Replies: 1
Views: 67

Gibbs Energy Study Guide

Here is a short study guide on Gibb's Free Energy
by Chem_Mod
Fri Feb 15, 2019 3:49 pm
Forum: Van't Hoff Equation
Topic: Assumptions
Replies: 1
Views: 70

Re: Assumptions

For the purpose of this class, these assumptions will hold when we use the Van't Hoff Equation. The assumption is that the difference between the entropies of reactants and products at one temperature is the same difference between the entropies of reactants and products at a different temperature.
by Chem_Mod
Fri Feb 15, 2019 3:44 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy
Replies: 1
Views: 37

Re: Gibbs Free Energy

Hi Stevin, I'm assuming you're talking about delta G of formation values. If you think about what the formation reaction is, it's the reaction from a compound's elements into 1 mole of that compound. Because the formation reaction for N 2 is N 2 --> N 2 , essentially the delta G is zero because both...
by Chem_Mod
Fri Feb 15, 2019 3:34 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Why do we care about ΔG
Replies: 3
Views: 59

Re: Why do we care about ΔG

The equation you proposed is the same as the ΔG = ΔH - T*ΔS equation we know and love, just in terms of different parameters. ΔG is related to ΔS, so yes, in a way, we can just use ΔS, but that is not always available to you. Plus, ΔG refers to the amount of free work available, whereas ΔS refers to...
by Chem_Mod
Fri Feb 15, 2019 3:31 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cp vs. Cv heat capacity
Replies: 1
Views: 36

Re: Cp vs. Cv heat capacity

For C v heat capacity, the condition entails a constant volume. This means that work would be zero (deltaV = 0). For C p heat capacity, the condition entails a constant pressure, so work is possible under constant pressure conditions. This means the deltaU would be higher for the substance when it i...
by Chem_Mod
Fri Feb 15, 2019 3:23 pm
Forum: Calculating Work of Expansion
Topic: Free Expansion
Replies: 3
Views: 65

Re: Free Expansion

Free expansion refers to a positive change in volume where there is no external pressure that the gas is pushing against (pushing against a vacuum). Thus, work would be zero.
by Chem_Mod
Thu Feb 14, 2019 11:21 pm
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 179
Views: 5645

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Hi students, there will be no workshop on Sunday because of the long weekend. Sessions will resume 2/24.

Enjoy the weekend after your midterm!

-K
by Chem_Mod
Thu Feb 14, 2019 11:03 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Finding the change in H from a reaction/molecules
Replies: 2
Views: 35

Re: Finding the change in H from a reaction/molecules

If you are working on a Hess' Law problem, when you flip a reaction, you need to flip the sign of the reaction enthalpy as well.
by Chem_Mod
Thu Feb 14, 2019 10:59 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isothermal and reversible
Replies: 1
Views: 47

Re: Isothermal and reversible

Note that not all isothermal processes are reversible, for example, a free expansion is an irreversible but isothermal process
by Chem_Mod
Thu Feb 14, 2019 10:47 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: HOTDOG problem
Replies: 3
Views: 81

Re: HOTDOG problem

Can you post the question in details?
by Chem_Mod
Thu Feb 14, 2019 10:46 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Adding reaction entropies
Replies: 8
Views: 76

Re: Adding reaction entropies

Because entropy is a state function and is path independent
by Chem_Mod
Thu Feb 14, 2019 4:32 pm
Forum: Student Social/Study Group
Topic: week 6 homework
Replies: 2
Views: 81

Re: week 6 homework

Thermodynamics
by Chem_Mod
Wed Feb 13, 2019 4:57 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: 6th edition 9.75
Replies: 1
Views: 60

Re: 6th edition 9.75

Trans-MX2Y4 can have the X atoms trans along the x-, y-, or z-axis

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