## Search found 58 matches

Sat Mar 17, 2018 10:06 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Solids in cell diagrams
Replies: 4
Views: 356

### Solids in cell diagrams

For the cell diagram that Dr. Lavelle covers in his review session, Ag(s)|AgBr(s)||Br-(aq)|Br2(g)|Pt(s), do we need a line between Ag(s) and AgBr(s)?
Tue Mar 13, 2018 12:12 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: HW 15.85
Replies: 2
Views: 211

### HW 15.85

In the answer key of 15.85, what does it mean by the dots in the structures of the activated complex? Also, is the activated complex equal to the intermediate?
Tue Mar 13, 2018 12:11 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediates
Replies: 2
Views: 231

### Intermediates

Which part of the reaction profile indicates the intermediates?
Tue Mar 13, 2018 12:09 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Organic solvent
Replies: 1
Views: 137

### Organic solvent

What is different if the reaction takes place in organic solvent?
Fri Mar 09, 2018 2:21 pm
Forum: First Order Reactions
Topic: 15.37C
Replies: 5
Views: 729

### Re: 15.37C

It is possible to solve the question without the volume, but you can still calculate the concentration with the mass and the volume first and then calculate the final mass.
Fri Mar 09, 2018 2:17 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Rate Constant Calculations [ENDORSED]
Replies: 3
Views: 361

### Re: Rate Constant Calculations[ENDORSED]

There several ways to solve rate constant: the differential rate law (rate = k[R]^n ) and the integral rate law (vary depending on the order of the reaction). For both of them you would probably need something more than the order and the initial concentration.
Fri Mar 09, 2018 2:08 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Order less than 0
Replies: 4
Views: 381

### Order less than 0

Are there reactions with a order less than 0? For example, the rate law = k [R]^-1
Wed Feb 28, 2018 4:02 pm
Forum: General Rate Laws
Topic: Rate constant = k
Replies: 1
Views: 142

### Re: Rate constant = k

There are multiple ways of calculating k. If we have the initial concentrations and rates, we can use the differential rate law, rate = k [A]^n to calculate k, in which n is the order of the reaction, and [A] is the initial concentration of the reactants.
Wed Feb 28, 2018 3:58 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.19
Replies: 2
Views: 262

### Re: 15.19

I have the same question. I think the answer key is wrong. It should either be 2.85 x 10-^12 mol/Ls or 2.85 mmol/Ls.
Wed Feb 28, 2018 3:54 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: HW 15.17 [ENDORSED]
Replies: 1
Views: 191

### HW 15.17[ENDORSED]

For this question, I think we should divide the initial rate by 3 when calculating k, since it's the initial rate of G. But the answer key gives the value that are calculated without dividing by 3. Could anyone explain this?
Sun Feb 25, 2018 11:16 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Order of Same State Molecules
Replies: 4
Views: 306

### Re: Order of Same State Molecules

Our TA told us to list the reactants first and then products.
Thu Feb 22, 2018 9:43 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 14.107 Solution Manual Error?
Replies: 4
Views: 661

### Re: 14.107 Solution Manual Error?

You can find this on the class website: https://lavelle.chem.ucla.edu/wp-conten ... rs_6Ed.pdf
it says the solution manual is wrong.
Thu Feb 22, 2018 9:41 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Current
Replies: 2
Views: 170

### Current

For HW 14.117 it asks for the current. Could someone remind me the equation for current?
Thu Feb 22, 2018 9:40 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: The order of cell diagrams
Replies: 1
Views: 158

### The order of cell diagrams

When we write cell diagrams, is there an rule for the order of substances in the same phase? Like Zn2+(aq), H+(aq)
Mon Feb 12, 2018 4:31 pm
Forum: Administrative Questions and Class Announcements
Topic: No class on Wednesday?
Replies: 2
Views: 307

### No class on Wednesday?

Just want to make sure are we not going to have class on Wednesday because of the midterm?
Mon Feb 12, 2018 4:16 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Units for enthalpy
Replies: 2
Views: 231

### Re: Units for enthalpy

I think he said we don't have to be too specific about the difference between kJ/mol and kJ. For the test and examples we cover in class we usually just use kJ.
Mon Feb 12, 2018 4:09 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: 9.25
Replies: 1
Views: 166

### Re: 9.25

I believe you are asking for question 9.75. For the trans molecules the two X (blue) atoms are on the opposite position. Given that the molecule is octahedral, there will be 3 microstates. And for the cis molecule there are 8 microstates.
Mon Feb 12, 2018 4:03 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.63
Replies: 2
Views: 239

### Re: 9.63

What you are thinking is right but I think the question asks for the stability of the compounds instead of the elements. If the formation energy is positive, the compound form has more energy and is thus more unstable.
Sat Feb 10, 2018 9:12 pm
Forum: Van't Hoff Equation
Topic: Constants and formulas
Replies: 7
Views: 508

### Constants and formulas

Is Van‘t Hoff equation going to be given during the test? I ask this because I could not find it on the constants and formulas page on test 1.
Thu Feb 08, 2018 6:52 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Positive cell potentials
Replies: 2
Views: 118

### Positive cell potentials

It is a minor thing but I just wonder that do we always have to put a + mark before positive cell potentials?
Thu Feb 08, 2018 5:51 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell diagrams
Replies: 1
Views: 97

### Cell diagrams

Do we have to put comma between substances of the same phases? Like H+(aq), OH-(aq).
Thu Feb 08, 2018 1:26 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: HW 14. 27
Replies: 1
Views: 150

### HW 14. 27

The question asks the redox potential of U^(4+) + 4e- = U(s). How to approach this question? I tried to add the redox potential for U^(3+) + 3e = U(s) and
U^(4+) + e- = U^(3+) but I got -2.4V instead of -1.5V in the answer keys.
Fri Feb 02, 2018 7:56 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: How to tell what happens to entropy by seeing a reaction?
Replies: 6
Views: 477

### Re: How to tell what happens to entropy by seeing a reaction?

You can just generally look at the phase of the phase of the reactants and products. In this reaction, the reactants are 1 solid and 1 gas, while the products are 1 liquid and 1 gas. Because liquid has higher entropy than solid, the entropy of the products is higher.
Fri Feb 02, 2018 7:08 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.15 and 9.19
Replies: 2
Views: 172

### Re: 9.15 and 9.19

I have the same question. Just replying to mark this.
Fri Feb 02, 2018 7:05 pm
Forum: Calculating Work of Expansion
Topic: Free expansion and irreversible expansion
Replies: 2
Views: 203

### Free expansion and irreversible expansion

Is the term "free expansion" the same as irreversible expansion?
Wed Jan 31, 2018 8:40 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: The value of Cp
Replies: 8
Views: 625

### The value of Cp

In 9.7 I believe we have to use the equation S = nCp lnT1/T2. Are we always given the value of Cp?
Fri Jan 26, 2018 1:13 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Reversible Vs Irreversible
Replies: 3
Views: 209

### Re: Reversible Vs Irreversible

For reversible expansion, it is isothermal because the system does work and lose energy, and then the loss of energy is replaced by the heat flow into the system. So U, the internal energy, remains constant. For U = 3/2 nRT, T also stays constant.
Fri Jan 26, 2018 1:06 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Reversible and Irreversible
Replies: 3
Views: 217

### Re: Reversible and Irreversible

The way works for me is to simply think that reversible expansion is a slow, equilibrium process, and the changes of pressure happen in a lot of small steps. For the irreversible expansion, the pressure changes in one step and stays there for the rest of the process.
Thu Jan 25, 2018 9:03 pm
Forum: Calculating Work of Expansion
Topic: Units
Replies: 2
Views: 347

### Units

What is the unit of P, pressure in the w=-P delta V ? And is Torr the same as Pa?
Thu Jan 18, 2018 8:59 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: HW 8.21
Replies: 2
Views: 140

### HW 8.21

The answer for this question is 25C, but shouldn't that be 24.7 with 3 sig figs?
Thu Jan 18, 2018 8:54 pm
Forum: Calculating Work of Expansion
Topic: The w equation
Replies: 2
Views: 142

### The w equation

Why is it w=-PV instead of w=PV? What does the minus mean?
Thu Jan 18, 2018 8:52 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta U？
Replies: 7
Views: 2398

### Delta U？

We talked about delta U in class. Could some one please explain to me again what exactly it is?
Sat Jan 13, 2018 12:52 pm
Forum: Phase Changes & Related Calculations
Topic: Phase Changes
Replies: 13
Views: 861

### Re: Phase Changes

Condensation, solidification and deposition are all exothermic phase change that release heat during the process.
Sat Jan 13, 2018 12:50 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.23
Replies: 5
Views: 357

### Re: 8.23

I believe the unite for heat capacity should be kJ/C
Thu Jan 11, 2018 11:29 am
Forum: Phase Changes & Related Calculations
Topic: Why steam burns are worse explained
Replies: 5
Views: 287

### Re: Why steam burns are worse explained

The steam and water all tend to cool down when it get exposed to a cooler surface like the skin. But it releases extra energy to convert steam to water first, and then the extra energy, or extra heat would burns the skin worse.
Thu Jan 11, 2018 11:25 am
Forum: Administrative Questions and Class Announcements
Topic: Lecture Outline
Replies: 2
Views: 232

### Re: Lecture Outline

I believe there is only lecture outlines on the class websites that list some central concepts and skills.
Mon Jan 08, 2018 3:46 pm
Forum: Administrative Questions and Class Announcements
Topic: Week 1 HW
Replies: 3
Views: 218

### Week 1 HW

Just want to make sure, we can hand in the homework for week 1 in the next week's discussion session right?
Wed Dec 06, 2017 12:59 pm
Forum: Naming
Topic: (en) and (EDTA)
Replies: 2
Views: 213

### (en) and (EDTA)

Are we supposed to know the full name of these two ligands?
Wed Dec 06, 2017 12:48 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Charge of ligands
Replies: 3
Views: 336

### Charge of ligands

Can ligands be positively charged？
Wed Nov 29, 2017 6:30 pm
Forum: Hybridization
Topic: Delocalized π bonds
Replies: 2
Views: 296

### Delocalized π bonds

Can anyone please explain how the delocalized π bonds in Benzene work?
Tue Nov 28, 2017 7:11 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Question 17.33(c)
Replies: 1
Views: 161

### Question 17.33(c)

According to the answer, CO3 2- can be mono- or bidentate. How can it be either way? In my understanding, it is bidentate because two oxygen atoms can bind to a central metal.
Wed Nov 22, 2017 11:15 am
Forum: Naming
Topic: Naming
Replies: 3
Views: 278

### Naming

Do we have to memorize all the prefix and names in the tests? Or are we getting the tables in the text book?
Tue Nov 21, 2017 6:45 pm
Forum: Naming
Topic: HW 17.31 b
Replies: 4
Views: 306

### HW 17.31 b

It asks for the formula of pentaamminesulfatocobalt(III) chloride. Is the answer wrong? I think it's [Co(NH3)5(SO4)]Cl3 since it said the (III).
Wed Nov 15, 2017 9:13 pm
Forum: Dipole Moments
Topic: Polar molecules relation to lone pair electrons
Replies: 2
Views: 318

### Re: Polar molecules relation to lone pair electrons

I think lone pairs won't directly change the dipole moment, but they do change the shape of the molecule, like the lone pair in NH3 which makes it a trigonal pyramidal shape instead of trigonal planar. And the shape of the molecule will in turn influence the dipole moment.
Wed Nov 15, 2017 9:10 pm
Forum: Photoelectric Effect
Topic: Midterm question [ENDORSED]
Replies: 6
Views: 486

### Midterm question[ENDORSED]

Why is the statement "higher frequency light always emits electrons with higher kinetic energies" incorrect?
Thu Nov 09, 2017 2:47 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Formula unit
Replies: 1
Views: 212

### Formula unit

What exactly is formula unit？
Tue Nov 07, 2017 7:58 pm
Forum: Resonance Structures
Topic: Lewis structure of SO3
Replies: 1
Views: 287

### Lewis structure of SO3

I think it is mentioned in class, but I am a little bit confused about it. Is there one double S=O bond which forms a resonance structure?
Tue Nov 07, 2017 7:54 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: The valence electron of Cu and Br
Replies: 2
Views: 792

### The valence electron of Cu and Br

How many valence electrons are there in elements like Cu and Br? Or specifically, does the electrons in d orbital count? The d orbital is from the inner shells so I'm not really sure.
Thu Nov 02, 2017 6:54 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: The configuration of tungsten
Replies: 2
Views: 385

### The configuration of tungsten

In homework question 2.43 the configuration of tungsten, there are 4 electrons fill in 5d and 2 electrons in 6s. Why is the electrons not acting as they do in chromium, making the d-orbital half-filled?
Thu Nov 02, 2017 6:45 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: shielding effect of s and p-orbitals
Replies: 4
Views: 420

### shielding effect of s and p-orbitals

In the homework question 2.37 it says "an electron in an s-orbital can penetrate to the nucleus of the atom". What does it mean by "penetrate"?
Wed Oct 25, 2017 1:05 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: #55 d
Replies: 3
Views: 246

### Re: #55 d

The orbitals are always the most stable when they are half filled or full, because of the electron repulsion force. So the electron will alway try to fill in the orbitals that way.
Wed Oct 25, 2017 10:43 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 3d and 4s orbitals
Replies: 1
Views: 162

### 3d and 4s orbitals

Since the electrons fill the 4s orbital first, can we say that the 4s orbital is in lower energy than the 3d orbital?
Wed Oct 18, 2017 12:32 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Bohr Condition/Rydberg Constant
Replies: 2
Views: 336

### Re: Bohr Condition/Rydberg Constant

Bohr condition states that only if the energy of the photon mathces the difference of the electron energy shells that the photon can be emitted or observed. And Rydberg constant is basically how you can calculate the difference. These two togetherrr can solve the atomic spectrum problems.
Mon Oct 16, 2017 2:09 pm
Forum: DeBroglie Equation
Topic: How do we get E=pv? [ENDORSED]
Replies: 2
Views: 264

### How do we get E=pv?[ENDORSED]

When deriving the DeBroglie equation we need the equation E=pv. Where do we get this equation?
Also, if p=mv then E=mv^2. What does this have to do with the Kinetic energy Ek=(1/2)mv^2?
Mon Oct 09, 2017 6:03 pm
Forum: Photoelectric Effect
Topic: Results of Photoelectric experiments
Replies: 3
Views: 292

### Re: Results of Photoelectric experiments

I think it would be from the wave mode to the photon or particle mode. Not sure which word is correct. Basically the experimental observations of photoelectric experiments is that no electrons are ejected unless the radiation has a frequency above a certain threshold value that is characteristic of ...
Mon Oct 09, 2017 3:11 pm
Forum: Administrative Questions and Class Announcements
Replies: 1
Views: 156

It is said that we get 1 point per post on this forum and there are 2 points at max each week. I wonder what is the last day of a "week", Friday or Sunday?
Fri Oct 06, 2017 3:40 pm
Forum: Limiting Reactant Calculations
Topic: Is either Method better?
Replies: 4
Views: 372

### Re: Is either Method better?

They both apply to every questions correctly. But the latter might involve more calculation.
Fri Oct 06, 2017 3:34 pm
Forum: Significant Figures
Topic: 3 Sig Figs 1795.507? [ENDORSED]
Replies: 5
Views: 534

### Re: 3 Sig Figs 1795.507?[ENDORSED]

Actually 1800 has 4 significant figures. the zeros count to the sig fig.