Search found 58 matches

by Sue Xu 2K
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: 279

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)?
by Sue Xu 2K
Tue Mar 13, 2018 12:12 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: HW 15.85
Replies: 2
Views: 146

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?
by Sue Xu 2K
Tue Mar 13, 2018 12:11 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediates
Replies: 2
Views: 126

Intermediates

Which part of the reaction profile indicates the intermediates?
by Sue Xu 2K
Tue Mar 13, 2018 12:09 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Organic solvent
Replies: 1
Views: 92

Organic solvent

What is different if the reaction takes place in organic solvent?
by Sue Xu 2K
Fri Mar 09, 2018 2:21 pm
Forum: First Order Reactions
Topic: 15.37C
Replies: 5
Views: 451

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.
by Sue Xu 2K
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: 269

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.
by Sue Xu 2K
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: 279

Order less than 0

Are there reactions with a order less than 0? For example, the rate law = k [R]^-1
by Sue Xu 2K
Wed Feb 28, 2018 4:02 pm
Forum: General Rate Laws
Topic: Rate constant = k
Replies: 1
Views: 93

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.
by Sue Xu 2K
Wed Feb 28, 2018 3:58 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.19
Replies: 2
Views: 147

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.
by Sue Xu 2K
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: 110

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?
by Sue Xu 2K
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: 171

Re: Order of Same State Molecules

Our TA told us to list the reactants first and then products.
by Sue Xu 2K
Thu Feb 22, 2018 9:41 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Current
Replies: 2
Views: 117

Current

For HW 14.117 it asks for the current. Could someone remind me the equation for current?
by Sue Xu 2K
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: 99

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)
by Sue Xu 2K
Mon Feb 12, 2018 4:31 pm
Forum: Administrative Questions and Class Announcements
Topic: No class on Wednesday?
Replies: 2
Views: 225

No class on Wednesday?

Just want to make sure are we not going to have class on Wednesday because of the midterm?
by Sue Xu 2K
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: 166

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.
by Sue Xu 2K
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: 106

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.
by Sue Xu 2K
Mon Feb 12, 2018 4:03 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.63
Replies: 2
Views: 146

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.
by Sue Xu 2K
Sat Feb 10, 2018 9:12 pm
Forum: Van't Hoff Equation
Topic: Constants and formulas
Replies: 7
Views: 321

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.
by Sue Xu 2K
Thu Feb 08, 2018 6:52 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Positive cell potentials
Replies: 2
Views: 79

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?  
by Sue Xu 2K
Thu Feb 08, 2018 5:51 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell diagrams
Replies: 1
Views: 66

Cell diagrams

Do we have to put comma between substances of the same phases? Like H+(aq), OH-(aq).
by Sue Xu 2K
Thu Feb 08, 2018 1:26 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: HW 14. 27
Replies: 1
Views: 86

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.
by Sue Xu 2K
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: 258

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.
by Sue Xu 2K
Fri Feb 02, 2018 7:08 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.15 and 9.19
Replies: 2
Views: 104

Re: 9.15 and 9.19

I have the same question. Just replying to mark this.
by Sue Xu 2K
Fri Feb 02, 2018 7:05 pm
Forum: Calculating Work of Expansion
Topic: Free expansion and irreversible expansion
Replies: 2
Views: 127

Free expansion and irreversible expansion

Is the term "free expansion" the same as irreversible expansion?
by Sue Xu 2K
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: 346

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?
by Sue Xu 2K
Fri Jan 26, 2018 1:13 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Reversible Vs Irreversible
Replies: 3
Views: 116

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.
by Sue Xu 2K
Fri Jan 26, 2018 1:06 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Reversible and Irreversible
Replies: 3
Views: 152

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.
by Sue Xu 2K
Thu Jan 25, 2018 9:03 pm
Forum: Calculating Work of Expansion
Topic: Units
Replies: 2
Views: 181

Units

What is the unit of P, pressure in the w=-P delta V ? And is Torr the same as Pa?
by Sue Xu 2K
Thu Jan 18, 2018 8:59 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: HW 8.21
Replies: 2
Views: 116

HW 8.21

The answer for this question is 25C, but shouldn't that be 24.7 with 3 sig figs?
by Sue Xu 2K
Thu Jan 18, 2018 8:54 pm
Forum: Calculating Work of Expansion
Topic: The w equation
Replies: 2
Views: 115

The w equation

Why is it w=-PV instead of w=PV? What does the minus mean?
by Sue Xu 2K
Thu Jan 18, 2018 8:52 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta U?
Replies: 7
Views: 524

Delta U?

We talked about delta U in class. Could some one please explain to me again what exactly it is?
by Sue Xu 2K
Sat Jan 13, 2018 12:52 pm
Forum: Phase Changes & Related Calculations
Topic: Phase Changes
Replies: 13
Views: 549

Re: Phase Changes

Condensation, solidification and deposition are all exothermic phase change that release heat during the process.
by Sue Xu 2K
Sat Jan 13, 2018 12:50 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.23
Replies: 5
Views: 226

Re: 8.23

I believe the unite for heat capacity should be kJ/C
by Sue Xu 2K
Thu Jan 11, 2018 11:29 am
Forum: Phase Changes & Related Calculations
Topic: Why steam burns are worse explained
Replies: 5
Views: 222

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.
by Sue Xu 2K
Thu Jan 11, 2018 11:25 am
Forum: Administrative Questions and Class Announcements
Topic: Lecture Outline
Replies: 2
Views: 161

Re: Lecture Outline

I believe there is only lecture outlines on the class websites that list some central concepts and skills.
by Sue Xu 2K
Mon Jan 08, 2018 3:46 pm
Forum: Administrative Questions and Class Announcements
Topic: Week 1 HW
Replies: 3
Views: 171

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?
by Sue Xu 2K
Wed Dec 06, 2017 12:59 pm
Forum: Naming
Topic: (en) and (EDTA)
Replies: 2
Views: 164

(en) and (EDTA)

Are we supposed to know the full name of these two ligands?
by Sue Xu 2K
Wed Dec 06, 2017 12:48 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Charge of ligands
Replies: 3
Views: 197

Charge of ligands

Can ligands be positively charged?
by Sue Xu 2K
Wed Nov 29, 2017 6:30 pm
Forum: Hybridization
Topic: Delocalized π bonds
Replies: 2
Views: 202

Delocalized π bonds

Can anyone please explain how the delocalized π bonds in Benzene work?
by Sue Xu 2K
Tue Nov 28, 2017 7:11 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Question 17.33(c)
Replies: 1
Views: 132

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.
by Sue Xu 2K
Wed Nov 22, 2017 11:15 am
Forum: Naming
Topic: Naming
Replies: 3
Views: 190

Naming

Do we have to memorize all the prefix and names in the tests? Or are we getting the tables in the text book?
by Sue Xu 2K
Tue Nov 21, 2017 6:45 pm
Forum: Naming
Topic: HW 17.31 b
Replies: 4
Views: 212

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).
by Sue Xu 2K
Wed Nov 15, 2017 9:13 pm
Forum: Dipole Moments
Topic: Polar molecules relation to lone pair electrons
Replies: 2
Views: 218

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.
by Sue Xu 2K
Wed Nov 15, 2017 9:10 pm
Forum: Photoelectric Effect
Topic: Midterm question [ENDORSED]
Replies: 6
Views: 397

Midterm question [ENDORSED]

Why is the statement "higher frequency light always emits electrons with higher kinetic energies" incorrect?
by Sue Xu 2K
Thu Nov 09, 2017 2:47 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Formula unit
Replies: 1
Views: 186

Formula unit

What exactly is formula unit?
by Sue Xu 2K
Tue Nov 07, 2017 7:58 pm
Forum: Resonance Structures
Topic: Lewis structure of SO3
Replies: 1
Views: 217

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?
by Sue Xu 2K
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: 372

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.
by Sue Xu 2K
Thu Nov 02, 2017 6:54 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: The configuration of tungsten
Replies: 2
Views: 273

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?
by Sue Xu 2K
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: 268

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"?
by Sue Xu 2K
Wed Oct 25, 2017 1:05 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: #55 d
Replies: 3
Views: 188

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.
by Sue Xu 2K
Wed Oct 25, 2017 10:43 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 3d and 4s orbitals
Replies: 1
Views: 126

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?
by Sue Xu 2K
Wed Oct 18, 2017 12:32 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Bohr Condition/Rydberg Constant
Replies: 2
Views: 230

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.
by Sue Xu 2K
Mon Oct 16, 2017 2:09 pm
Forum: DeBroglie Equation
Topic: How do we get E=pv? [ENDORSED]
Replies: 2
Views: 205

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?
by Sue Xu 2K
Mon Oct 09, 2017 6:03 pm
Forum: Photoelectric Effect
Topic: Results of Photoelectric experiments
Replies: 3
Views: 219

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 ...
by Sue Xu 2K
Mon Oct 09, 2017 3:11 pm
Forum: Administrative Questions and Class Announcements
Topic: Online discussions grading
Replies: 1
Views: 130

Online discussions grading

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?
by Sue Xu 2K
Fri Oct 06, 2017 3:40 pm
Forum: Limiting Reactant Calculations
Topic: Is either Method better?
Replies: 4
Views: 253

Re: Is either Method better?

They both apply to every questions correctly. But the latter might involve more calculation.
by Sue Xu 2K
Fri Oct 06, 2017 3:34 pm
Forum: Significant Figures
Topic: 3 Sig Figs 1795.507? [ENDORSED]
Replies: 5
Views: 392

Re: 3 Sig Figs 1795.507? [ENDORSED]

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

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