Search found 53 matches

by Wenjie Dong 2E
Sun Mar 11, 2018 10:23 pm
Forum: Balancing Redox Reactions
Topic: redox
Replies: 6
Views: 173

Re: redox

The oxidizing agent gains electrons and reducing agent losses electrons. A easy way to remember this is that Oxygen usually (not always!) acts as the oxidizing agent in redox reactions and it gains electrons during redox reactions.
by Wenjie Dong 2E
Sun Mar 11, 2018 10:18 pm
Forum: Balancing Redox Reactions
Topic: Ranking elements
Replies: 8
Views: 285

Re: Ranking elements

You could refer to activity series of metals. For example, https://www.thoughtco.com/activity-seri ... als-603960.
by Wenjie Dong 2E
Sun Mar 11, 2018 10:12 pm
Forum: Balancing Redox Reactions
Topic: 14.5 Part a
Replies: 4
Views: 132

Re: 14.5 Part a

No, you don't have to. It may be canceled out or doesn't never needed to balance the equation.
by Wenjie Dong 2E
Sun Mar 11, 2018 10:09 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test 2 Question 2
Replies: 4
Views: 137

Re: Test 2 Question 2

Ecell=-0.44 V-(-0.74 V)=0.30V, and then use the equation mentioned above to calculate K.
by Wenjie Dong 2E
Sun Mar 04, 2018 11:19 pm
Forum: General Rate Laws
Topic: Negative Order 15.3
Replies: 2
Views: 86

Re: Negative Order 15.3

Negative order means that increasing the concentration slows down the reaction. I believe it happens when products' concentrations affect the reaction rate.
by Wenjie Dong 2E
Sun Mar 04, 2018 11:14 pm
Forum: First Order Reactions
Topic: k
Replies: 16
Views: 465

Re: k

There is no need to do so unless other calculation is needed.
by Wenjie Dong 2E
Sun Mar 04, 2018 11:09 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Friday Lecture
Replies: 5
Views: 127

Re: Friday Lecture

It's because CO2 is the other reactant in this reaction. Since it does not occur in the reaction of NO2, there must be a subsequent reaction that involves CO2.
by Wenjie Dong 2E
Sun Mar 04, 2018 11:04 pm
Forum: General Rate Laws
Topic: Rate laws
Replies: 4
Views: 111

Re: Rate laws

I think graphs will be given or the correlation will be explained.
by Wenjie Dong 2E
Sun Mar 04, 2018 11:03 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: k units [ENDORSED]
Replies: 7
Views: 219

Re: k units [ENDORSED]

It's because the unit of the reaction rate is always the same.
by Wenjie Dong 2E
Sun Mar 04, 2018 11:01 pm
Forum: Administrative Questions and Class Announcements
Topic: Kinetics Test
Replies: 3
Views: 106

Re: Kinetics Test

Same question.
by Wenjie Dong 2E
Sun Feb 18, 2018 11:45 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Cell potential calculation
Replies: 4
Views: 104

Re: Cell potential calculation

I guess you should always reverse the less reactive one.
by Wenjie Dong 2E
Sun Feb 18, 2018 11:37 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge
Replies: 2
Views: 66

Re: Salt Bridge

Agar with solutions of high concentration.
by Wenjie Dong 2E
Sun Feb 18, 2018 11:34 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: redox
Replies: 7
Views: 201

Re: redox

Agree. The substance loss electrons is oxidized and that gain electrons is reduced.
by Wenjie Dong 2E
Sun Feb 18, 2018 11:32 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electromotive force and Why is E a Maximum
Replies: 2
Views: 89

Re: Electromotive force and Why is E a Maximum

As for other chemical experiments, there is always less an efficiency for actual operations than that by calculations.
by Wenjie Dong 2E
Mon Feb 05, 2018 12:42 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Heat transfer
Replies: 7
Views: 202

Re: Heat transfer

Same question!
by Wenjie Dong 2E
Mon Feb 05, 2018 12:40 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: q=-w [ENDORSED]
Replies: 5
Views: 170

Re: q=-w [ENDORSED]

Christina Bedrosian 1B wrote:This formula is true for instances of isothermal expansions since having deltaT=0 (no change in temp), then deltaU (internal energy) would be 0 and since deltaU=q+w, then q would equal -w

Agree.
by Wenjie Dong 2E
Mon Feb 05, 2018 12:39 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Test Number 1
Replies: 9
Views: 268

Re: Test Number 1

Bansi Amin 1D wrote:So the heat was transferred to make up for the change in energy in the system?

Heat is transferred because of a temperature different. The work is done by the system through giving off heat and the work is done to the system by increasing its heat.
by Wenjie Dong 2E
Mon Feb 05, 2018 12:37 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Test question [ENDORSED]
Replies: 16
Views: 490

Re: Test question [ENDORSED]

Kyung_Jin_Kim_1H wrote:Conservation of energy in the universe.

(I didn't even think of elaborating...)


Same.
by Wenjie Dong 2E
Mon Feb 05, 2018 12:35 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta S vs Delta U [ENDORSED]
Replies: 5
Views: 203

Re: Delta S vs Delta U [ENDORSED]

Abigail Yap 2K wrote:Hi,

Delta S is the change in entropy and delta U is the change in internal energy.


Agree.
by Wenjie Dong 2E
Mon Feb 05, 2018 12:27 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G equal Zero [ENDORSED]
Replies: 4
Views: 124

Re: Delta G equal Zero [ENDORSED]

Lily Guo 1D wrote:Not necessarily, but delta G = 0 does mean that the reaction is at equilibrium.

Agree.
by Wenjie Dong 2E
Mon Feb 05, 2018 12:25 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy
Replies: 7
Views: 160

Re: Gibbs Free Energy

Wenjie Dong 2E wrote:"It measures the maximum or reversible work that may be performed by a thermodynamic system at a constant temperature and pressure. (isothermal, isobaric)"

from Wikipedia
by Wenjie Dong 2E
Mon Feb 05, 2018 12:25 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy
Replies: 7
Views: 160

Re: Gibbs Free Energy

"It measures the maximum or reversible work that may be performed by a thermodynamic system at a constant temperature and pressure. (isothermal, isobaric)"
by Wenjie Dong 2E
Mon Feb 05, 2018 12:15 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Net Increases in Amount of Gas
Replies: 3
Views: 110

Re: Net Increases in Amount of Gas

Not sure. But an increase in the amount of gas increases the moles of molecules and thus increases the possibilities of microstate arrangements, which leads to higher entropy.
by Wenjie Dong 2E
Mon Feb 05, 2018 12:11 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: negative entropy [ENDORSED]
Replies: 10
Views: 255

Re: negative entropy [ENDORSED]

There is no such thing as negative entropy. The negative delta entropy means a decrease in disorder.
by Wenjie Dong 2E
Mon Feb 05, 2018 12:07 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: determining number of microstates
Replies: 3
Views: 113

Re: determining number of microstates

Ryan Sydney Beyer 2B wrote:I'm not too certain that we will have to calculate the number of microstates for a specific molecule, but rather if the molecule can be in place A or place B. I think it'll more like probability in place A vs. place B and that is the number of microstates.

Agree.
by Wenjie Dong 2E
Mon Feb 05, 2018 12:04 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Delta U (Concept Clarification)
Replies: 6
Views: 146

Re: Delta U (Concept Clarification)

There is no change in internal energy in the system when delta U=0.
by Wenjie Dong 2E
Sat Jan 20, 2018 1:17 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity Properties
Replies: 3
Views: 93

Re: Heat Capacity Properties

Heat capacity is an extensive property because for one substance it changes when the amount of substance changes. Specific Heat Capacity and Molar Heat Capacity are intensive property because they are identical for one substance, independent on the amount.
by Wenjie Dong 2E
Sat Jan 20, 2018 1:13 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: ∆U = U final-U initial
Replies: 1
Views: 85

Re: ∆U = U final-U initial

Just always subtract the initial U from the final one no matter which one is larger.
by Wenjie Dong 2E
Sat Jan 20, 2018 1:09 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: change in internal energy
Replies: 4
Views: 121

Re: change in internal energy

When there is no word done to the system, the change of internal energy is the same as the heat change. When there is no heat exchange, the change of internal energy is equal to the work done.
by Wenjie Dong 2E
Thu Jan 11, 2018 3:05 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law example from lecture
Replies: 3
Views: 127

Re: Hess's Law example from lecture

The equations should be:
N2 + O2 --> 2NO
2NO + O2 --> 2NO2
-----------------------
N2 + 2O2 --> 2NO2
by Wenjie Dong 2E
Thu Jan 11, 2018 3:03 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law vs. Using Bond Enthalpies
Replies: 3
Views: 111

Re: Hess's Law vs. Using Bond Enthalpies

Hess's Law is more macroscopic while bond enthalpies method is more microscopic. Hess's Law focuses merely on the heat changes during reactions and presents the conclusion that "the total enthalpy change for the reaction is the sum of all changes." Bond enthalpies method concentrates on th...
by Wenjie Dong 2E
Wed Jan 10, 2018 9:31 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Most Stable Form for an Element
Replies: 4
Views: 189

Re: Most Stable Form for an Element

It means the form when the element has the least energy.
by Wenjie Dong 2E
Thu Dec 07, 2017 8:09 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Change in concentration
Replies: 2
Views: 129

Re: Change in concentration

If not given, it's usually resulted from the change in volume.
by Wenjie Dong 2E
Thu Dec 07, 2017 8:01 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Dentates
Replies: 4
Views: 239

Re: Dentates

Same question!
by Wenjie Dong 2E
Thu Dec 07, 2017 7:59 pm
Forum: Conjugate Acids & Bases
Topic: HW 12.45
Replies: 4
Views: 238

Re: HW 12.45

Christina Cen 3E wrote:pkb = 14 - pka
The lower the pkb is, the stronger the base, so the higher the pka = smaller pkb = stronger base

I agree with your explanation!
by Wenjie Dong 2E
Fri Nov 24, 2017 10:01 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles Question
Replies: 3
Views: 161

Re: Bond Angles Question

Just remember lone pair has stronger repulsive force and results in relatively larger bond angles around it.
by Wenjie Dong 2E
Fri Nov 24, 2017 9:58 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Oxalate Ligand Bonding
Replies: 1
Views: 79

Re: Oxalate Ligand Bonding

I happened to see a picture that indicates it's two oxygens attached to one carbon but I'm not sure.
by Wenjie Dong 2E
Sun Nov 19, 2017 11:42 am
Forum: Hybridization
Topic: Electron density question
Replies: 4
Views: 201

Re: Electron density question

It will. For example, NH3 has a lone pair in N and its hybridization is sp3.
by Wenjie Dong 2E
Sun Nov 19, 2017 11:39 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pair Repulsion
Replies: 2
Views: 104

Re: Lone Pair Repulsion

Electrons are less stable in long pairs and thus have higher energy. Higher energy causes higher repulsion.
by Wenjie Dong 2E
Sun Nov 19, 2017 11:38 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Cis- & Trans-
Replies: 3
Views: 131

Re: Cis- & Trans-

Cis- is for atoms that are next to each other, while trans- is for those are opposite to each other.
For example, PtCl2(NH3)s, we use "cis-" for the molecule with the structure of Cl next to each other and "trans-" for Cl opposite to each other.
by Wenjie Dong 2E
Sun Nov 19, 2017 11:31 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Maximum number of ligands
Replies: 3
Views: 173

Re: Maximum number of ligands

I guess it is, but we might not go that further into that.
by Wenjie Dong 2E
Wed Oct 25, 2017 5:53 pm
Forum: Lewis Structures
Topic: Double or single bonds
Replies: 4
Views: 166

Re: Double or single bonds

Subtract total valence electrons from electrons needed to form octets structure in all atoms. Half that number we get, and then use the answer to determine whether we need single, double or triple bonds.
by Wenjie Dong 2E
Wed Oct 25, 2017 5:47 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Difference between subshell and orbital [ENDORSED]
Replies: 9
Views: 897

Re: Difference between subshell and orbital [ENDORSED]

We can have many orbitals (s, p, d, f) under one subshell.
by Wenjie Dong 2E
Sun Oct 22, 2017 9:26 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: P orbitals
Replies: 4
Views: 373

Re: P orbitals

StephanieDoan3B wrote:All three orbitals have the same energy, and the electron will fill any of them first. We designate that px is filled first, then py, and pz because of convention.

I agree. So there will be a second electron on any of the orbit only if px, py, and pz are all filled with one already.
by Wenjie Dong 2E
Sun Oct 22, 2017 9:22 pm
Forum: Photoelectric Effect
Topic: Work Function [ENDORSED]
Replies: 5
Views: 237

Re: Work Function [ENDORSED]

I agree with the above two answers. Both yes.
by Wenjie Dong 2E
Thu Oct 19, 2017 10:18 pm
Forum: Properties of Light
Topic: Converting Units [ENDORSED]
Replies: 11
Views: 464

Re: Converting Units [ENDORSED]

It is better to convert to the most used units.
by Wenjie Dong 2E
Thu Oct 19, 2017 10:17 pm
Forum: Properties of Light
Topic: Lyman and Balmer series.
Replies: 4
Views: 252

Re: Lyman and Balmer series.

I guess we don't need to.
by Wenjie Dong 2E
Thu Oct 19, 2017 10:15 pm
Forum: Photoelectric Effect
Topic: Ionization in energy levels
Replies: 4
Views: 186

Re: Ionization in energy levels

Julie Steklof 3C wrote:The energy required to ionize an electron is the same as the energy required to remove an electron.

I agree.
by Wenjie Dong 2E
Thu Oct 12, 2017 9:49 pm
Forum: Properties of Light
Topic: Electric Field and Magnetic Field of Light
Replies: 4
Views: 196

Re: Electric Field and Magnetic Field of Light

Mia Navarro 1J wrote:the shift of an electron's flight with respect to a photon's energy being shot at it.

What is this experiment? Can u explain more of it?
by Wenjie Dong 2E
Thu Oct 12, 2017 8:28 pm
Forum: Properties of Light
Topic: Electric Field and Magnetic Field of Light
Replies: 4
Views: 196

Electric Field and Magnetic Field of Light

Can anybody explain Electric Field and Magnetic Field of Light for me?
by Wenjie Dong 2E
Tue Oct 03, 2017 9:29 pm
Forum: Student Social/Study Group
Topic: Fundamental M.25
Replies: 3
Views: 476

Re: Fundamental M.25

1. Use the molecule formula C10H7OH to calculate mass percentage composition of C, H, O 2. Get the simplest ratio of mass of C, H, O in C10H7OH (C:H:O=15:1:2) 3. Get the percentage of O in C10H7OH in the sample using the ratio above (H : O = 5.20% : ? = 1:2 --> ? = 10.40%) 4. Add up the percentage o...

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