Search found 62 matches

by Danny Zhang 4L
Thu Mar 14, 2019 8:30 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Intermediate vs catalyst
Replies: 8
Views: 85

Re: Intermediate vs catalyst

Catalysts appear as a reactant for the first step of the reaction mechanism, while intermediates are formed during the reaction. They are both left out of the overall equation of the reaction.
by Danny Zhang 4L
Thu Mar 14, 2019 8:23 pm
Forum: Second Order Reactions
Topic: Hmwrk 15.39
Replies: 1
Views: 100

Re: Hmwrk 15.39

To my understanding, the question could have just told us that "k = 0.015 L mol-1 min-1 for the rate law of this reaction", and that would not change how you should approach the problem.
by Danny Zhang 4L
Wed Mar 13, 2019 2:09 pm
Forum: Administrative Questions and Class Announcements
Topic: Final Questions
Replies: 10
Views: 256

Re: Final Questions

It will be 8 questions just like the midterm, but there will be more small parts to each of them.
by Danny Zhang 4L
Sun Mar 10, 2019 8:29 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Midterm
Replies: 5
Views: 80

Re: Midterm

A large K suggests that the forward reaction is favored. This means that the products are relatively more stable compared to the reactants because the reactants will have a tendency to split/change.
by Danny Zhang 4L
Sun Mar 10, 2019 8:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: What does K say about stability?
Replies: 5
Views: 86

Re: What does K say about stability?

To my understanding, a large K tells us that the forward reaction is favored. This means that the reactants have a tendency to split and/or change, making them unstable. Therefore, the products are relatively stable when compared to the reactants.
by Danny Zhang 4L
Sun Mar 10, 2019 8:11 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Final Exam
Replies: 23
Views: 237

Re: Final Exam

Because this class is cumulative, chem equilibrium will definely show up in a problem or two on the final
by Danny Zhang 4L
Thu Feb 28, 2019 7:08 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Organization of cell diagrams
Replies: 9
Views: 97

Re: Organization of cell diagrams

You will need it in the absence of solid for either of the half reactions
by Danny Zhang 4L
Thu Feb 28, 2019 7:03 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: H+, OH-, water
Replies: 9
Views: 127

Re: H+, OH-, water

You will only need to include H+ and OH-.
by Danny Zhang 4L
Thu Feb 28, 2019 6:34 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.17
Replies: 3
Views: 70

Re: 11.17

Going further with the directions that is provided, you can calculate ΔG^(o) with the K given to you through -RTln(K).
by Danny Zhang 4L
Sun Feb 24, 2019 1:27 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free energy
Replies: 5
Views: 91

Re: Gibbs Free energy

When it's not given, it is usually suggested to be 298K.
by Danny Zhang 4L
Sun Feb 24, 2019 1:24 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneity
Replies: 8
Views: 138

Re: Spontaneity

I believe that the reaction is at equilibrium if delta G is zero.
by Danny Zhang 4L
Sun Feb 24, 2019 1:22 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Test 3
Replies: 14
Views: 218

Re: Test 3

^To add on to the previous comment, we only need to study electrochemistry material up to what we went over in lecture on Friday.
by Danny Zhang 4L
Sun Feb 17, 2019 1:11 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: ΔU = 0?
Replies: 4
Views: 126

Re: ΔU = 0?

Delta U=0 assumes an isothermal process because of delta U=(3/2)nR(delta T). When delta U is zero, delta T will have to be zero as well for the equation to be true.
by Danny Zhang 4L
Sun Feb 17, 2019 12:56 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Midterm Grades
Replies: 35
Views: 565

Re: Midterm Grades

Last quarter, they gave it back in lectures 1 week after we took the midterm.
by Danny Zhang 4L
Sat Feb 09, 2019 5:51 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Midterm [ENDORSED]
Replies: 48
Views: 949

Re: Midterm [ENDORSED]

In my opinion, the best way to prepare is doing the practice midterms that are given out during review sessions.
by Danny Zhang 4L
Sat Feb 09, 2019 5:44 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: deltaS=nCvln(t2/t1) what is Cv?
Replies: 7
Views: 122

Re: deltaS=nCvln(t2/t1) what is Cv?

Cv is the heat capacity of the system when the volume is constant.
by Danny Zhang 4L
Sat Feb 09, 2019 5:41 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: If not Gibbs Free Energy then what is the last topic for midterm?
Replies: 4
Views: 56

Re: If not Gibbs Free Energy then what is the last topic for midterm?

The topics tested on the midterm should cover everything about entropy up until the introduction of Gibbs free energy. According to the textbook, the last topic for midterm is the entropy of surroundings.
by Danny Zhang 4L
Fri Feb 01, 2019 1:37 pm
Forum: Phase Changes & Related Calculations
Topic: J vs. kJ
Replies: 9
Views: 127

Re: J vs. kJ

J is what is most commonly used to represent work. We can of course use kJ to represent work as well when specified by the problem.
by Danny Zhang 4L
Fri Feb 01, 2019 1:32 pm
Forum: Phase Changes & Related Calculations
Topic: U and its relations to work
Replies: 8
Views: 125

Re: U and its relations to work

U represents the internal energy of a system. Its relation to work can be seen in the first law of thermodynamics: change in U = q(heat exchanged) + w(work done on or by the system).
by Danny Zhang 4L
Fri Feb 01, 2019 1:19 pm
Forum: Calculating Work of Expansion
Topic: Work
Replies: 5
Views: 75

Re: Work

I believe that the main things to consider about work in thermodynamics are that negative work is done onto the system(compression of gas) and that positive work is done by the system(expansion of gas).
by Danny Zhang 4L
Sat Jan 26, 2019 2:41 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: pH
Replies: 9
Views: 138

Re: pH

pH tells us how acidic or basic something is. We can find pH through -log([H+]). We can also find pH if we only have pOH(log([OH-])) using the relationship pH+pOH=14.
by Danny Zhang 4L
Sat Jan 26, 2019 2:30 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Ka
Replies: 6
Views: 114

Re: Ka

Because H2SO4 is a strong acid, it will not have a Ka value because it completely dissociates into H and HSO4 when it first loses the hydrogen.
by Danny Zhang 4L
Sat Jan 26, 2019 2:17 pm
Forum: Ideal Gases
Topic: kc vs kp
Replies: 16
Views: 292

Re: kc vs kp

You can really only use kc in place of kp when all of the compounds involved in the reaction are in the gaseous phase.
by Danny Zhang 4L
Sun Jan 20, 2019 7:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ka and Kb as Inverses?
Replies: 7
Views: 117

Re: Ka and Kb as Inverses?

I don't believe I have ever seen Ka and Kb sharing an inverse relationship from the doing the textbook problems. I believe the only relevant relationship is Ka x Kb = Kw.
by Danny Zhang 4L
Sun Jan 20, 2019 7:17 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Concentrations Effect on K
Replies: 8
Views: 93

Re: Concentrations Effect on K

K will not change if the concentrations of both the reactants and the products change by the same amount. This is the case because their ratio would remain the same.
by Danny Zhang 4L
Sun Jan 20, 2019 7:13 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Kw
Replies: 6
Views: 121

Re: Kw

Yes, the concentration of hydronium and hydroxide are equal in pure(neutral) water.
by Danny Zhang 4L
Fri Jan 11, 2019 1:33 pm
Forum: Ideal Gases
Topic: What does K represent?
Replies: 9
Views: 141

Re: What does K represent?

K is the equilibrium constant. It represents the ratio of the concentration of products to the concentration of reactants in a reaction that tells us when the rate of forward reaction and the rate of reverse reaction are equal.
by Danny Zhang 4L
Fri Jan 11, 2019 1:16 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: defining Q
Replies: 6
Views: 86

Re: defining Q

When Q is smaller than K, it suggests that there is greater concentration of reactants and less concentration of products than suggested at equilibrium. Therefore, the reaction will take a forward direction to lower the concentration of reactants and increase the concentration of products until Q=K.
by Danny Zhang 4L
Fri Jan 11, 2019 1:07 pm
Forum: Ideal Gases
Topic: Q and K [ENDORSED]
Replies: 35
Views: 1073

Re: Q and K [ENDORSED]

The formulas for both Q and K are the same. K specifically tells us when the reaction is at equilibrium. Q can be be found during any instance of the reaction in order to determine which direction the reaction is going when it is compared to K.
by Danny Zhang 4L
Fri Dec 07, 2018 7:12 pm
Forum: Dipole Moments
Topic: Dipole dipole moments
Replies: 3
Views: 165

Re: Dipole dipole moments

There is no dipole-dipole interaction as the net dipole moment is zero.
by Danny Zhang 4L
Fri Dec 07, 2018 7:10 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pairs
Replies: 5
Views: 100

Re: Lone Pairs

The only things that affect the shape of a molecule are the central atom's lone pairs and the bonds it formed.
by Danny Zhang 4L
Fri Dec 07, 2018 7:05 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Correct Bond Angles
Replies: 6
Views: 124

Re: Correct Bond Angles

There will always be a slight difference because of the unique properties of molecules that affect their interactions.
by Danny Zhang 4L
Thu Nov 29, 2018 5:33 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: AX2E2
Replies: 14
Views: 245

Re: AX2E2

The VESPR formula AX2E2 suggests that the shape of the molecule is bent/angular, which means that the bond angles are less than 109.5 degrees.
by Danny Zhang 4L
Wed Nov 28, 2018 10:07 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Polarity
Replies: 5
Views: 82

Re: Polarity

Just as you mentioned, NO2 is polar because of the bent shape of the atoms as it prevents the dipole moments from canceling out.
by Danny Zhang 4L
Wed Nov 28, 2018 1:24 pm
Forum: Dipole Moments
Topic: 4.29
Replies: 3
Views: 56

Re: 4.29

I would always like to look at dipole moments as vectors. Looking at option 1, adding the two vectors (dipole moments) together gives us a resultant vector with a larger magnitude than the resultant vector for option 2.
by Danny Zhang 4L
Sat Nov 24, 2018 4:57 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: double and triple bonds
Replies: 10
Views: 137

Re: double and triple bonds

We treat double bonds and triple bonds like they are a single bond with one region of electron density in the VESPR model.
by Danny Zhang 4L
Sat Nov 24, 2018 4:55 pm
Forum: Hybridization
Topic: Writing out Hybridization
Replies: 8
Views: 95

Re: Writing out Hybridization

Either way is fine. It's just whether or not you prefer using sp^3d to follow the order of increasing energy of orbitals as we did for electron configurations.
by Danny Zhang 4L
Sat Nov 24, 2018 4:48 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: How to state bond angles.
Replies: 7
Views: 135

Re: How to state bond angles.

I believe just putting "less than 109.5 degrees" is fine for all bond angles around 100-109 degrees.
by Danny Zhang 4L
Sun Nov 18, 2018 10:00 pm
Forum: Student Social/Study Group
Topic: Turning in Homework (Thanksgiving Break)
Replies: 8
Views: 217

Re: Turning in Homework (Thanksgiving Break)

We just have to turn in 14 homework problems during week 9 to make up for missing week 8 discussion section.
by Danny Zhang 4L
Sun Nov 18, 2018 9:16 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Intermolecular Forces
Replies: 7
Views: 173

Re: Intermolecular Forces

I believe the main difference to know is that London forces occur in all molecules while dipole-dipole forces only occur in polar molecules.
by Danny Zhang 4L
Sun Nov 18, 2018 9:03 pm
Forum: Dipole Moments
Topic: Test
Replies: 15
Views: 231

Re: Test

It starts right after Thanksgiving break, which is great because more time to study!
by Danny Zhang 4L
Sat Nov 10, 2018 6:53 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg equation
Replies: 3
Views: 296

Re: Rydberg equation

Given that the energy is found through -(hR/n^2), increasing n would indicate greater energy as the result becomes less negative. If we use hR/n^2 to find the energy instead, increasing n would result in lower energy values, which is not correct.
by Danny Zhang 4L
Sat Nov 10, 2018 6:41 pm
Forum: Lewis Structures
Topic: Formal charge question
Replies: 9
Views: 187

Re: Formal charge question

For all of the Lewis structure questions I've done so far, I have only aimed for 0 formal charges for the most stable structure. If it was a polyatomic/monatomic ion, then I aim for one atom having the indicated charge.
by Danny Zhang 4L
Sat Nov 10, 2018 6:29 pm
Forum: Limiting Reactant Calculations
Topic: Actual Yield
Replies: 7
Views: 352

Re: Actual Yield

Our calculations will only give us the theoretical yields. The actual yield will always be given to us according to experimental results.
by Danny Zhang 4L
Sat Nov 10, 2018 6:10 pm
Forum: Electronegativity
Topic: Electronegativity
Replies: 8
Views: 166

Re: Electronegativity

Greater electronegativity is the same as saying greater attraction of other electrons.
by Danny Zhang 4L
Sat Nov 03, 2018 4:30 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg equation
Replies: 3
Views: 296

Re: Rydberg equation

They are both correct. However, professor Lavelle prefers using negative signs to clearly indicate that higher n results in higher energy.
by Danny Zhang 4L
Sat Nov 03, 2018 4:26 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: En Equation - Why the Negative?
Replies: 2
Views: 133

Re: En Equation - Why the Negative?

We use the negative sign to clearly indicate that energy increases as n increases.
by Danny Zhang 4L
Sat Nov 03, 2018 4:16 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 2.51 6th Edition
Replies: 1
Views: 35

Re: 2.51 6th Edition

For Bi and Si, you are finding the odd number of electrons in the p orbitals. However, for Ta and Ni, you are finding the odd number of electrons in the d orbitals
by Danny Zhang 4L
Sat Oct 27, 2018 5:44 pm
Forum: DeBroglie Equation
Topic: Kg vs Grams
Replies: 6
Views: 259

Re: Kg vs Grams

Within this class, I believe that we will only be using kg when dealing with energy and momentum.
by Danny Zhang 4L
Sat Oct 27, 2018 5:37 pm
Forum: Quantum Numbers and The H-Atom
Topic: Degeneracy
Replies: 7
Views: 304

Re: Degeneracy

For hydrogen, all orbitals share the same energy, so the degeneracy of an orbital simply depends on how many exist. For multi-electron atoms, only orbitals that share the same l quantum number have the same energy, so the degeneracy of an orbital would then depend on how many possible orbitals is po...
by Danny Zhang 4L
Sat Oct 27, 2018 5:14 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg- In relation to wavelength
Replies: 7
Views: 145

Re: Heisenberg- In relation to wavelength

Because of the inverse relationship between momentum and wavelength shown in the de Broglie equation(λ=h/p), increasing the uncertainty of momentum will decrease the uncertainty of wavelength.
by Danny Zhang 4L
Sat Oct 27, 2018 5:14 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg- In relation to wavelength
Replies: 7
Views: 145

Re: Heisenberg- In relation to wavelength

Because of the inverse relationship between momentum and wavelength shown in the de Broglie equation(λ=h/p), increasing the uncertainty of momentum will decrease the uncertainty of wavelength.
by Danny Zhang 4L
Sat Oct 20, 2018 6:37 pm
Forum: Properties of Light
Topic: Do I have to memorize the spectrum?
Replies: 20
Views: 337

Re: Do I have to memorize the spectrum?

I believe that it will be important to know the order of the regions of the electromagnetic spectrum, as I feel that questions on ordering waves based on frequency, wavelength, or energy will pop up on the test
by Danny Zhang 4L
Sat Oct 20, 2018 6:26 pm
Forum: Properties of Light
Topic: Grades
Replies: 7
Views: 141

Re: Grades

I believe that we will not see our grades until the end of the quarter, at least that is what is suggested by our syllabus. We can only keep track of our scores ourselves with the tests and homework being passed back.
by Danny Zhang 4L
Sat Oct 20, 2018 6:13 pm
Forum: Properties of Light
Topic: color of light
Replies: 11
Views: 218

Re: color of light

Both wavelength and frequency play a part in determining the color of light. It's just that visible spectrum diagrams always use wavelength to indicate the color.
by Danny Zhang 4L
Sun Oct 14, 2018 5:55 pm
Forum: Properties of Light
Topic: Speed of Light
Replies: 21
Views: 481

Re: Speed of Light

Anjali 4A wrote:Will we be provided all of these constants/equations during the tests, midterms and final?


I am sure that we will get a cover sheet with all of the constants/equations as we did on the first test on all future tests as well.
by Danny Zhang 4L
Sun Oct 14, 2018 5:49 pm
Forum: Administrative Questions and Class Announcements
Topic: Test #2
Replies: 3
Views: 152

Re: Test #2

By next week, are you referring to 10/15 through 10/19 or 10/22 through 10/26?
by Danny Zhang 4L
Sun Oct 14, 2018 2:05 pm
Forum: Properties of Light
Topic: E=hv
Replies: 13
Views: 203

Re: E=hv

Tamera Scott 3L wrote:I've also seen E=hf once, does anyone know if that is the same as E=hv?


I believe that f and v both symbolize frequency. I think that v is just more commonly used in chemistry while f is more preferred in physics.
by Danny Zhang 4L
Tue Oct 02, 2018 10:02 pm
Forum: Empirical & Molecular Formulas
Topic: Question F3(6th Edition)
Replies: 3
Views: 63

Question F3(6th Edition)

Question: (a) Write the formula for nitric acid. (b) Without doing a calculation, estimate which element in nitric acid occurs with the greatest mass percentage. I am only using this problem as an example. When the question asks for the formula of a certain compound, are we supposed to figure it out...
by Danny Zhang 4L
Tue Oct 02, 2018 9:49 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Question E1(6th Edition)
Replies: 7
Views: 197

Re: Question E1(6th Edition)

Considering what Dr.Lavelle said in class on Monday, I believe that it is fine for the answers' units to be in any form for problems in homework and tests when it is not specified. He mentioned that we may want our units to be simplified a certain way only if we are in a lab setting.
by Danny Zhang 4L
Sat Sep 29, 2018 9:24 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Question E1(6th Edition)
Replies: 7
Views: 197

Question E1(6th Edition)

Question: The field of nanotechnology offers some intriguing possibilities, such as the creation of fibers one atom wide. Suppose you were able to string together 1.00 mol Ag atoms, each of radius 144 pm, into one of these fibers by encapsulating them in carbon nanotubes (see Chapter 6). How long wo...

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