Search found 63 matches

by Michelle Wang 4I
Sat Mar 16, 2019 9:49 pm
Forum: First Order Reactions
Topic: Half-Lives
Replies: 4
Views: 208

Re: Half-Lives

No, it is possible that we could be asked to calculate the half life of zero or second order reactions. You just have to be careful because unlike with first order reactions, the inital/starting concentration changes the half life. So for each starting concentration there is a different half life.
by Michelle Wang 4I
Sat Mar 16, 2019 9:47 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction rate
Replies: 1
Views: 183

Re: Reaction rate

Typically, reactions that are termolecular are slow since it is less likely for three molecules to collide with the right amount of energy for the reaction to occur.
by Michelle Wang 4I
Sat Mar 16, 2019 9:46 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: E° is not a state function
Replies: 2
Views: 68

Re: E° is not a state function

Also, Lyndon said today that if you can add the half reactions and the electrons completely cancel out, then you don't need to convert it to delta G since they are half reactions.
by Michelle Wang 4I
Sat Mar 16, 2019 9:45 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysts
Replies: 9
Views: 272

Re: Catalysts

Catalysts work by giving an entirely new pathway for the reaction to occur with a lower activation energy. Therefore, the curve would be lower.
by Michelle Wang 4I
Sat Mar 16, 2019 9:43 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius Equation
Replies: 3
Views: 217

Re: Arrhenius Equation

You would use the Arrhenius equation to relate things like the rate constant with temperature, activation energy and the pre-exponential factor A. There can be questions asking you to solve for one of them given the others.
by Michelle Wang 4I
Sun Mar 10, 2019 9:38 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: What does the Arrhenius Equation tell us?
Replies: 1
Views: 46

What does the Arrhenius Equation tell us?

How can we use the Arrhenius equation to see how the activation energy and temperature affect k?
by Michelle Wang 4I
Sun Mar 10, 2019 9:30 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Order for Cell Diagram
Replies: 4
Views: 52

Re: Order for Cell Diagram

The order also goes from left to right on the anode: solid, gas, and aqueous is next to the salt bridge. For the cathode, it would be aqueous, gas, solid.
by Michelle Wang 4I
Sun Mar 10, 2019 9:28 pm
Forum: Administrative Questions and Class Announcements
Topic: Final Questions
Replies: 10
Views: 358

Re: Final Questions

There will be 8 questions total, but there will probably be like part A, B, C, etc for several of the questions.
by Michelle Wang 4I
Sun Mar 10, 2019 9:24 pm
Forum: Zero Order Reactions
Topic: Meaning of Zero, First, and Second Order?
Replies: 4
Views: 55

Meaning of Zero, First, and Second Order?

What exactly does it mean if a reaction is zero, first, or second order?
by Michelle Wang 4I
Tue Feb 26, 2019 10:33 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams and aq
Replies: 1
Views: 42

Cell Diagrams and aq

For cell diagrams, does there always have to be an aqueous next to the salt bridge?
by Michelle Wang 4I
Tue Feb 26, 2019 9:22 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Lyndon Review number 8/9?
Replies: 1
Views: 55

Re: Lyndon Review number 8/9?

“A reaction with a negative standard reduction potential favors oxidation of the reactant” is true because that means it has a -E value, and therefore it is not likely to be reduced (gain election), it is more likely to be oxidized (lose electrons). “A reactant in a reaction with a very positive sta...
by Michelle Wang 4I
Tue Feb 26, 2019 8:53 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Problem 14.15c 6th edition
Replies: 1
Views: 68

Problem 14.15c 6th edition

For question 15 part C, in the galvanic cell diagram the answer key has
Cd(s) | Cd(OH)2 (s) | KOH (aq) || Ni(OH)3 (s) |Ni(OH)2 | Ni(s)
I don't understand what the purpose of adding KOH to the anode side of the cell diagram is, and also why do we not add it to the cathode side as well?
by Michelle Wang 4I
Sun Feb 24, 2019 9:30 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge
Replies: 3
Views: 55

Salt Bridge

What is the point of a salt bridge?
by Michelle Wang 4I
Sun Feb 24, 2019 9:27 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Signs of delta G and E
Replies: 4
Views: 78

Re: Signs of delta G and E

A spontaneous reaction releases free energy, so delta G would be negative.
by Michelle Wang 4I
Sun Feb 24, 2019 7:48 pm
Forum: Balancing Redox Reactions
Topic: Oxidation and Reduction?
Replies: 6
Views: 88

Oxidation and Reduction?

Can someone explain what oxidation and reduction mean?
by Michelle Wang 4I
Sun Feb 24, 2019 7:46 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Free Energy is a state function?
Replies: 5
Views: 80

Free Energy is a state function?

Can someone explain why Gibbs Free Energy is a state function?
by Michelle Wang 4I
Wed Feb 13, 2019 1:20 am
Forum: Calculating Work of Expansion
Topic: Expansion Against a Vacuum
Replies: 4
Views: 108

Expansion Against a Vacuum

How come when a gas expands against a vacuum work = 0? What does delta S, delta U, and q equal for this situation as well?
by Michelle Wang 4I
Sun Feb 10, 2019 7:50 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Effects of Constant Volume or Temp
Replies: 1
Views: 39

Effects of Constant Volume or Temp

What are the effects that constant volume or temperature have on delta U and why?
by Michelle Wang 4I
Thu Feb 07, 2019 7:03 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: isolated vs closed system
Replies: 7
Views: 129

Re: isolated vs closed system

Oops yeah @Michelle I typed it in wrong I meant isolated system; I edited it now! Thank you!
by Michelle Wang 4I
Thu Feb 07, 2019 7:01 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Ideal Gas Equations?
Replies: 1
Views: 88

Ideal Gas Equations?

When do you use the ideal gas specific heat capacities as well as internal energy (U = 3/2nRT)? Do we have to use that internal energy formula or can we just calculate work and q and add it together like we do for other gases?
by Michelle Wang 4I
Sun Feb 03, 2019 6:12 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 2nd law of thermodynamics
Replies: 5
Views: 78

Re: 2nd law of thermodynamics

The second law of thermodynamics says that when energy changes from one form to another, entropy (or disorder) increases. I think this can help us understand how the systems are changing through reactions.
by Michelle Wang 4I
Sun Feb 03, 2019 6:05 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: isolated vs closed system
Replies: 7
Views: 129

Re: isolated vs closed system

An example of a closed system is a beaker that can allow energy to exchange with the surroundings but matter doesn't exchange with the surroundings. An example of an isolated system would be a really well-insulated coffee mug that doesn't allow energy or matter to exchange with surroundings.
by Michelle Wang 4I
Sun Feb 03, 2019 5:54 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: finding W
Replies: 6
Views: 93

Re: finding W

Yes they are the same and I think you can use both interchangeably.
by Michelle Wang 4I
Sun Jan 27, 2019 3:03 pm
Forum: Phase Changes & Related Calculations
Topic: Why are phase changes endothermic?
Replies: 11
Views: 156

Why are phase changes endothermic?

Why are phase changes from solid-->liquid-->vapor endothermic reactions?
by Michelle Wang 4I
Sun Jan 27, 2019 2:52 pm
Forum: Phase Changes & Related Calculations
Topic: Week 4 Homework
Replies: 12
Views: 226

Re: Week 4 Homework

Yes I believe that is correct.
by Michelle Wang 4I
Sun Jan 27, 2019 2:51 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies of Diatomic Molecules?
Replies: 1
Views: 31

Bond Enthalpies of Diatomic Molecules?

In the section of Prof Lavelle's notes Additional Comments, he said that the bond enthalpies of diatomic molecules are accurate, but the others are averages. Can someone explain why the enthalpies for diatomic molecules are accurate but not for other molecules?
by Michelle Wang 4I
Sun Jan 20, 2019 2:01 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Water in the Equilibrium Constant.
Replies: 4
Views: 71

Re: Water in the Equilibrium Constant.

I think we don't include water in the equilibrium constant because we ignore pure solids or liquids when we write it out since it doesn't really affect the equilibrium constant.
by Michelle Wang 4I
Sun Jan 20, 2019 1:58 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: pKa vs pH?
Replies: 3
Views: 101

pKa vs pH?

I'm kinda confused by the different between pKa and pH/pKb and pOH. Are they basically the same thing?
by Michelle Wang 4I
Sun Jan 20, 2019 1:51 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: equations
Replies: 1
Views: 47

Re: equations

If you go on Professor Lavelle's website, there is a link that has the constants and equations that will be given to us during the exam, https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14B/Constants_Equations.pdf. You should know equations like K=concentration of products over reaction...
by Michelle Wang 4I
Sat Jan 12, 2019 6:09 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium constant
Replies: 4
Views: 55

Re: Equilibrium constant

The equilibrium constant isn't affected because it is a ratio of the products to reactants. So when you add more products, for example, then more reactants are formed and the ratio remains the same.
by Michelle Wang 4I
Sat Jan 12, 2019 4:52 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE table calculation
Replies: 2
Views: 47

Re: ICE table calculation

You ignore pure liquids and solids in the ICE table and K equations.
by Michelle Wang 4I
Sat Jan 12, 2019 4:47 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: How to use ICE tables
Replies: 5
Views: 162

Re: How to use ICE tables

Hi Eruchi, In this situation we don't know the exact change in molarity that occurs in the reaction. We know that when the Cu(NH3)42+ dissociates, it forms 4 mol of NH3 and 1 mol of Cu2+. We use the stoichiometric coefficients of the balanced chemical equations to write the x that is added or taken ...
by Michelle Wang 4I
Sat Dec 08, 2018 8:52 pm
Forum: Calculating the pH of Salt Solutions
Topic: Concentration
Replies: 1
Views: 138

Re: Concentration

Yes, it is.
by Michelle Wang 4I
Sat Dec 08, 2018 8:46 pm
Forum: Identifying Acidic & Basic Salts
Topic: What are salts...
Replies: 4
Views: 219

What are salts...

Please help, I don't understand salts at all. What are they and how do they lower/raise pH of solutions?
by Michelle Wang 4I
Sat Dec 08, 2018 8:27 pm
Forum: Dipole Moments
Topic: Identifying Dipole-Dipole
Replies: 2
Views: 237

Re: Identifying Dipole-Dipole

If a molecule is polar, then one of its intermolecular forces would be dipole-dipole. To see if a molecule is polar, check if the dipole moments cancel through molecular geometry. If not, (and the atoms are not the same, like C-C) then the molecule is polar.
by Michelle Wang 4I
Sat Dec 08, 2018 8:24 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Shape - 4
Replies: 3
Views: 103

Re: Shape - 4

I'm not sure, but I don't think we need to be able to identify which one is which just from that. If we know that the complex is flat, however, then we would know it's square pyramidal. Overall though I think just putting either square planar or tetrahedral would be accepted.
by Michelle Wang 4I
Thu Dec 06, 2018 1:07 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 6B. 3 [ENDORSED]
Replies: 3
Views: 85

Re: 6B. 3 [ENDORSED]

Since HCl is a strong acid, we can assume that there is 100% dissociation. Since there is .025 M HCl, then there is .025 moles of HCl. When HCl dissociates, there would be .025 moles of H3O+. You would then divide that by the volumes to get the molarity, and use that to solve for the two pH levels.
by Michelle Wang 4I
Thu Dec 06, 2018 12:36 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Total Charge
Replies: 5
Views: 146

Re: Total Charge

If you have the oxidation state of the transition metal, then you can look at the charges of the ligands and add them together. If the oxidation state of the TM is +3, but the total charge of the ligands is -2, then the total charge of the coordination compound is +1.
by Michelle Wang 4I
Sun Nov 18, 2018 2:31 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Focus 2E.13 (7th Edition)
Replies: 1
Views: 42

Re: Focus 2E.13 (7th Edition)

N2O only has 16 valence electrons, but for there to be a lone pair on central nitrogen with a double bond on oxygen and a single bond with nitrogen, there would be 18 electrons. I think that the stablest structure would actually be a triple bond between the nitrogens, and a single bond on the oxygen...
by Michelle Wang 4I
Sun Nov 18, 2018 2:09 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: London force strength vs. electronegativity
Replies: 3
Views: 162

Re: London force strength vs. electronegativity

Yes, fluorine is more electronegative so it would have a stronger intramolecular bonds (bonds within the molecule between C and F) and it would require more energy to break this bond over CHI3. However, melting point questions are referring to the strength of the intermolecular forces. In this case,...
by Michelle Wang 4I
Sun Nov 18, 2018 2:05 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Shape and Polarity? [ENDORSED]
Replies: 4
Views: 113

Shape and Polarity? [ENDORSED]

Can someone explain again how the shape of a molecule can determine whether it is polar or non polar?
by Michelle Wang 4I
Sun Nov 11, 2018 3:02 am
Forum: Electronegativity
Topic: Electronegativity
Replies: 8
Views: 259

Re: Electronegativity

I’m not positive, but I think that electronegativity increases down a row and decreases down a group with no exceptions. Of course, the last group (noble gases) do not have electronegativity values since they have a stable configuration.
by Michelle Wang 4I
Fri Nov 09, 2018 11:32 pm
Forum: Dipole Moments
Topic: Boiling Points
Replies: 3
Views: 95

Re: Boiling Points

H2O has hydrogen bonding due to the large electronegativity difference between H and O, which causes a dipole in the molecule. With multiple molecules, the partial negative charge on the O interacts with the positive H charge, forming a hydrogen bond. This increases the boiling point of H2O since th...
by Michelle Wang 4I
Fri Nov 09, 2018 11:07 pm
Forum: Electronegativity
Topic: Electronegativity
Replies: 8
Views: 187

Re: Electronegativity

Yes, as Swetha said electronegativity is a periodic trend. Electronegativity is how much an atom wants to gain another electron to try to get a full shell. Therefore elements on the top right (fluorine) are the most electronegative since they want a full shell, while elements on the bottom left are ...
by Michelle Wang 4I
Sun Nov 04, 2018 12:37 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: s-block, p-block, d-block
Replies: 3
Views: 76

Re: s-block, p-block, d-block

I'm not positive, but I think I remember Professor Lavelle saying that those are what we have to know for exams. However, I think it is good to know how to find the configuration of all the elements.
by Michelle Wang 4I
Sun Nov 04, 2018 12:28 am
Forum: Lewis Structures
Topic: Drawing Lewis Structures
Replies: 4
Views: 103

Drawing Lewis Structures

If the question asks you to draw the Lewis structure of a molecule that has resonance, do you just draw one of the structures or do we need to draw all of them?
by Michelle Wang 4I
Fri Nov 02, 2018 9:03 pm
Forum: Lewis Structures
Topic: Midterm Chemical Formula Names
Replies: 3
Views: 82

Midterm Chemical Formula Names

Do we need to know how to recognize molecules just from the name? I keep getting conflicting information where some TAs tell me I need to be able to recognize the polyatomic ions from the name (like hydrogen sulfate) while others say that the formula will be written in parenthesis so we don't need t...
by Michelle Wang 4I
Sun Oct 28, 2018 2:59 pm
Forum: Lewis Structures
Topic: Lewis Structure Drawing
Replies: 6
Views: 89

Re: Lewis Structure Drawing

It might have been acceptable in your high school class, but since in Lavelle's lecture he said that the lines were only for bonds then representing the electrons with lines is incorrect. Drawing each dot is somewhat tedious but do it anyways so that you won't be marked off on the midterm/tests!
by Michelle Wang 4I
Sun Oct 28, 2018 2:53 pm
Forum: Properties of Electrons
Topic: Effective Nuclear Charge
Replies: 2
Views: 135

Re: Effective Nuclear Charge

Effective nuclear charge is the attraction between the protons and valence electrons. As the effective nuclear charge increases, the radius of the atom decreases since the valence electrons are being pulled closer to the nucleus. That is why atomic radius decreases from left to right down a row.
by Michelle Wang 4I
Sun Oct 28, 2018 3:14 am
Forum: Ionic & Covalent Bonds
Topic: electronegativity and ionization energy [ENDORSED]
Replies: 4
Views: 92

Re: electronegativity and ionization energy [ENDORSED]

Electronegativity is the ability of the atom to attract electrons into its orbital. For example, fluorine is the most electronegative element because it wants to reach the stable configuration of neon. Ionization energy is the amount of energy necessary to remove an electron from an atom. The two ar...
by Michelle Wang 4I
Mon Oct 22, 2018 5:46 pm
Forum: Properties of Light
Topic: The Uncertainty Principle
Replies: 2
Views: 118

Re: The Uncertainty Principle

1 eV is equal to 1.602e-19 J. It's on the constants and equations page, https://lavelle.chem.ucla.edu/wp-conten ... ations.pdf
by Michelle Wang 4I
Sun Oct 21, 2018 3:04 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Delta E [ENDORSED]
Replies: 1
Views: 53

Re: Delta E [ENDORSED]

If you are talking about the energy of the photon, it is always positive because a photon is basically the form that energy takes when it is released by an electron moving to a lower energy level. A photon cannot be negative energy, as if the electron was absorbing energy to move to a higher energy ...
by Michelle Wang 4I
Fri Oct 19, 2018 11:59 am
Forum: Student Social/Study Group
Topic: curve?
Replies: 20
Views: 1033

Re: curve?

The class is graded on a point basis, out of 500 points. You can find more info on it on the syllabus.
by Michelle Wang 4I
Tue Oct 16, 2018 2:03 am
Forum: Administrative Questions and Class Announcements
Topic: Chem Community Grading
Replies: 2
Views: 123

Re: Chem Community Grading

The sunday posts you made would count for week 2. The cutoff for the three posts of the week are sunday nights.
by Michelle Wang 4I
Mon Oct 15, 2018 6:59 pm
Forum: Properties of Light
Topic: When is the midterm?
Replies: 1
Views: 71

When is the midterm?

I didn't know where to post this question, but what date is the midterm? I couldn't find it on the syllabus.
by Michelle Wang 4I
Sun Oct 14, 2018 10:43 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Atomic Radius
Replies: 3
Views: 50

Re: Atomic Radius

I think that the covalent radius is the measure of the size of an atom that forms part of a covalent bond. The atomic radius is just the distance from the center of the nucleus to the electron cloud.
by Michelle Wang 4I
Fri Oct 12, 2018 2:43 am
Forum: Empirical & Molecular Formulas
Topic: M19 Finding O
Replies: 1
Views: 137

Re: M19 Finding O

To find the moles of O, you first convert the masses given of CO2, H2O, and N2 to find the mass of C, H, and N respectively. Then you subtract the masses of those three elements from the given weight of .376 g to get the mass of O. Use molar mass to get moles of O.
by Michelle Wang 4I
Thu Oct 11, 2018 8:36 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Mass percent composition [ENDORSED]
Replies: 4
Views: 252

Re: Mass percent composition [ENDORSED]

Yeah, mass percent composition is the percent of how much one element makes up a molecule by weight. For example in H2O, hydrogen makes up about 11% of the molecule.
by Michelle Wang 4I
Wed Oct 10, 2018 10:02 pm
Forum: SI Units, Unit Conversions
Topic: State of the molecules
Replies: 4
Views: 167

Re: State of the molecules

I think I remember Professor Lavelle saying that for now we don't need to know the phases, but that in the future we will need to know (and write the phases on chemical equations) without having them given to us.
by Michelle Wang 4I
Sun Oct 07, 2018 3:20 pm
Forum: Properties of Light
Topic: Problem #9 6th Edition
Replies: 1
Views: 36

Problem #9 6th Edition

I understand how to use the formulas to convert from frequency, wavelength, and the energy of the photon. But I don't get how to identify which event/activity the radiation corresponds with. Can someone explain how you know what event it is?
by Michelle Wang 4I
Fri Oct 05, 2018 12:40 am
Forum: Molarity, Solutions, Dilutions
Topic: Q G17 part b. (7th edition)
Replies: 5
Views: 122

Re: Q G17 part b. (7th edition)

For some reason when I first saw this problem I thought it would be one where we use the formula Minitial x Vinitial = Mfinal x Vfinal since it had to do with preparing a solution. Can someone explain why we don't solve it that way?
by Michelle Wang 4I
Wed Oct 03, 2018 11:48 pm
Forum: Empirical & Molecular Formulas
Topic: F 17 6th edition
Replies: 1
Views: 83

F 17 6th edition

I found the molecular and empirical formula, but I wrote the answer with Os last instead of first (which is the correct way to write it). Would I be marked off for not writing the proper order of elements, even if I have everything else correct? Is there a way to know what order the elements should ...
by Michelle Wang 4I
Tue Oct 02, 2018 1:19 am
Forum: Significant Figures
Topic: Periodic Table Sig Figs
Replies: 4
Views: 168

Periodic Table Sig Figs

Is there a particular number of sig figs that we should be using when looking at the periodic table? For example, should we use 16.00 or 15.999 as the atomic mass of oxygen? I know that the difference is slight but I'm just wondering.

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