Search found 63 matches
- Sat Mar 16, 2019 9:49 pm
- Forum: First Order Reactions
- Topic: Half-Lives
- Replies: 4
- Views: 837
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.
- Sat Mar 16, 2019 9:47 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Reaction rate
- Replies: 1
- Views: 488
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.
- 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: 299
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.
- Sat Mar 16, 2019 9:45 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Catalysts
- Replies: 28
- Views: 1776
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.
- Sat Mar 16, 2019 9:43 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Arrhenius Equation
- Replies: 3
- Views: 661
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.
- Sun Mar 10, 2019 9:38 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: What does the Arrhenius Equation tell us?
- Replies: 1
- Views: 228
What does the Arrhenius Equation tell us?
How can we use the Arrhenius equation to see how the activation energy and temperature affect k?
- 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: 571
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.
- Sun Mar 10, 2019 9:28 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Final Questions
- Replies: 10
- Views: 1211
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.
- Sun Mar 10, 2019 9:24 pm
- Forum: Zero Order Reactions
- Topic: Meaning of Zero, First, and Second Order?
- Replies: 4
- Views: 636
Meaning of Zero, First, and Second Order?
What exactly does it mean if a reaction is zero, first, or second order?
- 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: 205
Cell Diagrams and aq
For cell diagrams, does there always have to be an aqueous next to the salt bridge?
- 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: 218
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...
- 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: 268
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?
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?
- Sun Feb 24, 2019 9:30 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 3
- Views: 352
Salt Bridge
What is the point of a salt bridge?
- 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: 485
Re: Signs of delta G and E
A spontaneous reaction releases free energy, so delta G would be negative.
- Sun Feb 24, 2019 7:48 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidation and Reduction?
- Replies: 6
- Views: 871
Oxidation and Reduction?
Can someone explain what oxidation and reduction mean?
- Sun Feb 24, 2019 7:46 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Free Energy is a state function?
- Replies: 5
- Views: 633
Free Energy is a state function?
Can someone explain why Gibbs Free Energy is a state function?
- Wed Feb 13, 2019 1:20 am
- Forum: Calculating Work of Expansion
- Topic: Expansion Against a Vacuum
- Replies: 4
- Views: 686
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?
- 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: 193
Effects of Constant Volume or Temp
What are the effects that constant volume or temperature have on delta U and why?
- 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: 897
Re: isolated vs closed system
Oops yeah @Michelle I typed it in wrong I meant isolated system; I edited it now! Thank you!
- Thu Feb 07, 2019 7:01 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Ideal Gas Equations?
- Replies: 1
- Views: 243
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?
- Sun Feb 03, 2019 6:12 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: 2nd law of thermodynamics
- Replies: 5
- Views: 565
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.
- 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: 897
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.
- 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: 636
Re: finding W
Yes they are the same and I think you can use both interchangeably.
- Sun Jan 27, 2019 3:03 pm
- Forum: Phase Changes & Related Calculations
- Topic: Why are phase changes endothermic?
- Replies: 11
- Views: 1006
Why are phase changes endothermic?
Why are phase changes from solid-->liquid-->vapor endothermic reactions?
- Sun Jan 27, 2019 2:52 pm
- Forum: Phase Changes & Related Calculations
- Topic: Week 4 Homework
- Replies: 12
- Views: 1258
Re: Week 4 Homework
Yes I believe that is correct.
- 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: 113
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?
- Sun Jan 20, 2019 2:01 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Water in the Equilibrium Constant.
- Replies: 4
- Views: 415
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.
- Sun Jan 20, 2019 1:58 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: pKa vs pH?
- Replies: 3
- Views: 427
pKa vs pH?
I'm kinda confused by the different between pKa and pH/pKb and pOH. Are they basically the same thing?
- Sun Jan 20, 2019 1:51 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: equations
- Replies: 1
- Views: 209
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...
- Sat Jan 12, 2019 6:09 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Equilibrium constant
- Replies: 4
- Views: 399
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.
- Sat Jan 12, 2019 4:52 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE table calculation
- Replies: 2
- Views: 223
Re: ICE table calculation
You ignore pure liquids and solids in the ICE table and K equations.
- Sat Jan 12, 2019 4:47 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: How to use ICE tables
- Replies: 5
- Views: 721
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 ...
- Sat Dec 08, 2018 8:52 pm
- Forum: Calculating the pH of Salt Solutions
- Topic: Concentration
- Replies: 1
- Views: 333
Re: Concentration
Yes, it is.
- Sat Dec 08, 2018 8:46 pm
- Forum: Identifying Acidic & Basic Salts
- Topic: What are salts...
- Replies: 4
- Views: 682
What are salts...
Please help, I don't understand salts at all. What are they and how do they lower/raise pH of solutions?
- Sat Dec 08, 2018 8:27 pm
- Forum: Dipole Moments
- Topic: Identifying Dipole-Dipole
- Replies: 2
- Views: 552
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.
- Sat Dec 08, 2018 8:24 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Shape - 4
- Replies: 3
- Views: 423
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.
- Thu Dec 06, 2018 1:07 am
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: 6B. 3 [ENDORSED]
- Replies: 3
- Views: 433
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.
- Thu Dec 06, 2018 12:36 am
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Total Charge
- Replies: 5
- Views: 715
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.
- Sun Nov 18, 2018 2:31 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Focus 2E.13 (7th Edition)
- Replies: 1
- Views: 225
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...
- 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: 706
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,...
- Sun Nov 18, 2018 2:05 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Shape and Polarity? [ENDORSED]
- Replies: 4
- Views: 543
Shape and Polarity? [ENDORSED]
Can someone explain again how the shape of a molecule can determine whether it is polar or non polar?
- Sun Nov 11, 2018 3:02 am
- Forum: Electronegativity
- Topic: Electronegativity
- Replies: 8
- Views: 922
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.
- Fri Nov 09, 2018 11:32 pm
- Forum: Dipole Moments
- Topic: Boiling Points
- Replies: 3
- Views: 382
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...
- Fri Nov 09, 2018 11:07 pm
- Forum: Electronegativity
- Topic: Electronegativity
- Replies: 8
- Views: 748
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 ...
- Sun Nov 04, 2018 12:37 am
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: s-block, p-block, d-block
- Replies: 3
- Views: 267
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.
- Sun Nov 04, 2018 12:28 am
- Forum: Lewis Structures
- Topic: Drawing Lewis Structures
- Replies: 4
- Views: 375
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?
- Fri Nov 02, 2018 9:03 pm
- Forum: Lewis Structures
- Topic: Midterm Chemical Formula Names
- Replies: 3
- Views: 391
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...
- Sun Oct 28, 2018 2:59 pm
- Forum: Lewis Structures
- Topic: Lewis Structure Drawing
- Replies: 6
- Views: 529
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!
- Sun Oct 28, 2018 2:53 pm
- Forum: Properties of Electrons
- Topic: Effective Nuclear Charge
- Replies: 2
- Views: 398
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.
- Sun Oct 28, 2018 3:14 am
- Forum: Ionic & Covalent Bonds
- Topic: electronegativity and ionization energy [ENDORSED]
- Replies: 4
- Views: 590
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...
- Mon Oct 22, 2018 5:46 pm
- Forum: Properties of Light
- Topic: The Uncertainty Principle
- Replies: 2
- Views: 350
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
- Sun Oct 21, 2018 3:04 am
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Delta E [ENDORSED]
- Replies: 1
- Views: 207
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 ...
- Fri Oct 19, 2018 11:59 am
- Forum: Student Social/Study Group
- Topic: curve?
- Replies: 20
- Views: 3021
Re: curve?
The class is graded on a point basis, out of 500 points. You can find more info on it on the syllabus.
- Tue Oct 16, 2018 2:03 am
- Forum: Administrative Questions and Class Announcements
- Topic: Chem Community Grading
- Replies: 2
- Views: 230
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.
- Mon Oct 15, 2018 6:59 pm
- Forum: Properties of Light
- Topic: When is the midterm?
- Replies: 1
- Views: 186
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.
- Sun Oct 14, 2018 10:43 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Atomic Radius
- Replies: 3
- Views: 375
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.
- Fri Oct 12, 2018 2:43 am
- Forum: Empirical & Molecular Formulas
- Topic: M19 Finding O
- Replies: 1
- Views: 318
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.
- Thu Oct 11, 2018 8:36 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Mass percent composition [ENDORSED]
- Replies: 4
- Views: 887
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.
- Wed Oct 10, 2018 10:02 pm
- Forum: SI Units, Unit Conversions
- Topic: State of the molecules
- Replies: 4
- Views: 449
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.
- Sun Oct 07, 2018 3:20 pm
- Forum: Properties of Light
- Topic: Problem #9 6th Edition
- Replies: 1
- Views: 110
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?
- Fri Oct 05, 2018 12:40 am
- Forum: Molarity, Solutions, Dilutions
- Topic: Q G17 part b. (7th edition)
- Replies: 5
- Views: 1156
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?
- Wed Oct 03, 2018 11:48 pm
- Forum: Empirical & Molecular Formulas
- Topic: F 17 6th edition
- Replies: 1
- Views: 292
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 ...
- Tue Oct 02, 2018 1:19 am
- Forum: Significant Figures
- Topic: Periodic Table Sig Figs
- Replies: 4
- Views: 1288
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.