Search found 60 matches
- Sat Mar 16, 2019 12:21 pm
- Forum: Student Social/Study Group
- Topic: Studying for the Final
- Replies: 25
- Views: 2714
Re: Studying for the Final
My TA Joyce posts amazingly detailed review worksheets for each week. Bless her soul. Here's a link for Week 10: viewtopic.php?f=150&t=44734&p=154737&hilit=joyce&sid=67f6ec9f28f13271bf8509808c47037e#p154737
- Sat Mar 16, 2019 12:13 pm
- Forum: Student Social/Study Group
- Topic: Lyndon's Review Sess
- Replies: 6
- Views: 1078
- Sat Mar 16, 2019 12:12 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Phases Cell Diagram
- Replies: 2
- Views: 311
Re: Phases Cell Diagram
If you have multiple, solids, separate them by a line, not a comma. This is because the solids cannot mix.
- Sun Mar 10, 2019 4:13 pm
- Forum: General Rate Laws
- Topic: Rate Determining Step
- Replies: 5
- Views: 2932
Re: Rate Determining Step
Yup! the slowest step, or the step with the highest activation rate, is the slowest rate. The slowest rate is always the rate that determines the rate of the reaction.
- Sun Mar 10, 2019 4:08 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: reaction intermediates
- Replies: 2
- Views: 270
Re: reaction intermediates
Reaction intermediates are the reactants and products that end up canceling out when you write out all of the steps that it takes to get to the final product.
- Sun Mar 10, 2019 3:59 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Test 2 averages
- Replies: 4
- Views: 568
Re: Test 2 averages
While my discussion section's average was around 38/50, I believe the class as a total had a slightly lower average. This test was a killer one :(
- Mon Mar 04, 2019 1:03 am
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Study Advice
- Replies: 73
- Views: 6782
Re: Study Advice
If you look up the worksheets that the TA Joyce posts on chem community, they are really helpful. Lyndon's review sessions are also very helpful.
- Mon Mar 04, 2019 12:57 am
- Forum: Student Social/Study Group
- Topic: Final
- Replies: 24
- Views: 2126
Re: Final
Lyndon's review sessions are usually a few days before the final.
- Mon Mar 04, 2019 12:55 am
- Forum: Administrative Questions and Class Announcements
- Topic: Homework
- Replies: 7
- Views: 829
Re: Homework
Usually it is expected to do hw from the current chapter in the textbook. I think it is okay if you include a few problems from one chapter earlier if it is being covered in a test.
- Fri Feb 22, 2019 11:42 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: units
- Replies: 7
- Views: 974
Re: units
If you ever get pressure given int he units of "bar", you can just assume that its a 1:1 ratio with "atm". The conversion factor is very close to one, so Lavelle said we can treat bar as equal to atm.
- Fri Feb 22, 2019 11:37 am
- Forum: Student Social/Study Group
- Topic: Midterm Results
- Replies: 4
- Views: 514
Re: Midterm Results
When you get your midterm back, you can review your score and your answers using this link: https://lavelle.chem.ucla.edu/wp-conten ... am_ans.pdf
IF you want to dispute your score, make sure to double check the answer key first.
IF you want to dispute your score, make sure to double check the answer key first.
- Fri Feb 22, 2019 11:35 am
- Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
- Topic: Recharging Batteries [ENDORSED]
- Replies: 10
- Views: 1334
Re: Recharging Batteries [ENDORSED]
For batteries to be recharged, the reaction has to be reversed and electrical energy has to be supplied. Because we have to supply and input energy, this is not favorable.
- Wed Feb 20, 2019 4:39 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: 5/2R vs 3/2R
- Replies: 8
- Views: 7770
Re: 5/2R vs 3/2R
These values only work if you are dealing with monoatomic ideal gases.
- Wed Feb 20, 2019 4:35 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: What is pKa and Ka exactly?
- Replies: 16
- Views: 24780
Re: What is pKa and Ka exactly?
Ka is [product]/[reactant] in an acidic reaction. pKa is simply the neg log of Ka.
- Wed Feb 20, 2019 4:32 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 5
- Views: 528
Re: Salt Bridge
Another note is salt bridges have the same purpose as porous discs. The only difference is salt bridges connect the solutions between two different containers while porous discs connect the solutions separated in the same container.
- Sun Feb 10, 2019 9:28 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Midterm
- Replies: 2
- Views: 317
Re: Midterm
14B-1, 11am class:
Last name A-L in DODD 147.
Last name M-Z in LAKRETZ 110.
14B-2, 1pm class:
Last name A-L in HAINES 39.
Last name M-Z in FRANZ 1178.
14B-4, 3pm class: Last name A-Z in MOORE 100.
Last name A-L in DODD 147.
Last name M-Z in LAKRETZ 110.
14B-2, 1pm class:
Last name A-L in HAINES 39.
Last name M-Z in FRANZ 1178.
14B-4, 3pm class: Last name A-Z in MOORE 100.
- Sun Feb 10, 2019 1:59 am
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: midterm
- Replies: 3
- Views: 378
Re: midterm
https://lavelle.chem.ucla.edu/wp-conten ... ns_14B.pdf <--- this link lists all of the available hours in these few days.
- Sun Feb 10, 2019 1:50 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Converting Celsius to Kelvin
- Replies: 7
- Views: 668
Re: Converting Celsius to Kelvin
So far, simply adding 273 has worked well for me.
- Mon Feb 04, 2019 3:19 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Closed and Isolated
- Replies: 10
- Views: 692
Re: Closed and Isolated
The plant as a whole interacts with the environment in terms of mass (O2, CO2, water) and energy (sunlight and thermal).
- Mon Feb 04, 2019 3:14 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Midterm [ENDORSED]
- Replies: 49
- Views: 4719
Re: Midterm [ENDORSED]
LYNDON BUI WILL BE YOUR BEST FRIEND. Make sure you go to all of the review sessions that you can make. They will cover the most important topics and give you example questions that will prepare you well for the major tests.
- Mon Feb 04, 2019 3:10 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Final from 14A
- Replies: 2
- Views: 428
Re: Final from 14A
Right when you walk into the front of Young Hall, the office people should have your test. You just have to ask for the Chem 14 A Final and they'll take your bruincard and they'll give you your final right away.
- Sun Jan 27, 2019 2:25 pm
- Forum: Phase Changes & Related Calculations
- Topic: Phase Changes
- Replies: 7
- Views: 881
Re: Phase Changes
To turn ice to water (melting), heat must be added to the system (endothermic). In ice, the molecules have very little movement, adding heat energy to this increases the kinetic energy of the molecules, pushing it through a phase change and melting into water. The same is true for vaporization where...
- Sun Jan 27, 2019 2:23 pm
- Forum: Phase Changes & Related Calculations
- Topic: Phase changes
- Replies: 14
- Views: 1364
Re: Phase changes
Yes, to turn ice to water (melting), heat must be added to the system (endothermic) and the molecules move around quicker and melt. To turn water into ice (freezing), the water loses heat energy (exothermic) and the molecules slow down in movement and freeze into a solid.
- Sun Jan 27, 2019 2:20 pm
- Forum: Phase Changes & Related Calculations
- Topic: State Property
- Replies: 3
- Views: 344
Re: State Property
I understand state properties as values that are added and subtracted to find simple relationships of position. For example, the positions of two people can be compared. Person #1 is at the 5 meter mark while Person #2 is at the 8 meter mark. It doesn't matter how quickly someone traveled, what path...
- Thu Jan 17, 2019 11:31 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE Tables [ENDORSED]
- Replies: 11
- Views: 2357
Re: ICE Tables [ENDORSED]
ICE tables are typically used when finding the equilibrium concentrations of weak acids and bases. This is because with weak acids and bases, they don't fully dissociate and we have to calculate the specific concentrations of each reactant and product.
- Thu Jan 17, 2019 11:26 am
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: Approximation of x
- Replies: 3
- Views: 471
Re: Approximation of x
Just keep in mind that only the x in the (reactant-x) is negligible. The other changes in concentration for the products still have to be considered.
- Thu Jan 17, 2019 11:17 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE tables
- Replies: 3
- Views: 272
Re: ICE tables
The stoichiometric coefficients will be the same coefficients that you put in the "change" part of the table. If the coefficient is 1, the change will be =/- x. If the coefficient is 3, the change will be =/- 3x.
- Wed Jan 09, 2019 3:28 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Stability
- Replies: 3
- Views: 282
Re: Stability
Reactions will try to reach the most stable state as it reaches equilibrium. If products are more stable, more products will be produced and its concentration will be higher than the reactant concentration. This leads to a Higher K value. If reactants are more stable, the reactants will not react as...
- Wed Jan 09, 2019 3:24 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: example in class
- Replies: 3
- Views: 300
Re: example in class
He simply set up an ICE table with the provided information and the assumption that the initial concentrations of AD and Pi were 0 initially. With the initial and equilibrium concentrations of ADP provided in the problem, he calculated the change in concentration for ADP. Because the molar ratios of...
- Wed Jan 09, 2019 3:17 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: ICE Tables
- Replies: 3
- Views: 560
Re: ICE Tables
This video should help you understand the basics of the ICE Tables by giving you a few examples: https://www.youtube.com/watch?v=aJ0KNQ5-KaI
The ICE tables help you calculate concentrations when dealing with reactions in equilibrium.
The ICE tables help you calculate concentrations when dealing with reactions in equilibrium.
- Fri Dec 07, 2018 12:02 pm
- Forum: Conjugate Acids & Bases
- Topic: Inductive Effect
- Replies: 5
- Views: 547
Re: Inductive Effect
I consider the inductive effect as a fancy name for the same concept we already know about electronegativity and it’s effect on electron distribution. The more electronegative the atom, the more even the electron distribution is, and the more stable the molecule is. The more stable the molecule, the...
- Fri Dec 07, 2018 12:00 pm
- Forum: Air Pollution & Acid Rain
- Topic: acid rain
- Replies: 4
- Views: 558
Re: acid rain
The importance of this is recognizing that nonmetal oxides react with water and produce acidic products.
- Fri Dec 07, 2018 11:58 am
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Polydentate
- Replies: 3
- Views: 184
Re: Polydentate
Polydentates should have more than one element with lone pairs.
- Sun Dec 02, 2018 10:33 pm
- Forum: Hybridization
- Topic: Sigma bonds
- Replies: 9
- Views: 846
Re: Sigma bonds
All first bonds are sigma bonds. Any of the bonds on top of the first are considered pi bonds.
- Sun Dec 02, 2018 10:30 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: LDF
- Replies: 7
- Views: 1665
Re: LDF
While LDF is found between all molecules, it would only be important to point this out when dealing with two non-polar molecules.
- Sun Dec 02, 2018 10:29 pm
- Forum: Hybridization
- Topic: Double and Triple Bonds
- Replies: 17
- Views: 4226
Re: Double and Triple Bonds
Ignore the bonds and simply pay attention to ares of electron density to determine hybridization.
- Sun Dec 02, 2018 10:23 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: How to draw dipoles
- Replies: 3
- Views: 1028
Re: How to draw dipoles
I believe that within a molecule, you draw dipoles for each bond. When looking at the bond, you compare the two elements' electronegativity. Parallel to the bond, draw an arrow that points towards the element that is more electronegative. .
- Sun Dec 02, 2018 10:17 pm
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: Sigma and Pi Bonds
- Replies: 6
- Views: 922
Re: Sigma and Pi Bonds
Yep! Every first bond is a sigma bond. Any other bond added on top of the first ones are considered pi bonds.
- Sun Dec 02, 2018 10:14 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Square Planar
- Replies: 12
- Views: 1940
Re: Square Planar
All the angles in a square planar molecule are 90 degrees. You can easily remember this by recalling that a 2-d square is made up of 90 degree angles.
- Sun Nov 18, 2018 9:54 pm
- Forum: Properties of Light
- Topic: Test 3
- Replies: 24
- Views: 2112
Re: Test 3
My TA Anton listed these topics for Test 3: Bonding (trends), Shape (lewis structure), Molecular Shape, Polarity, and Hybridization.
- Sun Nov 18, 2018 9:40 pm
- Forum: Sigma & Pi Bonds
- Topic: Visualizing sigma and pi bonds
- Replies: 7
- Views: 747
Re: Visualizing sigma and pi bonds
https://www.youtube.com/watch?v=D0-oOwzc8P0
This video should help you visualize the difference between sigma and pi bonding in organic molecules.
This video should help you visualize the difference between sigma and pi bonding in organic molecules.
- Sun Nov 18, 2018 9:37 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Polar molecules
- Replies: 5
- Views: 756
Re: Polar molecules
Yes, your explanation is perfect for why this molecule is polar :)
- Sun Nov 11, 2018 9:39 pm
- Forum: Trends in The Periodic Table
- Topic: Atomic vs ionic radius
- Replies: 6
- Views: 941
Re: Atomic vs ionic radius
When the atom is neutral, the atomic and ionic radius are the same. This isn't true for anions and cations, though. If the atom loses an electron and becomes a cation,the atom becomes positively charged and the ionic radius is smaller than the atomic radius because the atom loses an electron energy ...
- Sun Nov 11, 2018 9:26 pm
- Forum: Student Social/Study Group
- Topic: Study Group Chat?
- Replies: 4
- Views: 624
Re: Study Group Chat?
Here's a link to a messenger group chat for Chem 14A with Lavelle --> https://m.me/join/AbZf3pS8xum6RSWb
- Sun Nov 11, 2018 9:22 pm
- Forum: Bond Lengths & Energies
- Topic: bond energy
- Replies: 4
- Views: 388
Re: bond energy
We will never be required to calculate bond energy on our own and it will usually be provided to us in the question. It is just good to understand that bond energy is higher for triple and double bonds compared to single bonds. This is because in triple and double bonds, there are more electrons bei...
- Sun Nov 04, 2018 9:41 pm
- Forum: Octet Exceptions
- Topic: Radicals
- Replies: 16
- Views: 1665
Re: Radicals
A radical is an atom, molecule, or ion that has an unpaired valence electron. These unpaired electrons make radicals highly chemically reactive. Most organic radicals have short lifetimes because of this.
- Sun Nov 04, 2018 9:30 pm
- Forum: Resonance Structures
- Topic: Resonance with formal charge
- Replies: 6
- Views: 591
Re: Resonance with formal charge
Molecules may still have resonance even when the specific molecule is not in its most stable form. Resonance has nothing to do with the stability of the molecule.
- Sun Nov 04, 2018 9:27 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Heisenburg equation units
- Replies: 2
- Views: 389
Re: Heisenburg equation units
Uncertainty of momentum is is kg*m/s, and uncertainty of position is m. Uncertainty of velocity is m/s.
- Sun Oct 28, 2018 3:07 pm
- Forum: Lewis Structures
- Topic: Lewis Structure Drawing
- Replies: 6
- Views: 484
Re: Lewis Structure Drawing
In my high school chem courses, lone pair electrons were always drawn as two separate dots while shared electrons were drawn as a line. While it may take a bit longer to draw, making this distinction helps you visualize and differentiate the electrons.
- Sun Oct 28, 2018 3:04 pm
- Forum: Properties of Electrons
- Topic: Effective Nuclear Charge
- Replies: 2
- Views: 387
Re: Effective Nuclear Charge
Effective nuclear charge, as stated before, is the net positive attraction between protons in the nucleus and the valence electrons. Many different factors affect the effective nuclear charge. For example, shielding leads to decreased effective nuclear charge, increasing atom size leads to decreased...
- Sun Oct 28, 2018 2:56 pm
- Forum: Trends in The Periodic Table
- Topic: Removing 2nd e- [ENDORSED]
- Replies: 4
- Views: 424
Re: Removing 2nd e- [ENDORSED]
By removing an electron, there is now a larger ratio of protons to electrons meaning that the electrons that are left are more attracted to the positive nucleus. This attraction is harder to overcome, therefore it takes more energy to remove the next electrons.
- Sun Oct 21, 2018 5:29 pm
- Forum: Trends in The Periodic Table
- Topic: Periodic Table
- Replies: 2
- Views: 215
Re: Periodic Table
S-block elements are more reactive because they want to lose their extra outer valence electrons and reactions between elements typically occur to fill a shell. The valence electrons from S-block elements are easily removed and added to an element that needs electrons to be stable.
- Sun Oct 21, 2018 4:41 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: What is the equation used for?
- Replies: 9
- Views: 847
Re: What is the equation used for?
I believe that my TA told us that for this equation, we mostly just need to understand the concept behind it and understand that the uncertainty exists because of the limits of our technology today. I would worry less about using the equation to actually solve any mathematical problems.
- Sun Oct 21, 2018 4:37 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Shielding
- Replies: 5
- Views: 1130
Re: Shielding
An analogy that helps you better understand shielding was given by Dr. Lavelle during Friday's lecture. Imagine you're camping and standing next to the campfire. The heat that you feel from the fire can be compared to the force of attraction between an electron and the nucleus. If someone stands bet...
- Sat Oct 13, 2018 2:53 pm
- Forum: Properties of Electrons
- Topic: energy transitions
- Replies: 6
- Views: 379
Re: energy transitions
When electrons transition from one energy level to another, energy is released as photons of light. But the type of light is dependent on which energy level the electrons drops to. For example, when electrons drop to the first energy level, it releases UV light.
- Sat Oct 13, 2018 2:40 pm
- Forum: Photoelectric Effect
- Topic: Work function
- Replies: 3
- Views: 214
Re: Work function
I looked through the index of the Chemical Principles 6th Edition textbook and the term workforce is never mentioned so I highly doubt it is a term we have to know or use. :)
- Sat Oct 13, 2018 2:28 pm
- Forum: Limiting Reactant Calculations
- Topic: Test 1
- Replies: 5
- Views: 753
Re: Test 1
Both homework and tests should be returned the week after in your discussions :)
- Wed Oct 03, 2018 10:07 am
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Calculating the number of atoms
- Replies: 5
- Views: 508
Re: Calculating the number of atoms
To go from grams to atoms, you have to do grams -> moles -> atoms. For grams -> moles, simply divide the mass (g) of the sample by its molar mass (g/mol). For moles -> atoms, multiply the # of moles * 6.022x10^23 (Avogadro's number). The final answer will be the # of atoms in the given sample.
- Wed Oct 03, 2018 9:55 am
- Forum: Balancing Chemical Reactions
- Topic: Mole Ratios & Stoichiometric Relations
- Replies: 2
- Views: 339
Re: Mole Ratios & Stoichiometric Relations
Stoichiometric coefficients are the numbers written before each compound in a balanced chemical equation that represent the moles of each reactant and product. For example, 2 Na(s) + 2 H20(l) -> 2 NaOH(aq) + [1] H2(g) is the same thing as saying 2 moles Na(s) + 2 moles H20(l) -> 2 moles NaOH(aq) + 1...
- Wed Oct 03, 2018 9:28 am
- Forum: Photoelectric Effect
- Topic: equation generated through the photoelectric experiment
- Replies: 1
- Views: 166
Re: equation generated through the photoelectric experiment
I believe that "C", the option you have already highlighted, is the correct answer. This is Einstein's photoelectric equation. Einstein assumed that light is made of photons and photons collide with electrons in an atom, giving all of its energy to the electron. However, some of the energy...