Search found 61 matches
- Fri Mar 15, 2019 11:09 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Past Finals
- Replies: 4
- Views: 824
Re: Past Finals
If you google "Bruin Test Bank at UCLA" and click the Chemistry tab, there is a 14B final from Lavelle's Winter 2014 class.
- Fri Mar 15, 2019 10:12 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: residual entropy T=0
- Replies: 2
- Views: 544
Re: residual entropy T=0
When absolute temperature equals zero (T=0), there is no thermal entropy (no movement). This means that residual entropy is based on the complexity and order of the molecule and its positions.
- Fri Mar 15, 2019 7:28 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: 15.85 6th Edition
- Replies: 1
- Views: 242
15.85 6th Edition
Question 15.85 asks us to draw a proposed structure for the activated complex of each chemical reaction given. Will we be required to know how to draw these structures for the final?
- Thu Mar 07, 2019 2:13 pm
- Forum: Van't Hoff Equation
- Topic: test 2
- Replies: 7
- Views: 1074
Re: test 2
Could someone who got this question correct explain step by step how they did it? I am still confused with this problem.
- Wed Mar 06, 2019 12:40 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Q: Partial Pressures and Concentration?
- Replies: 4
- Views: 1213
Re: Q: Partial Pressures and Concentration?
I am also confused as to why that conversion doesn't apply to galvanic cells.
- Tue Mar 05, 2019 7:47 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: 6th Edition 14.41
- Replies: 3
- Views: 390
Re: 6th Edition 14.41
Why is Q [H+]1/[H+]2?
- Sat Mar 02, 2019 6:50 pm
- Forum: *Free Energy of Activation vs Activation Energy
- Topic: Spontaneous reactions
- Replies: 11
- Views: 4522
Re: Spontaneous reactions
Many homework problems ask to solve for the temperature at which a reaction is spontaneous. This shows that spontaneity depends on more than it just being exothermic or endothermic and understanding this makes solving these problems easier.
- Sat Mar 02, 2019 6:34 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Final Topics
- Replies: 6
- Views: 625
Re: Final Topics
Yes the final is cumulative and I would focus more on 14B material than things taught in 14A.
- Sat Mar 02, 2019 6:29 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Test #2
- Replies: 10
- Views: 992
Re: Test #2
Yes, we normally get our tests back the following week in discussion.
- Fri Feb 22, 2019 12:09 pm
- Forum: Balancing Redox Reactions
- Topic: sections covered on test
- Replies: 4
- Views: 429
Re: sections covered on test
Even though we won't be directly tested on Enthalpy and Entropy, we still need to know how to calculate them to use in Gibbs Free Energy so I would make sure to still review them.
- Fri Feb 22, 2019 12:04 pm
- Forum: Van't Hoff Equation
- Topic: Practice Problems
- Replies: 3
- Views: 512
Re: Practice Problems
If you have the sixth edition text book there are homework problems in chapter 11 that deal with the Van't Hoff's equation!
- Fri Feb 22, 2019 12:00 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs free energy at phase changes
- Replies: 2
- Views: 326
Re: Gibbs free energy at phase changes
When G=0, there is no energy free to do work.
- Sat Feb 16, 2019 6:10 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Spontaneous vs boiling point?
- Replies: 4
- Views: 804
Re: Spontaneous vs boiling point?
It would be the reaction's natural tendency to go from a liquid to a gas at T=boiling point.
- Sat Feb 16, 2019 6:01 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 2764036
Re: Post All Chemistry Jokes Here
What do you do with a sick chemist?
If you can't helium, and you can't curium, then you might as well barium.
If you can't helium, and you can't curium, then you might as well barium.
- Sat Feb 16, 2019 5:47 pm
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Midterm Grades
- Replies: 35
- Views: 2482
Re: Midterm Grades
They are normally handed out after lecture, not in discussion.
- Sat Feb 09, 2019 11:16 am
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Midterm topics
- Replies: 3
- Views: 416
Re: Midterm topics
We will be tested on Friday's lecture material up to Gibbs Free Energy.
- Sat Feb 09, 2019 11:11 am
- Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
- Topic: Residual Entropy
- Replies: 5
- Views: 468
Re: Residual Entropy
Residual entropy is positional entropy. We can find it using SkblnW (this ignores thermal energy).
- Tue Feb 05, 2019 2:44 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Question 8.57 (Sixth Edition)
- Replies: 3
- Views: 475
Re: Question 8.57 (Sixth Edition)
I am also confused about this problem. My answer doesn't match the solutions manual either.
- Sun Feb 03, 2019 11:18 am
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Isolated System Example
- Replies: 4
- Views: 996
Re: Isolated System Example
The universe is also considered an isolated system because the energy of the universe is constant.
- Sun Feb 03, 2019 11:15 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: kJ vs J
- Replies: 9
- Views: 764
Re: kJ vs J
Lavelle said they are interchangeable so you could use either as long as the answer matches the units.
- Sun Feb 03, 2019 11:14 am
- Forum: Calculating Work of Expansion
- Topic: integral work equation
- Replies: 2
- Views: 342
Re: integral work equation
There are some problems in the text book where the integral equation is needed (for example problem 8.11 in the sixth edition) so I would know how to solve for those.
- Sun Jan 27, 2019 12:49 pm
- Forum: Phase Changes & Related Calculations
- Topic: Modules
- Replies: 17
- Views: 1202
Re: Modules
Lavelle posted the modules for only the first two sections in Chem 14A, so he may only post chemical equilibria modules for 14B.
- Sun Jan 27, 2019 12:44 pm
- Forum: Phase Changes & Related Calculations
- Topic: State Properties
- Replies: 3
- Views: 387
Re: State Properties
Work is dependent on the path taken because the intermediate steps taken to get to the final conclusion must be considered rather than just calculating final-initial.
- Sun Jan 27, 2019 12:37 pm
- Forum: Phase Changes & Related Calculations
- Topic: Phase Changes
- Replies: 7
- Views: 865
Re: Phase Changes
Another way to determine whether a reaction is endothermic or exothermic is by the value of delta H: an endothermic has a positive delta H because the reaction is absorbing energy, whereas an exothermic energy has a negative delta H because it is releasing energy.
- Thu Jan 17, 2019 3:15 pm
- Forum: Student Social/Study Group
- Topic: ICE Table
- Replies: 5
- Views: 505
Re: ICE Table
We can take this short cut when the value of K is < 1x10^-3
- Thu Jan 17, 2019 3:11 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 12.23 6th Edition
- Replies: 2
- Views: 223
Re: 12.23 6th Edition
Okay I understand how the Kw is equal to to x^2 now. Thank you.
- Thu Jan 17, 2019 9:27 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 12.23 6th Edition
- Replies: 2
- Views: 223
12.23 6th Edition
Hello, I am having trouble solving 12.23. Could someone please explain how to go about it? The question asks: The value of Kw for water at body temp (37 degrees C) is 2.1x10^-14. A) What is the molarity of H3O ions and the pH of neutral water at 37 degrees C? B) What is the molarity of OH in neutral...
- Sun Jan 13, 2019 7:28 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Reaction Quotient Meaning
- Replies: 2
- Views: 216
Re: Reaction Quotient Meaning
Q can be calculated at any given time, whether before equilibria is reached or after equilibria is subjected to change. It's just a measure to see whether more reactants or products are being formed until reaching equilibrium.
- Sun Jan 13, 2019 7:10 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: 6th Edition Hw#11.29
- Replies: 2
- Views: 219
Re: 6th Edition Hw#11.29
Will we need to know the Gibbs Free Energy equation for the first test?
- Sat Dec 08, 2018 4:16 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Polydentate
- Replies: 11
- Views: 1085
Re: Polydentate
Is dien tridentate or tetradentate?
- Thu Dec 06, 2018 10:09 pm
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: Conjugate?
- Replies: 5
- Views: 775
Re: Conjugate?
A conjugate base is the result of an acid donating its protons.
A conjugate acid is the result of a base accepting protons.
A conjugate acid is the result of a base accepting protons.
- Thu Dec 06, 2018 9:58 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Size and Polarizability
- Replies: 4
- Views: 647
Re: Size and Polarizability
Anions get larger as the number of electrons increase because the number of shells increase. Ionic radii increases down a group and decreases across a period. So determining size of anions does depend on the number of electrons but you also have to consider the strength of the nuclear charge and its...
- Sun Dec 02, 2018 10:13 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: calcium
- Replies: 2
- Views: 269
Re: calcium
Yes, quick means "active" and slake means to hydrate. This makes sense because calcium hydroxide is formed by mixing calcium oxide with water.
- Thu Nov 29, 2018 4:54 pm
- Forum: Naming
- Topic: Common Ligand Names
- Replies: 4
- Views: 503
Re: Common Ligand Names
Okay, hopefully they will be provided on the final.
- Wed Nov 28, 2018 2:32 pm
- Forum: Naming
- Topic: Common Ligand Names
- Replies: 4
- Views: 503
Common Ligand Names
Are we expected to memorize all of the common ligand names from Table 17.4 (6th edition)?
- Sun Nov 25, 2018 6:50 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: 4.21 6th edition
- Replies: 2
- Views: 223
Re: 4.21 6th edition
The best way to know bond angles is to memorize which bond angles are formed by each shape. Remember that lone pairs can effect these bond angles through repulsion and bond angles would therefore be a little smaller than without lone pairs attached to the molecule.
- Sun Nov 25, 2018 6:43 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: induced-dipole
- Replies: 4
- Views: 647
- Sun Nov 25, 2018 11:58 am
- Forum: Dipole Moments
- Topic: What are dipole moments used for?
- Replies: 3
- Views: 364
Re: What are dipole moments used for?
^this is correct. Atoms with higher electronegativity attract electrons more than atoms with low electronegativity, resulting in a net dipole moment. Remember that electronegativity increases across a period and decreases down a group.
- Wed Nov 14, 2018 3:39 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Remembering
- Replies: 8
- Views: 783
Re: Remembering
^This chart is super helpful thank you for sharing it!
- Wed Nov 14, 2018 3:37 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Bond Angles
- Replies: 3
- Views: 337
Re: Bond Angles
So the best way to know the angles is just through memorization of the structures right?
- Tue Nov 13, 2018 8:36 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: hydrogen bonding
- Replies: 11
- Views: 912
Re: hydrogen bonding
^Exactly. Higher melting points indicate more stability so this explains the example given in class: GC base pairs in DNA are more stable than AT base pairs.
- Fri Nov 09, 2018 3:06 pm
- Forum: Bond Lengths & Energies
- Topic: Tests
- Replies: 5
- Views: 595
Re: Tests
Yes to confirm the last test begins in your discussion section the week of November 26th.
- Fri Nov 09, 2018 2:59 pm
- Forum: Bond Lengths & Energies
- Topic: Grading
- Replies: 3
- Views: 339
Re: Grading
I am pretty sure than 93 is an A
- Thu Nov 08, 2018 4:15 pm
- Forum: Dipole Moments
- Topic: Polarizability
- Replies: 5
- Views: 346
Re: Polarizability
Polarizability depends on the number of electrons a molecule has and its size. Increasing size and electrons results in stronger attractive interactions.
- Sun Nov 04, 2018 7:08 pm
- Forum: Lewis Structures
- Topic: Question 3.55 (Sixth Edition)
- Replies: 6
- Views: 604
Re: Question 3.55 (Sixth Edition)
A faster way to find a radical is by counting how many electrons a molecule has. An odd number of electrons would signify a radical whereas an even number of electrons would signify paired electrons.
- Sun Nov 04, 2018 7:00 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Test 2 Alveoli question
- Replies: 5
- Views: 666
Re: Test 2 Alveoli question
Yes the position in question 1 is just the diameter, 2x10^-4 m.
- Sun Nov 04, 2018 2:59 pm
- Forum: Lewis Structures
- Topic: Lewis Structures
- Replies: 11
- Views: 967
Re: Lewis Structures
If there are only two atoms in a molecule, does it matter where the atom with the non-lowest ionization atom is put? Like does it matter if it is put to the left or right of the central atom?
- Sun Oct 28, 2018 12:07 pm
- Forum: Ionic & Covalent Bonds
- Topic: Second ionization of alkali metals
- Replies: 3
- Views: 699
Re: Second ionization of alkali metals
Second ionization energy is always higher because after the first electron is removed, the atom is more positive and the protons in the nucleus have a stronger pull on the electrons left
- Sun Oct 28, 2018 11:55 am
- Forum: Ionic & Covalent Bonds
- Topic: Valence electrons
- Replies: 8
- Views: 1465
Re: Valence electrons
We write the d group in electron configurations before p groups because the d state is lower in energy than the p state
- Thu Oct 25, 2018 3:39 pm
- Forum: Trends in The Periodic Table
- Topic: Sizes of ions and neutral atoms
- Replies: 4
- Views: 520
Re: Sizes of ions and neutral atoms
It also helps to consider why cations are smaller than their neutral atoms. Cations are smaller because they lose an electron, which decreases the size of the electron cloud.
- Sun Oct 21, 2018 4:16 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: 6th Edition HW 2.29
- Replies: 2
- Views: 154
Re: 6th Edition HW 2.29
Okay this makes sense. Thank you so much!
- Sun Oct 21, 2018 3:39 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: 6th Edition HW 2.29
- Replies: 2
- Views: 154
6th Edition HW 2.29
I don't really understand 2.29, the question asks to identify how many electrons can have the following quantum numbers in an atom. I don't know how to figure out the possible number of electrons that can have a specific quantum number. Can someone explain how to do this?
- Thu Oct 18, 2018 9:08 pm
- Forum: Properties of Light
- Topic: Test 2 [ENDORSED]
- Replies: 15
- Views: 1135
Re: Test 2 [ENDORSED]
Nothing from test 1 will be on test 2
- Sun Oct 14, 2018 8:47 pm
- Forum: Properties of Electrons
- Topic: Rydberg formula
- Replies: 5
- Views: 430
Re: Rydberg formula
First plug in n=4 into the formula to solve for the energy at that level. Then do the same for n=2. After calculating these answers, find the difference between the two using Energyfinal-Energyinitial. Finally plug this difference into equation: wavelength=h(c)/E.
- Sun Oct 14, 2018 8:24 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: post assessment #40
- Replies: 2
- Views: 105
Re: post assessment #40
Solve for the energy at n=6 and energy at n=5. After finding these two numbers, subtract Energyfinal-Energyinitial. Once you find this difference, plug the answer into equation: wavelength=h(c)/E
- Tue Oct 09, 2018 8:20 pm
- Forum: Photoelectric Effect
- Topic: Post-Mod Problem #28
- Replies: 4
- Views: 461
Re: Post-Mod Problem #28
and mass of e- will always be 9.11x10^-31 for that equation right?
- Wed Oct 03, 2018 3:13 pm
- Forum: Limiting Reactant Calculations
- Topic: Finding theoretical yield
- Replies: 6
- Views: 620
Re: Finding theoretical yield
You only need to know the molar ratio between the limiting reactant and products because the limiting reactant is completely used in the chemical reaction.
- Wed Oct 03, 2018 1:06 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Molarity and Dilution of a Solution Post Module Assessment Question 25
- Replies: 5
- Views: 654
Re: Molarity and Dilution of a Solution Post Module Assessment Question 25
Thank you both so much! I just wasn't using .02 L as the initial volume in the equation. Seeing it step by step helped a lot!
- Tue Oct 02, 2018 3:50 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Molarity and Dilution of a Solution Post Module Assessment Question 25
- Replies: 5
- Views: 654
Molarity and Dilution of a Solution Post Module Assessment Question 25
I am having a hard time solving question 25 on the Molarity and Dilution post assessment. The question is: 5.00 g of KMnO4 is dissolved in a 150.00 mL flask of water. If 20.00 mL of this solution is removed and placed in a new 2nd 250.00 mL flask and filled with water, what is the concentration of t...
- Thu Oct 05, 2017 7:58 pm
- Forum: Balancing Chemical Reactions
- Topic: Percent yield [ENDORSED]
- Replies: 6
- Views: 2122
Re: Percent yield [ENDORSED]
percent yield= actual yield (which will be given to you)/theoretical yield
- Thu Oct 05, 2017 7:54 pm
- Forum: Limiting Reactant Calculations
- Topic: Determining Limiting Reactant
- Replies: 6
- Views: 2022
Re: Determining Limiting Reactant
Just to clarify, when determining molar mass of a reactant you don't include the coefficient that was found when balancing the equation right?