Search found 60 matches
- Tue Mar 12, 2019 3:57 pm
- Forum: Ideal Gases
- Topic: Approximations for ICE
- Replies: 20
- Views: 1465
Re: Approximations for ICE
If the value of K is less than 10^-3 then the assumption can be made that x is very small and would be negligible.
- Tue Mar 12, 2019 3:54 pm
- Forum: Ideal Gases
- Topic: units
- Replies: 15
- Views: 1281
Re: units
The equilibrium value, K, is a ration of products to reactants, so mathematically the units should cancel out and the calculation would not have units.
- Tue Mar 12, 2019 3:49 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Slow Step
- Replies: 6
- Views: 488
Re: Slow Step
With most examples, the slow step should be identified. However, if we're given the rate law, we should be able to pinpoint the step out of a list based on this information.
- Mon Mar 04, 2019 9:42 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Finding n
- Replies: 12
- Views: 1043
Re: Finding n
n is the number of electrons transferred after you've balance the oxidation and half reactions.
- Mon Mar 04, 2019 9:41 am
- Forum: Student Social/Study Group
- Topic: Final
- Replies: 24
- Views: 2021
Re: Final
Dr. Lavelle usually sends an email or announces the date of the review sessions in class. Usually it starts during week 10!
- Mon Mar 04, 2019 9:40 am
- Forum: Administrative Questions and Class Announcements
- Topic: Homework
- Replies: 7
- Views: 800
Re: Homework
It depends on what your TA prefers, but usually you would do problems based on the information we're covering in lecture. However, I'm pretty sure you could include a few problems from previous topics.
- Sat Feb 23, 2019 2:37 pm
- Forum: Balancing Redox Reactions
- Topic: Test 2 Material
- Replies: 11
- Views: 862
Re: Test 2 Material
The test covers everything we learned after the midterm until the end of week 7. Dr. Lavelle's website gives more information regarding the test. "Test 2 covers all topics on Gibbs free energy and electrochemistry up to but not including the Nernst equation (which is all the new material covere...
- Sat Feb 23, 2019 2:36 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: gibbs free units
- Replies: 3
- Views: 361
Re: gibbs free units
I believe Gibbs Free Energy should almost always be measured in kj overall, however if the question asks for the Standard Gibbs Free Energy of formation of the reaction then the units should be kj/moles. Hope this helps!
- Sat Feb 23, 2019 2:29 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 3
- Views: 329
Re: Salt Bridge
The salt bridge keeps solutions from mixing. It consists of a gel containing a concentrated aqueous salt solution in an inverted U-tube and allows the flow of ions, which done affect the cell reaction. The salt bridge completes the circuit.
- Tue Feb 19, 2019 12:04 am
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Final exam
- Replies: 8
- Views: 861
Re: Final exam
The final exam is scheduled for Sunday, March 17th from 11:30-2:30.
- Tue Feb 19, 2019 12:02 am
- Forum: Administrative Questions and Class Announcements
- Topic: 14BL and 14C
- Replies: 5
- Views: 1005
Re: 14BL and 14C
I was planning on taking math, chem 14c, cheer 14bl, and a lab! I heard a lot of people combine 14c and 14bl and because 14bl is a lab, worth 3 units, it's not as much work as adding an entirely new class. A lot of people told me it's more busy work. Hope this helps.
- Mon Feb 18, 2019 11:57 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: TEST 3
- Replies: 7
- Views: 968
Re: TEST 3
Electrochemistry and Gibbs Free Energy!
- Sat Feb 09, 2019 2:57 pm
- Forum: Calculating Work of Expansion
- Topic: Units
- Replies: 7
- Views: 673
Re: Units
Try your best to use atm, since the gas constant (R) is in terms of atm.
- Sat Feb 09, 2019 2:56 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: entropy midterm
- Replies: 2
- Views: 253
Re: entropy midterm
Dr. Lavelle said in lecture on Friday that Gibbs Free Energy won't be on the midterm, which is section 4J. Therefore, I'm assuming everything from 4F-4I can be on the midterm.
- Sat Feb 09, 2019 2:55 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: midterm [ENDORSED]
- Replies: 4
- Views: 510
Re: midterm [ENDORSED]
This is the equation and constant sheet on Dr. Lavelle's website. https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14B/Constants_Equations.pdf
Hope this helps!
Hope this helps!
- Mon Feb 04, 2019 3:59 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Chem 14 BL
- Replies: 5
- Views: 744
Re: Chem 14 BL
I know that they do not need to be taken together, but I remember Dr. Lavelle saying in the beginning of the quarter that knowledge from 14B is needed for 14 BL, so it should be taken after. You can take 14 C and 14 BL together (I know multiple people who have done this), but it isn't required.
- Mon Feb 04, 2019 3:55 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: qv vs qp
- Replies: 9
- Views: 2446
Re: qv vs qp
qv is heat at constant volume, while qp is heat at constant pressure, as denoted by the subscripts. The question would typically ask you which one to solve for or would typically state which one is constant. Hope this helps!
- Mon Feb 04, 2019 3:51 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Units
- Replies: 7
- Views: 597
Re: Units
J.C^-1.mol^-1 = J/C.mol
- Sat Jan 26, 2019 11:59 am
- Forum: Ideal Gases
- Topic: Ideal Gas Law
- Replies: 7
- Views: 677
Re: Ideal Gas Law
The ideal gas law (PV=nRT) can be used to solve for any of the variable in it and can also be used to convert between partial pressure and molar concentration.
- Sat Jan 26, 2019 11:57 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: State Properties
- Replies: 6
- Views: 438
Re: State Properties
Heat and work aren't state properties because you would need to evaluate the path taken in order to determine its value, whereas with state functions only the final and initial values are needed.
- Sat Jan 26, 2019 11:55 am
- Forum: Phase Changes & Related Calculations
- Topic: Enthalpy and States
- Replies: 8
- Views: 720
Re: Enthalpy and States
Yes the state of matter will definitely affect enthalpy because different amounts of heat are required to change a substance through each phase.
- Sat Jan 19, 2019 3:58 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: When is X negligible.
- Replies: 6
- Views: 488
Re: When is X negligible.
You can approximate the x in the denominator when the value of K is less than 10^-3. However, it is not mandatory and you would still get the same value of x if you choose not do use the shortcut.
- Sat Jan 19, 2019 3:47 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Solving weak acid/base dissociations
- Replies: 4
- Views: 284
Re: Solving weak acid/base dissociations
Most of the time the quadratic formula needs to be used unless K<10^-3 in which case you can approximate the equation and get rid of the need to use the quadratic formula.
- Sat Jan 19, 2019 3:15 pm
- Forum: Ideal Gases
- Topic: PV=nRT
- Replies: 8
- Views: 1082
Re: PV=nRT
We use the ideal gas law to convert between partial pressure and molar concentration. R is a constant, therefore it will always be give and T will most probably be given in order to find either P or n/v.
- Tue Jan 15, 2019 6:21 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Temperature
- Replies: 3
- Views: 278
Re: Temperature
Kelvin is the most commonly and used unit for temperature when solving problems regarding equilibria. When using the formula PV=nRT, for example, the unit for temperature must be in Kelvin.
- Tue Jan 15, 2019 4:33 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Changes to K value
- Replies: 9
- Views: 649
Re: Changes to K value
Only temperature effects and changes the equilibrium constant K. Pressure, volume, and concentration adjust to match the same result as the equilibrium constant.
- Tue Jan 15, 2019 4:30 pm
- Forum: Ideal Gases
- Topic: Water
- Replies: 13
- Views: 993
Re: Water
An aqueous solution is a mixture of something with water, therefore water can be referred to as a solid, liquid, or gas, but cannot be considered aqueous.
- Thu Jan 10, 2019 8:49 pm
- Forum: Ideal Gases
- Topic: Pv=nRT [ENDORSED]
- Replies: 12
- Views: 688
Re: Pv=nRT [ENDORSED]
Yes, based on Dr. Lavelle's slides in lecture, the temperature in the ideal gas law is measured in Kelvin.
- Thu Jan 10, 2019 8:47 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: K vs Q [ENDORSED]
- Replies: 7
- Views: 718
Re: K vs Q [ENDORSED]
The formula to find K and Q are the same. However, K is the ratio of at equilibrium and therefore includes the values of the reaction at equilibrium. Meanwhile, Q is the reaction quotient and is the ratio at any given time in the reaction.
- Thu Jan 10, 2019 8:47 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Reaction quotient [ENDORSED]
- Replies: 4
- Views: 394
Re: Reaction quotient [ENDORSED]
Since the products are not gases, you put a 1 in the numerator. Then place the reactants that are gases in the denominator. Hope this helps!
- Sat Dec 01, 2018 5:40 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Final Exam
- Replies: 22
- Views: 1497
Re: Final Exam
The final will be cumulative and will cover everything on the syllabus.
- Sat Dec 01, 2018 5:39 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Dissociation energy
- Replies: 7
- Views: 591
Re: Dissociation energy
Dissociation energy is always positive because it is the energy required to break a bond, therefore it would require an input of energy, which is always positive. However, to form a bond, energy would have to be released, resulting in a negative charge.
- Sat Dec 01, 2018 5:32 pm
- Forum: Hybridization
- Topic: Pi bonds in triple bond
- Replies: 17
- Views: 1713
Re: Pi bonds in triple bond
There are two pi bonds and one sigma bond in a triple bond.
- Mon Nov 26, 2018 8:25 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Polarizability
- Replies: 5
- Views: 389
Re: Polarizability
The trend for polarizability is the same as the trend for atomic radii. Therefore it generally decreases when moving left to right on a period and increases when going down a group.
- Mon Nov 26, 2018 8:24 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Can an octahedral be polar?
- Replies: 4
- Views: 2144
Re: Can an octahedral be polar?
The octahedral shape is almost always non polar because it is symmetric, causing the dipole moments to cancel one another. Hope this helps!
- Mon Nov 26, 2018 8:21 pm
- Forum: Hybridization
- Topic: Just Kind of Confused
- Replies: 13
- Views: 943
Re: Just Kind of Confused
It doesn't matter. Professor Lavelle showed the class both because the book shows it differently, so it's just based on preference.
- Mon Nov 19, 2018 5:04 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Exam 3 Topics [ENDORSED]
- Replies: 6
- Views: 669
Re: Exam 3 Topics [ENDORSED]
Test 3 covers: End of Bonding from 3.12 (6 Ed.) and from 2D (7 Ed.); and all of Molecular Shape and Structure (see Syllabus and Outlines for details).
This is from Dr. Lavelle's class website. Hope this helps!!
This is from Dr. Lavelle's class website. Hope this helps!!
- Mon Nov 19, 2018 5:00 pm
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: AXE
- Replies: 7
- Views: 673
Re: AXE
A is the central atom, X is the number of bonded pairs, ad E is the number of lone pairs. Therefore, you can figure out a molecules AXE by looking at the molecule.
- Mon Nov 19, 2018 4:56 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Bond Angles
- Replies: 3
- Views: 116
Re: Bond Angles
Bond angles of a seesaw are <90 and 120 degrees.
- Mon Nov 12, 2018 2:33 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Formal Charge
- Replies: 12
- Views: 1198
Re: Formal Charge
In my opinion, it is always better to show work just in case. Especially if the grader prefers to see the steps.
- Mon Nov 12, 2018 2:29 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 Bonds
- Replies: 14
- Views: 922
Re: Hydrogen Bonds
Yes, Hydrogen Bonds are a type of dipole-dipole force that only occurs with Nitrogen, Oxygen, and Fluorine.
- Mon Nov 12, 2018 2:25 pm
- Forum: Dipole Moments
- Topic: Test
- Replies: 15
- Views: 1216
Re: Test
On Professor Lavelle's website, it says the next test will be administered starting November 27th in discussion classes. So, after Thanksgiving break.
- Mon Nov 05, 2018 8:44 pm
- Forum: Octet Exceptions
- Topic: Expanded Octet [ENDORSED]
- Replies: 5
- Views: 479
Re: Expanded Octet [ENDORSED]
Elements on and after period 3 can have an expanded octet because they have a d orbital, where they can accommodate more electrons in. Common ones include, Sulfur, Phosphorous, and Chlorine.
- Mon Nov 05, 2018 8:42 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Why does PCl5 break the Octet Rule?
- Replies: 8
- Views: 6868
Re: Why does PCl5 break the Octet Rule?
Phosphorous, Chlorine, and Sulfur can accommodate more than eight electrons and therefore break the octet rule because they contain a 3d orbital.
- Mon Nov 05, 2018 8:39 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Week 6 HOmework
- Replies: 4
- Views: 365
Re: Week 6 HOmework
Yes, we still have homework due in our discussion class.
- Mon Oct 29, 2018 2:28 pm
- Forum: Ionic & Covalent Bonds
- Topic: Question regarding ionic bonds
- Replies: 9
- Views: 588
Re: Question regarding ionic bonds
Yes!! Ionic bonds are always between metals and nonmetals, while covalent bonds are between two nonmetals.
- Mon Oct 29, 2018 2:21 pm
- Forum: Significant Figures
- Topic: Sig Figs in the Middle of a Problem
- Replies: 9
- Views: 2399
Re: Sig Figs in the Middle of a Problem
Although most of the time it doesn't have a drastic difference, it's better to apply significant figures for the final answer only. This way, your final answer can be more accurate, since no numbers were rounded in the process. Hope this helps!
- Mon Oct 29, 2018 2:17 pm
- Forum: Ionic & Covalent Bonds
- Topic: Formal Charges
- Replies: 3
- Views: 354
Re: Formal Charges
The sum of the formal charges of individual elements in an ion should add up to the overall charge of the ion. Hope this helps!
- Mon Oct 22, 2018 5:36 pm
- Forum: Einstein Equation
- Topic: The symbol v?
- Replies: 16
- Views: 8480
Re: The symbol v?
Although they look similar, the symbols used for velocity and frequency are not the same. The symbol for frequency is the Greek letter nu, while velocity is denoted the the lowercase letter v.
- Mon Oct 22, 2018 5:32 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: What is a nodal plane?
- Replies: 5
- Views: 3262
Re: What is a nodal plane?
A nodal plane is a plane, where the probability of finding an electron is zero. For example, the p orbitals have one nodal plane and d orbitals have two.
- Mon Oct 22, 2018 5:23 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Test 2
- Replies: 2
- Views: 224
Re: Test 2
On the class website, Professor Lavelle stated that Test 2 will cover the information relating to the quantum world up to quantum numbers. So no, we don't need to know electron configurations for this upcoming test. "Test 2 covers all quantum material up to and including quantum numbers (all qu...
- Mon Oct 15, 2018 4:02 pm
- Forum: Properties of Light
- Topic: Speed of Light
- Replies: 41
- Views: 2596
Re: Speed of Light
I'm pretty sure that for this class, we treat the speed of light as a constant all the time.
- Mon Oct 15, 2018 3:59 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Heisenberg
- Replies: 5
- Views: 421
Re: Heisenberg
The Heisenberg Uncertainty Principle states that there is a limit to the accuracy of determining both the position and momentum of an electron because photons change the path of the electron. Therefore, if the path is uncertain, so is the velocity and momentum. The Heisenberg Uncertainty Principle p...
- Mon Oct 15, 2018 3:38 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Heisenberg Indeterminacy Equation
- Replies: 4
- Views: 357
Re: Heisenberg Indeterminacy Equation
The precise value of the distance (x) and momentum (p) of an electron cannot be precisely known because the photons it is exposed to will affect the electron's path. Therefore, the distance of the electron is unknown, creating uncertainty in its velocity and momentum. The value of the position and m...
- Mon Oct 08, 2018 8:55 pm
- Forum: Limiting Reactant Calculations
- Topic: Reactants and Reagents
- Replies: 4
- Views: 456
Re: Reactants and Reagents
The terms reactant and reagent are usually used interchangeably and therefore it does not make much of a difference which one you use. However, for a detailed explanation, a reactant is a substance consumed during a chemical reaction, while a reagent refers more to the substance used in chemical ana...
- Mon Oct 08, 2018 8:24 pm
- Forum: Empirical & Molecular Formulas
- Topic: Mass Percent Composition
- Replies: 7
- Views: 1073
Re: Mass Percent Composition
All mass percent composition questions should provide you with information adding up to 100 or should give you a solution that is equal to 100. If not there is either in error in the question or the method used to solve.
- Mon Oct 08, 2018 8:20 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Changing Units
- Replies: 10
- Views: 760
Re: Changing Units
It depends on the units being asked for in the original question. However, if the answer itself is correct the units should not matter, unless the question has asked for the answer to be in mL or L.
- Mon Oct 01, 2018 10:23 pm
- Forum: SI Units, Unit Conversions
- Topic: Grams/mole
- Replies: 12
- Views: 1068
Re: Grams/mole
Both notations are virtually the same because g.mol^-1 is rewritten as g/mol when the negative exponent is moved to the denominator in order to make it positive. Therefore, the use of one of the notations is based on personal preference. Hope this helps!!
- Mon Oct 01, 2018 9:54 pm
- Forum: General Science Questions
- Topic: Periodic Table
- Replies: 16
- Views: 1558
Re: Periodic Table
It is best to not round the atomic weight in order to produce a more accurate result, especially when having to conform to the appropriate number of significant figures. However, if the number is very long, I usually round to the nearest thousands place.
- Mon Oct 01, 2018 5:25 pm
- Forum: Significant Figures
- Topic: Significant Figures
- Replies: 10
- Views: 2820
Re: Significant Figures
Significant figures only come into play when the final answer is being evaluated. Therefore, a more accurate answer would be calculated if you used the exact molar mass and then rounded your final answer to the appropriate number of significant figures, in this case two.