Search found 60 matches

Tue Mar 12, 2019 3:57 pm
Forum: Ideal Gases
Topic: Approximations for ICE
Replies: 20
Views: 590

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: 591

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: 182

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: 443

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: 1142

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: 337

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: 321

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: 136

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: 134

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: 462

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: 475

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: 568

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: 257

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: 123

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: 220

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!
Mon Feb 04, 2019 3:59 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem 14 BL
Replies: 5
Views: 422

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: 443

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: 270

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: 289

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: 156

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: 295

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: 166

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: 144

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: 633

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: 107

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: 268

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: 401

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: 363

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: 336

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: 179

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: 753

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: 270

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: 876

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: 187

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: 483

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: 419

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: 343

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!!
Mon Nov 19, 2018 5:00 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: AXE
Replies: 7
Views: 335

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: 67

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: 716

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: 444

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: 533

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: 151

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: 983

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: 252

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: 302

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: 938

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: 152

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: 2078

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: 851

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: 121

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: 1531

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: 218

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: 236

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: 226

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: 559

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: 491

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: 568

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: 936

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: 545

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.