## Search found 64 matches

Fri Mar 08, 2019 12:40 pm
Forum: General Rate Laws
Topic: Units for Rate Constants
Replies: 5
Views: 205

### Re: Units for Rate Constants

mol/Ls zero and first
1/mol/Ls second order
Fri Mar 08, 2019 12:37 pm
Forum: Zero Order Reactions
Topic: General “order” question
Replies: 6
Views: 454

### Re: General “order” question

Zero order is time vs concentration
First order is time vs ln concentration
Second order is time vs 1/concentration
Fri Mar 08, 2019 12:35 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Unique Rates
Replies: 3
Views: 188

### Unique Rates

I’m having trouble understanding what a unique rate is. Can someone clarify please?
Wed Mar 06, 2019 1:58 pm
Forum: Second Order Reactions
Topic: Reaction orders
Replies: 2
Views: 124

### Re: Reaction orders

You'd have to use the experimental data still because coefficients don't determine order
Wed Mar 06, 2019 1:56 pm
Forum: Second Order Reactions
Topic: graph for second order
Replies: 7
Views: 299

### graph for second order

How does the graph for second order look? Will it ever be exponential, or only linear?
Wed Mar 06, 2019 1:54 pm
Forum: First Order Reactions
Topic: 1/2 life
Replies: 7
Views: 287

### 1/2 life

Does the 1/2 life for first order depend on the initial concentration like it does for zero and second-order reactions?
Wed Mar 06, 2019 1:51 pm
Forum: First Order Reactions
Topic: First Order Reactions
Replies: 6
Views: 194

### Re: First Order Reactions

I believe it should be a straight line with decreasing slope
Wed Mar 06, 2019 1:00 pm
Forum: Van't Hoff Equation
Topic: Temp Units
Replies: 11
Views: 541

### Re: Temp Units

The units must cancel out. K cancels with the other units, so use K.
Wed Mar 06, 2019 12:58 pm
Forum: Van't Hoff Equation
Topic: test 2
Replies: 7
Views: 562

### test 2

There was a problem on test 2 asking whether the compound was acidic or basic using K and the other values given. I'm pretty sure we had to use the Van't Hoff equation as well. Does anyone know how to approach this problem?
Wed Mar 06, 2019 12:55 pm
Forum: Administrative Questions and Class Announcements
Topic: Class Curve
Replies: 11
Views: 881

### Re: Class Curve

I am confused on this as well, but I think 50% is the minimum and it goes in increments of 10-20% for the rest of the letter grades.
Wed Mar 06, 2019 12:50 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Test 2
Replies: 7
Views: 348

### Re: Test 2

More negative E for reducing and more positive E for oxidizing I believe
Tue Feb 19, 2019 10:40 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneity
Replies: 3
Views: 345

### Re: Spontaneity

deltaG must be negative for a spontaneous reaction, so T deltaS must be a positive term to make sure the number subtracted from deltaH in deltaG=deltaH-TdeltaS has deltaH as a large negative number.
Tue Feb 19, 2019 10:38 pm
Forum: Student Social/Study Group
Topic: Test
Replies: 17
Views: 663

### Re: Test

I don't think the test will be cumulative because it will mainly focus on Gibb's Free Energy and electrochem, but Lavelle told me you need to know thermodynamics prior to this for the test.
Tue Feb 19, 2019 10:36 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Test 2
Replies: 4
Views: 351

### Re: Test 2

There should be a link on the class website saying what is on the test, but it will cover thermodynamics, mainly in chapter 9 of the outline.
Tue Feb 12, 2019 11:11 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Equations
Replies: 5
Views: 464

### Re: Equations

I would focus on connecting the equations to each other because they will all be on the equation sheet. Know the main equation for enthalpy and entropy, then focus on manipulating the variables for each when needed. Basically, focus more on when to use what, not memorizing the formula itself.
Tue Feb 12, 2019 11:07 pm
Forum: Calculating Work of Expansion
Topic: Substituting -nrT for -PΔV
Replies: 4
Views: 179

### Re: Substituting -nrT for -PΔV

n and r are constant if T changes, but r and T are constant if the system is isothermal (same temperature)
Tue Feb 12, 2019 11:05 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: R constants
Replies: 21
Views: 726

### R constants

How do we know which value of R to use because aren't there two values? I know we usually use 8.3145, but when would we use the other value?
Tue Feb 12, 2019 10:55 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: C
Replies: 3
Views: 81

### C

What does C represent in the entropy equation for ln of temperature change?
Tue Feb 12, 2019 10:53 pm
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: Boltzmann Equation
Replies: 3
Views: 421

### Boltzmann Equation

When do we use the Boltzmann equation? Do questions specifically ask for it. I've been gone for the past week, so I am lost. Thank you.
Tue Feb 12, 2019 10:42 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Thermodynamics
Replies: 1
Views: 117

### Thermodynamics

Do we need to memorize the constants like 3/2, 5/2..etc. for tests?
Wed Jan 30, 2019 4:46 pm
Forum: Phase Changes & Related Calculations
Topic: Water phase change graph
Replies: 6
Views: 263

### Re: Water phase change graph

the slanted lines are in their own/same state, while the straight lines represent the phase change (sol->liq->gas)
Wed Jan 30, 2019 4:43 pm
Forum: Calculating Work of Expansion
Topic: reversible & irreversible expansion
Replies: 2
Views: 97

### Re: reversible & irreversible expansion

The irreversible wouldn't be doing the maximum amount of work because the outside pressure was only 1 atm compared to the inside pressure of 2 atm, so this doesn't represent the work against maximum pressure. On the other hand, the reversible pressure is at equilibrium, so it is expanding against th...
Wed Jan 30, 2019 4:41 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Thermo Test/Midterm
Replies: 9
Views: 282

### Re: Thermo Test/Midterm

I don't think so, but I'm not sure. I think you have to know the lewis structures on your own.
Tue Jan 29, 2019 1:10 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: When to use which method for calculating reaction enthalpies
Replies: 4
Views: 119

### Re: When to use which method for calculating reaction enthalpies

for 8.9, use 8.206e-2Latm/kmol and 8.314J/kmol then convert to kJ and subtract that answer from kJ given.
Tue Jan 29, 2019 12:56 am
Forum: Phase Changes & Related Calculations
Topic: 6th edition problem
Replies: 2
Views: 147

### 6th edition problem

I'm not understanding how to approach problem 8.3 in the 6th edition textbook. I was sick during this lecture, so I am behind on this section and I'm not understanding how 24J is the answer.
Tue Jan 29, 2019 12:53 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 7
Views: 244

### Re: Bond Enthalpies

Averages are going to be least exact and inaccurate, which is why bond enthalpies is the least accurate way to measure reaction enthalpies.
Thu Jan 17, 2019 6:24 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Conjugate base
Replies: 7
Views: 306

### Re: Conjugate base

acid+base-->conj. base+ conj. acid. The conjugate base is an anion so that will help you identify it.
Thu Jan 17, 2019 6:16 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Constants
Replies: 5
Views: 180

### Re: Equilibrium Constants

Kc is specific to concentration while Kp is for gases and partial pressures. Kc can be used for gaseous mixtures I believe, but it's more likely for Kp to be used.
Mon Jan 14, 2019 8:18 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 11.27
Replies: 2
Views: 48

### Re: 11.27

Ok that makes sense, thank you!
Mon Jan 14, 2019 4:24 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 11.27
Replies: 2
Views: 48

### 11.27

I am confused on how to do 6th edition 11.27 and solving for the partial pressure of PCL3 using the given partial pressures. Can someone help please?
Wed Jan 09, 2019 3:06 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: "lie to the right" vs "shifted to the right"
Replies: 6
Views: 88

### Re: "lie to the right" vs "shifted to the right"

There are more products, meaning that the reaction favors the products since products are on the right.
Wed Jan 09, 2019 3:04 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: What does it mean when a reaction is at equilibrium?
Replies: 4
Views: 171

### Re: What does it mean when a reaction is at equilibrium?

Q=K, meaning that the forwards and back reaction rates are equal
Wed Jan 09, 2019 1:07 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Favoring Products/Reactants
Replies: 3
Views: 131

### Re: Favoring Products/Reactants

If q is less than k, the reaction moves towards the products. If q is greater than k, the reaction moves towards the reactants. K is just equilibrium.
Fri Nov 30, 2018 3:42 pm
Forum: Bronsted Acids & Bases
Topic: Bronsted Acid
Replies: 2
Views: 98

### Re: Bronsted Acid

A bronzed acid must be the proton donor in the chemical equation. It's dissociation determines the strength of the acid.
Fri Nov 30, 2018 3:41 pm
Forum: Lewis Acids & Bases
Topic: Strength
Replies: 3
Views: 152

### Re: Strength

Strength is determined by the how readily acid/base dissociates into H+ and OH-.
Fri Nov 30, 2018 3:39 pm
Forum: Hybridization
Topic: 2s or s?
Replies: 7
Views: 196

### Re: 2s or s?

the number in front represents the period the element is in. S is the orbital.
Sat Nov 24, 2018 10:59 am
Forum: Hybridization
Topic: Writing out Hybridization
Replies: 8
Views: 258

### Re: Writing out Hybridization

I think Dr. Lavelle said either way is acceptable in lecture because it's whatever you prefer.
Sat Nov 24, 2018 10:57 am
Forum: Sigma & Pi Bonds
Topic: Sigma and Pi Bonds
Replies: 2
Views: 100

### Re: Sigma and Pi Bonds

A sigma bond is a single bond, a double bond is a sigma and pi, a triple is a sigma and 2 pi. Single is the longest, double is medium-length, and triple is the shortest.
Sat Nov 24, 2018 10:53 am
Forum: Hybridization
Topic: hybridization
Replies: 1
Views: 78

### Re: hybridization

X is the bonds formed and E is the lone pairs
Wed Nov 14, 2018 9:23 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Strengths
Replies: 5
Views: 227

### Re: Bond Strengths

I think it's because the electrostatic forces hold ionic bonds together tightly and because they are between metal and nonmetal, while hydrogen bonds consist of hydrogen and an element of a higher electronegativity. Ionic bonds are when electrons are transferred from one element to the other. Hydrog...
Wed Nov 14, 2018 9:07 pm
Forum: Lewis Structures
Topic: Boron Trifluoride
Replies: 8
Views: 294

### Re: Boron Trifluoride

B, Be, Li, H all exceptions to octet rule because they don't complete valence shell
Wed Nov 14, 2018 9:06 pm
Forum: Lewis Structures
Topic: Expanded Octets
Replies: 9
Views: 432

### Re: Expanded Octets

Atoms that can hold electrons in the d-orbital (P3 and below)
Wed Nov 14, 2018 8:56 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: How are polarity and polarizability different?
Replies: 3
Views: 625

### Re: How are polarity and polarizability different?

Polarity: Charge distribution causing polar or nonpolar molecules due to differences in electronegativity
Polarizability: How easily an electron cloud can be distorted
Wed Nov 14, 2018 8:46 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polarizability
Replies: 4
Views: 179

### Re: Polarizability

Polarizability is how easy it is to cause distortion to an electron cloud. Anions are highly polarizable because they have more electrons/are larger. Cations are small/less electrons and have high polarizing power, but low polarizability.
Wed Nov 14, 2018 8:41 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 8
Views: 561

### Re: Bond Angles

You just have to know the bond angles from VSEPR, and Dr. Lavelle was saying 360/# of bonds, but that doesn't always work.
Wed Nov 14, 2018 8:29 pm
Forum: Lewis Structures
Topic: Formal Charge
Replies: 14
Views: 472

### Re: Formal Charge

Just try to get formal charges to equal zero or match the charge that the molecule is supposed to have.
Wed Nov 14, 2018 8:26 pm
Forum: Administrative Questions and Class Announcements
Replies: 7
Views: 414

I believe so because it doesn't specify that you need 50% on any one assignment category, so it would be 250/500 in the course.
Wed Nov 14, 2018 8:22 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Shape
Replies: 6
Views: 226

### Re: Molecular Shape

Lone pairs on the Iodine lead to repulsion making it t-shaped
Mon Nov 12, 2018 12:44 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.11 6th Edition
Replies: 1
Views: 145

### Re: 4.11 6th Edition

Trigonal bipyramidal, trigonal bipyramidal, octahedral/square planar, trigonal pyramidal
Fri Nov 02, 2018 8:45 pm
Forum: Resonance Structures
Topic: Determine Number of Resonance Structures
Replies: 2
Views: 176

### Re: Determine Number of Resonance Structures

Count the valence electrons you can have for the molecule, determine how many you've used. If you used too many, you create a double/triple bond and it can be on either side of the central element between the other elements that are the same as each other (ex. NO2) (resonance structures). The amount...
Fri Nov 02, 2018 8:37 pm
Forum: Trends in The Periodic Table
Topic: Oxidation Number
Replies: 1
Views: 88

### Re: Oxidation Number

You determine the valence electrons it needs to lose or gain to reach an octet.
Fri Nov 02, 2018 8:36 pm
Forum: Ionic & Covalent Bonds
Topic: 3.23 6th Edition
Replies: 3
Views: 92

### Re: 3.23 6th Edition

You have to lose 7 (+7) to reach an octet or gain 1(-1) to reach an octet (electrons).
Sat Oct 27, 2018 9:14 am
Forum: Student Social/Study Group
Topic: Studying
Replies: 7
Views: 415

### Re: Studying

I would go to the review session talked about in beginning of lecture on Friday/look up the “garlic bread” review topic because it has mock midterm problems. It seems very useful and the review session date should be posted on there soon. https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=157&t...
Sat Oct 27, 2018 9:13 am
Forum: Trends in The Periodic Table
Topic: electron affinity 1F.11
Replies: 3
Views: 208

### Re: electron affinity 1F.11

Sulfur has higher electron affinity because oxygen electrons experience more repulsion between each other, since the valence shell is held closer to the nucleus. The repulsion causes more energy to be consumed when an electron is introduced than with sulfur due to the repulsion of electrons being im...
Sat Oct 27, 2018 8:58 am
Forum: Ionic & Covalent Bonds
Topic: Ground State
Replies: 6
Views: 276

### Re: Ground State

Ground state would be the lowest energy state of the atom. So the electron configuration has to show the lowest energy state.
Mon Oct 22, 2018 12:29 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Coulomb's Law and Effective Nuclear Charge on test
Replies: 2
Views: 57

### Re: Coulomb's Law and Effective Nuclear Charge on test

I would know these just because we had practice problems on these topics in lecture and in the text. It's better to have a basic understanding.
Mon Oct 22, 2018 12:27 am
Forum: *Particle in a Box
Topic: Midterm
Replies: 17
Views: 1716

### Re: Midterm

The midterm from last year is also on ccle :)
Mon Oct 22, 2018 12:26 am
Forum: Trends in The Periodic Table
Topic: Electron Affinity
Replies: 2
Views: 95

### Re: Electron Affinity

If something has a high electron affinity, it means it has a higher ability to attract other electrons. This will in turn make the bond stronger because of the greater pull.
Mon Oct 22, 2018 12:23 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Wave Functions
Replies: 4
Views: 129

### Re: Wave Functions

px, py, and pz correlate to the ml=-1,0,+1. px and pz can be either -1 or +1, but pt must be the middle number for the list of ml values is what I understood.
Mon Oct 22, 2018 12:19 am
Forum: Einstein Equation
Topic: Units
Replies: 17
Views: 902

### Re: Units

Joule is kgm^2/s^2, but multiplying my 1/s cancels one of the s units, making kgm^2/s
Mon Oct 22, 2018 12:16 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg equation
Replies: 2
Views: 123

### Re: Heisenberg equation

h bar is h/2pi, but in uncertainty problems you use deltap*deltax is greater than or equal to h/4pi
Thu Oct 04, 2018 8:38 pm
Forum: Significant Figures
Topic: Significant figures for molar mass
Replies: 7
Views: 2100

### Re: Significant figures for molar mass

You should definitely use the most accurate molar mass given. I wouldn't worry about sigfigs until the end. Either way with rounding, your answer won't be too far off from the answer you should have, but it is more accurate to use the most digits given on your periodic table for molar mass. It's bes...
Thu Oct 04, 2018 8:33 pm
Forum: Significant Figures
Topic: Determining Sig Figs
Replies: 6
Views: 228

### Re: Determining Sig Figs

Sigfigs should always match the lowest significant number given in the problem. For example, if a problem has 3.2+4.88=?, your answer should be rounded to two sigfigs.
Thu Oct 04, 2018 8:28 pm
Forum: Significant Figures
Topic: Regarding the Homework
Replies: 2
Views: 78

### Re: Regarding the Homework

I would personally try to match the sigfigs given in the problem, but you can use however many sigfigs between calculations. Just round at the end :).