## Search found 65 matches

Mon Mar 11, 2019 5:43 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Finding heat(q)
Replies: 3
Views: 129

### Re: Finding heat(q)

It just depends on the information you're given
If they give you moles, for example, you would in most cases just use n and not convert to grams because the estimation would throw off your answer
Mon Mar 11, 2019 5:40 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Ideal Gas C
Replies: 5
Views: 426

### Re: Ideal Gas C

R is the gas constant
Mon Mar 11, 2019 5:40 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Delta U
Replies: 5
Views: 341

### Re: Delta U

Yes, because temp doesnt change
Mon Mar 04, 2019 5:41 pm
Forum: General Rate Laws
Topic: Derivatives
Replies: 5
Views: 190

### Re: Derivatives

I think like the section on thermodynamics, knowing how to derive the equations makes it easier if you get stuck on a problem, but I dont think we have to memorize them as long as we know what to use in what situation
Mon Mar 04, 2019 5:38 pm
Forum: Second Order Reactions
Topic: 7th edition 7B.13
Replies: 3
Views: 392

### Re: 7th edition 7B.13

you use the half life equation for second order reactions first. With it, you can use the half life and [A]0 value they give you to solve for k. once you have k, you can solve for the t values by using the integrated rate law equation (you'll have to use (1/n)([A]o) where 1/n represents the concentr...
Mon Mar 04, 2019 5:28 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 7A. 1 in the 7th edition
Replies: 4
Views: 137

### Re: 7A. 1 in the 7th edition

you basically just have to look at the ratios of the gases they're asking for.
For a) the ratio of N2 to H2 is 1:3, so the rate N2 is consumed at would be 1/3 the rate of consumption of H2
Mon Feb 25, 2019 11:26 am
Forum: Balancing Redox Reactions
Topic: Redox in Basic compounds
Replies: 2
Views: 126

### Re: Redox in Basic compounds

in basic solution, we first have to balance O by using H2O just like acidic solution. in order to balance the H, though, we have to add H2O to the side of the reaction that needs it and then balance the other side with OH- in the 7th edition, toolbox 6K.1 helps explain balancing redox in both acidic...
Mon Feb 25, 2019 11:22 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Delta G
Replies: 2
Views: 117

### Re: Delta G

n refers to the amount of electrons being transferred
so for example if we're dealing with the equation
Zn(s) + Cu2+ (aq) → Zn2+ (aq) + Cu(s)
the n value would be 2 mol because 2e- is being transferred in the reaction
Mon Feb 25, 2019 11:18 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: salt bridge vs porous disk
Replies: 2
Views: 97

### Re: salt bridge vs porous disk

they basically have the same purpose, so i dont think its important to know the distinction for this class
Wed Feb 20, 2019 9:04 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Potential Difference
Replies: 2
Views: 88

### Re: Potential Difference

cell potential is basically the force (voltage) that exists between the two parts of the battery
Wed Feb 20, 2019 8:50 pm
Forum: Balancing Redox Reactions
Topic: Salt Bridge
Replies: 4
Views: 163

### Re: Salt Bridge

Usually questions specify whether a salt bridge or porous disk is being used, so i dont think we have to worry about it.
They basically do the same thing
Wed Feb 20, 2019 8:48 pm
Forum: Balancing Redox Reactions
Topic: Week 7 Homework
Replies: 15
Views: 473

### Re: Week 7 Homework

I think this weeks should be Gibbs Free energy or electrochem (so the new outline)
Tue Feb 12, 2019 12:21 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 4H.1 and 3
Replies: 1
Views: 86

### Re: 4H.1 and 3

usually the more complex molecule is the one with a greater entropy because there's more bonds and therefore more vibrational energy states. for a, HBr will have the greater entropy because it is the larger molecule. for b, NH3 would have the greater entropy because it is more complex for c, the liq...
Tue Feb 12, 2019 12:15 am
Forum: Administrative Questions and Class Announcements
Topic: Midterm
Replies: 6
Views: 248

### Re: Midterm

It's stops at Gibb's Free Energy! so until the end of all the entropy material
Tue Feb 12, 2019 12:13 am
Forum: Administrative Questions and Class Announcements
Topic: Week 6/7 homework
Replies: 2
Views: 165

### Re: Week 6/7 homework

i think for this week we're supposed to do the second and third law homework or Outline 4.
Im assuming next week will be Outline 5
Tue Feb 05, 2019 10:45 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm
Replies: 6
Views: 248

### Re: Midterm

I think its going to depend on whatever he covers in the next two lectures because the website says "Chemical Equilibrium, Acid and Base Equilibria, Thermochemistry, Thermodynamics to the end of entropy" is all on the midterm.
Tue Feb 05, 2019 10:36 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: thermo equation explanation
Replies: 4
Views: 200

### Re: thermo equation explanation

This equation is calculating the change in the entropy of a system
Temperature is in Kelvin and Heat is in joules because the units for entropy is (J K^-1)
Tue Feb 05, 2019 10:28 pm
Forum: Calculating Work of Expansion
Topic: +/- work values
Replies: 5
Views: 218

### Re: +/- work values

if work is positive, it means that work is done on the system by the surroundings an example would be compression if work is negative, it means that work is done by the system on the surroundings an example would be expansion in this case, work is positive because work is done on the air (compressio...
Mon Jan 28, 2019 3:39 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Q and H
Replies: 2
Views: 125

### Re: Q and H

H is enthalpy which is the amount of heat released or absorbed, and it is NOT dependent on the path taken to obtain whatever current state it's in

q is the energy transferred to a system as heat and it depends on the path the reaction takes
Mon Jan 28, 2019 3:32 pm
Forum: Phase Changes & Related Calculations
Topic: Standard entalpy of formation
Replies: 6
Views: 209

### Re: Standard entalpy of formation

Basically anything that is already in its standard form and doesnt have to change to form.
Elements are an example of this because theyre in their natural state
Mon Jan 28, 2019 3:26 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Neutralization reactions
Replies: 6
Views: 198

### Re: Neutralization reactions

yes, i think they are always exothermic because when the acid and base react, bonds are formed to create the salt and water. This releases energy to the surroundings which would constitute an exothermic reaction
Wed Jan 23, 2019 11:29 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: HW problem 12.69 (6th edition)
Replies: 2
Views: 329

### Re: HW problem 12.69 (6th edition)

(Sorry the tables I'm referring to are labeled this way in the 7th edition!) Yes, for part a), you use the Kb value for NH3 in table 6C.2 to find the Ka value of its conjugate acid NH4+ (KaKb = Kw) For part b), you can use table 6D.1 to find the Ka value of common cations in water, which includes Al...
Wed Jan 23, 2019 11:23 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Strong vs Weak Acids
Replies: 2
Views: 138

### Re: Strong vs Weak Acids

The pH value is based on the amount of hydronium ions in the solution. Because we assume that strong acids are fully deprotonated in solution, this means that there is a much higher concentration of H+ ions in the solution than in weak acids, which leads to a lower pH value. Basically, the higher th...
Wed Jan 23, 2019 11:16 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: HW Problem 6D. 17
Replies: 2
Views: 110

### Re: HW Problem 6D. 17

For this question, we actually have to refer to table 6C.1 which the acidity constants. In the case of a), you know that you have to work with CH3CO2-, so we can use the Ka value of acetic acid (CH3COOH) to find the Kb value of its conjugate base. Since Ka for acetic acid is 1.8 x 10^-5, the Kb valu...
Mon Jan 14, 2019 11:37 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Pure Liquids and Pure Solids
Replies: 5
Views: 1762

### Re: Pure Liquids and Pure Solids

Because the molar concentrations of solids and liquids don't change during a reaction, they are not included in calculating the K value
Mon Jan 14, 2019 11:34 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Types of Chemical Reactions
Replies: 3
Views: 103

### Re: Types of Chemical Reactions

I believe all chemical reactions need to have some sort of energy change, so they are all classified under the categories of either endothermic or exothermic.
Mon Jan 14, 2019 11:28 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Forward vs. Reverse Reactions
Replies: 4
Views: 248

### Re: Forward vs. Reverse Reactions

When Q < K, that means that the ratio of products to reactants is less than it is at equilibrium, so the forward reaction is favored because by producing more products, the ratio of products:reactants will increase.
Wed Jan 09, 2019 3:02 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Partial Pressures for Different Temperatures
Replies: 2
Views: 69

### Re: Partial Pressures for Different Temperatures

Molarity and Partial Pressure are directly related.
We can tell from PV=nRT when the equation is written
- (n/V) = P/(RT) or
- concentration = P/(RT)
that when the pressure increases the concentration will also increase.
Wed Jan 09, 2019 2:57 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5H.3 7th edition
Replies: 2
Views: 110

### Re: 5H.3 7th edition

it helps if you write out the K values for all of the equations 2BrCl >>> Br2 + Cl2 H2 +Cl2 >>> 2HCl ----------------------- 2BrCl + H2 >>> Br2 + 2HCl K1 = [Br2][Cl2]/[BrCl]^2 K2 = [HCl]^2/[H2][Cl2] K3 = [Br2][HCl]^2/[H2][BrCl]^2 = K1 x K2 Hope this helps!
Wed Jan 09, 2019 2:45 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Q
Replies: 6
Views: 144

### Re: Q

Use the same approach you use to find K (products/reactants).

a) for example would be -- Q = 1/(P BCl3)^2
Tue Dec 04, 2018 11:59 pm
Forum: Naming
Topic: Knowing oxidation states
Replies: 11
Views: 387

### Re: Knowing oxidation states

Table 9C.1 in the seventh edition is a good reference point. I think the most important ones to know, though, are aqua, ammine, nitrosyl, and carbonyl
Tue Dec 04, 2018 11:55 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Ligands
Replies: 7
Views: 232

### Re: Ligands

Yes, ligands have to have at least one lone pair
Tue Dec 04, 2018 11:53 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Strong Acids
Replies: 1
Views: 65

### Re: Strong Acids

Yea I think for the sake of this class we can say that.
All the molecules are deprotonated
Tue Nov 27, 2018 2:27 pm
Forum: Sigma & Pi Bonds
Topic: Pi bonds and hybridization
Replies: 2
Views: 130

### Re: Pi bonds and hybridization

I think a good example for this idea is ethane, C2H4, because both of the carbon atoms in the molecule are sp2 hybridized and they will each have one unpaired electron in the p orbital. So this parallel overlap of the p-orbitals will be unhybridized.
Tue Nov 27, 2018 2:16 pm
Forum: Dipole Moments
Topic: Hydrogen Bonding Strength
Replies: 2
Views: 103

### Re: Hydrogen Bonding Strength

Hydrogen bonding is unique because it relies on a partially positively charged hydrogen atom that is attached to an electronegative atom bonding to another electronegative atom. The more electronegative the atom is, the stronger the Hydrogen bond will be. It's because of these qualities that water h...
Tue Nov 27, 2018 2:05 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond lengths
Replies: 1
Views: 32

### Re: Bond lengths

Drawing out all the molecules helps.
Single bonds are the longest and weakest, while triple bonds are the shortest and strongest.

So, NO+, for example, has one triple bond, so you know it will have a shorter N-O bond length than NO2- which has one double bond and one single bond.
Wed Nov 21, 2018 11:25 am
Forum: Hybridization
Topic: Forming the different types of bonds
Replies: 2
Views: 121

### Re: Forming the different types of bonds

p-p orbital overlaps can be sigma or pi bonds.
it depends on the type of overlap.
i thought these pictures were helpful
Wed Nov 21, 2018 11:10 am
Forum: Hybridization
Topic: Hybrid orbitals pointing to corners?
Replies: 4
Views: 141

### Re: Hybrid orbitals pointing to corners?

I think all the book is referring to here is the shape the orbitals form because of their regions of electron density
Wed Nov 21, 2018 11:08 am
Forum: Hybridization
Topic: Sp3
Replies: 2
Views: 117

### Re: Sp3

We only use up to sp3 because there are only three p orbitals. Anything beyond that, will go into the d orbital
ex. sp3d - five dsp3 hybridized orbitals which would be trigonal bipyramidal
Tue Nov 13, 2018 11:15 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: 2
Views: 82

### Re: hydrogen bonding

You're right about the partial negative charge, which is determined by the electronegativity of the atoms in the molecule. I think the reason Lavelle made that distinction in class is because a partially negative atom with at least one lone pair has a high density of negative charge, so it is ideal ...
Tue Nov 13, 2018 10:49 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lewis Structures/Shape
Replies: 3
Views: 130

### Re: Lewis Structures/Shape

Because Be has the lowest electronegativity, it would be the central atom. It forms two bonds, so it will bond to each of the carbons, and each of the carbons will have three hydrogen bonds.
Because of the two bonded pairs, this structure would be linear in respect to the Be.
Tue Nov 13, 2018 10:41 pm
Forum: Hybridization
Topic: Bond Angels
Replies: 5
Views: 262

### Re: Bond Angels

We can determine bond angles using the VSEPR theory. Because of electron repulsion, molecules form shapes that will give them the lowest repulsion energy. The basic idea, though, is to look at how many bonds a central atom forms and how many lone pairs surround it. (In this case triple bonds and dou...
Sun Nov 04, 2018 4:58 pm
Forum: Sigma & Pi Bonds
Topic: Midterm1
Replies: 10
Views: 598

### Re: Midterm1

I dont think we need to know about them for this midterm.
Sun Nov 04, 2018 4:54 pm
Forum: Ionic & Covalent Bonds
Topic: Homework question
Replies: 1
Views: 70

### Re: Homework question

I don't think we have to know how to write out the compounds. They will probably give us the formulas on the test. Because the compounds are ionic or polyatomic, the Lewis structures are separated into cations and anions. This is because the electrons are not being shared like with covalent compound...
Sun Nov 04, 2018 4:31 pm
Forum: Lewis Structures
Topic: 7th edition 2B.9
Replies: 4
Views: 154

### Re: 7th edition 2B.9

The actual compounds are not covalently bonded to each other.They're ionic.
That's why the lewis structures are drawn so that the electrons are transferred to the anion to complete its octet and the cation is shown with its charge.
Sun Nov 04, 2018 4:24 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge
Replies: 7
Views: 411

### Re: Formal Charge

In some cases, the formal charge will not be equal to zero.
In looking for the most stable lewis structure, though, we should be looking for the structure that has the most individual formal charges close to 0.
Tue Oct 30, 2018 10:24 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm Electron Configuration
Replies: 1
Views: 171

### Re: Midterm Electron Configuration

I think we should be familiar with f orbitals. You should know how to do electron configurations and be aware of the special cases that the TAs have been covering in discussion this week.
Tue Oct 30, 2018 10:21 pm
Forum: Student Social/Study Group
Topic: Midterm Review Sessions
Replies: 4
Views: 339

### Re: Midterm Review Sessions

Gail covered Heisenberg, de Broglie, the photoelectric effect, and electron configurations.
She also went over test questions that were commonly missed like the one about the Alveoli sac where we had to use the uncertainty equation.
Tue Oct 30, 2018 10:13 pm
Topic: Midterm
Replies: 4
Views: 406

### Re: Midterm

I don't think black body radiation will be on the midterm because we didn't need it for test 2 and it hasn't been covered in the reviews
Sun Oct 21, 2018 11:10 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 7th edition 1D.25
Replies: 3
Views: 76

### Re: 7th edition 1D.25

Both 2d and 4g don't satisfy the requirements for the angular momentum quantum numbers (or l). l can only have the values 0,1,....n-1 In the case of 2d, n=2. This means l can either be 0 or 1. These 2 numbers are l values for s-orbitals and p-orbitals. Because l cannot be equal to 2, it cannot have ...
Sun Oct 21, 2018 11:04 pm
Forum: Administrative Questions and Class Announcements
Topic: Test 2
Replies: 8
Views: 259

### Re: Test 2

The test covers just quantum material up to Friday's lecture. I think thats about half of section 1D in the 7th edition
This is the outline for what we should know on the website.

https://lavelle.chem.ucla.edu/wp-conten ... _World.pdf
Sun Oct 21, 2018 11:00 pm
Forum: Properties of Light
Topic: Test 2 Equations
Replies: 14
Views: 481

### Re: Test 2 Equations

My TA said most of the equations we need will be given to us on the front page of the test. For convenience and just to be safe, I would memorize: (frequency)(wavelength) = c (speed of light) Rydberg (or at least remember the Balmer series corresponds to the visible region and Lyman to the UV region...
Sun Oct 21, 2018 10:49 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Problem 1.43
Replies: 2
Views: 129

### Re: Problem 1.43

You would use the Heisenberg principle in this problem. 350 pm is your uncertainty in position (delta x) Because the problem is asking for uncertainty in velocity, we have to use (m)(delta v) as opposed to its equivalent delta p The m is the mass of an electron or 9.11 x 10^31 kg. h is always the co...
Sun Oct 21, 2018 10:41 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Test Question
Replies: 8
Views: 271

### Re: Test Question

I don't think we're required to know the shapes for this upcoming test specifically, but for the midterm and final understanding the idea behind it and concepts like the probability of finding an electron will probably be important
Thu Oct 18, 2018 1:19 am
Forum: Einstein Equation
Topic: Question 1.25
Replies: 1
Views: 91

### Re: Question 1.25

B and C are pretty similar to part A! b) In order to determine the energy emitted, you need to know the number of atoms in the sample. Since we have a 5.00 mg mass we should first convert to grams. From there, use the molar mass to find the number of moles and then multiply that number by Avogadro's...
Thu Oct 18, 2018 1:05 am
Forum: Photoelectric Effect
Topic: Equation units
Replies: 4
Views: 175

### Re: Equation units

I think we're supposed to use kg. If given g, for the photoelectric effect equation in particular, convert to kg first.
This is because when determining values for things like kinetic energy, the units are kgm2s-2, which is equivalent to Joules.
Thu Oct 18, 2018 12:56 am
Forum: Photoelectric Effect
Topic: Pre Assessment Module Question #13
Replies: 2
Views: 148

### Re: Pre Assessment Module Question #13

I also think the answer would be yes because otherwise you can't guarantee that the photo electrons maintain their energy.
With the vacuum, you would be able to ensure the frequencies have contact with the sample and aren't influenced by collisions with the air.
Thu Oct 11, 2018 9:59 pm
Forum: Properties of Light
Topic: Problem 1A.9 (7th edition)
Replies: 5
Views: 76

### Re: Problem 1A.9 (7th edition)

Yea I thought that was strange too because 1A doesn't address Energy of the photon much apart from Table 1A.1
Thu Oct 11, 2018 9:49 pm
Forum: SI Units, Unit Conversions
Topic: formula units [ENDORSED]
Replies: 69
Views: 24645

### Re: formula units[ENDORSED]

You can use Avogadro's number for atoms, molecules, or formula units.
Formula Units apply to ionic compounds, molecules apply to molecular compounds, and you calculate atoms when in reference to elements.
Thu Oct 11, 2018 9:43 pm
Forum: Properties of Light
Topic: spectrum [ENDORSED]
Replies: 2
Views: 56

### Re: spectrum[ENDORSED]

The absorption spectrum basically shows that gases absorb certain wavelengths through the black bars displayed on the spectrum.
Mon Oct 08, 2018 3:34 pm
Forum: Administrative Questions and Class Announcements
Topic: Number of questions on test one [ENDORSED]
Replies: 39
Views: 18480

### Re: Number of questions on test one[ENDORSED]

My TA mentioned the test will be structured a lot like the homework problems, so they are all free response and it's possible to get partial credit.
Wed Oct 03, 2018 9:07 pm
Forum: SI Units, Unit Conversions
Topic: Homework Questions [ENDORSED]
Replies: 14
Views: 533

### Re: Homework Questions[ENDORSED]

I think we're allowed to submit our questions from either one section or all the sections as long as we have a minimum of 7. The main thing the TAs are grading for is accuracy so any combination of problems should be fine.
Tue Oct 02, 2018 11:36 pm
Forum: Empirical & Molecular Formulas
Topic: Molar Mass
Replies: 2
Views: 126

### Re: Molar Mass

Do you have an example of a question you were confused on?
Tue Oct 02, 2018 11:20 pm
Forum: SI Units, Unit Conversions
Topic: Week 1 Homework Assignment [ENDORSED]
Replies: 16
Views: 702

### Re: Week 1 Homework Assignment[ENDORSED]

The modules are basically the material Lavelle has been covering in class. They are pretty helpful if you want to easily follow along with his lecture or if you aren't as familiar with the high school chem material. I also thought they were a good review before attempting the homework.
Tue Oct 02, 2018 11:09 pm
Forum: Properties of Light
Topic: Finding Energy required to remove an electron from one metal atom
Replies: 3
Views: 326

### Re: Finding Energy required to remove an electron from one metal atom

I think the problem is addressing threshold energy. Because the question asks for the energy needed to remove 1 electron, I think you need to convert the kJ mol-1 to J/electron. To do that you can divide the value you calculated (150.6) by Avogadro's number (6.022 x 10^23) because in this case it re...