## Search found 65 matches

Wed Mar 13, 2019 2:53 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram
Replies: 1
Views: 40

### Re: Cell Diagram

Since both are neutral electrodes, i don't think so. Except I just use platinum because that's how it is in the solutions manual.
Wed Mar 13, 2019 2:52 am
Forum: General Rate Laws
Topic: reaction rate vs. unique reaction rate
Replies: 3
Views: 49

### Re: reaction rate vs. unique reaction rate

As of what I understood, a reaction rate is just the average change of concentration over time while a unique reaction rate is that value divided by the stoichiometric coefficient.
Wed Mar 13, 2019 2:49 am
Forum: General Rate Laws
Topic: Problem 7A17
Replies: 1
Views: 29

### Re: Problem 7A17

You multiply the rate in experiment 1 by (3.02/1.25)^2 and get around 50.78 which is approximately 50.8, so that data matches that B is second order. I don't think you do experiment 2 because you need to account for A also, which doubles.
Wed Mar 13, 2019 2:43 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 7D.7b
Replies: 1
Views: 25

### Re: 7D.7b

If the Activation energy for the forward rxn is smaller than that of the reverse reaction, it is exothermic. If it's the other way around, it is endothermic.
Wed Mar 06, 2019 6:30 pm
Forum: Student Social/Study Group
Topic: Final
Replies: 24
Views: 578

### Re: Final

The review sessions will be updated soon when rooms are figured out. He should also mention them in class!
Wed Mar 06, 2019 6:24 pm
Forum: General Rate Laws
Topic: does k change if rxn is multiplied?
Replies: 6
Views: 84

### Re: does k change if rxn is multiplied?

k doesn't change because it is the same value for the equation.
Wed Mar 06, 2019 6:22 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: zero and first
Replies: 5
Views: 69

### Re: zero and first

Another way to tell the difference between zero and first is that for a zero order reaction, the plot of [Reactant] vs t is a straight line graph while for a first order reaction, the plot of ln[Reactant] vs t is a straight line graph.
Tue Feb 26, 2019 4:04 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell diagram
Replies: 4
Views: 50

### Re: Cell diagram

If in one of the half reactions, all the reactants/products are gas/aqueous and there's no metal/solid, then you need to add in the inert metal.
Tue Feb 26, 2019 4:00 pm
Forum: Balancing Redox Reactions
Topic: redox homework question
Replies: 3
Views: 44

### Re: redox homework question

Oxygen isn't in peroxide form anywhere nor is it in O2 form anywhere so it's oxidation number remains at -2. Cr goes from 6+ to 3+ so it is reduced and I think there's a typo in what you wrote, but I remember seeing this problem and Carbon is oxidized.
Tue Feb 26, 2019 3:41 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: galvanic/voltaic
Replies: 2
Views: 34

### Re: galvanic/voltaic

Galvanic and Voltaic Cells are the same thing
Thu Feb 21, 2019 9:56 am
Forum: Balancing Redox Reactions
Topic: Writing Half Reactions
Replies: 2
Views: 59

### Writing Half Reactions

When writing half reactions for Redox rxns, are we allowed to add in molecules, or are we restricted to those given in the original equation?
Thu Feb 21, 2019 9:54 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G of Formation for O2
Replies: 1
Views: 41

### Delta G of Formation for O2

How is the Gibbs free energy of formation for O2 0kj/mol even though the standard entropy isn't 0. Shouldn't G = H-TS, and by this the Gf for O2 have a value?
Thu Feb 21, 2019 9:52 am
Forum: Balancing Redox Reactions
Topic: Weekly Homework
Replies: 3
Views: 56

### Re: Weekly Homework

With hw, I like to do topics we learned in the last week. So for example, if your discussion is on Wednesday, choose topics/problems that you learned last Wednesday, Friday and this Monday.
Tue Feb 12, 2019 10:46 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Temperature
Replies: 3
Views: 84

### Re: Temperature

Use 273.15 and don't round until the end of the problem.
Tue Feb 12, 2019 10:45 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: hess law equations
Replies: 3
Views: 79

### Re: hess law equations

For 4D15, the reason you write out equations is because you are given enthalpy of combustion and I think for the exam we should know how to write out combustion reactions.
Tue Feb 12, 2019 10:23 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.25 6th edition
Replies: 4
Views: 136

### Re: 9.25 6th edition

To find W, you would draw out possible configurations for SO2F2 and get a value of 6. You then simply plug it into the equation getting S = kb*ln(6)
Wed Feb 06, 2019 12:02 am
Forum: Administrative Questions and Class Announcements
Topic: negative and positive entropy
Replies: 3
Views: 80

### Re: negative and positive entropy

Entropy is the amount of disorder in a system. So a positive change in entropy is when disorder increases, while a negative change in entropy is when disorder decreases (order increases). Usually in reactions where the products are more ordered, the entropy has decreased (negative deltaS) while if t...
Wed Feb 06, 2019 12:01 am
Forum: Calculating Work of Expansion
Topic: +/- work values
Replies: 5
Views: 86

### Re: +/- work values

w = -P(deltaV) by definition. So an increase in volume (expansion), makes dV positive, so the work done is negative. However, if deltaV is negative (compression), then work is going to be positive (compression).
Tue Feb 05, 2019 11:57 pm
Forum: Administrative Questions and Class Announcements
Topic: Equation sheet for midterm
Replies: 3
Views: 77

### Re: Equation sheet for midterm

Yes, Lavelle keeps the same equation sheet and periodic table for every test
Tue Jan 29, 2019 5:20 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 7th Ed. 4C3
Replies: 2
Views: 50

### Re: 7th Ed. 4C3

I think the answer in the book is wrong. Do you have the solutions manual, because in the solutions manual there is a detailed answer.
Tue Jan 29, 2019 5:06 pm
Forum: Calculating Work of Expansion
Topic: Work and Internal Energy
Replies: 1
Views: 25

### Re: Work and Internal Energy

I don't think we've covered thermo or work yet?
Tue Jan 29, 2019 5:05 pm
Forum: Phase Changes & Related Calculations
Topic: Units: Joules vs kJ
Replies: 5
Views: 86

### Re: Units: Joules vs kJ

You should be consistent with units. If they say kJ in the problem, use kJ if they say J then use J. I think it will be specified in problems on the test though.
Tue Jan 22, 2019 10:24 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 12.79 6th Edition
Replies: 1
Views: 46

### Re: 12.79 6th Edition

Since Ka1 is large, all of the H2SO4 dissociates. So yes, you assume the HSO4- and H+ are both .15M and use that value in your ice table for the next step where you use Ka2. When you find the concentration in the second step, add that to the 0.15 from the first step and do -log[H3O+] to find the pH.
Tue Jan 22, 2019 10:22 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Including mol/L in K calculations
Replies: 2
Views: 42

### Re: Including mol/L in K calculations

As of what I saw in lecture, you just use the numbers because K has no units. So just don't include concentrations in the expression.
Tue Jan 22, 2019 10:21 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Temperature change
Replies: 5
Views: 94

### Re: Temperature change

With temperature, in an endothermic (reaction that requires heat), increasing temperature favors formation of products; In an exothermic reaction (a reaction that releases heat), increasing temperature favors formation of reactants.
Tue Jan 15, 2019 4:47 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kp vs. Kc
Replies: 2
Views: 42

### Re: Kp vs. Kc

It usually depends on numbers you're given. Kp is generally used if all compounds are gases, but you can also use Kc if the numbers are given in mols and you know the volume of the flask. When writing the equilibrium expression it is usually better to use partial pressures and Kp.
Tue Jan 15, 2019 4:45 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.37 6th edition
Replies: 3
Views: 63

### Re: 11.37 6th edition

When you multiply a certain reaction by a number n, the new K for the new equation is the old K to the power of n. So here, the equation is multiplied by 2 so the K of the reaction would be K^2 so 41^2.
Mon Jan 14, 2019 4:07 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K changing with temperature [ENDORSED]
Replies: 3
Views: 76

### Re: K changing with temperature[ENDORSED]

Lavelle told us in class that pressure doesn't affect K. K is only changed when the temperature changes
Mon Jan 14, 2019 4:03 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Solids and Liquids in K
Replies: 4
Views: 81

### Re: Solids and Liquids in K

Solids and liquids have no concentration/partial pressures so they can't be included in the expression.
Mon Jan 07, 2019 4:46 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc Value
Replies: 4
Views: 87

### Re: Kc Value

Another way to conceptualize this is that in Kc, products are the numerator while reactants are the denominator. If Kc is larger in 1 scenario than another, that means you have more product formed in that scenario. This means the reaction is proceeding forward.
Mon Jan 07, 2019 4:43 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Solids and Liquids
Replies: 4
Views: 71

### Re: Solids and Liquids

Another thing Lavelle said is there's no such thing as a concentration/partial pressure for solids and liquids, so they won't be included in your Kc or Kp.
Mon Jan 07, 2019 4:29 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Help on 11.9: b and c
Replies: 4
Views: 68

### Re: Help on 11.9: b and c

I think we just need to use the general Kp and Kc. You don't need the complex equation, I'm pretty sure that's for later.
Wed Dec 05, 2018 9:51 pm
Forum: Administrative Questions and Class Announcements
Topic: FINAL PRACTICE - Lyndon's Churro Review Session [ENDORSED]
Replies: 118
Views: 4918

### Re: FINAL PRACTICE - Lyndon's Churro Review Session[ENDORSED]

For question 34, once I have the Molarity of both compounds how do I find the pH with the two Molarities of HCl and CaO? I'm not completely sure if this is right but, for #34, I did the neutralization rxn between HCl and CaO. One of them is limiting, so if you use all of it up, you form water. The ...
Tue Dec 04, 2018 2:52 pm
Forum: Identifying Acidic & Basic Salts
Topic: ch 12 6th ediiton 12.65
Replies: 1
Views: 79

### Re: ch 12 6th ediiton 12.65

We were just beginning to learn this in class, but I can help with the first one. In class, Lavelle gave NH4Cl as an example. So If you write the equation for NH4Br reacting with water, you get NH4Br+H2O --> NH3 + Br- + H3O+. So NH4Br would be acidic because when you put it in solution, it creates m...
Tue Dec 04, 2018 2:50 pm
Forum: Bronsted Acids & Bases
Topic: Determining Acidity
Replies: 3
Views: 75

### Re: Determining Acidity

Another thing we learned in class is the stability of the ion when it is broken from the H. So ClO4 is the strongest because it has more oxygens, and hence, more resonance, making the ion stronger than the others.
Tue Dec 04, 2018 2:47 pm
Forum: Naming
Topic: 7th Edition 9C. 1
Replies: 3
Views: 67

### Re: 7th Edition 9C. 1

I think Lavelle taught us in class to use chloro, fluoro, etc so I think using cyano should be fine
Tue Nov 27, 2018 3:51 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: how to determine coordination number
Replies: 1
Views: 20

### Re: how to determine coordination number

I don't think it was clear in lecture, but I'm assuming it's because transition metals are group 3, so they can access d-orbitals to make more bonds.
Tue Nov 27, 2018 3:41 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Number 19 Chapter 4 part b.
Replies: 1
Views: 20

### Re: Number 19 Chapter 4 part b.

Haha I just typed out an answer to this XD. What you would do is since its written (CH3)2Be, you know the CH3 (methyl) groups are going to be separate. And technically, Be is the least electronegative atom in this structure, so it would be in the center connecting to each of the CH3's on its sides.
Tue Nov 27, 2018 3:38 pm
Forum: Lewis Structures
Topic: Complicated Lewis Structures
Replies: 3
Views: 35

### Re: Complicated Lewis Structures

A lot of the time it's written a certain way which helps you figure it out. So for example in that one, it's written (CH3)2Be. This means the CH3 group is together. and since Be forms two bonds you use intuition to know that its in the middle and connects to CH3 on each side.
Fri Nov 23, 2018 7:24 pm
Forum: Ionic & Covalent Bonds
Topic: Bond Variations
Replies: 4
Views: 64

### Re: Bond Variations

angelagd3l wrote:Do lone pairs also affect the way the model is oriented? Because of the repulsion?

Yes, they do because lone pairs repel the bonding pairs, which changes the orientation. The best example is how in a linear molecule, if you add a lone-pair, the molecule becomes bent.
Tue Nov 20, 2018 6:43 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lewis structure of CNO- with regards to formal charge
Replies: 2
Views: 98

### Re: Lewis structure of CNO- with regards to formal charge

The Oxygen gets the negative formal charge because it is more electronegative.
Mon Nov 19, 2018 5:13 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Dipole moments
Replies: 8
Views: 114

### Re: Dipole moments

For an example in which dipoles don't cancel out, look at CH3Cl. C is the central atom with 3 H's and 1 Cl around it. Since Cl is way more electronegative than H, the dipole moment (or partial charge) on Cl is greater than the partial charges on any of the H's. Since the electrons are unequally attr...
Mon Nov 19, 2018 5:11 pm
Forum: Hybridization
Topic: Ethene Hybridization
Replies: 4
Views: 50

### Re: Ethene Hybridization

I'm also a bit confused but as of what I understood, there are a total of 4 bonds on the Carbons. The electrons occupy 3 sp2 orbitals on the carbons which accounts for 3 bonds and then I think the fourth bond has electrons in an unhybridized p orbital
Wed Nov 14, 2018 3:28 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Question 4.11
Replies: 2
Views: 40

### Re: Question 4.11

By adding a lone pair on Sulfur, and only forming single bonds with Cl, it makes the formal charge 0 for every atom
Wed Nov 14, 2018 3:26 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Homework Question 4.1 (6th edition)
Replies: 4
Views: 119

### Re: Homework Question 4.1 (6th edition)

Actually, in discussion today, we learned about T shape molecules. IT is possible to have 2 or 3 or even 4 lone pairs around the central atom and then 2 other atoms connected to it to form a linear shape. So part b) would be that it MAY be possible to have lone pairs.
Wed Nov 14, 2018 3:23 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Drawing shape based off of lewis structure
Replies: 4
Views: 90

### Re: Drawing shape based off of lewis structure

We don't need to know how to draw wedge and dash notation. We just need to understand that its a representation of the molecule's shape in 3D space. And it doesn't really matter where the atoms go I think
Tue Nov 06, 2018 5:14 pm
Forum: Resonance Structures
Topic: Bond Lengths
Replies: 7
Views: 177

### Re: Bond Lengths

so NO3- is a resonance hybrid so the electrons in the double bonds can exist anywhere. This causes the bond length of N-O to be an average of the NO double and single bonds. The overall bond lengths are all the same
Tue Nov 06, 2018 5:10 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge of Oxygen
Replies: 6
Views: 136

### Re: Formal Charge of Oxygen

As the others said, the electronegativity of Carbon is lower than Oxygen, which causes oxygen to "hog" the electrons more, giving it a negative formal charge.
Thu Nov 01, 2018 6:33 pm
Forum: Lewis Structures
Topic: HClO3
Replies: 2
Views: 83

### HClO3

In class, we discussed the Lewis structure of HClO3, which has Cl in the center (with a lone pair) and two oxygens double bonded to it, an oxygen single bonded and then the Hydrogen attached to the single bonded oxygen. This minimizes formal charge. However, when you single bond the Hydrogen to the ...
Tue Oct 30, 2018 5:48 pm
Forum: Student Social/Study Group
Topic: Midterm- what do we need to know about atomic orbitals
Replies: 2
Views: 132

### Re: Midterm- what do we need to know about atomic orbitals

Definitely ask Lavelle or the TAs, but my thinking is that we just need to know that the wave functions represent orbitals and the wave function squared represents electron density distribution or the probability of finding an electron. Know nodal planes and how there's 0 probability of finding an e...
Tue Oct 30, 2018 5:43 pm
Forum: Ionic & Covalent Bonds
Topic: Likely ion charge for Ga?
Replies: 2
Views: 82

### Re: Likely ion charge for Ga?

Ga becomes 3+ because it is easier to remove 3 electrons than add on 5 more
Tue Oct 30, 2018 5:41 pm
Forum: Octet Exceptions
Topic: Octet exception chlorine and xenon
Replies: 1
Views: 67

### Re: Octet exception chlorine and xenon

Xenon has n = 5, which means l can be 0,1,2,3 and 4. This means it has access to s p d and f and g orbitals. Chlorine has n =3, which means it has l = 0,1,2 and this means it has access to the s p and d orbital. This means xenon has access to more orbitals than chlorine, which means more electrons
Tue Oct 30, 2018 5:40 pm
Forum: Resonance Structures
Topic: Resonance hybrids on the test?
Replies: 2
Views: 103

### Re: Resonance hybrids on the test?

I think you're gonna have to write out the resonance structures. It'll definitely not be something crazy, I think something like the NO3 example will show up.
Tue Oct 23, 2018 12:44 am
Forum: Quantum Numbers and The H-Atom
Topic: Question 1E.7 B Seventh Edition
Replies: 1
Views: 47

### Re: Question 1E.7 B Seventh Edition

It is because the 2py is down spin because everything should be up spin in a ground state Nitrogen atom. Hund's rule says that the electron needs to be parallel in spin.
Tue Oct 23, 2018 12:38 am
Forum: Quantum Numbers and The H-Atom
Topic: 6th ed. problem 2.27
Replies: 2
Views: 50

### Re: 6th ed. problem 2.27

I think a lot of confusion comes from the fact that we call it the s-orbital, p-orbital, etc. S, P, D, and F are all subshells, and S has 1 orbital, P has 3 orbitals (Px, Py, Pz), D has 5 orbitals (Dx, Dy, Dz, Dx2-y2, Dz2) and so on. n = energy level, l = subshell (0=s; 1=p; 2=d) and then the amount...
Tue Oct 23, 2018 12:31 am
Forum: *Shrodinger Equation
Topic: Test 2 and Shrodinger Equation
Replies: 3
Views: 186

### Re: Test 2 and Shrodinger Equation

I think all you need to know is that orbitals are wave functions that take values of n, l, and ml, and that the square of the wave function is the electron density distribution. Also I remember him saying in office hours to know the concept behind hamiltonian derivatives, but I was confused on this ...
Mon Oct 15, 2018 10:58 pm
Forum: Administrative Questions and Class Announcements
Topic: Required knowledge for test/midterm [ENDORSED]
Replies: 13
Views: 288

### Re: Required knowledge for test/midterm[ENDORSED]

Another helpful resource to see what will be tested for Quantum is the outline. Go to the "Quantum World" outline on his site and you can find everything he requires for this test.
Mon Oct 15, 2018 10:56 pm
Forum: *Particle in a Box
Topic: Hw assignment?
Replies: 7
Views: 331

### Re: Hw assignment?

We just go by what is taught in class. So for example, we are still on Sections 1A and 1B, which means just do problems from there. There are definitely 7 problems based on topics we learned over the last couple of days that you can submit as homework for this week.
Mon Oct 15, 2018 12:29 pm
Forum: DeBroglie Equation
Topic: 1B19 Edition 7
Replies: 2
Views: 48

### 1B19 Edition 7

Problem: "Protons and neutrons have nearly the same mass. How different are their wavelengths? Calculate the wavelength of each particle when traveling at 2.75*10^5 m/s in a particle accelerator and report the difference as a percentage of the wavelength of the neutron. I was confused as to wha...
Mon Oct 08, 2018 7:41 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect
Replies: 6
Views: 71

### Re: Photoelectric Effect

The formula for Kinetic Energy is K = (1/2)mv^2

The formula you listed is the formula for the Kinetic Energy of an electron.
Mon Oct 08, 2018 7:33 pm
Forum: Properties of Light
Topic: Speed of light constant (c)
Replies: 6
Views: 102

### Re: Speed of light constant (c)

I used 3.00 *10^8 m/s because that's what Dr. Lavelle put in his notes I'm pretty sure.
Mon Oct 08, 2018 7:33 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect
Replies: 4
Views: 58

### Re: Photoelectric Effect

I'm pretty sure they expected higher intensity of any wavelength to be able to excite electrons but it turned out only certain wavelengths of light had photons that had enough energy to excite electrons
Thu Oct 04, 2018 10:50 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Accuracy and Precision
Replies: 4
Views: 76

### Re: Accuracy and Precision

Let's say you did an experiment trying to find out how much water is produced from a combustion reaction. And lets also say the actual value you should have gotten should be 1 Liter of water. So if you do your trials and you get 0.2L, 0.16L, 0.18L, and 0.22L, your data is precise because all of your...
Mon Oct 01, 2018 11:48 am
Forum: SI Units, Unit Conversions
Replies: 7
Views: 227