## Search found 54 matches

Sun Mar 10, 2019 6:30 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Ecell and pH
Replies: 3
Views: 143

### Re: Ecell and pH

Yes as the above comments have stated, I believe it is best to use the equation involving Q. There were many times Dr. Lavelle advised against using some methods the book suggested.
Sun Mar 10, 2019 6:27 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: oxidizing power vs reducing power
Replies: 3
Views: 811

### Re: oxidizing power vs reducing power

I may be wrong but I believe the above comment might be inaccurate. The reducing agent has a reducing power because it is reducing another atom and the oxidizing agent has an oxidizing power because it oxidizes another atom. Correct me if I am wrong.
Sun Mar 10, 2019 6:17 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: van't hoff equation
Replies: 6
Views: 199

### Re: van't hoff equation

Raising both sides of the equation to the exponent of e will cancel the ln. You then solve for one of the K values.
Sun Mar 03, 2019 11:39 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Cell Potential Spontaneity
Replies: 7
Views: 220

### Re: Cell Potential Spontaneity

Responding to an above question, yes it is possible for a cell potential to be negative. That’s why in galvanic cell problems, it is important to make sure it is positive or else it is not a galvanic cell.
Sun Mar 03, 2019 11:32 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Gibbs free energy and temperature
Replies: 3
Views: 187

### Re: Gibbs free energy and temperature

Adding on, many questions deal with how temperature affects Gibbs free energy. For example, determining the temperature when the reaction changes from spontaneous to nonspontaneous is in other words finding the temperature when Gibbs free energy changes from a negative value to a positive value. So ...
Sun Mar 03, 2019 11:22 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Finding n
Replies: 12
Views: 344

### Re: Finding n

Yeah a lot of people get it mixed up with the total moles of reactants and products but it is the electrons transferred. Always make sure it is the number of electrons after you balance the half-reactions and make sure the electrons cancel out.
Thu Feb 21, 2019 1:04 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Porous disc explanation?
Replies: 6
Views: 167

### Re: Porous disc explanation?

The porous disk serves essentially the same function as a salt bridge. Both allow ion transfer so that the two solutions stay neutral.
Thu Feb 21, 2019 1:00 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge/Porous Disk
Replies: 5
Views: 161

### Re: Salt Bridge/Porous Disk

Adding a salt bridge or porous disk allows ion transfer (two solutions stay neutral).
Thu Feb 21, 2019 12:51 am
Forum: Balancing Redox Reactions
Topic: Oxidation Numbers
Replies: 2
Views: 85

### Re: Oxidation Numbers

Yes for example if we look at the problem Dr. Lavelle gave in class: 8H+ + (MnO4)- + 5Fe2+ -> Mn2+ + 5Fe3+ + 4H2O, Mn is reduced from +7 to +2.
Thu Feb 21, 2019 12:47 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isobaric
Replies: 11
Views: 608

### Re: Isobaric

To further complement the above responses, know that W = -PdeltaV is used to calculate work done by expansion against constant P. So since isobaric means constant pressure, this equation would be used.
Thu Feb 21, 2019 12:42 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible Reactions
Replies: 8
Views: 505

### Re: Reversible Reactions

Lyndon in his review session said that in this class, we can pretty much assume that isothermal means reversible.
Thu Feb 21, 2019 12:41 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible vs irreversible
Replies: 6
Views: 401

### Re: Reversible vs irreversible

Adding onto the above responses, just remember that reversible does maximum work and is always at equilibrium. In this class, reversible will be pretty much synonymous to isothermal.
Sat Feb 09, 2019 11:41 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Decreasing volume and chemical equilibrium
Replies: 8
Views: 276

### Re: Decreasing volume and chemical equilibrium

A nice way to visualize is this: when you are decreasing the volume you are increasing the pressure. When you apply pressure to something, it would want to move to a place more open to lessen the pressure. This is the case for reactants and products experiencing increases pressure. The side with mor...
Sat Feb 09, 2019 11:38 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Replies: 10
Views: 663

The only time when a change of pressure will have an effect is when the volume changes. A decrease in volume creates an increase in pressure. However the addition of inert gas does not change the volume and it does not react with the present reactants or products.
Sat Feb 09, 2019 11:35 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Temp affecting K
Replies: 4
Views: 147

### Re: Temp affecting K

As the above responses have stated, K is the only factor that causes a change in K. Changes in elements like pressure, volume, or moles creates a Q which is temporary.
Sun Jan 27, 2019 4:47 pm
Forum: Phase Changes & Related Calculations
Topic: Delta H
Replies: 11
Views: 558

### Re: Delta H

This is how Dr. Lavelle explained it. Positive delta H signifies that it is endothermic which means energy is being put into the system. Negative delta H is exothermic which means energy is leaving the system. In this way, you can rationalize the positive and negative better as gain and loss of ener...
Sun Jan 27, 2019 4:43 pm
Forum: Phase Changes & Related Calculations
Topic: Why are phase changes endothermic?
Replies: 11
Views: 293

### Re: Why are phase changes endothermic?

Phase change from solid to liquid to gas requires energy in order for the bonds to be broken. Therefore, they are endothermic.
Sun Jan 27, 2019 4:41 pm
Forum: Phase Changes & Related Calculations
Topic: Steam
Replies: 7
Views: 174

### Re: Steam

It helps to take a look at the phase change graphically. You would see that there is a lot more energy involved as the steam condenses to liquid. This heat energy, which is significantly greater than the energy liquid water holds, is being absorbed by the skin causing severe burns.
Mon Jan 21, 2019 12:32 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: pressure and volume
Replies: 5
Views: 133

### Re: pressure and volume

Looking at PV=nRT you can see that pressure and volume are inversely related. An increase in pressure results in a decrease in volume. And a decrease in pressure results in an increase in volume.
Mon Jan 21, 2019 12:28 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Pressure
Replies: 8
Views: 238

### Re: Pressure

Look at how many mols are on both sides of the equation. If the pressure increases, the equilibrium shifts towards the side with less mols.
Mon Jan 21, 2019 12:24 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Pressure
Replies: 7
Views: 197

### Re: Pressure

I am sure you would only look at aqueous and gases.
Fri Jan 11, 2019 6:02 pm
Forum: Student Social/Study Group
Topic: New to Lavelle
Replies: 32
Views: 3842

### Re: New to Lavelle

For me personally, I found that paying close attention to his lectures and doing most of the homework problems really prepared me for the tests, midterm, and final. A huge help is also Lyndon Bui's, the TA, review sessions. They are very thorough and refresh your memory on everything that was covered.
Fri Jan 11, 2019 5:37 pm
Forum: Ideal Gases
Topic: Units
Replies: 19
Views: 335

### Re: Units

Yeah use K. Whenever you are confused as to which unit to use, look at the constant values in the equation and use the units that will cancel out with them. In this case of PV = nRT, R uses K.
Fri Jan 11, 2019 5:28 pm
Forum: Ideal Gases
Topic: Pressure of gasses
Replies: 5
Views: 230

### Re: Pressure of gasses

Yeah just to confirm the above responses, Dr. Lavelle hasn't gone over that equation so I don't think we have to know that one. For now at least.
Sun Dec 09, 2018 6:14 pm
Forum: Naming
Topic: Order of ligands
Replies: 6
Views: 410

### Re: Order of ligands

Lyndon said that when writing the symbols, it doesn't matter the order of the ligands. However, for the letter names, alphabetical order is necessary.
Sun Dec 09, 2018 6:13 pm
Forum: Naming
Topic: Chloro vs Chlorito
Replies: 10
Views: 484

### Re: Chloro vs Chlorito

Dr. Lavelle has used chloro in his lecture notes so that would be a safe bet.
Sun Dec 09, 2018 6:12 pm
Forum: Naming
Topic: -ate in naming
Replies: 7
Views: 492

### Re: -ate in naming

For example [Ni(CN)5]3- has a negative overall charge so you would add -ate to the end of nickel.
Sun Dec 02, 2018 3:45 pm
Forum: Naming
Topic: Naming
Replies: 5
Views: 227

### Re: Naming

^I'm not too sure about that but I know that when drawing out the Lewis Structures, Dr. Lavelle wants the ligand bonded to the central ion to be written so that the atom with lone electron pairs is connected to the bond line. For example in the lewis structure for [NiCl2(NH3)4] . 2H20, it would look...
Sun Dec 02, 2018 3:40 pm
Forum: Naming
Topic: Chelate vs Polydentate
Replies: 1
Views: 83

### Re: Chelate vs Polydentate

A chelation is a process in which a polydentate ligand bonds with a metal ion, forming a ring. The complex produced from this is called the chelate and the polydentate ligand is the chelating agent. More information I found was from this website: https://chem.libretexts.org/Textbook_Maps/Inorganic_C...
Sun Dec 02, 2018 3:23 pm
Forum: Naming
Topic: Coordination Sphere
Replies: 2
Views: 82

### Re: Coordination Sphere

So for example, we have [NiCl2(NH3)4] . 2H20. Everything inside the square brackets is inside the coordination sphere. Ligands directly attached to central ion make up the coordination sphere.
Sat Nov 24, 2018 11:49 pm
Forum: Hybridization
Topic: Sigma/Pi Bonds
Replies: 5
Views: 119

### Re: Sigma/Pi Bonds

Single bonds involve one sigma bond and double bonds involve one sigma and one pi bond. The importance of a pi bond is that it restricts rotation while sigma bonds do not.
Sat Nov 24, 2018 11:42 pm
Forum: Hybridization
Topic: reason for hybridization
Replies: 9
Views: 1075

### Re: reason for hybridization

Another way to understand it better is to have a visual of it. The unhybridized orbitals morph to become new hybridized orbitals which have been experimentally observed.
Sat Nov 24, 2018 11:37 pm
Forum: Hybridization
Topic: Regions of electron density
Replies: 6
Views: 199

### Re: Regions of electron density

Yes you would only look at the regions around the central atom, not the bonded atoms.
Sat Nov 17, 2018 10:12 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR Shapes
Replies: 4
Views: 181

### Re: VSEPR Shapes

Remember to name the shape of the molecule using position of only bound atoms (bonding electron pairs only). However, the molecular shape is determined by both lone pairs and bonding pairs because of repulsion.
Sat Nov 17, 2018 10:08 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond angles
Replies: 5
Views: 122

### Re: Bond angles

Reiterating an above response, for many of the shapes, lone electron pairs causes angles to decrease. In that instance, you only need to know that the angle is less than an established value. For example, for trigonal pyramidal, you just need to know that the angle is less than 109.5 degrees. You wo...
Sat Nov 17, 2018 10:06 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining a Dipole Moment
Replies: 2
Views: 123

### Re: Determining a Dipole Moment

So for example, in C2H2Cl2, C is bonded to Cl. The Cl would be more negative because it has a higher electronegativity, it wants electrons more than the C. Thus, the C would be more positive. These are the positive and negative dipole moments.
Sat Nov 10, 2018 2:11 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Naming the molecular shape
Replies: 4
Views: 167

### Re: Naming the molecular shape

Lone pairs matter! The steric number is the amount of lone pairs and bonds the central atom has and so the steric number might be the same for multiple molecules but the shape of the molecule could be very different depending on the amount of lone pairs the atom has. For example, H2O has a steric n...
Sat Nov 10, 2018 2:10 am
Forum: Determining Molecular Shape (VSEPR)
Topic: HW for discussion
Replies: 9
Views: 394

### Re: HW for discussion

I'd say do the homework problems that relate to the information you learned in the most recent lecture, and maybe a few from previous lectures. It's possible to be docked off points for not including homework covering current material (I know from experience).
Sat Nov 10, 2018 2:07 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Repulsion Strength
Replies: 2
Views: 92

### Repulsion Strength

Hi in the lecture notes it said:
Repulsion strength: lone-lone pair > lone-bonding pair > bonding-bonding pair
Can anyone clarify what this means?
Sun Nov 04, 2018 5:28 pm
Forum: Electronegativity
Topic: Electron Affinity vs. Ionization Energy
Replies: 8
Views: 312

### Re: Electron Affinity vs. Ionization Energy

Just a reminder too that there are some exceptions in these trends like C, N, O, F. Make sure to look out for those.
Sun Nov 04, 2018 5:27 pm
Forum: Electronegativity
Topic: electronegativity vs electron affinity
Replies: 4
Views: 119

### Re: electronegativity vs electron affinity

Another way to look at it is how my TA defined them:
electron affinity = how much an atom "wants" an electron
electronegativity = polarizability, attracts electron in a bond
Sun Nov 04, 2018 5:24 pm
Forum: Electronegativity
Topic: (10d) are Ionization Energy trends different from Electron Affinity trends?
Replies: 1
Views: 62

### Re: (10d) are Ionization Energy trends different from Electron Affinity trends?

So electron affinity is how much the element wants an electron. The reason why the order for increasing electron affinity is N<C<O<F instead of the intuitive C<N<O<F is because C wants to reach a half-filled subshell, or 3 electrons out of the 6 electrons in the p subshell. Half-filled and completel...
Sun Oct 28, 2018 11:51 pm
Forum: Trends in The Periodic Table
Topic: Ionization energies
Replies: 9
Views: 552

### Re: Ionization energies

Ionization energy is the energy required to take an electron away from an atom. In other words, a higher ionization energy signifies that it is harder to strip an electron away. It gets higher as you move from the bottom left to the top right of the periodic table because of higher proton counts and...
Sun Oct 28, 2018 11:45 pm
Forum: Trends in The Periodic Table
Topic: Sizes of ions and neutral atoms
Replies: 4
Views: 198

### Re: Sizes of ions and neutral atoms

The anion is larger than the neutral atom because as stated above, the proton number stays the same but the electron number increases. So, while the positive attraction stays the same, the negative charge increases. This causes repulsion among the electrons which increases the size. However, if the ...
Sun Oct 28, 2018 11:33 pm
Forum: Trends in The Periodic Table
Replies: 6
Views: 273

Just to add on to the above responses, as you go from the bottom left to the top right of the periodic table, the atomic radius generally gets smaller because there are less energy levels as you go up and more protons as you go to the right. More protons means that there is a stronger positive attra...
Mon Oct 22, 2018 3:07 am
Forum: Photoelectric Effect
Topic: Test 2
Replies: 16
Views: 471

### Re: Test 2

Test 2 will cover Quantum world but only up to Friday's lecture inclusive. Any material from Week 4 won't be on this test.
Mon Oct 22, 2018 3:04 am
Forum: Photoelectric Effect
Topic: Visible Light Spectrum
Replies: 6
Views: 174

### Re: Visible Light Spectrum

Dr. Lavelle gave the values red = 700 nm and violet = 400 nm in class lecture. So I would assume these numbers to be pretty reliable.
Mon Oct 22, 2018 2:55 am
Forum: Einstein Equation
Topic: Units
Replies: 17
Views: 777

### Re: Units

Just another reminder too is that Herz = s^-1. I find it helpful to convert Hz to s^-1 so that if units are being multiplied or divided, it's easier to see how things cancel out.
Sun Oct 14, 2018 6:02 pm
Forum: Einstein Equation
Topic: Symbol for frequency
Replies: 12
Views: 568

### Re: Symbol for frequency

Saw a chem mod reply to someone saying we use nu. It's basically just a cursive v.
Sun Oct 14, 2018 5:58 pm
Forum: Properties of Light
Topic: Example from Friday's Lecture (10/12/18)
Replies: 3
Views: 65

### Re: Example from Friday's Lecture (10/12/18)

Yes, Lavelle said that the mass is given. So it is safe to assume that the mass will be on the constants sheet for any tests/exams.
Sun Oct 14, 2018 5:56 pm
Forum: Properties of Light
Topic: Visible Light Spectrum
Replies: 3
Views: 93

### Re: Visible Light Spectrum

Yes, what the two above have mentioned is correct. Also, Lavelle said in lecture that we will be mostly focusing on ultraviolet rays, visible light, and infrared rays in class so we don't have to worry about the others too much.
Fri Oct 05, 2018 4:03 am
Forum: SI Units, Unit Conversions
Topic: Clarification on unit conversions
Replies: 4
Views: 186

### Re: Clarification on unit conversions

I would just like to underscore the importance of visualization as the previous response has stated. Before converting, I find it very helpful to compare the size of both units. For example, if I were to convert meters to kilometers, I would first realize that a kilometer is a larger unit than a met...
Fri Oct 05, 2018 3:44 am
Forum: Significant Figures
Topic: Sig figs for Avogadro's number
Replies: 3
Views: 100

### Re: Sig figs for Avogadro's number

Allow me to reaffirm the statements of the above responses. I have physical evidence of Dr. Lavelle approval of the use of 6.022*10^23 for Avogadro's number in my notes that I have taken on the first lecture day.
Fri Oct 05, 2018 3:39 am
Forum: Significant Figures
Topic: Significant Figures for E.21 (b)
Replies: 4
Views: 144

### Re: Significant Figures for E.21 (b)

Fascinating. Yes, based off of the work you have shown, it appears to to me that there should indeed be four sig figs. I believe the solutions manual at times chooses to disregard sig figs, so I wouldn't stress about it too much. I hope this response of agreement eases your conscience.