Search found 67 matches

Sat Mar 16, 2019 4:39 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Test 2 Q 7 [ENDORSED]
Replies: 5
Views: 572

Re: Test 2 Q 7[ENDORSED]

Just think about it conceptually -- the melting of ice is spontaneous in most temperatures, so deltaG should be negative.
Sat Mar 16, 2019 4:37 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: ∆H and q [ENDORSED]
Replies: 6
Views: 365

Re: ∆H and q[ENDORSED]

Delta H equal q under conditions of constant pressure.
Sat Mar 16, 2019 4:34 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: How to calculate W
Replies: 9
Views: 688

Re: How to calculate W

(number of orientations) ^ (number of molecules). Side note: I've seen some problems where one has to use Avogadro's number to find the number of molecules.
Sat Mar 16, 2019 4:32 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Internal energy (U) of an isolated system
Replies: 17
Views: 1030

Re: Internal energy (U) of an isolated system

There was a question like this on the midterm -- if an isolated system has an internal energy of +5 J, then after 100 years it will have an internal energy of +5 J.
Sat Mar 16, 2019 4:29 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: What is a porous disk?
Replies: 3
Views: 184

Re: What is a porous disk?

It is essentially of the same function as a salt bridge. However, in the cell diagram it is indicated as 1 vertical line instead of how a salt bridge is indicated as two vertical lines.
Sat Mar 16, 2019 4:23 pm
Forum: Balancing Redox Reactions
Topic: multiplying half reactions [ENDORSED]
Replies: 4
Views: 771

Re: multiplying half reactions[ENDORSED]

Yes, if you want a reaction to be the oxidation reaction you flip the sign of the associated cell potential found in the standard reduction potentials table. Otherwise, you never mess with the given cell potential.
Sat Mar 16, 2019 4:20 pm
Forum: Van't Hoff Equation
Topic: Overview
Replies: 8
Views: 564

Re: Overview

Eruchi Okpara 2E wrote:For the final exam, will the test specify between whether we need to use bond enthalpies or standard enthalpy reaction?

Yes, the test should specify or it should be obvious by the given values.
Sat Mar 16, 2019 4:17 pm
Forum: Ideal Gases
Topic: Bar for partial pressure [ENDORSED]
Replies: 4
Views: 453

Re: Bar for partial pressure[ENDORSED]

Since the conversion between bar and atm is 1 atm = 1.01325 bar, do we treat them each unit as virtually the same thing?
Sat Mar 16, 2019 4:09 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Final [ENDORSED]
Replies: 9
Views: 364

Re: Final[ENDORSED]

Yes, the standard reduction table will be provided.
Sat Mar 16, 2019 4:02 pm
Forum: Student Social/Study Group
Topic: Final Jitters
Replies: 178
Views: 34474

Re: Final Jitters

Don't study ten minutes before the final because psychologically you're telling yourself that you don't know the material well enough. Be prepared and be confident in your preparation. Some deep breaths before you enter the exam room helps too.
Wed Feb 27, 2019 5:33 pm
Forum: Balancing Redox Reactions
Topic: Balancing Hydrogen
Replies: 2
Views: 105

Re: Balancing Hydrogen

Yes, like stated above, use H+ (protons) in all redox reactions unless they are basic, in which case you should use OH- (hydroxides).
Wed Feb 27, 2019 5:25 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Recharging Batteries [ENDORSED]
Replies: 10
Views: 670

Re: Recharging Batteries[ENDORSED]

Remember that in a battery electrical energy --> chemical energy.
Wed Feb 27, 2019 5:19 pm
Forum: Van't Hoff Equation
Topic: Derivation
Replies: 3
Views: 364

Re: Derivation

Perfect, thank you both.
Mon Feb 25, 2019 3:00 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Test 2
Replies: 1
Views: 133

Re: Test 2

Unfortunately the problems on Gibbs Free Energy are all in a designated section in the sixth edition and it's hard to comb through them and see immediately if it requires the Nernst Equation. I would just focus on the more general conceptual problems on spontaneity and the basic calculations of Delt...
Mon Feb 25, 2019 2:54 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Moles in -nFEcell
Replies: 5
Views: 247

Re: Moles in -nFEcell

To be clear n is the number of moles of electrons in the balanced redox reaction, not the number of electrons.
Mon Feb 25, 2019 2:42 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Recharging Batteries [ENDORSED]
Replies: 10
Views: 670

Re: Recharging Batteries[ENDORSED]

Charging a reaction is endergonic and thus not spontaneous.
Mon Feb 25, 2019 2:41 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Electrolysis on Test 2
Replies: 1
Views: 261

Re: Electrolysis on Test 2

No, electrolysis will not be on the test. Only material covered during Weeks 6 and 7 will be on Test 2.
Mon Feb 25, 2019 2:22 pm
Forum: Van't Hoff Equation
Topic: Derivation
Replies: 3
Views: 364

Derivation

Do we need to know/is it beneficial to know the derivation of the Van't Hoff Equation? If so, would someone like to derive it please?
Mon Feb 25, 2019 2:20 pm
Forum: Environment, Fossil Fuels, Alternative Fuels
Topic: Why energy crisis?
Replies: 8
Views: 2994

Re: Why energy crisis?

Thank you, this was very helpful. These kinds of discussion threads really help cement my understanding of the concepts.
Mon Feb 25, 2019 2:10 pm
Forum: Biological Examples (*DNA Structural Transitions, etc.)
Topic: Examples for Final [ENDORSED]
Replies: 1
Views: 378

Examples for Final[ENDORSED]

Did Dr. Lavelle go over specific biological examples that we should be aware of for the final?
Mon Feb 25, 2019 1:14 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Finding K or Q with Nernst's Equation
Replies: 2
Views: 214

Re: Finding K or Q with Nernst's Equation

Remember to take the inverse of the log (exponentiate) to isolate and solve for K or Q.
Mon Feb 25, 2019 1:11 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: n in -nFE
Replies: 14
Views: 236

Re: n in -nFE

As mentioned above, n is the number of moles of electrons. To find n, one must balance the complete redox reaction (not just each half rxn separately).
Mon Feb 25, 2019 1:10 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: n value
Replies: 11
Views: 266

Re: n value

N is the number of moles of electrons in the balanced redox reaction.
Mon Feb 25, 2019 1:08 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Galvanic Cell
Replies: 3
Views: 160

Re: Galvanic Cell

It would be safe to assume that the cell potential is positive in a galvanic cell when doing problems in the textbook or on a test because there would not be much to prove or calculate if the cell potential was negative.
Mon Feb 25, 2019 1:05 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Spontaneous?
Replies: 13
Views: 442

Re: Spontaneous?

I think there is some general confusion about what spontaneity is. "Spontaneous" describes a process or reaction, so values of delta H, G, or S themselves cannot be spontaneous, but they can be used to prove spontaneity through the equation Delta G = Delta H - Temp(Delta S). The process is...
Mon Feb 25, 2019 1:00 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Tips for Discussion Test
Replies: 6
Views: 269

Re: Tips for Discussion Test

Also KhanAcademy and YouTube in general has some pretty great content if you're struggling with the general concepts. But textbook practice problems are definitely the key to mastery.
Mon Feb 25, 2019 12:59 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Tips for Discussion Test
Replies: 6
Views: 269

Re: Tips for Discussion Test

Homework problems on Gibbs Free Energy and Electrochemistry (up to, not including, the Nernst Eqn) would be a great place to start.
Mon Feb 25, 2019 12:57 pm
Forum: Balancing Redox Reactions
Topic: Test #2
Replies: 9
Views: 400

Re: Test #2

Yes, Week 6 and 7 content will be covered on Test 2.
Mon Feb 11, 2019 2:38 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Using R
Replies: 10
Views: 384

Re: Using R

As stated above, on the midterm we will be provided with the formula sheet with the R gas constant in different forms due to different units. You just have to select the correct one based on the units of the given values.
Mon Feb 11, 2019 2:35 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Constant Vol.
Replies: 8
Views: 518

Re: Constant Vol.

Since work (w) is equal to (pressure) * (change in volume), if there is no change in volume then work must be equal to zero.
Mon Jan 21, 2019 5:12 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Water in ICE tables
Replies: 10
Views: 707

Re: Water in ICE tables

Pure substances (solids, liquids) such as water do not affect the equilibrium expression.
Mon Jan 21, 2019 5:08 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatelier's Principle
Replies: 4
Views: 173

Re: Le Chatelier's Principle

Le Chatelier's Principle states that if a constraint (such as a change in pressure, temperature, or concentration of a reactant) is applied to a system in equilibrium, the equilibrium will shift so as to tend to counteract the effect of the constraint.
Mon Jan 21, 2019 5:03 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 5% rule
Replies: 12
Views: 396

Re: 5% rule

The 5% rule is useful because it allows us to simplify the equilibrium expression and avoid using the quadratic formula.
Mon Jan 21, 2019 4:54 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Using Equilibrium Constants to Predict Solubility
Replies: 2
Views: 160

Re: Using Equilibrium Constants to Predict Solubility

Yes, you essentially answered your own question -- just pay attention to the K value and the phases of the reactants/products and the answer should be clear, just as the previous answer stated.
Mon Jan 21, 2019 4:51 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Q and K
Replies: 10
Views: 418

Re: Q and K

The value Q is useful because in comparison to a K value for a reaction it tells us whether products or reactants are favored (which direction the reaction will go towards)
Mon Jan 21, 2019 4:46 pm
Forum: Ideal Gases
Topic: ICE table
Replies: 11
Views: 666

Re: ICE table

ICE tables can be used for questions of both reactant/product equilibrium partial pressure and concentration, as long as the correct K values are used.
Sat Dec 08, 2018 2:09 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: boiling point
Replies: 5
Views: 557

Re: boiling point

Since NH3 exhibits hydrogen bonding while PH3 does not, NH3 has the higher boiling point.
Sat Dec 08, 2018 2:07 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Shape
Replies: 5
Views: 251

Re: Shape

Yes, shape means molecular geometry. Professor Lavelle will be explicit about it on the final though.
Sat Dec 08, 2018 2:03 pm
Forum: Lewis Acids & Bases
Topic: Lewis acids and bases vs. Bronsten
Replies: 2
Views: 95

Re: Lewis acids and bases vs. Bronsten

Lewis acid: substance that donates H+ (proton)
Lewis base: accepts H+
Bronsted acid: accepts electron pair
Bronsted base: donates electron pair
Sat Dec 08, 2018 1:57 pm
Forum: Conjugate Acids & Bases
Topic: Water as an Acid/Base
Replies: 20
Views: 673

Re: Water as an Acid/Base

Yes, water is amphoteric and amphiprotic.
Sat Dec 08, 2018 1:34 pm
Forum: Naming
Topic: naming compounds
Replies: 6
Views: 327

Re: naming compounds

The compound [Co(NH2CH2CH2NH2)2(CN)(Cl)]Cl (pardon the lack of subscripts) would be written as chlorocyanobisethylenediaminecobalt (III) chloride because the ethylenediamine already has a "di-" in it, or in other words it is already a polydentate molecule, so if there are two in the comple...
Sat Dec 08, 2018 1:25 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Polydentate
Replies: 11
Views: 482

Re: Polydentate

It's also helpful to see if the molecule has nitrogen, oxygen, or sulfur atoms with lone pairs because these are common binding sites for ligands and thus would make the molecule polydentate.
Wed Dec 05, 2018 8:56 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: HW for this week
Replies: 4
Views: 211

Re: HW for this week

Yes
Wed Dec 05, 2018 8:51 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination Number
Replies: 7
Views: 280

Re: Coordination Number

The oxidation number is the charge of the central transition metal in the coordination compound, which can be found if you know the charge of the ligands and the overall charge of the compound. The coordination number is the number of ligands that can be bonded to the central transition metal in the...
Wed Dec 05, 2018 8:46 pm
Forum: Naming
Topic: Polyatomic ions and naming
Replies: 7
Views: 213

Re: Polyatomic ions and naming

It would be helpful to know the charges of the more common polyatomic ions, especially for determining the oxidation state of the transition metal in a coordination compound.
Mon Nov 26, 2018 7:02 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: Dipole
Replies: 3
Views: 170

Re: Dipole

AlexandraZuniga1L wrote:Does a polar molecule have to have polar bonds with dipoles that do not cancel?

Yes, polar molecules have to have polar bonds with dipole moments that do not cancel.
Mon Nov 26, 2018 5:28 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.19 6th Edition
Replies: 2
Views: 143

Re: 4.19 6th Edition

It would be less than 120 degrees because the electron geometry is trigonal planar not tetrahedral. Thus, when one of the regions of electron density is a lone pair, the bond angles become less than 120 degrees. You would be correct if the electron geometry was tetrahedral i.e. there was one more re...
Mon Nov 26, 2018 5:25 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: T shaped
Replies: 6
Views: 210

Re: T shaped

I believe it has to do with the bond angles. The two lone pairs cause the angles between the central atom and each ligand to be less than 90 degrees, whereas the angles between the ligands and the central atom in a trigonal planar molecule are 120 degrees.
Mon Nov 26, 2018 5:08 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: Polar vs Non-polar
Replies: 2
Views: 122

Re: Polar vs Non-polar

The question should be how do determine if a molecule is polar. This, just as the above answer indicates, is determined by first finding the shape of the molecule using VSEPR and then seeing if the dipole moments cancel each other out or not.
Sat Nov 10, 2018 3:50 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge of Oxygen
Replies: 6
Views: 603

Re: Formal Charge of Oxygen

Also keep in mind that formal charge only applies to compounds and not individual atoms.
Sat Nov 10, 2018 3:47 pm
Forum: Lewis Structures
Topic: Molecular shape and structure
Replies: 5
Views: 261

Re: Molecular shape and structure

You only need to indicate shape in VSEPR models, and even then it is not necessary to depict a 3D drawing of the structure. Simply naming the shape (trigonal planar, linear, etc) will suffice.
Sat Nov 10, 2018 3:45 pm
Forum: Ionic & Covalent Bonds
Topic: Ionization Energies
Replies: 13
Views: 474

Re: Ionization Energies

Yes, Helium (He) has the greatest ionization energy.
Sun Nov 04, 2018 9:42 am
Forum: Formal Charge and Oxidation Numbers
Topic: shortcut for FC
Replies: 6
Views: 324

Re: shortcut for FC

Considering the shortcut would save you approximately 2 seconds for multiplying by 2 and then dividing by 2, I would just stick to how you've been doing it if it's getting you the correct results. :)
Sun Nov 04, 2018 9:38 am
Forum: Electronegativity
Topic: What are the trends useful for?
Replies: 12
Views: 425

Re: What are the trends useful for?

When drawing a Lewis Structure, the atom with the lowest ionization energy is the central atom. So, for example, hydrogen is never the central atom.
Sun Nov 04, 2018 9:35 am
Forum: Lewis Structures
Topic: Central Atom
Replies: 3
Views: 141

Re: Central Atom

The central atom is the one with the lowest ionization energy. So, for example, hydrogen is never the central atom in a Lewis structure.
Sun Oct 28, 2018 11:12 pm
Forum: Ionic & Covalent Bonds
Topic: bound atoms
Replies: 8
Views: 386

Re: bound atoms

Bound atoms are more stable and have lower energy than separate atoms because forming a chemical bond releases energy.
Sun Oct 28, 2018 11:09 pm
Forum: Lewis Structures
Topic: Lewis Structures
Replies: 13
Views: 434

Re: Lewis Structures

Choose the atom with the lowest ionization energy to be the central atom; hence, hydrogen is never a central atom.
Sun Oct 28, 2018 11:06 pm
Forum: Ionic & Covalent Bonds
Topic: Cations/Anions
Replies: 4
Views: 162

Re: Cations/Anions

Yes, as stated above, 5p^1 represents one electron in the outermost 5p subshell of Indium, so when Indium loses an electron to become the cation In+ it will lose the outermost electron, or 5p^1. When Nitrogen gains 3 electrons to become the anion N^3-, 3 electrons are added to the outermost energy l...
Sun Oct 21, 2018 9:09 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Superscript
Replies: 3
Views: 127

Re: Superscript

Yes exactly, in your example of the 2s^2 orbital, the superscript of 2 indicates that there can be 2 electrons in the 2s orbital.
Sun Oct 21, 2018 4:22 pm
Forum: Trends in The Periodic Table
Topic: Periodic Table Trends
Replies: 5
Views: 281

Re: Periodic Table Trends

Atomic radius increases down and to the left on the periodic table because electrons are farther away from the nucleus. Ionization energy decreases farther down the periodic table because it is easier to remove an electron when they are farther away from the nucleus. Electron affinity increases up a...
Sun Oct 21, 2018 4:02 pm
Replies: 3
Views: 450

Is the intensity of the black body radiation related to a wave's amplitude? Or is it related to the number of electrons emitting a certain frequency?
Sun Oct 14, 2018 6:27 pm
Forum: Properties of Electrons
Topic: Photoelectric Experiment
Replies: 9
Views: 216

Re: Photoelectric Experiment

Yes, intensity is very different from frequency. We care about the fact that a photon needs to be of a greater energy than the electron to remove the electron, which is determined by a higher frequency as high frequency corresponds to high energy. Intensity merely means how many photons interact wit...
Sun Oct 14, 2018 6:20 pm
Forum: Einstein Equation
Topic: Symbol for frequency
Replies: 12
Views: 854

Re: Symbol for frequency

Yes, I have not seen "f" used in many textbooks or academic sources; I would stick with "v" (nu).
Sun Oct 14, 2018 6:09 pm
Forum: Properties of Electrons
Topic: Wavelength Properties
Replies: 4
Views: 149

Re: Wavelength Properties

Yes, I believe all matter exhibits wavelike properties, but with our current techniques for measuring these wavelike properties we can only measure it for objects with relatively small mass and momentum, hence the 10^-15 (m) or 10^-18 (m) threshold.
Tue Oct 09, 2018 10:54 am
Forum: Balancing Chemical Reactions
Topic: Balancing Procedure
Replies: 7
Views: 396

Re: Balancing Procedure

Yes, you can't throw in an extra O atom because of the law of conservation of mass. Instead, manipulate stoichiometric coefficients such that the chemical equation is balanced, or that each side of the equation has the same number of atoms of each element.
Tue Oct 09, 2018 10:51 am
Forum: Empirical & Molecular Formulas
Topic: when to multiply empirical formula [ENDORSED]
Replies: 9
Views: 1520

Re: when to multiply empirical formula[ENDORSED]

You want to make sure all the stoichiometric coefficients are whole numbers. So if you have 3.5, you will most likely multiply all of the coefficients by 2 or a multiple of 2 to ensure whole numbers.
Tue Oct 09, 2018 10:48 am
Forum: Molarity, Solutions, Dilutions
Topic: Finding the volume of stock solution to dilute
Replies: 13
Views: 785

Re: Finding the volume of stock solution to dilute

I don't think it matters, I just prefer to keep it in liters because molarity of a solution is moles/liters. But for the M1V1 equation, since you are essentially finding a value using a ratio, whether you choose mL or L does not matter as long as you are consistent and that you specify.