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: 1010
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: 776
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: 1474
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: 2726
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: 988
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: 4428
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: 1145
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: 702
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: 1168
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: 457
- Views: 423067
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: 277
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: 1434
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: 670
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: 282
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: 657
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: 1434
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: 452
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: 670
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: 4446
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: 1023
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: 621
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: 900
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: 962
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: 434
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: 1597
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: 595
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: 595
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: 938
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: 1043
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: 1065
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: 2636
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: 440
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: 21873
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: 306
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: 831
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: 1347
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: 1268
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: 582
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: 250
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
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: 1598
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: 614
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: 1189
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: 468
- Wed Dec 05, 2018 8:51 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Coordination Number
- Replies: 7
- Views: 639
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: 552
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: 369
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: 380
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: 590
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: 294
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: 1655
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: 601
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: 3707
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: 731
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: 1018
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: 339
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: 1263
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: 1043
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: 359
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: 306
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: 645
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
- Forum: *Black Body Radiation
- Topic: Intensity of radiation
- Replies: 3
- Views: 723
Intensity of radiation
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: 564
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: 2301
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: 315
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: 791
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: 4588
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: 1360
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.