Search found 62 matches
- Sat Mar 16, 2019 11:38 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Changing E˚ values
- Replies: 2
- Views: 459
Re: Changing E˚ values
Nope, E naught doesn't change
- Sat Mar 16, 2019 11:36 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Activation Energy
- Replies: 2
- Views: 347
Re: Activation Energy
A is the frequency factor. It takes into account what percentage of collisions between molecules will actually make the reaction progress (the molecules have to be oriented correctly, etc)
- Sat Mar 16, 2019 11:32 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Temperature and Le Chatlier's Principle
- Replies: 6
- Views: 835
Re: Temperature and Le Chatlier's Principle
If the reaction is endothermic and the temperature is increased, the reaction will be pushed towards the products and K will increase.
If the reaction is exothermic and the temperature is increased, the reaction will be pushed towards the reactants and K will decrease.
If the reaction is exothermic and the temperature is increased, the reaction will be pushed towards the reactants and K will decrease.
- Mon Mar 04, 2019 1:26 pm
- Forum: First Order Reactions
- Topic: First Order Reactions
- Replies: 6
- Views: 578
Re: First Order Reactions
In the slides it says a straight line plot of ln[R] vs time means the reaction is 1st-order.
- Mon Mar 04, 2019 1:25 pm
- Forum: Balancing Redox Reactions
- Topic: Acidic vs basic solutions
- Replies: 10
- Views: 993
Re: Acidic vs basic solutions
In acidic solutions, balance half-reactions by adding H2O and H+; in basic solutions, balance by adding H2O and OH-.
- Mon Mar 04, 2019 1:22 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Week 9 HW
- Replies: 6
- Views: 638
Re: Week 9 HW
You should probably mix in some kinetics in there.
- Mon Mar 04, 2019 1:20 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: "N" in Kinetics
- Replies: 4
- Views: 485
Re: "N" in Kinetics
It's usually a lower-case n, though.
- Mon Mar 04, 2019 1:18 pm
- Forum: Van't Hoff Equation
- Topic: K value- Temp
- Replies: 6
- Views: 993
Re: K value- Temp
A temperature change pushes the reaction to either the left or right depending on whether heat is a reactant or product (depending on whether the rxn is exo or endothermic). This gives the reaction a new equilibrium point, so k changes.
- Mon Mar 04, 2019 1:16 pm
- Forum: Balancing Redox Reactions
- Topic: Cell diagrams
- Replies: 8
- Views: 779
Re: Cell diagrams
Pt is sometimes added when one half of the reaction only involves aqueous solutions and a solid electrode is needed.
- Sun Feb 24, 2019 9:53 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 3
- Views: 345
Re: Salt Bridge
Without a salt bridge, charge builds up on either side of the cell and stops transferring. The salt bridge puts ions into solution, keeping them neutral so that charge can keep flowing.
- Sun Feb 24, 2019 9:51 pm
- Forum: Balancing Redox Reactions
- Topic: Half Reaction
- Replies: 2
- Views: 263
Re: Half Reaction
A half reaction is half of a redox reaction; either the part of the reaction that oxidizes a reactant or the half that reduces a reactant. We separate redox reactions into half reactions because they're easier to balance that way, and then once they're balanced we can add them together to see the wh...
- Sun Feb 24, 2019 9:50 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Oxidation number
- Replies: 2
- Views: 342
Re: Oxidation number
The oxidation number is the charge on an atom or molecule. O2-, for example.
- Fri Feb 15, 2019 1:28 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: enthalpy, entropy, Gibbs Free Energy signs
- Replies: 3
- Views: 340
Re: enthalpy, entropy, Gibbs Free Energy signs
When Gibbs free energy is negative the process is spontaneous.
- Fri Feb 15, 2019 1:24 pm
- Forum: Biological Examples (*DNA Structural Transitions, etc.)
- Topic: Structures of the Human Body and Systems
- Replies: 5
- Views: 1338
Re: Structures of the Human Body and Systems
I'd think the human body must be an open system because we give off heat, and we intake and output substances (O2, CO2, nutrients, waste) all the time.
- Fri Feb 15, 2019 1:21 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Microstate
- Replies: 7
- Views: 805
Re: Microstate
A microstate is a specific arrangement of molecules. Degeneracy is the number of possible microstates/arrangements of a group of molecules, and entropy is calculated using degeneracy.
- Fri Feb 15, 2019 1:20 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Quick Conceptual question
- Replies: 7
- Views: 905
Re: Quick Conceptual question
Enthalpy is the heat transferred in/out of the system, while entropy is the disorder of the system (how many possible positions, vibrations, etc).
- Tue Feb 05, 2019 1:38 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: residual energy
- Replies: 3
- Views: 822
Re: residual energy
Residual entropy or positional entropy is the entropy that a sample has when you disregard thermal entropy. This residual/positional entropy results from the different positions the atoms can be found in.
- Tue Feb 05, 2019 1:35 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: U
- Replies: 7
- Views: 614
Re: U
A state property depends on the current state of the system, as opposed to the path it took to get to that state.
- Tue Feb 05, 2019 1:33 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Microstate
- Replies: 7
- Views: 805
Re: Microstate
From what I understand from lecture, a microstate is a specific arrangement of molecules, a specific set of positions for each molecule in a sample. The more possible microstates or arrangements there are for a sample, the more entropy that sample has. (If anyone wants to correct/add to that, pls do)
- Thu Jan 31, 2019 8:00 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Reaction Enthalpy
- Replies: 3
- Views: 452
Re: Reaction Enthalpy
What's delta U?
- Thu Jan 31, 2019 4:23 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: When to use Quadratic equation
- Replies: 10
- Views: 6475
Re: When to use Quadratic equation
You can use the 5% approximation when K<10^-3 (when the reaction strongly favors the reactants). This means that no quadratic equation solving will be necessary. But if this is not the case and the reaction doesn't strongly favor the reactants, you will end up having to solve a quadratic.
- Wed Jan 30, 2019 7:49 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: ICE
- Replies: 19
- Views: 1443
Re: ICE
Initial concentration/pressure, Change in concentration/pressure, Equilibrium concentration/pressure
- Thu Jan 24, 2019 8:27 pm
- Forum: Phase Changes & Related Calculations
- Topic: Enthalpy and States
- Replies: 8
- Views: 758
Re: Enthalpy and States
The enthalpy of a substance in its gaseous form > enthalpy in liquid form > enthalpy in solid form.
This is because heat is required to change a substance from solid to liquid, and liquid to gas.
This is because heat is required to change a substance from solid to liquid, and liquid to gas.
- Thu Jan 24, 2019 8:25 pm
- Forum: Phase Changes & Related Calculations
- Topic: Change in Enthalpy
- Replies: 3
- Views: 310
Re: Change in Enthalpy
The change in enthalpy of liquid water to water vapor is positive because the phase change from liquid to vapor requires heat to be added to the water. Since heat was added to the water for it to become vapor, the vapor will have higher enthalpy than the water. The change in enthalpy is calculated a...
- Thu Jan 24, 2019 8:22 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Weak Acids and Bases
- Replies: 5
- Views: 680
Re: Weak Acids and Bases
If the Kb value is lower than 10^-3 then it's considered a weak base, since the reaction favors the reactants. (This also applies to Ka with weak acids)
- Fri Jan 18, 2019 9:47 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Inert Gas
- Replies: 3
- Views: 232
Re: Inert Gas
When you double the pressure of the gases in a reaction by halving the volume, it increases the concentration of the gases, which pushes the reaction left or right depending on the moles of gas on either side. However, when you double the pressure by adding an inert gas, it doesn't change the concen...
- Fri Jan 18, 2019 9:44 am
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: Ka Kb significance
- Replies: 3
- Views: 2335
Re: Ka Kb significance
Ka*Kb=Kw=10^-14
pKa+pKb=14
and
[OH-][H3O+]=Kw=10^-14
pKa+pKb=14
and
[OH-][H3O+]=Kw=10^-14
- Fri Jan 18, 2019 9:40 am
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: when is x negligible
- Replies: 7
- Views: 6711
Re: when is x negligible
X is negligible when x is less than 5% of the initial concentration, or when K is less than 10^-3.
- Thu Jan 10, 2019 5:24 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Activity
- Replies: 3
- Views: 221
Re: Activity
I have the same question, all I got from lecture is that it's unit-less and that the concentrations we use are approximations. Does anyone understand?
- Thu Jan 10, 2019 5:22 pm
- Forum: Ideal Gases
- Topic: Units
- Replies: 19
- Views: 1108
Re: Units
Since R is in Kelvin, use Kelvin. You almost always use Kelvin in chemistry.
- Thu Jan 10, 2019 5:15 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Explaining Q<K and Q>K [ENDORSED]
- Replies: 7
- Views: 2242
Re: Explaining Q<K and Q>K [ENDORSED]
If Q is less than K, it means that there are more reactants and less products than at equilibrium, which means more of the reactants have to react and become products in order to reach equilibrium.
- Sat Dec 08, 2018 11:37 am
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: CO3 2- (carbonato)
- Replies: 2
- Views: 4242
Re: CO3 2- (carbonato)
Wouldn't that mean that it's just bidentate, since it always has the potential to form two coordinate bonds?
- Thu Dec 06, 2018 9:06 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: polydentate ligands
- Replies: 1
- Views: 146
polydentate ligands
Are there any polydentate ligands we need to know for naming compounds other than edta, en, dien, and oxolato?
Also, am I right in saying that edta is hexadentate, oxolato and en are bidentate, and dien is tridentate?
Thanks
Also, am I right in saying that edta is hexadentate, oxolato and en are bidentate, and dien is tridentate?
Thanks
- Thu Dec 06, 2018 9:01 pm
- Forum: Naming
- Topic: edta charge and formula?
- Replies: 1
- Views: 954
edta charge and formula?
What is the charge for ethylenediaminetetraacetato? The textbook table of ligands just says it's an anion.
Also, is its formula C10H16N2O8?
Thanks
Also, is its formula C10H16N2O8?
Thanks
- Fri Nov 30, 2018 10:18 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Axial and equatorial atoms
- Replies: 2
- Views: 494
Axial and equatorial atoms
What are axial and equatorial atoms? I saw a few posts that mentioned them but don't remember them being mentioned in lecture...?
- Fri Nov 30, 2018 9:55 am
- Forum: Lewis Structures
- Topic: Octet Rule
- Replies: 5
- Views: 488
Re: Octet Rule
Expanded octets are possible for elements in period 3 and greater, because those elements have d-orbitals that extra electrons can occupy.
- Fri Nov 30, 2018 9:53 am
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Transition Metals
- Replies: 4
- Views: 315
Re: Transition Metals
Transition metals tend to have multiple oxidation states, because the energy difference between the oxidation states isn't that large. Since they can have multiple oxidation states, and gain and lose elections easily, they're good for electron transfers.
- Sun Nov 25, 2018 3:21 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Molecular Shape
- Replies: 7
- Views: 697
Re: Molecular Shape
A seesaw structure happens whenever an atom is surrounded by four atoms and one lone electron pair, or AX4E1.
- Sun Nov 25, 2018 3:20 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Trigonal Planar or Trigonal Pyramidal?
- Replies: 4
- Views: 908
Re: Trigonal Planar or Trigonal Pyramidal?
If a molecule has a tetrahedral electron pair arrangement with one lone pair, the atom arrangement will be trigonal pyramidal because the lone pair takes up as much (and more) space than an atom in its place would. It repels the atoms into a trigonal pyramidal shape.
- Sun Nov 25, 2018 3:13 pm
- Forum: Hybridization
- Topic: Hybridization and Hybrid Orbitals
- Replies: 4
- Views: 537
Re: Hybridization and Hybrid Orbitals
As far as I know they mean the same thing. If anyone knows better please correct me
- Fri Nov 16, 2018 10:34 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Vsepr Formula
- Replies: 7
- Views: 410
Re: Vsepr Formula
Lewis structures are the drawings we've been doing of where the electrons and bonds are in molecules. VSEPR formulas indicate the number of atoms and lone pairs of electrons around the central atom in a molecule, written as AXnEm, where A is the central atom, X are the surrounding atoms, n is the nu...
- Fri Nov 16, 2018 10:30 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Repulsion Strength
- Replies: 7
- Views: 685
Re: Repulsion Strength
I believe bent and angular are different names for the same shape. The VSEPR model predicting things qualitatively but not quantitatively means that the VSEPR model can't predict the exact bond angles between atoms; when the atoms are different or there are lone pairs, it can only predict the relati...
- Fri Nov 16, 2018 10:23 am
- Forum: Dipole Moments
- Topic: Dipoles
- Replies: 3
- Views: 479
Re: Dipoles
Dipole moments happen when one atom in a molecule is more polar than another, like H2O. Electrons are pulled toward O, the more electronegative atom. This gives the end of the molecule with O a slightly negative charge compared to the H ends. Dipole-dipole attractions: this is when 2 polar molecules...
- Fri Nov 09, 2018 10:01 am
- Forum: Dipole Moments
- Topic: Dipole induced dipole
- Replies: 3
- Views: 336
Re: Dipole induced dipole
Dipole-induced dipole: this is when you have a polar molecule and a neutral molecule. When they get close enough together, the negative end of the polar molecule repels the electrons in the neutral molecule, causing the neutral molecule to have a positive end and a negative end, called an induced di...
- Fri Nov 09, 2018 9:58 am
- Forum: Bond Lengths & Energies
- Topic: Dipole interaction
- Replies: 3
- Views: 423
Re: Dipole interaction
Dipole-dipole attractions: this is when 2 polar molecules (like H2O) are attracted to each other because each molecule has a positive end and a negative end, so the positive end of one molecule is attracted to the negative end of the other. Dipole-induced dipole: this is when you have a polar molecu...
- Fri Nov 09, 2018 9:52 am
- Forum: Electronegativity
- Topic: electronegativity trends
- Replies: 6
- Views: 619
Re: electronegativity trends
Electronegativity is calculated using electron affinity and ionization energy; high electron affinity and ionization energy mean high electronegativity. Electron affinity and ionization energy decrease down a group because as you go down a group, the atoms get larger, and so the electrons are farthe...
- Fri Nov 09, 2018 9:43 am
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Disperson forces
- Replies: 4
- Views: 615
Re: Disperson forces
Br2 is a liquid because Br is a larger atom than F and Cl. The larger the atom, the stronger the dispersion force between them. So since F2 and Cl2 are smaller and have less attraction between them, they're held less closely together and are gases at room temperature. Br2 is a liquid because the Br2...
- Wed Nov 07, 2018 6:47 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: Electron density fluctuation
- Replies: 1
- Views: 282
Electron density fluctuation
Hi, I'm pretty sure Prof. Lavelle said that induced dipole attraction is caused when by chance, the electrons of an atom/molecule are condensed more on one side of the atom, making one side negative and the other positive, which attracts them to other atoms/molecules...what I'm confused about is tha...
- Wed Nov 07, 2018 6:41 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: Sign of induced dipole--induced dipole attractive force?
- Replies: 1
- Views: 254
Sign of induced dipole--induced dipole attractive force?
In class Prof. Lavelle said that the interaction potential energy of induced dipole--induced dipole attraction was always negative, meaning that it was always attractive. Could someone explain why it being always negative means that it's attractive?
- Fri Oct 26, 2018 7:46 pm
- Forum: Photoelectric Effect
- Topic: HW Question 1.57
- Replies: 4
- Views: 640
Re: HW Question 1.57
Hi! I'll try to explain it as far as I understand it... All the lines in the Balmer series result from electrons transitioning from various energy levels down to the n=2 energy level. As the electron drops from higher energy levels, more energy is released from the transition. The more energy, the h...
- Thu Oct 25, 2018 6:21 pm
- Forum: Photoelectric Effect
- Topic: HW Question 1.57
- Replies: 4
- Views: 640
Re: HW Question 1.57
Here's my work. What I did makes sense to me but I didn't know where to look for the solution so I don't know for sure that it's right. Hope it helps :)
- Mon Oct 22, 2018 12:05 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Electron density?
- Replies: 4
- Views: 203
Re: Electron density?
As far as I understand, electron density is the probability of finding an electron in a given spot. For example, the 1s orbital has uniform electron density, so there's an equal probability of finding the electron anywhere in the orbital.
- Mon Oct 22, 2018 12:00 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Rydberg's Equation
- Replies: 1
- Views: 182
Re: Rydberg's Equation
I think what you mean is Dr. Lavelle wanted us to use En= -hR/(n^2) instead of deltaE= hR(1/n1^2 - 1/n2^2). The two equations are closely related; the second one is easily derived from the 1st. Dr. Lavelle used the first because he said it better conceptualized what was happening. My TA said that th...
- Mon Oct 22, 2018 11:54 am
- Forum: Properties of Light
- Topic: Visible Light Spectrum... ?
- Replies: 6
- Views: 507
Re: Visible Light Spectrum... ?
It's enough to know 400-700nm :)
- Sun Oct 21, 2018 9:12 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: HW Question Regarding 1B.27
- Replies: 6
- Views: 586
Re: HW Question Regarding 1B.27
Here's my work, hope it helps
- Sun Oct 21, 2018 8:49 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3056564
Re: Post All Chemistry Jokes Here
Why does hamburger yield lower energy than steak?
...because it's in the ground state.
...because it's in the ground state.
- Fri Oct 12, 2018 11:32 am
- Forum: Empirical & Molecular Formulas
- Topic: Order of Molecules
- Replies: 4
- Views: 987
Order of Molecules
When we're told that a compound is made of some percentages of elements, like C, O, H, and N, and then we calculate the empirical and molecular formulas, how do we know which order to put the elements in the formula? Like if the ratios are 6 C to 4 O to 1 H to 2 N, how do we know if it's C6O4HN2 or ...
- Fri Oct 12, 2018 11:14 am
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Balmer and Lyman series
- Replies: 4
- Views: 308
Re: Balmer and Lyman series
The Lyman series are the lines that occur from electrons dropping down to the n=1 energy level. The Balmer series is when electrons drop to n=2.
- Fri Oct 12, 2018 9:58 am
- Forum: Einstein Equation
- Topic: Symbol for frequency
- Replies: 12
- Views: 2210
Re: Symbol for frequency
I had the same question...in high school we used f for frequency and v (nu) for other stuff. But I suppose v (nu) for frequency is the best way to go now to avoid confusion.
- Thu Oct 04, 2018 4:21 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Conversion of grams to moles
- Replies: 4
- Views: 417
Re: Conversion of grams to moles
Yes, if I understand what you're asking.
For example, the molar mass of plain oxygen, O, is 16 g/mol.
But the molar mass of oxygen gas, O2, is 2x16= 32 g/mol.
Hope that helps.
For example, the molar mass of plain oxygen, O, is 16 g/mol.
But the molar mass of oxygen gas, O2, is 2x16= 32 g/mol.
Hope that helps.
- Thu Oct 04, 2018 4:08 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Q G.13
- Replies: 1
- Views: 110
Re: Q G.13
Hi! I did this problem for hw too. I first found what the molarity of the solution would be once it had been diluted to a total volume of 4L (0.050M), and then figured out how many moles of NH4NO3 would be in 100mL of that diluted solution, which ends up being 0.0050 mol. Since there's 2 N atoms in ...
- Thu Oct 04, 2018 3:56 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Question G25 (6th Edition)
- Replies: 1
- Views: 231
Re: Question G25 (6th Edition)
Hi! The solution manual's solution didn't make much sense to me either. I did the problem a little differently, by figuring out what the final volume of the diluted solution would be after 90 doublings of the volume, and showing that in 10mL of the diluted solution there would be less than a single ...