Search found 62 matches

by LedaKnowles2E
Sat Mar 16, 2019 11:38 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Changing E˚ values
Replies: 2
Views: 53

Re: Changing E˚ values

Nope, E naught doesn't change
by LedaKnowles2E
Sat Mar 16, 2019 11:36 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Activation Energy
Replies: 2
Views: 48

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)
by LedaKnowles2E
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: 226

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.
by LedaKnowles2E
Mon Mar 04, 2019 1:26 pm
Forum: First Order Reactions
Topic: First Order Reactions
Replies: 6
Views: 92

Re: First Order Reactions

In the slides it says a straight line plot of ln[R] vs time means the reaction is 1st-order.
by LedaKnowles2E
Mon Mar 04, 2019 1:25 pm
Forum: Balancing Redox Reactions
Topic: Acidic vs basic solutions
Replies: 10
Views: 166

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-.
by LedaKnowles2E
Mon Mar 04, 2019 1:22 pm
Forum: Administrative Questions and Class Announcements
Topic: Week 9 HW
Replies: 6
Views: 123

Re: Week 9 HW

You should probably mix in some kinetics in there.
by LedaKnowles2E
Mon Mar 04, 2019 1:20 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: "N" in Kinetics
Replies: 4
Views: 72

Re: "N" in Kinetics

It's usually a lower-case n, though.
by LedaKnowles2E
Mon Mar 04, 2019 1:18 pm
Forum: Van't Hoff Equation
Topic: K value- Temp
Replies: 6
Views: 295

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.
by LedaKnowles2E
Mon Mar 04, 2019 1:16 pm
Forum: Balancing Redox Reactions
Topic: Cell diagrams
Replies: 8
Views: 152

Re: Cell diagrams

Pt is sometimes added when one half of the reaction only involves aqueous solutions and a solid electrode is needed.
by LedaKnowles2E
Sun Feb 24, 2019 9:53 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge
Replies: 3
Views: 55

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.
by LedaKnowles2E
Sun Feb 24, 2019 9:51 pm
Forum: Balancing Redox Reactions
Topic: Half Reaction
Replies: 2
Views: 59

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...
by LedaKnowles2E
Sun Feb 24, 2019 9:50 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Oxidation number
Replies: 2
Views: 54

Re: Oxidation number

The oxidation number is the charge on an atom or molecule. O2-, for example.
by LedaKnowles2E
Fri Feb 15, 2019 1:28 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: enthalpy, entropy, Gibbs Free Energy signs
Replies: 3
Views: 69

Re: enthalpy, entropy, Gibbs Free Energy signs

When Gibbs free energy is negative the process is spontaneous.
by LedaKnowles2E
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: 250

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.
by LedaKnowles2E
Fri Feb 15, 2019 1:21 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Microstate
Replies: 7
Views: 174

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.
by LedaKnowles2E
Fri Feb 15, 2019 1:20 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Quick Conceptual question
Replies: 7
Views: 149

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).
by LedaKnowles2E
Tue Feb 05, 2019 1:38 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: residual energy
Replies: 3
Views: 104

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.
by LedaKnowles2E
Tue Feb 05, 2019 1:35 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: U
Replies: 7
Views: 127

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.
by LedaKnowles2E
Tue Feb 05, 2019 1:33 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Microstate
Replies: 7
Views: 174

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)
by LedaKnowles2E
Thu Jan 31, 2019 8:00 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Reaction Enthalpy
Replies: 3
Views: 60

Re: Reaction Enthalpy

What's delta U?
by LedaKnowles2E
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: 359

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.
by LedaKnowles2E
Wed Jan 30, 2019 7:49 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: ICE
Replies: 19
Views: 306

Re: ICE

Initial concentration/pressure, Change in concentration/pressure, Equilibrium concentration/pressure
by LedaKnowles2E
Thu Jan 24, 2019 8:27 pm
Forum: Phase Changes & Related Calculations
Topic: Enthalpy and States
Replies: 8
Views: 121

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.
by LedaKnowles2E
Thu Jan 24, 2019 8:25 pm
Forum: Phase Changes & Related Calculations
Topic: Change in Enthalpy
Replies: 3
Views: 45

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...
by LedaKnowles2E
Thu Jan 24, 2019 8:22 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Weak Acids and Bases
Replies: 2
Views: 219

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)
by LedaKnowles2E
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: 72

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...
by LedaKnowles2E
Fri Jan 18, 2019 9:44 am
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Ka Kb significance
Replies: 3
Views: 389

Re: Ka Kb significance

Ka*Kb=Kw=10^-14
pKa+pKb=14
and
[OH-][H3O+]=Kw=10^-14
by LedaKnowles2E
Fri Jan 18, 2019 9:40 am
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: when is x negligible
Replies: 7
Views: 537

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.
by LedaKnowles2E
Thu Jan 10, 2019 5:24 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Activity
Replies: 3
Views: 53

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?
by LedaKnowles2E
Thu Jan 10, 2019 5:22 pm
Forum: Ideal Gases
Topic: Units
Replies: 19
Views: 238

Re: Units

Since R is in Kelvin, use Kelvin. You almost always use Kelvin in chemistry.
by LedaKnowles2E
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: 161

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.
by LedaKnowles2E
Sat Dec 08, 2018 11:37 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: CO3 2- (carbonato)
Replies: 2
Views: 1621

Re: CO3 2- (carbonato)

Wouldn't that mean that it's just bidentate, since it always has the potential to form two coordinate bonds?
by LedaKnowles2E
Thu Dec 06, 2018 9:06 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: polydentate ligands
Replies: 1
Views: 60

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
by LedaKnowles2E
Thu Dec 06, 2018 9:01 pm
Forum: Naming
Topic: edta charge and formula?
Replies: 1
Views: 73

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
by LedaKnowles2E
Fri Nov 30, 2018 10:18 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Axial and equatorial atoms
Replies: 2
Views: 59

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...?
by LedaKnowles2E
Fri Nov 30, 2018 9:55 am
Forum: Lewis Structures
Topic: Octet Rule
Replies: 5
Views: 117

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.
by LedaKnowles2E
Fri Nov 30, 2018 9:53 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Transition Metals
Replies: 4
Views: 78

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.
by LedaKnowles2E
Sun Nov 25, 2018 3:21 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Shape
Replies: 7
Views: 137

Re: Molecular Shape

A seesaw structure happens whenever an atom is surrounded by four atoms and one lone electron pair, or AX4E1.
by LedaKnowles2E
Sun Nov 25, 2018 3:20 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Trigonal Planar or Trigonal Pyramidal?
Replies: 4
Views: 94

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.
by LedaKnowles2E
Sun Nov 25, 2018 3:13 pm
Forum: Hybridization
Topic: Hybridization and Hybrid Orbitals
Replies: 4
Views: 100

Re: Hybridization and Hybrid Orbitals

As far as I know they mean the same thing. If anyone knows better please correct me
by LedaKnowles2E
Fri Nov 16, 2018 10:34 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Vsepr Formula
Replies: 7
Views: 81

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...
by LedaKnowles2E
Fri Nov 16, 2018 10:30 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Repulsion Strength
Replies: 7
Views: 132

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...
by LedaKnowles2E
Fri Nov 16, 2018 10:23 am
Forum: Dipole Moments
Topic: Dipoles
Replies: 3
Views: 112

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...
by LedaKnowles2E
Fri Nov 09, 2018 10:01 am
Forum: Dipole Moments
Topic: Dipole induced dipole
Replies: 3
Views: 82

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...
by LedaKnowles2E
Fri Nov 09, 2018 9:58 am
Forum: Bond Lengths & Energies
Topic: Dipole interaction
Replies: 3
Views: 93

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...
by LedaKnowles2E
Fri Nov 09, 2018 9:52 am
Forum: Electronegativity
Topic: electronegativity trends
Replies: 6
Views: 136

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...
by LedaKnowles2E
Fri Nov 09, 2018 9:43 am
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Disperson forces
Replies: 4
Views: 94

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...
by LedaKnowles2E
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: 28

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...
by LedaKnowles2E
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: 42

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?
by LedaKnowles2E
Fri Oct 26, 2018 7:46 pm
Forum: Photoelectric Effect
Topic: HW Question 1.57
Replies: 4
Views: 194

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...
by LedaKnowles2E
Thu Oct 25, 2018 6:21 pm
Forum: Photoelectric Effect
Topic: HW Question 1.57
Replies: 4
Views: 194

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 :)
1.57Solution.JPG
by LedaKnowles2E
Mon Oct 22, 2018 12:05 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Electron density?
Replies: 4
Views: 67

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.
by LedaKnowles2E
Mon Oct 22, 2018 12:00 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg's Equation
Replies: 1
Views: 75

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...
by LedaKnowles2E
Mon Oct 22, 2018 11:54 am
Forum: Properties of Light
Topic: Visible Light Spectrum... ?
Replies: 6
Views: 128

Re: Visible Light Spectrum... ?

It's enough to know 400-700nm :)
by LedaKnowles2E
Sun Oct 21, 2018 9:12 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: HW Question Regarding 1B.27
Replies: 6
Views: 157

Re: HW Question Regarding 1B.27

Here's my work, hope it helps
Chem 14A 1B.27.JPG
by LedaKnowles2E
Sun Oct 21, 2018 8:49 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7569
Views: 1012077

Re: Post All Chemistry Jokes Here

Why does hamburger yield lower energy than steak?


...because it's in the ground state.
by LedaKnowles2E
Fri Oct 12, 2018 11:32 am
Forum: Empirical & Molecular Formulas
Topic: Order of Molecules
Replies: 4
Views: 279

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 ...
by LedaKnowles2E
Fri Oct 12, 2018 11:14 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Balmer and Lyman series
Replies: 4
Views: 86

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.
by LedaKnowles2E
Fri Oct 12, 2018 9:58 am
Forum: Einstein Equation
Topic: Symbol for frequency
Replies: 12
Views: 246

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.
by LedaKnowles2E
Thu Oct 04, 2018 4:21 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Conversion of grams to moles
Replies: 4
Views: 98

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.
by LedaKnowles2E
Thu Oct 04, 2018 4:08 pm
Forum: Molarity, Solutions, Dilutions
Topic: Q G.13
Replies: 1
Views: 58

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 ...
by LedaKnowles2E
Thu Oct 04, 2018 3:56 pm
Forum: Molarity, Solutions, Dilutions
Topic: Question G25 (6th Edition)
Replies: 1
Views: 105

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 ...

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