## Search found 60 matches

Wed Mar 13, 2019 11:38 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: enthalpy and spontaneity/favorability
Replies: 1
Views: 254

### Re: enthalpy and spontaneity/favorability

Theoretically, yes, but not on its own. You would need other information to figure that out, namely, the temperature and the entropy to find the Gibbs Free Energy, the sign of which will tell you the spontaneity. However, it is more likely that exothermic reactions are favored, especially in cool te...
Wed Mar 13, 2019 11:35 am
Forum: Phase Changes & Related Calculations
Topic: Homework number 41 Ch.8 (6th ed.)
Replies: 1
Views: 266

### Re: Homework number 41 Ch.8 (6th ed.)

Like you said, the ice needs two calculations because it undergoes a phase change and each phase has a separate heat capacity. Also, I think you may be referring to the change in heat energy or the heat energy transfer in which both values would be positive since heat is flowing into the ice and wat...
Wed Mar 13, 2019 11:32 am
Forum: Student Social/Study Group
Topic: Chemistry Community
Replies: 8
Views: 710

### Re: Chemistry Community

Most likely at the end of the course since last quarter I didn't know it was a thing until week 4 but still got full credit because I had 30 posts overall.
Sun Mar 10, 2019 8:00 pm
Forum: Balancing Redox Reactions
Topic: Part c of question 6 on test 2
Replies: 1
Views: 74

### Re: Part c of question 6 on test 2

All of the Voltage values ended up being negative and asked you to order each three by strength of the OA and RA. The two that would make a cell with the largest voltage would be the two that, when added, would amount to the largest number. If I remember correctly, the correct answer happened to be ...
Sun Mar 10, 2019 7:57 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Temperature
Replies: 1
Views: 98

### Re: Temperature

Standard conditions are 1 atm and room temp. I don't think we have ever had a question on a test where the temperature isn't given.
Sun Mar 10, 2019 7:56 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell diagram
Replies: 6
Views: 211

### Re: Cell diagram

We include these typically when there is no solid involved on that side of the reaction. If there's no solid, there's usually no conductor to actually transfer these electrons so we use an inert one.
Tue Feb 26, 2019 7:39 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L.5 7th ed
Replies: 3
Views: 108

### Re: 6L.5 7th ed

I think those half reactions are only considering what is happening to the reactant ion in question. In reality, it would produce HCl, but since each half reaction only considers one ion, they don't include the other. But then again, since HCl is a strong acid, it would fully dissociate anyway.
Tue Feb 26, 2019 7:36 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.13b 6th edition
Replies: 1
Views: 86

### Re: 14.13b 6th edition

Even though I2 is a solid, it doesn't conduct. Therefore, we need to include platinum, which acts as an inert conductor.
Tue Feb 26, 2019 7:32 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 6th ed. 14.23: value of n
Replies: 2
Views: 116

### Re: 6th ed. 14.23: value of n

The solutions manual answer was pretty long, so I'm assuming there's not really a shortcut. However, you can determine the value of n by figuring out how many electrons are being exchanged. You can do this by just looking at the diagram and using your intuition, but to ensure that it's correct, you ...
Sun Feb 24, 2019 6:50 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Relation to Enthalpy and Entropy
Replies: 4
Views: 1244

### Re: Relation to Enthalpy and Entropy

You can calculate all of these values in the equation in one of the replies above in order to make extrapolations about whether the reaction will be spontaneous, whether its exothermic or endothermic, etc. These qualities tell us a lot about the reaction past just the quantified values of these terms.
Sun Feb 24, 2019 6:44 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Positional disorder vs. thermal disorder
Replies: 2
Views: 133

### Re: Positional disorder vs. thermal disorder

It depends on which equation you use to find entropy. They will end up being the same value but positional refers to the equation with botzman's constant and degeneracy, while thermal refers to q/T.
Sun Feb 24, 2019 6:39 pm
Forum: Balancing Redox Reactions
Topic: Order to balance
Replies: 6
Views: 206

### Re: Order to balance

Once the elements are balanced, it will be clear how many electrons are involved in the appropriate half reactions.
Sun Feb 17, 2019 4:52 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Meaning of Spontaneity
Replies: 3
Views: 597

### Re: Meaning of Spontaneity

Like all concepts and equations in thermodynamics, etc., they always refer back to the system itself (e.g. Work the system did on the surroundings, work the surroundings did on the system). Therefore, if DeltaG is negative, we know that it represents that the system does not need to use energy to ca...
Sun Feb 17, 2019 4:47 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 4J.13 Seventh Edition
Replies: 2
Views: 110

### Re: 4J.13 Seventh Edition

You use a similar technique as determining the stability based on K value. Like if a K value is extremely large, we can assume that the products are more stable than the reactants because the reaction carries out so that it creates a lot more of them. Similarly, if the deltaG associated with a react...
Sun Feb 17, 2019 4:44 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Standard Entropy of Fusion at Freezing Point (Self-Test 9.8A- 6th Ed.)
Replies: 1
Views: 114

### Re: Standard Entropy of Fusion at Freezing Point (Self-Test 9.8A- 6th Ed.)

This is because Delta H or S fusion actually refers to the enthalpy change when a substance is melting. I know this is lowkey stupid because it would make sense for fusion to be freezing, but that's just the way it is. So when considering the S fusion for a substance, it equals deltaH fusion /T free...
Tue Feb 05, 2019 9:38 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4.15 (7th edition)
Replies: 2
Views: 142

### Re: 4.15 (7th edition)

The reason the book has the enthalpy of formation of the reactants-products is because the signs of these values flip. Considering that most enthalpies of formation are given as negative values, we know that that is the energy required to break the initial bonds. For this reason, the sign of the val...
Tue Feb 05, 2019 9:31 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: Determining the Number of Orientations/Degeneracy & Microstates
Replies: 3
Views: 214

### Re: Determining the Number of Orientations/Degeneracy & Microstates

Degeneracy and the number of micro states are the same thing. The example he used in class was that the base equaled the number of places an atom could conceivably be. He used in example of a double sided flask with a very very very small tube between them; the tube was too small for an atom to conc...
Tue Feb 05, 2019 9:28 pm
Forum: Calculating Work of Expansion
Topic: Units
Replies: 5
Views: 401

### Re: Units

Volume should always be in L while P is apparently in Pascals.
Sat Feb 02, 2019 7:13 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta U
Replies: 4
Views: 180

### Re: Delta U

I believe it's because when we find U we're only concerned with the final and initial states. Regardless of how it's calculated or what happens between the initial and final points, we are just concerned with the change in energy.
Sat Feb 02, 2019 7:09 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Reaction Constant P
Replies: 3
Views: 145

### Re: Reaction Constant P

I think it's a similar concept of not including solids or liquids in equilibrium expressions. The gas is the only phase that is able to affect volumetric change. But idk lol
Sat Feb 02, 2019 7:06 pm
Forum: Phase Changes & Related Calculations
Topic: Negative work
Replies: 11
Views: 406

### Re: Negative work

Negative Work is definitely a thing. All it means is that the system is doing work on the surroundings instead of getting work done on itself. This happens when the piston moves out for example.
Tue Jan 22, 2019 8:55 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Making more product
Replies: 3
Views: 125

### Re: Making more product

To be more clear, a shift to make more products would only occur if some change were to happen to the receptacle in which the reaction was occurring that all of a sudden increased the amount of reactants. Specifically: Addition of reactants would increase the [reactants] and the reaction would creat...
Tue Jan 22, 2019 8:42 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Q reaction quotient
Replies: 2
Views: 106

### Re: Q reaction quotient

As stated above, liquids are not included in Q or K equations. But as for whether to use terms of pressures or concentrations, it depends on the question. It will ask you to find either Kc (conc.) or Kp (pressure). Otherwise, if it gives you values of conc, use them and just find Kc.
Tue Jan 22, 2019 8:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Polyprotic Solutions on Test 1?
Replies: 1
Views: 99

### Re: Polyprotic Solutions on Test 1?

It's nothing new. Just treat each step as it's own reaction and add the concentrations from each step in question to find the overall Ka or pH or whatever. If needed, it will give you each step's Ka or whatever you need to solve the problem. You can just add the concentrations from each step to find...
Thu Jan 17, 2019 5:01 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: How to tell if a chemical is an acid or base?
Replies: 4
Views: 270

### Re: How to tell if a chemical is an acid or base?

Consider what would likely happen in a reaction with water. Does the H atom have anywhere to be accepted? Or will it dissociate. Many times molecules are amphoteric and can do both but a lot of it will be memorization and understanding of where a proton can go. One big indicator for bases that Dr. L...
Thu Jan 17, 2019 4:53 pm
Forum: Administrative Questions and Class Announcements
Topic: Posts on Chemistry Community
Replies: 3
Views: 115

### Re: Posts on Chemistry Community

Last quarter I didn't even know Chem Community was a thing until week 4 and freaked out thinking I had lost 12 points, so I freaked out and made up the posts I missed so that I had 30 at the end of the quarter and I still got 30 points. It might depend on your TA but I think the 3 posts a week thing...
Thu Jan 17, 2019 4:51 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Conjugate base
Replies: 7
Views: 333

### Re: Conjugate base

A conjugate base is any molecule that is conjugate to the original acid from the equation. In a reaction with an acid, the conjugate base is whatever molecule is made after the acid donates its proton or loses an H.
Wed Jan 09, 2019 9:26 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Pressure
Replies: 1
Views: 50

### Re: Pressure

Values of partial pressure for products and reactants affect K in the same way that concentrations do. That's why K has two forms Kc and Kp. Kc is when using concentrations and Kp is when using Partial Pressures. It's just the ratio of Partial Pressures of the Products/Partial Pressures of the React...
Wed Jan 09, 2019 9:24 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating Kp
Replies: 2
Views: 30

### Re: Calculating Kp

The solutions manual includes answers with bars and atm so I believe either is fine. Not sure which, if either, are considered SI units
Wed Jan 09, 2019 9:22 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Chemical Equilibrium Part 2 Question 24
Replies: 2
Views: 84

### Re: Chemical Equilibrium Part 2 Question 24

Bars are units of partial pressure. Treat them the same way you would concentration in the product/reactant expression for Kc, only this time, it's Kp.
Mon Dec 03, 2018 11:42 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8203
Views: 1432484

### Re: Post All Chemistry Jokes Here

What is the chemical formula for a Banana?

BaNa2
Mon Dec 03, 2018 11:34 am
Forum: Photoelectric Effect
Topic: Work Function
Replies: 2
Views: 396

### Re: Work Function

Substitute known values into equations. If the Frequency of the photon is known, it can be multiplied by Plank's Constant (h) to find the energy of the photon in J. Then, we know the Kinetic Energy of the resulting emitted electron to be equal to 1/2*m*v^2. The mass of the electron is known but the ...
Mon Dec 03, 2018 11:29 am
Forum: Balancing Chemical Reactions
Topic: Aqueous compounds
Replies: 5
Views: 421

### Re: Aqueous compounds

Biological Compounds are always assumed to be aqueous. Otherwise it should be given in a formula or reaction equation. You should be able to tell by the information given to you by the equation. You can't tell the state of a compound based on the compound alone, it only becomes known to be aqueous i...
Mon Nov 26, 2018 5:20 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Octahedral
Replies: 3
Views: 246

### Re: Octahedral

Every bond angle in an octahedron is 90 degrees. When there is one LP (Square Pyramidal) it is slightly less that 90 degrees. When it has 2 LPs (Square Planar) the repulsions cancel out and the bond angles are all 90 degrees. When there are three LPs it becomes T-Shaped with slightly less than 90 de...
Mon Nov 26, 2018 5:18 pm
Forum: Resonance Structures
Topic: Intermolecular Forces
Replies: 1
Views: 257

### Re: Intermolecular Forces

A dipole-dipole force is between two polar molecules that already have two oppositely charged poles as a result of their orientation/electronegativity of their bonds. This force exists because the opposite charges of the poles of two polar molecules are attracted to each other. Dipole-induced dipole...
Mon Nov 26, 2018 5:12 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Location of Lone Pairs
Replies: 2
Views: 84

### Location of Lone Pairs

In lecture, while referencing a molecule with 5 regions of electron density in a trigonal bipyramidal electron region orientation, Dr. Lavelle said that a Lone Pair on the central atom would go in the trigonal plane of the orientation rather than the top or bottom "peaks" of the pyramids b...
Mon Nov 19, 2018 12:41 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Electron density of lone pairs
Replies: 3
Views: 103

### Re: Electron density of lone pairs

Think about it as if you saw the shape of the molecule blown up in size, like when Lavelle took off an atom from the Trig. Bipyramidal shape to demonstrate the see saw shape. You can't "see" Lone pairs, so they shouldn't contribute to the shape of the molecule since there is no atom being ...
Mon Nov 19, 2018 12:37 pm
Forum: Administrative Questions and Class Announcements
Topic: Discussion
Replies: 6
Views: 344

### Re: Discussion

I believe Lavelle said that we would turn in two weeks worth of homework in week 9, so I'm assuming there will be no discussion, at least on wednesday.
Mon Nov 19, 2018 12:35 pm
Forum: Hybridization
Topic: Hybridization bonds
Replies: 2
Views: 47

### Re: Hybridization bonds

Because sigma bonds overlap head on and pi bonds overlap side by side. It has to do with orbital configuration. In today's lecture, the C2H4 molecule had a pi bond where the double bond was because the left over unhybridized orbital at the 2p level was oriented at 90 degrees outward, resulting in a ...
Mon Nov 19, 2018 12:31 pm
Forum: Bond Lengths & Energies
Topic: Polarity of different bond lengths
Replies: 3
Views: 264

### Re: Polarity of different bond lengths

I don't believe so, because Polarity is determined by difference in electronegativity, which isn't changed by the presence of a double bond. However, in a larger molecule I'm not sure whether or not the presence of a double bond on one side and a single on the other would create a dipole moment. I d...
Mon Nov 19, 2018 12:28 pm
Forum: Hybridization
Topic: Hybridization
Replies: 1
Views: 37

### Re: Hybridization

Since each C atom only has 3 regions of electron density, and we know that the number of these regions needs to be equal to the number of hybridized orbitals, the resulting hybrid orbitals will be 3 orbitals at the sp2 level. However, since there is one p orbital unaccounted for (there are 3 p orbit...
Mon Nov 19, 2018 12:24 pm
Forum: Dipole Moments
Topic: Polarity and Nonpolarity of the Same Molecule
Replies: 1
Views: 48

### Re: Polarity and Nonpolarity of the Same Molecule

It's a matter of different isomers. I think that the important thing to consider is knowing that if dipole moments cancel, it will result in a non polar molecule overall and vice versa. It probably doesn't matter as much as to how different isomers exist for our purposes.
Sun Nov 11, 2018 2:24 am
Forum: Dipole Moments
Topic: induced-dipole
Replies: 3
Views: 338

### Re: induced-dipole

The word dipole refers to any molecule that experiences Polar sides with the negative charge on one side and a positive charge on the other side. The word induced refers to a molecule that is not necessarily polar all the time but experiences a positive charge on one side and a negative charge on th...
Sun Nov 11, 2018 2:21 am
Forum: Dipole Moments
Topic: Induced-Dipole Induced-Dipole
Replies: 5
Views: 359

### Re: Induced-Dipole Induced-Dipole

An induced dipole occurs either randomly as a result of increased concentration of e- on one side of an atom/molecule or by the repulsion of said e- from another dipole. These molecules experience van der waals forces bc opposites attract.
Sun Nov 11, 2018 2:09 am
Forum: Hybridization
Topic: How to Determine
Replies: 12
Views: 547

### Re: How to Determine

Hybridization comes from the random dispersion of electrons in an atom or molecule. The e- are in constant motion, so if they randomly all happen to be mostly to one side, that creates a dipole dispersion, allowing for another dipole molecule to bond via Van der Waals forces to the opposite charge o...
Sun Nov 04, 2018 5:54 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Question 3.23 (Sixth Edition)
Replies: 1
Views: 84

### Re: Question 3.23 (Sixth Edition)

We haven't learned that yet. No need to worry about it for the midterm.
Sun Nov 04, 2018 5:52 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: PROBLEM 1A.15 (7th edition)
Replies: 2
Views: 423

### Re: PROBLEM 1A.15 (7th edition)

This is listed as one of the solution manual errors, the full list of which you can find here: https://lavelle.chem.ucla.edu/wp-conten ... rs_7Ed.pdf . You are correct
Sun Nov 04, 2018 5:50 pm
Forum: DeBroglie Equation
Topic: 13a on practice midterm?
Replies: 2
Views: 271

### Re: 13a on practice midterm?

39.1 g is approximately the mass of a mole of K ions. You need to divide by avogadro's number to find the actual mass of a single ion. Hope that helps.
Tue Oct 23, 2018 9:30 pm
Forum: Properties of Electrons
Topic: colombic potential
Replies: 2
Views: 238

### Re: colombic potential

You use the equation Coulomb Energy = (Charge 1*Charge 2)/Distance between e-

I not sure if we will use it on the test, though because I don't know if it is on the equation sheet. But it could be.
Tue Oct 23, 2018 9:25 pm
Forum: Electron Configurations for Multi-Electron Atoms
Replies: 2
Views: 52

I'm assuming its just for clarity/ease. The value +1/2 or -1/2 doesn't actually affect the energy levels of the electron in any equation, its just a symbolic notation of which specific electron is being referred to.
Tue Oct 23, 2018 9:23 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 3d and 4s
Replies: 2
Views: 147

### Re: 3d and 4s

I think it has something to do with electron affinity and inter-molecular forces, which we haven't learned about yet. But for know, I think we just need to understand that 4s comes is filled before 3d except for when the d orbital steals an e- from the 4s for Cr and Cu.
Tue Oct 23, 2018 9:18 pm
Forum: Student Social/Study Group
Replies: 5
Views: 323

The Solutions Manual for 1.45 is incorrect. This is listed on Prof. Lavelle's list of Solution Manual errors. You can find the link into a post of mine from tonight. The value for delta v would be 0.2.
Tue Oct 23, 2018 9:12 pm
Forum: Trends in The Periodic Table
Topic: Energy and Effective Nuclear Charge
Replies: 2
Views: 88

### Re: Energy and Effective Nuclear Charge

I believe its the other way around. I wrote in my notes that s<p<d<f in the same shell/energy level. Hope this helps.
Tue Oct 23, 2018 9:10 pm
Forum: Student Social/Study Group
Topic: Experiment supporting de Broglie's
Replies: 3
Views: 216

### Re: Experiment supporting de Broglie's

When considering the wave-particle duality of matter, the wave part comes from the experiment showing that electrons are capable of diffraction because diffraction occurs when there is constructive and/or destructive interference of waves. If an electron is capable of diffraction, then that implies ...
Tue Oct 23, 2018 8:24 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Exercise 1.45, 6th Edition
Replies: 1
Views: 109

### Exercise 1.45, 6th Edition

A bowling ball of mass 8.00 kg is rolled with velocity 5.00 +/- 5.0 m/s. What's the uncertainty of position? For the question pasted above, I got a different answer than the solution manual because I inserted a value of 10 for the velocity uncertainty because it is +/- 5, but the manual only put a v...
Tue Oct 23, 2018 7:38 pm
Forum: DeBroglie Equation
Topic: DeBroglie Equation Post Assessment
Replies: 3
Views: 221

### Re: DeBroglie Equation Post Assessment

Hi,

Using the De Broglie equation (Wavelength = h/m*v), we can insert the given wavelength, the Planck constant, and the known mass of an electron, which is given on the test btw, to solve for v. Hope that helps.
Tue Oct 23, 2018 7:35 pm
Forum: Photoelectric Effect
Topic: Question 1.B.15 7th
Replies: 2
Views: 198

### Re: Question 1.B.15 7th

Hi,

Since electrons have wave-particle duality, you can use the De Broglie equation for this, inserting the velocity into the calculation for p. Hope that helps!
Tue Oct 23, 2018 6:43 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: What AS information is given on Test 2
Replies: 1
Views: 131

### What AS information is given on Test 2

Hi all,

How much of the H-Atom Atomic Spectroscopy Information are we expected to memorize? For example, do we have to know the wavelengths and the series names for lines in the series? Will the energy (n) levels for these lines be given or will we have to derive them. Please advise. Thank you!
Tue Oct 23, 2018 6:29 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty in Kinetic Energy
Replies: 1
Views: 183

### Re: Uncertainty in Kinetic Energy

Hi Madison, You would have to use the equation E K = 0.5(m)(v 2 ). We know the mass of the electron and 0.5 is a constant so by inserting the uncertainty of the velocity, it would return the uncertainty of Kinetic Energy for one electron. Then use stoichiometry to find the value for a mole of electr...
Tue Oct 23, 2018 6:24 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Bohr Freq Cond relation to Spectroscopy
Replies: 1
Views: 2290

### Bohr Freq Cond relation to Spectroscopy

Hello,

I was wondering if anyone could please help explain how the Bohr equation specifically (V=(Change in E)/h) relates to the origin of the lines on a spectroscopic analysis and how we derive them from this equation. Thanks!