## Search found 51 matches

Mon Mar 12, 2018 1:13 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Replies: 4
Views: 327

### Re: Reading a Cell Diagram

The oxidized reaction is on the left side, where the anode is, and the reduced reaction is on the right side, where the cathode is.
Mon Mar 12, 2018 1:11 pm
Forum: First Order Reactions
Topic: 15.37C
Replies: 5
Views: 588

### Re: 15.37C

In this case, the volume cancels out. However, it is good practice to use the volume to solve for molarity and use molarity in the equation to ensure you do not make an arithmetic mistake on a test.
Mon Mar 12, 2018 1:08 pm
Forum: First Order Reactions
Topic: Equation variations
Replies: 9
Views: 537

### Re: Equation variations

Yes, this equation yields the same answer. The book uses logarithm rules to rearrange the equation to make kt positive. ln(Af/Ao)=-kt is the same as ln(Ao/Af)=kt.
Fri Mar 09, 2018 1:41 pm
Forum: First Order Reactions
Topic: 15.27
Replies: 2
Views: 201

### Re: 15.27

Yes, the rules of logarithms make this possible. ln(At/Ao)=-kt is the same as ln(Ao/At)=kt.
Fri Mar 09, 2018 1:37 pm
Forum: Zero Order Reactions
Topic: graph of 0 order
Replies: 10
Views: 680

### Re: graph of 0 order

The graph of a 0 order reaction plots time and concentration. The graph is linear and has a slope of -k and a y intercept of the initial concentration.
Fri Mar 09, 2018 1:35 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.9 part c
Replies: 3
Views: 365

### Re: 15.9 part c

The rate constant is a "constant" for that particular reaction, and therefore does not change between experiments. While it isn't necessary, doing this calculation twice can ensure your arithmetic is correct and therefore might be helpful on a test.
Wed Feb 28, 2018 2:34 pm
Forum: Administrative Questions and Class Announcements
Topic: Test 3
Replies: 6
Views: 381

### Re: Test 3

I believe this only covers problems up through #39.
Wed Feb 28, 2018 2:32 pm
Forum: First Order Reactions
Topic: Derivation
Replies: 8
Views: 406

### Re: Derivation

I don't think we will be asked to directly derive the equations. However, understanding the derivations may help with the conceptual questions on Test 3.
Wed Feb 28, 2018 2:31 pm
Forum: Balancing Redox Reactions
Topic: Balancing number of electrons
Replies: 10
Views: 461

### Re: Balancing number of electrons

The electrons on the left side of the equation must cancel with the electrons on the right side of the equation. It is simplest to do this using the least common multiple. However, as long as the electrons cancel, you can use a higher multiple and then simplify the equation after.
Fri Feb 23, 2018 1:03 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: n
Replies: 3
Views: 220

### Re: n

N is the number of electrons transferred in the reaction. To find this value, write out the half reactions and balance them so the number of electrons gained equals the number of electrons lost. This is the value of n you should use in the equation.
Fri Feb 23, 2018 1:01 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Textbook Problem
Replies: 2
Views: 151

### Re: Textbook Problem

The sign changes because pH is equal to -log[H+]. Therefore, when converting, you must account for this negative sign in front of the log.
Fri Feb 23, 2018 1:00 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Finding n
Replies: 15
Views: 900

### Re: Finding n

N is the number of electrons transferred in the reaction. To find this value, first balance the reaction so the electrons gained match the electrons lost. This is the value you should use for n.
Tue Feb 20, 2018 4:48 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.15 given half reactions?
Replies: 3
Views: 204

### Re: 14.15 given half reactions?

You should use the appendix to find the half reaction.
Tue Feb 20, 2018 4:46 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 14.35
Replies: 2
Views: 172

### Re: 14.35

This is an error. It should be n=1.
Tue Feb 20, 2018 4:45 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic cells
Replies: 2
Views: 84

### Re: Galvanic cells

Yes, you would reverse it when you use the equation E(cell)=E(anode)+E(cathode).
Tue Feb 13, 2018 9:55 pm
Forum: Calculating Work of Expansion
Topic: Practice Midterm 4
Replies: 3
Views: 300

### Re: Practice Midterm 4

Why does T=1015.5 K in the last step?
Fri Feb 09, 2018 1:15 pm
Forum: Phase Changes & Related Calculations
Topic: Units for Internal Energy
Replies: 5
Views: 252

### Re: Units for Internal Energy

As long as you are consistent, I do not believe it matters whether you use kj or j.
Fri Feb 09, 2018 1:08 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: delta G=0
Replies: 6
Views: 346

### Re: delta G=0

It does not necessarily mean that delta H an delta S are zero. When delta G =0, the system is at equilibrium. Therefore, either delta H or delta S is zero or delta S is equal to delta H.
Fri Feb 09, 2018 1:05 pm
Forum: Administrative Questions and Class Announcements
Topic: Lecture Slides
Replies: 6
Views: 433

### Re: Lecture Slides

He does not post the lecture slides online.
Sun Feb 04, 2018 3:10 pm
Forum: Phase Changes & Related Calculations
Topic: Endothermic or Exothermic
Replies: 20
Views: 753

### Re: Endothermic or Exothermic

Condensation is exothermic because bonds are being formed.
Sun Feb 04, 2018 3:08 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: G=H-TS
Replies: 4
Views: 370

### Re: G=H-TS

Lavelle clarified this in lecture. As a general rule of thumb:
+deltaH and +deltaS= spontaneous at high temperatures
+deltaH and -deltaS=not spontaneous
-deltaH and +deltaS= spontaneous at all temperatures
-deltaH and -deltaS= spontaneous at low temperature
Sun Feb 04, 2018 3:04 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible systems
Replies: 7
Views: 384

### Re: Reversible systems

In this case, both the pressure and volume contribute to the overall deltaS. Therefore, you would calculate each individually using Cp and Cv and add those respective values together.
Fri Jan 26, 2018 1:14 pm
Forum: Calculating Work of Expansion
Topic: Homework 8.11
Replies: 6
Views: 323

### Re: Homework 8.11

This is the equation for isothermal reversible expansion. It is derived from PV=nRT and w=-P*deltaV. However, Professor Lavelle specified that we do not need to know this for the test.
Fri Jan 26, 2018 1:07 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Combustion
Replies: 3
Views: 240

### Re: Combustion

It produces water in the liquid state. However, if you are referring to enthalpy of combustion, the H2O should normally cancel out in a Hess's Law problem and therefore the state does not matter.
Fri Jan 26, 2018 1:04 pm
Forum: Phase Changes & Related Calculations
Topic: 8.41
Replies: 6
Views: 333

### Re: 8.41

In this problem, the ice melts and turns into water. Therefore, you use the specific heat capacity of water.
Fri Jan 19, 2018 1:11 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimeter vs. Bomb Calorimeter
Replies: 2
Views: 187

### Re: Calorimeter vs. Bomb Calorimeter

A bomb calorimeter is a more advanced form of a calorimeter. A bomb calorimeter consists of a sealed metal container which is sealed and thus provides constant pressure and volume. It is an isolated system. A normal calorimeter is more simplified and cannot withstand high pressures and volumes. Howe...
Fri Jan 19, 2018 1:07 pm
Forum: Phase Changes & Related Calculations
Topic: Delta U
Replies: 2
Views: 172

### Re: Delta U

Yes, delta U is the change in internal energy of the system. It can be found in the first law of thermodynamics which states deltaU=(q+w), where q is the net heat transfer of the system and w is the net work done on the system.
Fri Jan 19, 2018 1:02 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimeter Calibration [ENDORSED]
Replies: 2
Views: 121

### Re: Calorimeter Calibration[ENDORSED]

Is there a specific question you are referring to? I believe it is referring to calibrating the thermometer of the system, meaning the thermometer was adjusted to accurately measure the change in temperature of the reaction.
Fri Jan 12, 2018 1:13 pm
Forum: Administrative Questions and Class Announcements
Topic: Can homework be written in pencil?
Replies: 6
Views: 383

### Re: Can homework be written in pencil?

I would ask your TA! Last quarter, my TA accepted homework in pencil but it would be a good idea to check, just in case. However, make sure to use pen for tests.
Fri Jan 12, 2018 1:07 pm
Forum: Administrative Questions and Class Announcements
Topic: HW for week 2 disc
Replies: 5
Views: 310

### Re: HW for week 2 disc

You get to choose what problems you would like to do as long as it is a recent topic we have gone over. So you can choose to submit chapter 8 or chapter 9 problems next week. However, make sure to remember that you have to turn in 14 problems next week as opposed to the usual 7!
Fri Jan 12, 2018 1:05 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Celsius the same as Kelvin? [ENDORSED]
Replies: 9
Views: 2043

### Re: Celsius the same as Kelvin?[ENDORSED]

In this case, you are only concerned with the change in temperature, not the actual temperatures themselves. Since the conversion between Celsius and Kelvin is additive, the change in temperature is the same, regardless of units. Therefore, it does not matter if you use Celsius or Kelvin. However, i...
Fri Dec 08, 2017 10:24 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 11.77 textbook problem
Replies: 2
Views: 162

### Re: 11.77 textbook problem

It requires energy, in this case, heat, to break apart a molecule. Therefore, the forward reaction is endothermic and will be favored.
Fri Dec 08, 2017 10:22 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Volume vs Pressure
Replies: 1
Views: 119

### Re: Volume vs Pressure

Reducing the volume will result in the reaction shifting in the direction that minimizes the number of moles of gas produced.
Mon Dec 04, 2017 12:06 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Problem 11.81
Replies: 3
Views: 382

### Re: Problem 11.81

The reaction will favor the direction that makes the reaction endothermic. In this case, the formation of reactants is favored because it makes the reaction endothermic as opposed to exothermic.
Mon Dec 04, 2017 12:02 pm
Forum: Polyprotic Acids & Bases
Topic: Polyprotic Acid Ka [ENDORSED]
Replies: 3
Views: 620

### Re: Polyprotic Acid Ka[ENDORSED]

Dr. Lavelle said in class today that we do not need to know polyprotic acids so you can omit problems 12.79 and 12.81 in the textbook.
Mon Nov 20, 2017 12:12 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Are moleculary geometry and shape different? [ENDORSED]
Replies: 3
Views: 307

### Re: Are moleculary geometry and shape different?[ENDORSED]

I believe they are the same thing. Molecular geometry and molecular shape are synonymous. However, there is a difference between electron geometry and molecular shape/geometry as molecular geometry/shape only considers bond arrangement and does not consider lone pairs.
Mon Nov 20, 2017 12:02 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K=1 [ENDORSED]
Replies: 2
Views: 170

### Re: K=1[ENDORSED]

The ratio of products to reactants would be exactly 1:1. For every mole of reactants, there is one mole of reactants.
Sun Nov 19, 2017 4:44 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 4
Views: 268

### Re: Bond Angles

I don't think you need to know any other specific angles as long as you know the general trend. For example, I think it would be acceptable to know that a trigonal pyramidal molecule has a bond angle slightly less than 109.5 degrees if you are able to explain why.
Sun Nov 19, 2017 4:40 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm on myucla
Replies: 6
Views: 452

### Re: Midterm on myucla

I think it is different every year depending on the class average. I think the curve is meant to help our grades and not hurt them, so I wouldn't worry about it.
Fri Nov 10, 2017 5:41 pm
Forum: Quantum Numbers and The H-Atom
Topic: principal quantum number
Replies: 2
Views: 288

### Re: principal quantum number

If n=5, it is the row of the periodic table and the actual shell for the s and p orbitals. However, it is not for d and f.
Fri Nov 10, 2017 5:37 pm
Forum: Electronegativity
Topic: Polar or non polar [ENDORSED]
Replies: 4
Views: 350

### Re: Polar or non polar[ENDORSED]

A good example of this was on the midterm. The question asked if N2 and SO2 were polar or non polar. N2 is non polar because the N atoms do not have a difference in electronegativity. SO2 is polar because the S and O atoms have differences in electronegativity less than 2.
Fri Nov 03, 2017 12:55 pm
Forum: Trends in The Periodic Table
Topic: Second Ionization Energy
Replies: 2
Views: 208

### Re: Second Ionization Energy

The second ionization energy is always higher than the first because it is harder to remove an electron from a cation than a neutral atom.
Fri Nov 03, 2017 12:47 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 2.55 part C
Replies: 2
Views: 167

### Re: 2.55 part C

If you are referring to part C, it asks for the valence-shell configuration of the group 5 transition metals. I was confused on this as well. I think the solution manual made an error and is referring to the group 7 transition metals (Mg, Tc, Re, etc.).
Thu Oct 26, 2017 5:34 pm
Forum: Trends in The Periodic Table
Topic: HW 2.85
Replies: 1
Views: 155

### Re: HW 2.85

I agree that the solution manual's answer was somewhat vague. I think it is trying to say that because the energy spacing between orbitals is smaller, the energy pattern is not very rigid as it requires less energy to rearrange it. Therefore, there are exceptions to the regular order of orbital conf...
Thu Oct 26, 2017 5:27 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Units [ENDORSED]
Replies: 4
Views: 299

### Re: Units[ENDORSED]

As long as you are consistent with your units, it does not matter unless the homework or test problem specifies that the answer should be in meters or picometers. However, it is very simple to convert between meters and picometers if the question does specify. A picometer is equal to 1*10^-12 meters...
Mon Oct 23, 2017 10:59 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Balmer and Lyman Wavelengths [ENDORSED]
Replies: 4
Views: 304

### Re: Balmer and Lyman Wavelengths[ENDORSED]

There are no exceptions to this as far as I am aware. The Balmer series represent all of the spectral lines within the visible spectrum and the Lyman series represents all of the spectral lines within the UV region of the spectrum. Therefore, for each transition to n=2 and n=1 respectively, is part ...
Mon Oct 23, 2017 10:48 am
Forum: Administrative Questions and Class Announcements
Replies: 3
Views: 347

I asked Lavelle about this on the first day of class and he said that they are no longer allowed to sell course readers. However, because of Lavelle's extensive website, I don't think course readers make that much of a difference.
Wed Oct 11, 2017 12:24 pm
Forum: Properties of Light
Topic: Photo electric effect
Replies: 3
Views: 263

### Re: Photo electric effect

The photoelectric effect is highly important because it demonstrates that light has both wave and particle characteristics. Before the photoelectric experiment, light was largely regarded as being a wave and was modeled as a wave in the scientific world. However, the photoelectric effect demonstrate...
Wed Oct 11, 2017 12:14 pm
Forum: Properties of Light
Topic: Clarification on C=λv
Replies: 10
Views: 1471

### Re: Clarification on C=λv

Yes, c is a constant. C is the speed of light and does not change. Therefore, in all C=λv problems, you should set c equal to 3.00*10^8 m/s. The wavelength and frequency are what will change in this equation.
Mon Oct 02, 2017 11:39 pm
Forum: Significant Figures
Topic: All students read this sig fig post [ENDORSED]
Replies: 116
Views: 13201

### Re: All students read this sig fig post[ENDORSED]

A good way to ensure you have the correct number of sig figs is to convert each value to scientific notation. Therefore, if you were given the number 0.0020, you should write it as 2.0*10^-3. It is thus clearer that this number has 2 significant figures.
Mon Oct 02, 2017 11:36 pm
Forum: Limiting Reactant Calculations