## Search found 52 matches

Sun Mar 17, 2019 11:26 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Question 14.55
Replies: 1
Views: 261

### Re: Question 14.55

I also have this question and am not sure of what concept is being applied
Sun Mar 17, 2019 11:25 am
Forum: Second Order Reactions
Topic: Termolecular
Replies: 15
Views: 433

### Re: Termolecular

There are three molecules of reactants involved in the rate law.
Thu Mar 14, 2019 12:27 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Including n or m in "q" Equation
Replies: 2
Views: 280

### Including n or m in "q" Equation

I have seen some problems worked out where neither moles nor mass are included in the equation involving heat capacity (q=nC(deltaT)). Can someone explain why that is?
Sun Mar 10, 2019 11:11 pm
Forum: Zero Order Reactions
Topic: Zero order reactions
Replies: 4
Views: 119

### Re: Zero order reactions

I don’t think the professor ranked how common the first three orders were, just that they are the most common and that anything above a third order reaction became rarer and rarer.
Sun Mar 10, 2019 11:10 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: molecularity
Replies: 4
Views: 374

### Re: molecularity

Molecularity depends on the number of reactants in a reaction (including the number of moles of a reactant).
Sun Mar 10, 2019 11:07 pm
Forum: General Rate Laws
Topic: Rate Laws
Replies: 8
Views: 259

### Re: Rate Laws

The rate laws for the different orders and their half lives are on the constants and equations sheet
Fri Mar 01, 2019 2:37 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.7 (6th Ed.): Figuring out reactant rate order
Replies: 1
Views: 114

### 15.7 (6th Ed.): Figuring out reactant rate order

How do we know which experiments to use in order to figure out a reactants rate order? I thought it was by choosing experiments where one reactant concentration changes while the other don't, but that doesn't seem to be the case for finding [B] (the solutions uses exp. 2 and 3, where there is also a...
Tue Feb 26, 2019 7:29 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 6th ed. 14.23: value of n
Replies: 2
Views: 103

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

For the reactions in this problem, are we supposed to work out the half-reactions in order to figure out how many moles we use in the equation to find standard G, or is there a faster way to find it?
Tue Feb 26, 2019 7:26 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6th Ed. 14.23 [ENDORSED]
Replies: 2
Views: 83

### Re: 6th Ed. 14.23[ENDORSED]

What does it mean for something to be a pure conductor?
Mon Feb 25, 2019 1:23 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6th Ed. 14.23 [ENDORSED]
Replies: 2
Views: 83

### 6th Ed. 14.23[ENDORSED]

In part a, the cell diagram includes Pt(s) on only the right side of the reaction (for the cathode). Why wouldn’t it be included on both sides?
Mon Feb 25, 2019 12:20 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Using commas in cell diagram
Replies: 3
Views: 126

### Using commas in cell diagram

When do we use commas in a cell diagram as opposed to using a straight line?
Fri Feb 22, 2019 12:44 pm
Forum: Balancing Redox Reactions
Topic: Homework 14.5 part d
Replies: 4
Views: 171

### Re: Homework 14.5 part d

I checked the Errors PDF as well, but I still have no idea how they got 4P4 by multiplying by 3.
Fri Feb 22, 2019 12:42 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Using reverse reactions (Problem 14.11)
Replies: 1
Views: 87

### Using reverse reactions (Problem 14.11)

In 14.11 part b, the final balanced reaction reverses the half-reaction of Cl- to Cl2. First of all, why does the standard cell potential not become negative when it’s flipped, and why are we able to flip the half-reaction for the final reaction? Is it because it’s in order to get the electrons on d...
Thu Feb 21, 2019 12:34 pm
Forum: Balancing Redox Reactions
Topic: Homework 14.5 part d
Replies: 4
Views: 171

### Homework 14.5 part d

For letter d) in problem 14.5 (6th edition), the answe key says to multiply the first half-reaction by 3, but then the new reaction contains 4P4, not 3P4.

Is this a mistake in the answer key or the actual answer? If it’s correct, could someone explain why?
Mon Feb 18, 2019 12:17 am
Forum: Calculating Work of Expansion
Topic: Units for R
Replies: 10
Views: 602

### Re: Units for R

The constants and equations sheet show that there are a couple of ways to write out the units.
Mon Feb 18, 2019 12:16 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Negative Temperature
Replies: 5
Views: 184

### Re: Negative Temperature

Mon Feb 18, 2019 12:11 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy vs. Standard Gibbs Free Energy
Replies: 3
Views: 117

### Gibbs Free Energy vs. Standard Gibbs Free Energy

I was wondering what the difference between Gibbs Free Energy vs. Standard Gibbs Free Energy is.
Sun Feb 10, 2019 9:58 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: ln in Boltzmann Equation
Replies: 1
Views: 71

### ln in Boltzmann Equation

How is the ln derived in the Boltzmann equation?
Sun Feb 10, 2019 9:55 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Which does more work?
Replies: 3
Views: 111

### Re: Which does more work?

I am also confused with this. I think it may be reversible systems that do more work but I am not sure.
Sun Feb 10, 2019 9:53 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthlapy
Replies: 1
Views: 82

### Bond Enthlapy

Did the method we learned in lecture about finding bond enthalpies relate to Hess’s Law, or was that just a different method?
Mon Feb 04, 2019 11:22 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: Gas taking up more states
Replies: 2
Views: 128

### Gas taking up more states

Why do molecules occupy more states in a gaseous compared to being in solid or liquid states?
Mon Feb 04, 2019 11:19 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: PdeltaV with Solids and Liquids
Replies: 3
Views: 119

### PdeltaV with Solids and Liquids

IN the equation, deltaU=deltaH-PdeltaV, why is PdeltaV insignificant with solids and liquids when there is a constant Pressure?
Mon Feb 04, 2019 11:14 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Purpose of ln
Replies: 2
Views: 72

### Purpose of ln

What is the natural log supposed to represent in the equation?
Sun Jan 27, 2019 10:53 pm
Forum: Phase Changes & Related Calculations
Topic: Delta Hº versus delta H
Replies: 2
Views: 122

### Re: Delta Hº versus delta H

The first is just the measure of any kind of change in enthalpy in a reaction.

The second represents Standard Reaction Enthalpy, which is when reactants and products are in their standard state at 1 atm.
Sun Jan 27, 2019 10:50 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: When to use Quadratic equation
Replies: 10
Views: 1202

### Re: When to use Quadratic equation

The quadratic formula will naturally end up being used in ICE tables typically when the unknown concentrations for the products in equilibrium are the same and the reactant at equ. has the initial conc. minus the change in conc. This is because, when the K equation is written out with these values, ...
Sun Jan 27, 2019 10:44 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: How Le Chat's Principle is Applied
Replies: 2
Views: 116

### Re: How Le Chat's Principle is Applied

When a new gas is added to the system (not including inert gases), the chemical reaction goes out of equilibrium. According to Le Chatelier's Principle, the reaction will adjust itself in order to restore itself back to equilibrium (its K value) by either increasing or decreasing gas pressures on ea...
Sun Jan 20, 2019 12:26 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Stoichiometric Coefficients
Replies: 4
Views: 169

### Re: Stoichiometric Coefficients

I don't know what would be exactly on exams, but it could be possible because the only additional work you would have to do is multiply the x (representing change of concentrations of products) in your ICE table by the coefficient of whichever product has a coefficient that's not 1.
Sun Jan 20, 2019 12:18 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: 6th Edition 12.35
Replies: 1
Views: 244

### 6th Edition 12.35

For problem d, the information given provides K2, while the rest of the problems give the values for K1. What does this exactly mean, and does it require solving the problem differently?
Sun Jan 20, 2019 12:16 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: 6th Edition 12.39
Replies: 1
Views: 270

### 6th Edition 12.39

When identifying the Kb values of these molecules, why can we use the same values if the molecule is not exactly the same? For example, question 2 is not exactly the same molecule as the one whose pB we use to find the Kb value.
Sun Jan 13, 2019 11:19 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Replies: 4
Views: 125

### Re: Quadratic Formula in Equilibrium

The quadratic formula ends up being used most often when we use ICE tables. While we place the concentrations of the products over the concentrations of the reactants at equilibrium over each other, we do not know the change in concentration from their initial molarities. Ultimately, the quadratic f...
Fri Jan 11, 2019 6:21 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 6th Edition 11.115
Replies: 1
Views: 83

### 6th Edition 11.115

For question b, the solution explains that the compressing the system would lead to no change to the equilibrium equation because the number of moles are equal on either side. However, it looks like there are 12 moles on the left side and 7 on the other. Can someone explain how they came to this con...
Fri Jan 11, 2019 3:07 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Q 11.49
Replies: 1
Views: 52

### Q 11.49

The correct answer to Q 11.43 in the book is c) K=x^2/(1.0-2x)^2. I was wondering why this is the case. I understand why the numerator is x^2, and I understand that the denominator has to do with the difference in stoichiometric coefficients, but I do not understand why 1.0-2x is squared or why ther...
Fri Dec 08, 2017 11:56 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 12.27 part B
Replies: 1
Views: 170

### 12.27 part B

Why do we divide the concentration by .250 in the pH calculation?
Fri Dec 08, 2017 11:49 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Difference in Calculating pH for Strong and Weak Acids
Replies: 3
Views: 296

### Difference in Calculating pH for Strong and Weak Acids

What difference does it make if an acid is strong or weak when calculating its pH?
Fri Dec 01, 2017 10:34 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Delocalized Pi Bonds [ENDORSED]
Replies: 2
Views: 357

### Delocalized Pi Bonds[ENDORSED]

When is a case where pi bonds would be delocalized?
Fri Dec 01, 2017 10:31 pm
Forum: Naming
Topic: Nitrogen and Ligands
Replies: 2
Views: 247

### Nitrogen and Ligands

When determining the coordination number for compounds, I’ve heard two ways of figuring it out but am confused. Do we look at the number of nitrogen atoms or the most electronegative atoms?
Fri Nov 24, 2017 11:09 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Shape Memorization
Replies: 6
Views: 534

### Re: Molecular Shape Memorization

Study the VSEPR shapes that Dr. Lavelle taught in lecture, which can all be found in the beginning of Chapter 4.
Fri Nov 24, 2017 11:07 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Knowing VSEPR Shapes
Replies: 3
Views: 351

### Re: Knowing VSEPR Shapes

Study the VSEPR shapes that Dr. Lavelle taught in lecture, which can all be found in the beginning of Chapter 4.
Fri Nov 17, 2017 3:31 pm
Forum: Sigma & Pi Bonds
Topic: Pi bonds
Replies: 6
Views: 929

### Re: Pi bonds

To have a pi bond present means that there is already a sigma bond present, thus making the bond strength much stronger. Additionally, pi bonds will bond side by side, so if the atoms rotate, then the pi bonds will be broken.
Fri Nov 17, 2017 3:09 pm
Forum: Hybridization
Topic: Hybridization
Replies: 6
Views: 351

### Re: Hybridization

It’s not the addition of orbitals but rather of a merging of the two. If you look at the amount of energy of the hybrized orbital, it will fall in between the two original ones. There is a conservation in the number of electrons for hybridization, it’s just their placement that changes.
Sat Nov 11, 2017 12:00 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Shape Memorization [ENDORSED]
Replies: 7
Views: 944

### Shape Memorization[ENDORSED]

With all of the VSEPR names of the shapes that we have to memorize, does anyone have any ways of memorizing the number of the types and the names of the shapes we need to know?
Fri Nov 10, 2017 11:47 pm
Forum: Molarity, Solutions, Dilutions
Topic: Molarity conversions [ENDORSED]
Replies: 3
Views: 263

### Re: Molarity conversions[ENDORSED]

Use the formula M=n/L and manipulate the equation to where the number of moles equals the molarity times the volume.
Fri Nov 03, 2017 4:01 pm
Forum: Resonance Structures
Topic: Question 3.69
Replies: 1
Views: 192

### Question 3.69

After determining formal charge, how do you identify the Lewis structure of lower energy?
Fri Nov 03, 2017 3:42 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Trigonal planar vs. Trigonal bipyramidal
Replies: 4
Views: 656

### Trigonal planar vs. Trigonal bipyramidal

When would the VSEPR shape be trigonal planar as opposed to trigonal bipyramidal, and vice versa?
Fri Oct 27, 2017 4:32 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: electron spin quantum number (ms) [ENDORSED]
Replies: 4
Views: 568

### Re: electron spin quantum number (ms)[ENDORSED]

Ms represents the direction and magnitude of an electron in an orbital. It is not a positive or negative value but rather something more like clockwise or counterclockwise rotation on an axis. Two electrons cannot spin in the same direction in an orbital, and this is why no two electrons will have t...
Mon Oct 23, 2017 6:09 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Core Electron Question
Replies: 2
Views: 248

### Core Electron Question

Why do we only use the noble gas elements for core electrons and not others?
Wed Oct 18, 2017 12:40 pm
Forum: Properties of Electrons
Topic: Atomic Spectra and Energy Levels
Replies: 3
Views: 313

### Re: Atomic Spectra and Energy Levels

You can also look at n—>infinity as a limit in calculus. We also know that the larger the number in the denominator, the smaller the answer becomes, and when the number in the denominator is getting nearer to infinity’s, the energy becomes so small that it eventually becomes negligible.
Wed Oct 18, 2017 12:22 pm
Forum: Properties of Light
Topic: test 2 topic
Replies: 9
Views: 730

### Re: test 2 topic

Professor Lavelle teaches from the notes, and the book is used to supplement his lectures and give the homework problems. A lot of the time, the book will correspond with his lectures and notes, but not always. In those cases, it’s probably best to ask your TA or Lavelle himself to make sure, but lo...
Tue Oct 10, 2017 5:52 pm
Forum: Properties of Light
Topic: Chapter 1 #3
Replies: 9
Views: 567

### Re: Chapter 1 #3

We know that the electrical field (as opposed to the magnetic field) corresponds to the amplitude of a wave. Because the frequency is decreasing, this means that there are less cycles being completed per second, meaning that the waves must be getting longer since it will take a longer duration of ti...
Tue Oct 10, 2017 5:38 pm
Forum: Photoelectric Effect
Topic: Chapter 1, Question 1.23
Replies: 3
Views: 272

### Chapter 1, Question 1.23

Q 1.23 “The y-ray photons emitted by the nuclear decay of a technetium-99 atom used in radiopharmaceuticals have an energy of 140.511 keV. Calculate the wavelength of these y-rays.”

I‘m not sure how to begin this problem. What measurement is keV exactly, and how do you convert it to joules?
Fri Oct 06, 2017 12:18 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: E7 [ENDORSED]
Replies: 9
Views: 715

### Re: E7[ENDORSED]

In order to have the most precise and accurate answer, it is best to not round sig figs until the end once you have finished the problem. To figure out the number of sig figs you use, look at the number of sig figs used in the original problem.
Wed Oct 04, 2017 12:03 am
Forum: Molarity, Solutions, Dilutions
Topic: Molarity Module Q#16
Replies: 1
Views: 175

### Re: Molarity Module Q#16

In order to convert the grams of KCl to m/L (Mi), you should first find the molar mass of KCl and divide the mass of KCl given (55.1 g) by its molar mass. This finds the number of KCl moles, and since M=n/V, you just divide the number of moles by the volume given (75 mL, or .075 L). This finds Mi (t...