## Search found 45 matches

Wed Mar 07, 2018 4:26 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.47
Replies: 1
Views: 115

### 15.47

This problem requires you to go from the molecular structures to the formula... would we be expected to be able to do this on the test? I was having trouble naming the compounds to put in the formula because they seemed more complicated.
Wed Mar 07, 2018 4:24 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Using pre-equilibrium approach
Replies: 3
Views: 165

### Re: Using pre-equilibrium approach

From my understanding that is correct!
Wed Mar 07, 2018 4:23 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pre-Equilibrium Mechanism Reaction
Replies: 1
Views: 109

### Re: Pre-Equilibrium Mechanism Reaction

I believe you will be given the observed rate law (experimentally determined) and the elementary reactions. Usually I believe you are also told which reaction is the slow one, unless they want you to determine that (as in problem 15. 89).
Wed Mar 07, 2018 4:21 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Elementary Steps for Reaction Mechanisms
Replies: 2
Views: 179

### Re: Elementary Steps for Reaction Mechanisms

I believe he said in lecture today that we would be given the steps! I don't think we are expected to have the knowledge to come up with the equations; we just need to know how to analyze them.
Wed Feb 28, 2018 12:13 pm
Forum: Second Order Reactions
Topic: Order reactions
Replies: 6
Views: 604

### Re: Order reactions

You can determine which type of reaction it is by looking at how the rate changes in response to concentrations. Based on this, you can determine which order reaction it is and use the correlating equation.
Wed Feb 28, 2018 12:08 pm
Forum: First Order Reactions
Topic: Direct Proportions and First Order
Replies: 5
Views: 274

### Re: Direct Proportions and First Order

If it is second order, then I believe that means that as concentration of reactants doubled, then the rate would quadruple (concentration =2, n=2---> 2^2=4)
Wed Feb 28, 2018 12:06 pm
Forum: First Order Reactions
Topic: Deriving these Equations
Replies: 7
Views: 403

### Deriving these Equations

Does [A] always mean [A] initial? Or does it have to be explicitly shown? ( [A]0)
Fri Feb 23, 2018 12:22 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Homework 14.25
Replies: 4
Views: 241

### Re: Homework 14.25

I was wondering this too. Maybe you have to compare the ones with the same oxidation state/number of electrons if there is more than one option?
Fri Feb 23, 2018 12:17 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Standard State with Nernst Equation
Replies: 4
Views: 282

### Re: Standard State with Nernst Equation

I think you assume that it is standard states unless it is otherwise specified- for anything that is not in standard state they usually give you the concentrations/partial pressures.
Fri Feb 16, 2018 12:15 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic vs Concentration
Replies: 3
Views: 222

### Galvanic vs Concentration

What is the difference between how you use information from a Galvanic cell and information from a Concentration cell? Do they allow you to calculate the same thing with different formulas? Or do they give different information?
Fri Feb 16, 2018 12:08 pm
Forum: Balancing Redox Reactions
Topic: Basic vs Acidic
Replies: 2
Views: 202

### Basic vs Acidic

How does it affect it differently if you are balancing a redox reaction in a basic solution, acidic solution, or neutral solution? What changes in the way you go about balancing the equation?
Fri Feb 16, 2018 12:06 pm
Forum: Balancing Redox Reactions
Topic: Balancing redox rxns [ENDORSED]
Replies: 7
Views: 426

### Balancing redox rxns[ENDORSED]

When you are given a redox reaction to balance, is there a general set of steps you can use to do it? What do you balance first, second, etc?
Fri Feb 09, 2018 8:50 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Calculations on Internal Energy
Replies: 4
Views: 362

### Re: Calculations on Internal Energy

Yes I believe they will be- the midterm covers ch 8, 9, and part of 11-- if you look at the syllabus above the homework problems are listed exactly which sections from each chapter were covered in class, and therefore will probably be tested. (There were a couple of sections not covered from those c...
Fri Feb 09, 2018 8:46 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.1
Replies: 4
Views: 314

### Re: 9.1

Your body is generating the 100 J/s, which means that the surroundings is absorbing 100 J/s (positive) which is why the entropy of the surroundings is a positive value.
Fri Feb 09, 2018 8:44 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: K to Kc equation
Replies: 2
Views: 176

### Re: K to Kc equation

K usually refers to the equilibrium constant at equilibrium pressures, while Kc is the equilibrium calculated using the equilibrium concentrations. I believe that gases are usually given in partial pressures though.
Thu Feb 01, 2018 11:24 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Calculation methods
Replies: 3
Views: 206

### Calculation methods

For the equation deltaG = deltaH - delta(TS), when calculating the standard enthalpy of the reaction, can you also use Hess's law or mean bond enthalpies? Professor Lavelle mentioned using standard enthalpies of formation in class but not the other two methods so I wasn't sure.
Thu Feb 01, 2018 11:17 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9. 43
Replies: 5
Views: 321

### 9. 43

In problem 9.43, when calculating the entropy changes for the different volume and temperature changes, they used the number 75.3 KJ/ K mol as the specific molar heat capacity. How did they calculate this value?
Thu Feb 01, 2018 11:13 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.13
Replies: 3
Views: 218

### Re: 9.13

You need to have a value in moles so that the units will cancel-- multiplying "n (mol)" times "R (J/ mol K) allows the moles to cancel so you get the correct units. If it is given, you use that, but sometimes you must solve for "n" using the ideal gas law.
Tue Jan 23, 2018 10:09 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: homework problem 111
Replies: 1
Views: 132

### homework problem 111

In part b, you are asked to calculate the enthalpy change, which they find using standard enthalpies of formation. Why is water excluded from this calculation?
Tue Jan 23, 2018 10:04 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.65
Replies: 6
Views: 323

### Re: 8.65

I was confused on this too.. Is there another way to do this without adding them together and ending up with fractions?
Tue Jan 23, 2018 10:00 pm
Forum: Phase Changes & Related Calculations
Replies: 1
Views: 166

I believe that one way energy could be transferred is by compressing the gas inside, which would increase the energy in the system.
Fri Jan 19, 2018 2:45 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.41
Replies: 3
Views: 269

### Re: 8.41

On the left side of your equation you have to also account for the amount of heat that will be used to melt the ice into water before the temperature equalizes.
Fri Jan 19, 2018 2:43 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: (g) vs (l) state of H2O in combustion rxn. Homework 93
Replies: 2
Views: 185

### Re: (g) vs (l) state of H2O in combustion rxn. Homework 93

I think for this equation it is a liquid because it is a combustion reaction, which always produces carbon dioxide and water (liquid) as products. I think for other equations the states should be given unless it is obvious which one it is.
Fri Jan 19, 2018 2:41 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Work Equation
Replies: 4
Views: 296

### Re: Work Equation

I also think that if the system is doing work on the surroundings, then energy is being released and therefore the work has a negative value... am I thinking about this right?
Wed Jan 10, 2018 3:15 pm
Forum: Phase Changes & Related Calculations
Topic: Heat and Phase Transition
Replies: 3
Views: 247

### Re: Heat and Phase Transition

I believe that it is because during the phase change, all the heat added is being used to break the bonds between the molecules to convert them to a different state, and so the temperature of the substance will not begin to rise again until the phase change is complete. At the freezing or boiling po...
Wed Jan 10, 2018 3:10 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Change in Enthalpy of the Reverse Reaction
Replies: 5
Views: 1507

### Re: Change in Enthalpy of the Reverse Reaction

If the reaction is reversed, then for the reversed equation you just switch the sign on the enthalpy from the original equation. To go from fusion to freezing, it would go from a positive to negative.
Wed Jan 10, 2018 3:06 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 5
Views: 304

### Re: Bond Enthalpies

The reactants have positive enthalpy because the bonds are being broken, which requires an input of energy, giving them the positive value. However, in the products, bonds are being formed, which releases energy, and therefore the enthalpy values are negative because energy is released.
Sat Dec 09, 2017 2:00 pm
Forum: Conjugate Acids & Bases
Topic: 12.35
Replies: 1
Views: 249

### 12.35

I was able to come up with the same values as the solution manual for Ka1; however, it seems like the order they listed the acids in is wrong. I got:
H3PO4 < H2SeO3< HSeO4- < H3PO3
because the smaller the Ka the weaker the acid. Am I missing something?
Tue Dec 05, 2017 1:39 pm
Forum: Lewis Acids & Bases
Topic: 12.15
Replies: 3
Views: 323

### 12.15

When drawing the product of the reaction between PF5 and F-, how do you know that the resulting compound, PF6, has a negative charge?
Tue Dec 05, 2017 1:36 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Determinig Strength of Acids
Replies: 1
Views: 181

### Determinig Strength of Acids

When looking at a group of acids and trying to determine which one is stronger, which is more important? Bond length or electron pulling power (electronegativity)? Do you determine only move on to looking at electron pulling power if the bond lengths are the same?
Mon Nov 27, 2017 2:14 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination number [ENDORSED]
Replies: 3
Views: 315

### Re: Coordination number[ENDORSED]

I think you just have to figure out how many bonds the central atom is going to have, either with individual molecules or with a compound (such as CN) , which you can usually do just by looking at the formula.
Mon Nov 27, 2017 2:11 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Determining if polydentate [ENDORSED]
Replies: 1
Views: 141

### Determining if polydentate[ENDORSED]

Does the number of lone pairs correspond to the number of ligands it can attach to? For example, if a molecule has an oxygen with 2 lone pairs then does that mean the molecule is bidentate?
Mon Nov 06, 2017 11:41 pm
Forum: Octet Exceptions
Topic: Expanded Octed
Replies: 2
Views: 292

### Expanded Octed

When you are drawing a Lewis structure, how do you know if you are going to be dealing with an expanded octet or not? I'm afraid I'm going to give a compound an expanded octet because if fits the number of electrons that should be present but end up with the wrong configuration.
Mon Nov 06, 2017 11:39 pm
Forum: Lewis Structures
Replies: 4
Views: 445

In order to determine if something is a radical, you just have to find out if there is an odd number of electrons; if there is, then it means you will be left with one unpaired electron and therefore the molecule will be a radical.
Mon Oct 30, 2017 4:12 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Wave functions
Replies: 2
Views: 254

### Wave functions

I was confused after reading the book about the purpose of wave functions... the book seemed to go more in depth than Professor Lavelle did in the lecture and the homework barely addresses the concept. What specific ideas do we need to understand for the test? Just that wave functions are used to pr...
Mon Oct 30, 2017 4:08 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: d orbital [ENDORSED]
Replies: 2
Views: 240

### Re: d orbital[ENDORSED]

The 4s orbital is at a lower energy than the 3d, so the 4s fills up before the 3d. Once the 3d fills up then it switches back and 3d is at a lower energy level than 4s. It is the same as this for the rest of the periods, so usually the d orbital is one number behind whichever period you are dealing ...
Mon Oct 30, 2017 4:03 pm
Forum: Formal Charge and Oxidation Numbers
Topic: when to calculate formal charge [ENDORSED]
Replies: 3
Views: 315

### Re: when to calculate formal charge[ENDORSED]

Going along with this, is it correct that whichever Lewis structure results in the most formal charges of zero is the most stable? In other words, how do you use the calculated Lewis structures to determine stability?
Fri Oct 20, 2017 4:30 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Building up on electron configurations
Replies: 2
Views: 328

### Re: Building up on electron configurations

The first element in the P block has one electron in its P orbital, which is written as Px^1. As you move right, you will add one electron to the Py orbital and then the Pz orbital, and then begin to fill up the orbitals from the beginning until you reach the element at the end of that row, where th...
Fri Oct 20, 2017 4:25 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbitals, Subshells, and Shells
Replies: 4
Views: 215

### Re: Orbitals, Subshells, and Shells

I think that orbitals are made up of shells, which are made up of subshells. The subscripts used today represent how in the p orbital, there are three sub orbitals, each of which can hold two electrons.
Fri Oct 20, 2017 4:24 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbitals, Subshells, and Shells
Replies: 4
Views: 215

### Re: Orbitals, Subshells, and Shells

I think that orbitals are made up of shells, which are made up of subshells. The subscripts used today represent how in the p orbital, there are three sub orbitals, each of which can hold two electrons.
Mon Oct 16, 2017 3:43 pm
Forum: Properties of Light
Topic: Lyman vs Balmer Series
Replies: 4
Views: 279

### Re: Lyman vs Balmer Series

So you can deduce if an electron is in the Balmer or Lyman series by looking at the wavelength of light it absorbs? and then in terms of energy levels if it is a Lyman series that means the electron is starting from or returning to the n=1 energy level and if it is in the Balmer series that means it...
Mon Oct 16, 2017 3:39 pm
Forum: Properties of Light
Topic: Quiz #2 References [ENDORSED]
Replies: 4
Views: 313

### Re: Quiz #2 References[ENDORSED]

I believe that the reference sheet will be given to us in class.
Mon Oct 09, 2017 2:50 pm
Forum: Administrative Questions and Class Announcements
Topic: Where to find Bruincast?
Replies: 3
Views: 537

### Re: Where to find Bruincast?

Whenever I click on the Chemistry 14A site at CCLE it goes directly to Professor Lavelle's website, and I cant find the link for media resources on his website anywhere. Where should I go?
Thu Oct 05, 2017 9:55 pm
Forum: Significant Figures
Topic: Sig Figs- Addition and Subtraction [ENDORSED]
Replies: 4
Views: 494

### Re: Sig Figs- Addition and Subtraction[ENDORSED]

Okay thank you Miranda- so then you only have to look at the number of significant figures and just do the one with the least amount? You don't even have to really worry about decimal places?
Tue Oct 03, 2017 9:59 pm
Forum: Molarity, Solutions, Dilutions
Topic: Problem G.25 in Fundamentals
Replies: 3
Views: 354

### Re: Problem G.25 in Fundamentals

I was confused on this question as well. I understand that doubling it 90 times dramatically reduces the amount of solute per L of solution so that it almost becomes obsolete but I don't understand the solution manual's method of solving the problem. Could someone please help explain why they are tr...