## Search found 47 matches

Sat Mar 17, 2018 10:23 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Kinetically controlled reactions
Replies: 3
Views: 619

### Re: Kinetically controlled reactions

Even if a reaction is exothermic and seems to be thermodynamically favorable, it may happen at a very slow rate in which case it is not kinetically favorable. It also might have a high activation energy which is difficult to achieve which would effect the spontaneity of the reaction.
Fri Mar 16, 2018 6:46 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Homework 11.111
Replies: 1
Views: 424

### Homework 11.111

Can someone explain how to do number 111 in chapter 11? The question reads "A certain enzyme-catalyzed reaction in a biochemical cycle has an equilibrium constant that is 10 times the equilibrium constant of the next step in the cycle. If the standard Gibbs free energy of the 1st reaction is 20...
Fri Mar 16, 2018 1:57 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: delta S sys and delta S surr
Replies: 2
Views: 698

### delta S sys and delta S surr

Can someone please explain when delta s of the system would be different than delta s for the surrounding?
Sun Mar 11, 2018 9:07 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Homework 15.67
Replies: 1
Views: 161

### Re: Homework 15.67

To start this problem calculate the rate constant for the uncatalyzed reaction and for the catalyzed reaction by using the equation k=Ae^(-Ea/RT). Then find the factor that it increases between these two values.
Wed Mar 07, 2018 10:43 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Elementary reaction rate laws [ENDORSED]
Replies: 1
Views: 116

### Elementary reaction rate laws[ENDORSED]

Why can we write the rate law of an elementary reaction using the chemical equation if we can't write the general rate law using the chemical equation?
Tue Mar 06, 2018 5:08 pm
Forum: General Rate Laws
Topic: Coefficients
Replies: 6
Views: 347

### Coefficients

Do coefficients have any effect on the rate law?
Sun Mar 04, 2018 5:36 pm
Forum: Zero Order Reactions
Topic: Significance of Zero order reactions
Replies: 3
Views: 232

### Re: Significance of Zero order reactions

Zero order reactions are significant because we may encounter a reaction where the rate is independent of the product such as an enzyme or catalyst reaction but we still may need to calculate a half life or rate constant. This is why we have equations for the zero order reactions.
Thu Mar 01, 2018 7:39 pm
Forum: First Order Reactions
Topic: 15.27
Replies: 6
Views: 556

### Re: 15.27

What happens to the k when you rearrange the equation?
Tue Feb 27, 2018 8:35 pm
Forum: General Rate Laws
Topic: Negative in 15.5
Replies: 3
Views: 374

### Negative in 15.5

Can someone explain what happens to the negative sign in 15.5 a if O2 is a product? The question reads: Ethene is a minor but important component of natural gas, and its combustion has been thoroughly studied. At a certain temperature and pressure, the unique rate of the combustion reaction C2H4(g) ...
Sat Feb 24, 2018 10:34 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Gas in Products [ENDORSED]
Replies: 2
Views: 199

### Re: Gas in Products[ENDORSED]

Yes, in class he said that we can assume this but I believe he also said that we are assuming this for all reactions right now because we have not yet learned how to factor in the reverse reaction.
Sat Feb 24, 2018 10:32 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Kinetics vs. Thermodynamics
Replies: 2
Views: 234

### Kinetics vs. Thermodynamics

How do we know which controls the reaction if it is favorable in one aspect but not favorable in another (for example favorable thermodynamically but not kinetically)? Is this something we can calculate?
Mon Feb 19, 2018 5:13 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Working Cells
Replies: 1
Views: 165

### Working Cells

Can someone explain why "working cells," or ones that produce an electric current, will have a smaller potential difference than what we calculate in deltaG=-nFE?
Sun Feb 18, 2018 2:55 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8019
Views: 1403928

### Re: Post All Chemistry Jokes Here

You can freeze yourself at -273 degrees celsius and still be 0K
Sun Feb 18, 2018 2:54 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8019
Views: 1403928

### Re: Post All Chemistry Jokes Here

You would think atoms bonding with other atoms would mean they're being friendly, but really they steal each other's electrons. How ionic
Sun Feb 18, 2018 2:47 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Cell Potentials
Replies: 5
Views: 218

### Re: Standard Cell Potentials

No, unlike Hess's Law when you multiply a redox half reaction by a factor you do not also multiply the cell potential by that factor.
Sun Feb 11, 2018 2:42 pm
Forum: Balancing Redox Reactions
Topic: Oxidation vs. reduction
Replies: 8
Views: 322

### Re: Oxidation vs. reduction

Michael Cheng 1C wrote:How can you tell which reaction to flip when doing the redox problems?

The overall E should be positive for the reaction in order for it to be spontaneous. So you have to look at the two seperate E's and decide which to flip in order for Erxn to be positive.
Tue Feb 06, 2018 3:34 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.83
Replies: 3
Views: 475

### 11.83

For question 11.83: Calculate the equilibrium constant at 25 C and at 150 C for each of the following reactions, using data available in Appendix 2A: (a) NH4Cl(s) <--> NH3(g) + HCl(g) (b) H2(g) + D2O(l) <--> D2(g) + H2O(l) Is the calculation different when the temperature is at 150 other than the va...
Tue Feb 06, 2018 2:27 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.19
Replies: 1
Views: 170

### 11.19

Can someone explain how to do 11.19? The question asks Calculate the equilibrium constant at 25 C for each of the following reactions, using data in Appendix 2A: (a) the combustion of hydrogen: 2 H2(g) + O2(g) <--> 2 H2O(g). I tried using the equation deltaGrxn = -RTlnK and using the free energy of ...
Sun Feb 04, 2018 10:47 am
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: Residual Entropy
Replies: 4
Views: 281

### Re: Residual Entropy

Ashley Macabasco 2K wrote:Residual entropy is a specific type of entropy and is the same as positional entropy in which the entropy is based upon the arrangement of molecules or atoms.
Is there a difference in the way we would calculate them?
Sun Feb 04, 2018 10:41 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible reactions
Replies: 1
Views: 183

### Reversible reactions

Is a reversible reaction always at equilibrium?
Tue Jan 30, 2018 8:23 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.11
Replies: 4
Views: 286

### 9.11

For this question it asks "Calculate the change in entropy when the pressure of 1.50 mol Ne(g) is decreased isothermally from 15.0 atm to 0.500 atm. Assume ideal behavior." I am using the equation deltaS= nRln(P2/P1) but I am getting the wrong answer. I found that the problem was that to g...
Sat Jan 27, 2018 9:19 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8019
Views: 1403928

### Re: Post All Chemistry Jokes Here

Don't tell jokes to noble gases... you'll get no reaction.
Sat Jan 27, 2018 8:30 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: units for delta H
Replies: 4
Views: 301

### Re: units for delta H

I think that it is kJ/mol unless it asks you to calculate it for a certain number of moles in which case you would multiply by the number of moles and the answer would be in kJ
Wed Jan 24, 2018 10:46 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Homework question 8.41
Replies: 4
Views: 283

### Re: Homework question 8.41

Also, remember that enthalpy of fusion is given in Kj per mole so you have to multiply by the number of moles you are working with. Another problem I encountered was units. Enthalpy of fusion uses kJ while specific heat uses J so make sure to account for that!
Wed Jan 24, 2018 10:43 pm
Forum: Administrative Questions and Class Announcements
Topic: Homework Problems
Replies: 4
Views: 390

### Re: Homework Problems

My TA told us to do problems from chapter 9 but it may depend on your TA's preference
Tue Jan 16, 2018 4:44 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Molar Heat Capacity
Replies: 6
Views: 1441

### Re: Molar Heat Capacity

On page 21 in the course reader (page 6 of the section), specific heat capacity is defined as the heat required to raise the temperature of 1 GRAM of a substance by 1°C. Its units are kJ*/(°C*g). MOLAR heat capacity is the heat required to raise the temperature of 1 MOLE of a substance by 1°C. To c...
Tue Jan 16, 2018 3:28 pm
Forum: Phase Changes & Related Calculations
Topic: question 8.41
Replies: 5
Views: 321

### question 8.41

For question 8.41 I set q(ice)=-q(water) and then used cmdeltaT=-cmdeltaT and solved for Tfinal but i keep getting 42 degrees C instead of 31. Can someone explain what I am doing wrong? The question is A 50.0-g ice cube at 0.0 C is added to a glass containing 400.0 g of water at 45.0 C. What is the ...
Sun Jan 14, 2018 9:49 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8019
Views: 1403928

### Re: Post All Chemistry Jokes Here

post
Sun Jan 14, 2018 9:44 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8019
Views: 1403928

### Re: Post All Chemistry Jokes Here

What do you call an acid with an attitude?
A-mean-oh acid
Sun Jan 14, 2018 9:31 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Units when calculating reaction enthalpy
Replies: 1
Views: 61

### Units when calculating reaction enthalpy

Can someone explain when we are supposed to use kJ and when we use kJ/mol?
Fri Dec 08, 2017 4:51 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: pH at the same concentration
Replies: 1
Views: 148

### pH at the same concentration

On the syllabus for acids and bases it says that we should be able to "Explain why solutions of weak acids have higher pH values than solutions of strong acids at the same concentration." Can someone explain this to me? If they have the same concentration of hydronium ions shouldn't they h...
Thu Dec 07, 2017 12:12 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Oxidation Numbers
Replies: 2
Views: 196

### Oxidation Numbers

Are Oxidation numbers always positive?
Tue Nov 28, 2017 6:50 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: ordering Ligands
Replies: 1
Views: 175

### ordering Ligands

Is there a specific way to order the ligands when writing out a formula after being given the name? I know that in the name they are supposed to be in alphabetical order does it follow the same rule in the formula?
Tue Nov 28, 2017 6:18 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Repulsion Strength
Replies: 1
Views: 319

### Re: Repulsion Strength

The lone pairs repel each other more than they repel another bonding pair and more than bonding pairs repel each other. This is mostly important when figuring out bond angles. For instance, a tetrahedral shape has bond angles of 109.5 degrees. Yet, when you remove one atom and it becomes a trigonal ...
Tue Nov 21, 2017 11:00 am
Forum: Hybridization
Topic: 4.95
Replies: 3
Views: 219

### Re: 4.95

I think that it is related to the number on the periodic table. So for example hybridization between a 2s orbital and a 2p orbital could be a 2sp^2 hybridization.
Tue Nov 21, 2017 10:56 am
Forum: Ideal Gases
Topic: Example in Monday's Lecture
Replies: 3
Views: 350

### Re: Example in Monday's Lecture

The equilibrium constant would be 1/([Ca2+][OH-]^2). The concentrations will remain the same at equilibrium whether the reaction is a forward reaction or reverse reaction.
Sun Nov 19, 2017 5:23 pm
Forum: Hybridization
Topic: bond strength
Replies: 3
Views: 251

### Re: bond strength

I read that pi bonds are weaker than sigma bonds because they overlap side to side rather than end to end. So the pi bond is weaker because there is less overlap.
Sun Nov 19, 2017 5:19 pm
Forum: Hybridization
Topic: Hybrid orbitals and bonds
Replies: 3
Views: 179

### Re: Hybrid orbitals and bonds

Hybridized orbitals use sigma or pi bonds or both in their bonding depending on the molecule. I don't think that you are able to know how many sigma bonds and pi bonds are formed simply from knowing the hybridization. To know the type of bond formed you need more information about the atoms that are...
Sun Nov 12, 2017 11:04 pm
Forum: Resonance Structures
Topic: Determining Resonance Structures
Replies: 3
Views: 409

### Re: Determining Resonance Structures

Sometimes it is clear to see how many resonance structures there are such as when you have 3 atoms bonded to a central atom and one double bond and 2 single bonds. It is clear that there will be 3 different possibilities for the double bond to be in a different place and therefore there will be 3 re...
Wed Nov 08, 2017 5:08 pm
Forum: Lewis Structures
Topic: Lewis Structure of N2O
Replies: 2
Views: 305

### Lewis Structure of N2O

I am trying to find the lowest energy lewis structure for N2O for number 8c of the practice midterm and I have found 2 different structures but I'm unsure which is lower in energy because they have the same formal charges. One structure has 2 double bonds which gives the outside N a formal charge of...
Thu Nov 02, 2017 8:41 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic Bonds w/ Covalent Character
Replies: 2
Views: 262

### Re: Ionic Bonds w/ Covalent Character

All ionic bonds have some covalent character because the electrons are pulled into the bonding region and the ion is distorted. This causes it have some covalent character. As the ion becomes larger, it has more covalent character because the electrons are farther from the nucleus and it is easier t...
Sun Oct 29, 2017 7:34 pm
Forum: Trends in The Periodic Table
Topic: electron shielding 2.37(c) [ENDORSED]
Replies: 3
Views: 340

### electron shielding 2.37(c)[ENDORSED]

Why is it that electrons having l=1 are better at shielding than electrons having l=2?
Thu Oct 26, 2017 1:25 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Units [ENDORSED]
Replies: 4
Views: 344

### Re: Units[ENDORSED]

I don't think he will mind either way as long as you add the units onto your answer to specify and use the right number of significant figures.
Tue Oct 24, 2017 2:34 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: ch1 question 43
Replies: 8
Views: 720

### Re: ch1 question 43

When doing this problem do we not have to take into account the diameter of the electron?
Fri Oct 20, 2017 11:23 pm
Forum: DeBroglie Equation
Topic: Conceptual Wavelength measurement
Replies: 3
Views: 306

### Re: Conceptual Wavelength measurement

I vaguely remember Dr. Lavelle saying in class that if the wavelength was less than 10^-15 then we should consider it too small when he did the example with the wavelength of a baseball.
Fri Oct 13, 2017 6:11 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Spectroscopy - Balmer Series
Replies: 1
Views: 193

### Re: Spectroscopy - Balmer Series

I think that it depends on the photon that excites the electron. It "stops" at an energy level if a photon hits it with the exact energy that it takes to excite it to that level. At least this was the way that i understood it during the lecture.
Tue Oct 10, 2017 11:58 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Chapter 1 question 15
Replies: 4
Views: 664

### Re: Chapter 1 question 15

When I do the calculation using Rydberg's equation to find the energy level n2, I am getting 3.29. Shouldn't this be a whole number since it is discrete and cannot jump up .29 of a energy level? Does this mean that I am doing the calculations wrong or am i simply supposed to round to 3?