Search found 65 matches

Sat Mar 16, 2019 10:53 pm
Forum: Administrative Questions and Class Announcements
Replies: 179
Views: 12857

could someone please explain #8 part a on the electrochemistry worksheet? How do we know that S2O8 2- is reduced and NO is oxidized? I also have this question You look at the chart of reduction potentials. The one with the higher reduction potential will be reduced. For the other half reaction, it ...
Sat Mar 16, 2019 12:39 pm
Forum: Administrative Questions and Class Announcements
Replies: 179
Views: 12857

For worksheet 4, is the answer for 6a wrong? I did (3/2)(31.9 mol)(8.314 J/Kmol)(311.15 K) = 124 kJ. When I didn't convert the temperature from C to K I got 15.1 kJ which is the answer given in the key. We don’t have to convert it to kelvin as it is change in temperature (38-0) Why do we use that e...
Sat Mar 16, 2019 12:14 pm
Forum: Administrative Questions and Class Announcements
Replies: 179
Views: 12857

For the first law worksheet, how do you do #2? First you have to do stoichiometry to find how many moles of Pb is made from 49.7 g PbO. You multiply the number of moles of product times the enthalpy value given, which gives you the q to plug into your regular q=mC s (Tf-Ti). Once you solve for mass...
Thu Mar 07, 2019 9:45 pm
Forum: Balancing Redox Reactions
Topic: Test #2
Replies: 6
Views: 313

Re: Test #2

Okay awesome thank you !
Thu Mar 07, 2019 9:44 pm
Forum: General Science Questions
Topic: Final
Replies: 7
Views: 642

Re: Final

He does not.
Thu Mar 07, 2019 9:39 pm
Forum: General Rate Laws
Topic: Units for Rate Constants
Replies: 5
Views: 219

Re: Units for Rate Constants

Basically the rate the reaction ((-1/a)(d[A]/dt)) is equal to mol x L^-1 x s ^-1. This rate is equal to the either k[A]^0, k[A]^1, k[A]^2 depending on whether or not the reaction is zeroth order, first order, or second order respectively. [A] represents the concentration of an unknown reactant and t...
Thu Mar 07, 2019 9:25 pm
Forum: Second Order Reactions
Topic: 7th Edition 7A.11 2nd Order RXN
Replies: 2
Views: 170

7th Edition 7A.11 2nd Order RXN

In this problem it says that these reactants react in a second order process so that k[H2][I2] is the rate. However I thought that a second order process was k[A]^2 . Does A just represent reactants and the square mean there is two reactants hence a second order process?
Thu Mar 07, 2019 9:21 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 7th edition 7A.11
Replies: 1
Views: 133

7th edition 7A.11

In this problem the temperature is given but not included in the final answer. Is the temperature not important ? Why was it not accounted for ?
Thu Mar 07, 2019 9:19 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 7A. 1 in the 7th edition
Replies: 4
Views: 146

Re: 7A. 1 in the 7th edition

Basically isolate what you are looking at in the equation to the gases that the question is asking about and then set them equal to each other. If you divide the molar coefficients (what side you solve for depends on what chemical the question is asking about) and you will get the ratio of the rate ...
Fri Mar 01, 2019 9:54 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Finding n for the equation ΔG⁰=-nFE⁰
Replies: 8
Views: 315

Re: Finding n for the equation ΔG⁰=-nFE⁰

Thank you!
Fri Feb 22, 2019 9:18 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Midterm #1 14B
Replies: 17
Views: 1028

Re: Midterm #1 14B

What TA's review sessions did y'all find to be the most helpful? Because I've gone to a few where I feel more lost when I leave then helped. From the review sessions for the midterm, I found those by Morris, Nathan, and Ronald the most helpful because they were fun and covered the material in a way...
Fri Feb 22, 2019 9:10 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isochoric
Replies: 3
Views: 388

Isochoric

What does it mean for a reaction to be isochoric?
Fri Feb 22, 2019 9:09 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: S=qrev/ T
Replies: 3
Views: 376

Re: S=qrev/ T

Any isothermal reaction can be assumed to also be reversible In this class.
Fri Feb 22, 2019 9:07 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Midterm Question
Replies: 8
Views: 278

Re: Midterm Question

if you used the constant given for constant pressure 5/2R you should have gotten a value close the actual C that as even about an hour into the test.
Fri Feb 22, 2019 9:04 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 5/2R vs 3/2R
Replies: 6
Views: 3146

Re: 5/2R vs 3/2R

If the question says that the pressure is being kept constant(Cp) or that the volume is being kept constant (Cv) you will use 5/2R and 3/2R respectively if the molecule in question is a monatomic gas.
Fri Feb 22, 2019 9:01 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: delta S= q(rev)/ T
Replies: 5
Views: 355

delta S= q(rev)/ T

Under what circumstances do we use this entropy equation ?
Fri Feb 08, 2019 10:11 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Practice Midterm
Replies: 3
Views: 197

Practice Midterm

Has Lyndon announced anything about a practice midterm ?
Fri Feb 08, 2019 10:09 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: delta H
Replies: 1
Views: 122

delta H

What does delta H represent? And what does a negative delta H value stand for? I'm sorry I'm just becoming really confused by all these different variables and what exactly it means and when to solve for them.
Fri Feb 08, 2019 10:06 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta U
Replies: 3
Views: 139

Delta U

What exactly is delta U ? I know that it is solved for with q and w but what exactly are we solving when we solve for delta u?
Fri Feb 01, 2019 9:11 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: HW problem 4B. 13
Replies: 5
Views: 493

Re: HW problem 4B. 13

How do we know when we to use ln(V1/V2) ?
Fri Feb 01, 2019 9:09 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4B13 7th edition
Replies: 1
Views: 95

4B13 7th edition

For part B of this problem two different constant values of R were used. One was R=.08206(L)(ATM)/(K)(MOL) and the other R=8.3145(J)/(K)(MOL), how do we distinguish when to use this two different constants?
Fri Feb 01, 2019 9:05 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Cvm and Cpm ?
Replies: 2
Views: 1374

Cvm and Cpm ?

What is the difference between these two ? I saw the chart in the book but I am not sure which one to use when a question is asking to use them.
Wed Jan 30, 2019 4:26 pm
Forum: Phase Changes & Related Calculations
Topic: Test #1
Replies: 11
Views: 434

Re: Test #1

Okay good to know thank you !
Wed Jan 30, 2019 4:23 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Decreasing volume and chemical equilibrium
Replies: 8
Views: 368

Decreasing volume and chemical equilibrium

What happens to a reaction at equilibrium when you decrease the volume ?
Wed Jan 30, 2019 4:21 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: pKa vs. pH
Replies: 15
Views: 2263

Re: pKa vs. pH

pKa and pH measure different quantities. pKa measurers acid strength and pH measures H+ concentration, which are similar but Ka is used to find pKa as opposed to a molar cpncenztrartion of H+ ions in a solution.
Wed Jan 30, 2019 4:14 pm
Forum: Ideal Gases
Topic: kc vs kp
Replies: 19
Views: 895

Re: kc vs kp

Kc and Kp are interchangeable they just denote different measuring methods!
Thu Jan 24, 2019 11:02 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: pKa and pH
Replies: 2
Views: 159

pKa and pH

Are pKa and the pH the same thing ?
Thu Jan 24, 2019 9:53 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Does [H3O+][OH-] always equal 10^-14?
Replies: 9
Views: 332

Re: Does [H3O+][OH-] always equal 10^-14?

Michelle Song 1G wrote:Under what conditions does it not equal 10^-14? For 6B.9 [H3O+][OH-] does not equal 10^-14...

I ran into this same problem and I am not 100% sure why it does not work because it works for the last two parts but it may be because we can not assume that the values of the temperature are constant.
Thu Jan 17, 2019 9:23 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homework error?
Replies: 2
Views: 141

Re: Homework error?

I'm glad I'm not the only one who thought this because if you do divide Kw by 3.1 mol/l you get a concentration with a value of 10^-15 which I'm not sure is possible
Fri Jan 11, 2019 9:29 am
Forum: Ideal Gases
Topic: Pv=nRT [ENDORSED]
Replies: 12
Views: 347

Re: Pv=nRT[ENDORSED]

Yes the temperature should be in Kelvin but you must make sure that the temperature stays the same throughout the reaction or the equilibrium constant will be correct.
Fri Jan 11, 2019 9:27 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: HW Problem 5H.1 [ENDORSED]
Replies: 4
Views: 193

Re: HW Problem 5H.1[ENDORSED]

For part B, since you are technically working with the exponents, you'd have to square root the K to get the answer. Whereas, for part c the coefficients (which become exponents) are doubled so you would have to square the K. So does this mean that every time you have molar coefficients that are le...
Fri Jan 11, 2019 9:21 am
Forum: Ideal Gases
Topic: What does K represent?
Replies: 9
Views: 330

What does K represent?

I know how to find K but what does it mean ?
Sun Dec 09, 2018 10:02 am
Forum: Naming
Topic: -ate in naming
Replies: 7
Views: 578

Re: -ate in naming

Thank you so much I thought it was only based on the overall charge of the compound !
Fri Dec 07, 2018 12:14 am
Forum: Determining Molecular Shape (VSEPR)
Topic: HW 2E3 PART B (7TH EDITION)
Replies: 4
Views: 192

Re: HW 2E3 PART B (7TH EDITION)

Thank you so much I appreciate it :)
Fri Dec 07, 2018 12:13 am
Forum: Bond Lengths & Energies
Topic: HW 2.25 part a
Replies: 3
Views: 447

Re: HW 2.25 part a

Thank you so much!
Fri Dec 07, 2018 12:03 am
Forum: Bronsted Acids & Bases
Topic: Strong Acids vs Weak Acids
Replies: 2
Views: 266

Strong Acids vs Weak Acids

How can you tell which is which? I know that string acids apparently pronate in water but how can you tell by just looking at them ?
Thu Dec 06, 2018 11:15 pm
Forum: Bronsted Acids & Bases
Topic: Problem J.7 - 7th Ed.
Replies: 4
Views: 256

Re: Problem J.7 - 7th Ed.

I had the same problem I looked at the answer book and Im not sure how the equation was balanced just from knowing the product .
Thu Nov 29, 2018 8:50 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR Formula
Replies: 2
Views: 175

Re: VSEPR Formula

Thank you so much this is really helpful !
Thu Nov 29, 2018 8:49 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Oxidation numbers
Replies: 1
Views: 120

Re: Oxidation numbers

From what I understand the oxidation number is the number of electrons an atom either loses or gains to fulfill or help another atom fulfill the octet rule. So because Carbon has 4 valence electrons it donates those to another atom to help it fulfill its octet rule, thus giving the carbon atom a +4 ...
Thu Nov 29, 2018 8:39 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR Formula: Central Atom
Replies: 4
Views: 174

Re: VSEPR Formula: Central Atom

For the vsepr model to work you need one central atom and the vsepr shape is determined by the way in which surrounding atoms or lone pair electrons interact with each other around the central atom.
Thu Nov 29, 2018 8:10 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining polar and non polar molecules from a lewis structure
Replies: 8
Views: 409

Determining polar and non polar molecules from a lewis structure

How do we do determine polar and non polar structures from looking at lewis structures ?
Thu Nov 29, 2018 8:09 pm
Forum: Hybridization
Topic: Lone Pairs in hybridization
Replies: 3
Views: 201

Lone Pairs in hybridization

Do lone pairs get their own hybridization orbital ?
Thu Nov 29, 2018 8:07 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR Formula
Replies: 2
Views: 175

VSEPR Formula

A lot of the hw problems in the book ask for you to give a VSEPR formula what is that ?
Thu Nov 15, 2018 2:55 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: number of different molecular shapes
Replies: 3
Views: 185

Re: number of different molecular shapes

thank you so much !
Thu Nov 15, 2018 2:54 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: bond angles with lone electrons
Replies: 2
Views: 146

bond angles with lone electrons

How do we know what the bond angles are when there re lone electrons pair on the central atom ?
Thu Nov 15, 2018 2:23 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: number of different molecular shapes
Replies: 3
Views: 185

number of different molecular shapes

How many molecular shapes are we supposed to be able to identify?
Thu Nov 15, 2018 9:51 am
Forum: Determining Molecular Shape (VSEPR)
Topic: HW 2E3 PART B (7TH EDITION)
Replies: 4
Views: 192

HW 2E3 PART B (7TH EDITION)

Do the lone pairs around atoms that are not the central atom affect the molecular shape ? For example the hw asks for the shape of CH2F2 and the two fluorine molecules bonded to the carbon have three lone pairs while the hydrogen have none. Do these affect the shape or is it only lone pairs that sur...
Thu Nov 08, 2018 10:41 am
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge & Stable lewis structures
Replies: 6
Views: 359

Formal Charge & Stable lewis structures

When you calculate the formal charge I know that boy the end ll of the each individual changes must add up to the overall charge of molecule/ion. However if they add up does that means it is in its most stable or should you and try and make it so that you reduce the number of formal charges you have...
Thu Nov 08, 2018 10:37 am
Forum: Bond Lengths & Energies
Topic: HW 2.25 part a
Replies: 3
Views: 447

HW 2.25 part a

Question: Which bond is longer ? The CN bond in HCN or in H3CNH2? I know that bond lengths tend to correspond with atomic radius size but does the addition of the extra hydrogens make the molecule necessarily larger?
Thu Nov 08, 2018 10:33 am
Forum: Bond Lengths & Energies
Topic: 2.25 Homework Problem
Replies: 4
Views: 356

Re: 2.25 Homework Problem

From what I looked up bond lengths correspond with atomic radius, so the smaller the radius of the two bonded atoms the smaller the overall bond length.
Thu Nov 01, 2018 10:25 pm
Forum: Octet Exceptions
Topic: Odd Lewis Structures
Replies: 3
Views: 219

Re: Odd Lewis Structures

How do we account for electrons in the 3d orbital in our lewis structure ?
Thu Nov 01, 2018 10:20 pm
Forum: Lewis Structures
Topic: Drawing Lewis Structures
Replies: 14
Views: 727

Re: Drawing Lewis Structures

annabel 1 1F wrote:How do we know how many resonance structures to draw?

I think you use the amount of possible double bonds between the same atoms to determine how many resonance structures you can have.
Thu Nov 01, 2018 10:17 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal charge purpose
Replies: 40
Views: 2801

Re: Formal charge purpose

How do we know when it is necessary to calculate the formal charge?
Thu Oct 25, 2018 10:05 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Module Question 20
Replies: 4
Views: 346

Re: Module Question 20

How do we calculate the uncertainty of the kinetic energy ?
Thu Oct 25, 2018 9:40 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Module #18
Replies: 3
Views: 301

Re: Module #18

Have you converted this answer into sig figs ?
Thu Oct 25, 2018 8:56 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Module Question #17
Replies: 4
Views: 295

Re: Module Question #17

Why do the answers have 1 sig fig ?
Thu Oct 18, 2018 11:31 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8196
Views: 1429940

Re: Post All Chemistry Jokes Here

Don't trust atoms they make up everything.
Thu Oct 18, 2018 11:26 pm
Forum: Administrative Questions and Class Announcements
Topic: Required knowledge for test/midterm [ENDORSED]
Replies: 13
Views: 612

Re: Required knowledge for test/midterm[ENDORSED]

Im pretty sure this second test will pretty much cover the entire Quantum world unit we've been doing aka the majority if the video modules
Thu Oct 18, 2018 11:24 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: #42 In Post-Module Assessment [ENDORSED]
Replies: 5
Views: 249

Re: #42 In Post-Module Assessment[ENDORSED]

This was super helpful thank you!
Thu Oct 11, 2018 11:29 pm
Forum: Properties of Electrons
Topic: HW problem Focus 1 B5 7th edition
Replies: 2
Views: 106

HW problem Focus 1 B5 7th edition

The problem asks to solve for the wavelength of yrays with an energy of 140.511 keV and I am not sure how to convert these units to joules or if I need to convert them at all.
Thu Oct 11, 2018 11:26 pm
Forum: Properties of Light
Topic: Kinetic energy equation
Replies: 4
Views: 135

Kinetic energy equation

I know that to solve for the kinetic energy of a photon the equation is Ek=(1/2)mv^2 but where do we find the values of the mass of the specific electron ?
Thu Oct 11, 2018 11:14 pm
Forum: Properties of Light
Topic: Question 1B.7 7th Edition
Replies: 2
Views: 79

Re: Question 1B.7 7th Edition

I was stuck on this same problem thank you so much !
Fri Oct 05, 2018 12:13 am
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student [ENDORSED]
Replies: 221
Views: 115647

Re: Advice from a Medical Student[ENDORSED]

This definitely encourages me to attend more step up/peer learning sessions.
Fri Oct 05, 2018 12:10 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: atoms vs molecules vs formula units?
Replies: 3
Views: 99

Re: atoms vs molecules vs formula units?

I'm pretty sure the phrase formula units is just generic, and varies based on what the question is asking i.e; for someone looking to answer a question about volume the formula units would be milliliters/liters etc. while a question about number of atoms could possibly be moles. I'm not 100% sure th...
Fri Oct 05, 2018 12:04 am
Forum: Empirical & Molecular Formulas
Topic: Compound Names
Replies: 9
Views: 530

Re: Compound Names

I wasn't sure either but for the learning objectives given to us for the basic chem review he only said know the main elements not how to name the compounds.