Search found 60 matches

Sat Mar 17, 2018 3:20 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: wmax
Replies: 4
Views: 443

Re: wmax

Yeah, I have this question too and can't seem to find a solid answer.
Fri Mar 16, 2018 1:07 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.85
Replies: 1
Views: 164

Re: 15.85

Nancy Dinh 2J posted a really good explanation!: "First you're finding the balanced equation. After that, look at the number of different reactants of the balanced equation. This will determine the molecularity. 1 reactant is unimolecular, 2 is bimolecular, 3 termolecular. Finally, you draw the...
Fri Mar 16, 2018 1:00 am
Forum: *Enzyme Kinetics
Topic: 15.85
Replies: 2
Views: 599

Re: 15.85

But the answer to c) according to the solutions manual is O----O----NO with the products NO2 and O. Is there another way to do this?
Thu Mar 15, 2018 11:30 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Example 8.5
Replies: 3
Views: 309

Re: Example 8.5

Path A is a reversible expansion and Part B is an irreversible expansion but both still take place isothermally.
Thu Mar 15, 2018 11:28 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Example 8.5
Replies: 3
Views: 309

Re: Example 8.5

Delta U=0 for the isothermal expansion of an ideal gas.
Wed Mar 14, 2018 10:34 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.23
Replies: 3
Views: 458

Re: 14.23

Why doesn't part a) have platinum then on the oxidation side?
The answer in the solutions manual is $Hg(l)|Hg_{2}^{2+} (aq)||NO_{3}^{-}(aq), H^{+}(aq)|NO(g)|Pt(s)$
Sat Mar 10, 2018 8:48 pm
Forum: Second Order Reactions
Topic: the slope
Replies: 12
Views: 827

Re: the slope

The slope is k. For zero order reactions, you plot [A] against time which gives you a negative slope. Because k is always positive -slope=k. For first order reactions, you plot ln[A] against time which gives you a negative slope. So -slope=k. For second order reactions, you plot 1/[A] against time w...
Sat Mar 10, 2018 8:39 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test 2, Question #7 [ENDORSED]
Replies: 2
Views: 312

Re: Test 2, Question #7[ENDORSED]

This is similar to HW problem 14.27. So basically to get Cr2O72-(aq)+14H+(aq)+12e-->2Cr(s)+7H2O(l) from the reactions given on the last page of the test you have to combine the two reactions Cr2O72-(aq)+14H+(aq)+6e-->2Cr3+(aq)+7H2O(l) and Cr3+(aq)+3e--->Cr(s). However E^{\circ } isn't a state functi...
Sat Mar 10, 2018 8:16 pm
Forum: Second Order Reactions
Topic: 3rd order?
Replies: 7
Views: 762

Re: 3rd order?

What would we be asked about third order reactions other than their units?
Sat Mar 03, 2018 4:11 pm
Forum: First Order Reactions
Topic: 15.21
Replies: 3
Views: 481

Re: 15.21

For this problem, I was just wondering does it matter if the formula is written ln[A]=-kt+ln[A]o, ln[A]/ln[A]o=-kt, or [A]=[A]oe^-kt to solve? In discussion we derived the third one from the first to solve, but won't it give you the same answer? Why take the time to manipulate the equation?
Sat Mar 03, 2018 3:55 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.19
Replies: 4
Views: 301

Re: 15.19

I have the same question. Would the answer be acceptable in mmol? I'm assuming the test would specify right?
Fri Mar 02, 2018 5:27 pm
Forum: Zero Order Reactions
Topic: Will we need to know how to derive equations? [ENDORSED]
Replies: 9
Views: 630

Re: Will we need to know how to derive equations?[ENDORSED]

I don't think we'll directly be asked to derive anything, but I'm sure we'll need to know how to derive in order to get the equation we need to solve the problem. Knowing how to derive will probably be more helpful than just memorizing.
Tue Feb 20, 2018 7:24 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 14.51
Replies: 1
Views: 166

14.51

Hi! This question asks about the cell Ag(s)|Ag+(aq,5.0mmol/L)||Ag+(aq,0.15mol/L)|Ag(s) and whether or not it can do work. I was just wondering, how do you know that $E^{\circ }$=0?
Tue Feb 20, 2018 7:16 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 14.47 a
Replies: 6
Views: 457

Re: 14.47 a

Yeah, I am stuck on this too. Maybe it's a typo? I can't seem to figure out how they would get 10^6.
Mon Feb 19, 2018 10:26 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.13 c
Replies: 2
Views: 144

Re: 14.13 c

Okay thanks! I understand why the line is between them. I just thought it went cathode(reactant)|cathode(product) so I was wondering if anyone could explain why Cl-(aq) is before Cl2(g)?
Mon Feb 19, 2018 6:49 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.13 c
Replies: 2
Views: 144

14.13 c

Cl2(g) + H2(g)--> HCl (aq) I don't really understand how they got the cell diagram that's in the solutions manual. They put Pt(s)|H2(g)|H+(aq)||Cl-(aq)|Cl2(g)|Pt(s). I'm confused about the cathode side of the diagram. Why is Cl-(aq) before Cl2(g)? Also, I'm still a little bit unsure how you tell whe...
Wed Feb 14, 2018 11:42 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.47 Isothermal Irreversible Free Expansion
Replies: 3
Views: 303

9.47 Isothermal Irreversible Free Expansion

When solving part b asking about the isothermal irreversible free expansion of an ideal gas, if the expansion is irreversible and w=0, how do we calculate the entropy change of the system? The solutions manual says it is equal to 3.84J/K (the entropy change in the isothermal reversible expansion). C...
Tue Feb 13, 2018 9:55 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.99
Replies: 1
Views: 166

9.99

For this problem "show that, if another molecule such as ethene is present to act as a hydrogen acceptor then the overall process is spontaneous" why do you have to multiply the reaction of ethene with hydrogen by 3?
Tue Feb 13, 2018 4:12 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Heat Capacity
Replies: 1
Views: 157

Heat Capacity

How can you tell when something is a monatomic gas, linear molecule, or nonlinear molecule when determining the heat capacity? For example, in Example 9.6 in the book (page 329), how do you know to use 4R for the Cp,m rather than say 7/2R when cooling the acetone vapor?
Tue Feb 13, 2018 4:05 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy equation
Replies: 2
Views: 207

Entropy equation

Why is the change in entropy equation for a change in temperature sometimes written \Delta S=Cln(T2/T1) and sometimes written \Delta S=nCln(T2/T1) ? Do you always multiply the Cv/Cp by moles? In Example 9.2 in the book they say C=nCv,m. I was just wondering if anyone can clarify this...
Sat Feb 10, 2018 2:32 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.37 entropy change [ENDORSED]
Replies: 1
Views: 227

9.37 entropy change[ENDORSED]

For letter d, find the standard reaction enthalpy for the decomposition of potassium chlorate 4KClO3(s) -> 3KClO4(s) + KCl(s) and interpret the sign and magnitude of the reaction entropy, the solutions manual says that the four moles of solid products are more ordered than the four moles of solid re...
Thu Feb 08, 2018 2:51 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.37
Replies: 3
Views: 274

9.37

For this problem, I was just wondering what the difference was between $\Delta S^{\circ }_{f}$ and $\Delta S^{\circ }_{r}$? Thanks!
Thu Feb 08, 2018 2:38 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.35
Replies: 1
Views: 148

9.35

On the solution manual errors page, why do they use .5 mol for B and C rather than 1 mol? And how do you know that 1 vibrational degree of freedom changes the Cv from 5R/2 to 3R? Errors page explanation: Gas B (0.5 mol diatomic, no vibrational degrees of freedom): ∆S = nCv ln(T2/T1) = (0.5 moles)(5R...
Fri Feb 02, 2018 3:58 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: The Third Law
Replies: 3
Views: 257

Re: The Third Law

A perfect crystal only has one microstate so w=1. When you plug 1 into the equation S=kb*ln(w) and solve, you get zero.
Fri Feb 02, 2018 3:55 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: The Third Law
Replies: 3
Views: 257

Re: The Third Law

The third law of thermodynamics states that entropy of a perfect crystal is zero when the temperature is zero Kelvin. If it isn't a perfect crystal or if it is at a different temperature there will be residual entropy.
Fri Feb 02, 2018 3:45 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Quiz 1, #1
Replies: 2
Views: 257

Re: Quiz 1, #1

The question is comparing using bond enthalpies and standard enthalpies of formation to find the change in enthalpy of the reaction. In this case you would expect there to be a difference in the answers because bond enthalpies are averages from many different molecules. Therefore, that method will b...
Fri Feb 02, 2018 2:07 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Steps to getting equations
Replies: 1
Views: 123

Re: Steps to getting equations

For the test, I don't think we'll be asked to derive anything. That being said it will probably help to know how the equations are related in order to form the right equation to use for whatever you are trying to solve for. That way you don't really have to memorize all the different equations.
Tue Jan 23, 2018 8:57 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 109
Replies: 2
Views: 298

Re: 109

For this question, why in question a) is q=-1.0x10^4 kJ but in question b) the solutions manual uses positive q (converted to joules 1.0x10^7 J) to solve the problem?
Mon Jan 22, 2018 4:25 pm
Forum: Phase Changes & Related Calculations
Topic: 8.87 Temperatures
Replies: 5
Views: 325

Re: 8.87 Temperatures

Ok thanks guys! Say it's for something other than water, how are we supposed to know what the melting point and boiling point is?
Mon Jan 22, 2018 4:17 pm
Forum: Phase Changes & Related Calculations
Topic: 8.87 Temperatures
Replies: 5
Views: 325

8.87 Temperatures

"How much heat is required to convert a 42.30g block of ice at -5.042 degrees C into water vapor at 150.35 degrees C?" I think understand why you have to break it up into different steps based on the graph, but how do you know which temperature to go to. Like for the first step why do you ...
Tue Jan 16, 2018 11:19 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Problem 8.65
Replies: 2
Views: 167

Re: Problem 8.65

2NO (g) + (3/2)O2 (g) --> N2O5 (g) is crucial to solving the problem. When you multiply the second reaction 4NO2 (g) + O2 (g) --> 2N2O5 (g) by 0.5 you get 2NO (g) + (1/2)O2 (g) --> N2O5 (g). You then add this to the first reaction 2NO (g) + O2 (g) --> 2NO2 (g) to get 2NO (g) + (3/2)O2 (g) --> N2O5 (...
Tue Jan 16, 2018 10:31 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.57
Replies: 2
Views: 154

Re: 8.57

You have to write combustion reactions because you are given \Delta H^{\circ}_{c} . The subscript c tells you it is for a combustion reaction. After setting up AND balancing the combustion equations you use Hess's Law. Add up the three reactions to form the one you are solving for. If you reverse a ...
Tue Jan 16, 2018 8:23 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.49
Replies: 1
Views: 180

8.49

For HW 8.49

OF2(g) + H2O(g) --> O2(g) + 2HF(g)
DeltaH = -318 kJ
What is the change in internal energy for the reaction of 1.00 mol OF2?

Would work always be negative for this kind of problem?
Fri Jan 12, 2018 1:06 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Question 8.35
Replies: 2
Views: 206

Re: Question 8.35

8.35 isn't on the syllabus so I don't think we'll be expected to know this. But basically there is a given equation for the density of a face-centered cubic unit cell which is given in example 6.3 in the textbook and then you just find the molar mass, convert the radius from pm to cm and plug everyt...
Fri Jan 12, 2018 12:46 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.51
Replies: 3
Views: 170

Re: 8.51

Don't forget to multiply by the moles
$\Delta H=\sum nH^{\circ }_{f products}-\sum nH^{\circ }_{f reactants}$
Which is the energy per mole of reaction
Fri Jan 12, 2018 12:36 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Most Stable/Pure Form
Replies: 2
Views: 99

Re: Most Stable/Pure Form

So from what I understand, pure elements in their most common state (like carbon graphite or O2 gas) are in their most stable form. So, since the standard enthalpy of formation is defined as the enthalpy to form a mole of a substance from pure elements in their standard states, these pure forms have...
Thu Jan 11, 2018 10:55 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.51
Replies: 3
Views: 170

Re: 8.51

N2 and O2 are in their most stable form so their enthalpies of formation are zero.
Sat Dec 09, 2017 6:56 pm
Forum: Biological Examples
Topic: #21 on Practice Final
Replies: 2
Views: 305

Re: #21 on Practice Final

In what instances do you just treat the bond as a lone pair?
Thu Dec 07, 2017 8:54 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: 12.53 Names of acidic compounds
Replies: 2
Views: 247

Re: 12.53 Names of acidic compounds

I was curious about this too. We never went over naming acids so perhaps we will be given the formula? Knowing a few doesn't hurt, but I might just ask my TA for clarification if this post doesn't get an answer.
Thu Dec 07, 2017 5:29 pm
Forum: Amphoteric Compounds
Topic: Acidic, basic, or amphoteric? [ENDORSED]
Replies: 4
Views: 1283

Re: Acidic, basic, or amphoteric?[ENDORSED]

If amphoteric oxides act both as acids or bases, what is the difference between amphiprotic and amphoteric oxides?
Tue Dec 05, 2017 8:02 pm
Forum: Lewis Acids & Bases
Topic: 12.29
Replies: 2
Views: 250

12.29

Hi guys! I'm a little confused on chapter 12 number 29 letter c "Calculate the pH and pOH for 0.0092M of Ba(OH)2(aq)." Why did they multiply the concentration by 2? How do you know it produces 2 hydroxide ions? Thanks!
Thu Nov 30, 2017 10:37 am
Forum: Hybridization
Topic: 4.95
Replies: 3
Views: 303

Re: 4.95

so why doesn't the oxygen atom have a 2sp2 hybridization?
Wed Nov 29, 2017 11:37 pm
Forum: Hybridization
Topic: 4.95
Replies: 3
Views: 303

4.95

For chapter 4 number 95, what do the arrows pointing at the lone pairs on the oxygen labeled sp2 refer to?
Wed Nov 29, 2017 4:54 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: T-shape [ENDORSED]
Replies: 1
Views: 156

T-shape[ENDORSED]

Hi guys! I was just wondering when drawing the T-shape for a molecule with 5 regions of electron density, why wouldn't the 2 lone pairs be at the axial positions instead of 2 of the 3 equatorial positions?
Sat Nov 25, 2017 11:02 pm
Forum: Naming
Topic: Latin stem
Replies: 1
Views: 186

Latin stem

In step 7 on toolbox 17.1 it says that if the metal originates from a Latin name to use the Latin stem. How should we know when to do this and what the Latin stem is?
Fri Nov 24, 2017 3:54 pm
Forum: Dipole Moments
Topic: Dipole arrows
Replies: 2
Views: 297

Dipole arrows

In the book, the dipole arrows are drawn with the arrow pointing to the partial positive charge. In my discussion, we had the arrow pointing towards the negative one. Which way should we draw it for the test?
Thu Nov 16, 2017 2:58 pm
Forum: Hybridization
Topic: 2 regions of electron density
Replies: 4
Views: 368

Re: 2 regions of electron density

A molecule with two regions of electron density can only have a linear molecular formula.
Thu Nov 16, 2017 2:48 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pairs
Replies: 5
Views: 438

Lone Pairs

When drawing the molecular shape, how do you know where to put the lone pair(s)?
Thu Nov 16, 2017 2:38 pm
Forum: Hybridization
Topic: Pi bonds
Replies: 4
Views: 337

Pi bonds

Hi guys! So I'm a little confused on pi bonds. Are they just the overlapping of unhybridized p orbitals? Thanks!
Thu Nov 09, 2017 11:42 am
Forum: Administrative Questions and Class Announcements
Topic: Midterm: What to do with backpacks
Replies: 1
Views: 257

Midterm: What to do with backpacks

Hi guys! On the website it says not to bring anything other than a calculator, pen, and ID to the midterm. What should we do if we have class before and don't have enough time to drop off our backpacks?
Thanks!
Wed Nov 08, 2017 3:00 pm
Forum: Octet Exceptions
Replies: 3
Views: 389

Hey guys! When there's a radical, how do you know which atom gets the unpaired electron? For instance on chapter 3 number 59a why do you place it on Cl as opposed to O?

Thanks!
Mon Nov 06, 2017 2:30 pm
Forum: Lewis Structures
Topic: Lone Pair Placement
Replies: 2
Views: 172

Lone Pair Placement

Hi guys! So in lecture, we talked about the lone pairs having a preference in placement. For example, on SF4 (sulfur tetrafluoride) the lone pair is in the equatorial plane. For the midterm, when we are asked to draw lewis structures are we going to need to place the lone pair in a certain spot with...
Tue Oct 31, 2017 9:08 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Post- Module #18 and #23
Replies: 1
Views: 204

Post- Module #18 and #23

Hi guys! I'm confused on how to determine what delta x to use to solve both of these questions. #18 states "The hydrogen atom has a radius of approximately 0.05nm. Assume that we know the position of an electron to an accuracy of 1% of the hydrogen radius, calculate the uncertainty in the speed...
Sat Oct 28, 2017 12:32 pm
Forum: Quantum Numbers and The H-Atom
Topic: 2.19
Replies: 1
Views: 226

2.19

I'm confused on 2.19 letter b) How many values of ml are allowed for an electron in a 6d-subshell? I know that d correlates to l=2 so then there would be 5 ml values (-2, -1, 0, 1, 2) but doesn't n=6 which would mean l=5 and there would be more values of ml?
Wed Oct 25, 2017 11:28 pm
Forum: Quantum Numbers and The H-Atom
Topic: Magnetic Quantum Number
Replies: 4
Views: 768

Magnetic Quantum Number

Can anyone explain what the Magnetic Quantum Number (ml) is and how you figure out what values it can be? I don't understand how to apply l, l-1,...-l. Thanks!
Wed Oct 18, 2017 6:48 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Question 1.15
Replies: 6
Views: 340

Re: Question 1.15

So for this equation, we just order the energy levels to insure it's positive rather than doing final - initial energy level?
Sat Oct 14, 2017 12:58 am
Forum: Properties of Electrons
Topic: Constructive vs. Destructive Interference [ENDORSED]
Replies: 4
Views: 720

Re: Constructive vs. Destructive Interference[ENDORSED]

Diffraction just refers to what happens when a wave encounters an object and bends around it. Constructive Interference is when two waves meet and the crests (top of the wave) of both waves are aligned so the resulting wave increases in amplitude. The two waves converge into a bigger wave, so to spe...
Thu Oct 12, 2017 2:13 pm
Forum: Properties of Light
Topic: Clarification on C=λv
Replies: 10
Views: 1774

Re: Clarification on C=λv

Energy of a photon=hv
c=λν or v=c/λ
Therefore, E=h(c/λ)
So, you could say energy of a photon and wavelength are inversely proportional while energy and frequency are directly proportional.
Thu Oct 05, 2017 10:45 pm
Forum: SI Units, Unit Conversions
Topic: Exercise E35
Replies: 2
Views: 299

Re: Exercise E35

Yes, percent change is found by doing [(Final Value minus Initial Value)/ Initial Value] times 100
Thu Oct 05, 2017 5:32 pm
Forum: Limiting Reactant Calculations
Topic: M.9
Replies: 4
Views: 505

M.9

Hi Chemistry friends! For Fundamental M question 9, can someone explain how to set up a net ionic equation? Do you guys think this is something we should know for the test tomorrow?