## Search found 67 matches

Fri Mar 15, 2019 11:53 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Review Session-Thermo-files- Wednesday-Q11-clarification [ENDORSED]
Replies: 10
Views: 841

### Re: Review Session-Thermo-files- Wednesday-Q11-clarification[ENDORSED]

For #8, can someone explain why deltaH is negative? Shouldn't the enthalpy change of the reaction be positive since the temperature of the solution increases? So the solution absorbed heat?
Fri Mar 15, 2019 11:07 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Review Session-Thermo-files- Wednesday-Q11-clarification [ENDORSED]
Replies: 10
Views: 841

### Re: Review Session-Thermo-files- Wednesday-Q11-clarification[ENDORSED]

For #5b, would the reaction only be reversible if deltaG=0?
Fri Mar 15, 2019 10:15 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: intermediates
Replies: 4
Views: 106

### Re: intermediates

Intermediates are in the rate laws for elementary steps but not in the overall rate law of the reaction
Fri Mar 15, 2019 10:12 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Test 2 Q 7 [ENDORSED]
Replies: 5
Views: 545

### Re: Test 2 Q 7[ENDORSED]

Although deltaH is positive, deltaS is also positive (water is less orderly than ice), and deltaS*T is probably a greater value than deltaH which makes deltaG=deltaH-TdeltaS negative
Wed Mar 13, 2019 11:04 pm
Forum: Administrative Questions and Class Announcements
Replies: 179
Views: 12688

For the integrated rate law worksheet #5a, I found the answer using
1/((7.0*10^9 M*s)*(120 sec) + 1/0.086M)
= 1/ (8.4*10^11 M*s^2 + 11.63 M^-1)
and I got the right answer but I'm confused by the units. How do the units work out to be M? And how do you add 8.4*10^11 M*s^2 with 11.63 M^-1?
Sun Mar 10, 2019 2:12 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6th edition, 14.17
Replies: 2
Views: 126

### Re: 6th edition, 14.17

Why is it Fe2+ --> Fe3+ and not Fe2+ --> Fe or any of the other ones? Should we just assume that it will be Fe2+ --> Fe3+?
Sat Mar 09, 2019 10:02 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: #14.13 Part C (Sixth Edition)
Replies: 3
Views: 140

### Re: #14.13 Part C (Sixth Edition)

I think that you're supposed to assume that HCl dissociates into its ions in an aqueous solution because it is a strong acid, so you're supposed to see the equation as Cl2(g) + H2(g) --> 2H+(aq) + 2Cl-(aq)
Sat Mar 09, 2019 3:43 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Equilibrium Constant and Temperature
Replies: 2
Views: 106

### Equilibrium Constant and Temperature

When asked to calculate the equilibrium constant from deltaG°=-RTlnK, will we always be told what temperature to calculate it at?

For example, on Karen's Gibbs Free Energy worksheet #1d, how do we know what temperature to calculate the equilibrium constant at?
Tue Mar 05, 2019 12:37 am
Forum: General Rate Laws
Topic: Rate of Formation vs Unique Rate of a Reaction
Replies: 2
Views: 121

### Re: Rate of Formation vs Unique Rate of a Reaction

The rate of formation is specific to each product, while the unique rate of a reaction is the same value for all reactants and products in the unique reaction.
Tue Feb 26, 2019 10:29 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Pt
Replies: 2
Views: 93

### Re: Pt

Include Pt as the electrode for any half reaction that doesn't have a solid metal.
Tue Feb 26, 2019 10:27 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram
Replies: 3
Views: 120

### Re: Cell Diagram

I think H2O is the solvent so you don't need to include it in the cell diagram. It's implied?
Tue Feb 26, 2019 10:26 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Platinum
Replies: 2
Views: 86

### Re: Platinum

If one of the half reactions does not include a solid metal, then use platinum
Tue Feb 26, 2019 1:41 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram Order
Replies: 3
Views: 169

### Re: Cell Diagram Order

But why is Cl-(aq) on the left and Cl2(g) on the right?
Tue Feb 26, 2019 1:40 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams
Replies: 2
Views: 90

### Re: Cell Diagrams

| is used to separate phase changes and to indicate a porous barrier. Since Sn are both aqueous, they are separated by a comma.
Mon Feb 18, 2019 4:41 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Calculating Gibbs Free Energy Equations
Replies: 2
Views: 120

### Calculating Gibbs Free Energy Equations

For 6th Edition Chapter 9 #55: Write a balanced chemical equation for the formation reaction of (a) NH3 (g); (b) H2O(g); (c)CO(g); (d) NO2(g). For each reaction, determine H,S, and G from data in Appendix 2A. When calculating the Grxn, can we use the equation "deltaG = deltaGformation(products)...
Sun Feb 17, 2019 8:19 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Calculating G if H and S are gven
Replies: 3
Views: 165

### Re: Calculating G if H and S are gven

Why can we use the same deltaH and deltaS to calculate deltaG at any temperature? (like in this problem: 9.53 Calculate the change in molar Gibbs free energy for the process NH3(l) --> NH3 (g) at 1atm and (a) 15.0 C; (b) 45. C (see Tables 8.3 and 9.1 for standard enthalpy and entropy of vaporization...
Sun Feb 17, 2019 8:04 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy
Replies: 3
Views: 133

### Re: Gibbs Free Energy

The spontaneity of a reaction does not indicate the reaction rate, so not necessarily.
Mon Feb 11, 2019 6:42 pm
Forum: Administrative Questions and Class Announcements
Replies: 179
Views: 12688

Chem_Mod wrote:
005199302 wrote:for #6, shouldn't the work be -12.4kJ?

w=-PxdV = (-122atm/L)(101.33J/atmL) = -12.4kJ

Why do we need to find a different pressure if pressure is constant?
Sun Feb 10, 2019 10:15 pm
Forum: Administrative Questions and Class Announcements
Topic: Lyndon's HOTDOG MIDTERM REVIEW SESSION!! FINALLY!
Replies: 49
Views: 3864

### Re: Lyndon's HOTDOG MIDTERM REVIEW SESSION!! FINALLY!

How do you calculate internal energy for #6 without knowing the temperature?
Sun Feb 10, 2019 9:28 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: entropy of vaporization of water [ENDORSED]
Replies: 3
Views: 615

### Re: entropy of vaporization of water[ENDORSED]

Does that mean that water/substances can undergo phase change without input of heat?
Sun Feb 10, 2019 12:00 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimeters
Replies: 2
Views: 96

### Re: Calorimeters

Also for this question why do we ignore the heat used to raise the temperature of the water? For reference, the question is: A calorimeter was calibrated with an electric heater, which supplied 22.5 kJ of energy as heat to the calorimeter and increased the temperature of the calorimeter and its wate...
Sun Feb 03, 2019 8:52 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 2
Views: 95

### Re: Bond Enthalpies

If you want to be really extra you can write out all the bonds in the reactants and all the bonds in the products. Then you can tell which bonds changed in the reaction.
Sun Feb 03, 2019 8:47 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Equipartition Theorem
Replies: 2
Views: 107

### Re: Equipartition Theorem

Dr. Lavelle will probably go over it in lecture this week if it's on the syllabus.
Sun Feb 03, 2019 8:46 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Enthalpy of Formation
Replies: 3
Views: 95

### Re: Standard Enthalpy of Formation

We don't need to memorize them.
Sun Jan 27, 2019 10:20 pm
Forum: Phase Changes & Related Calculations
Topic: Standard Enthalpy of Formation in Most Stable Form
Replies: 1
Views: 86

### Re: Standard Enthalpy of Formation in Most Stable Form

I think it was supposed to be a really redundant obvious point... so I think you're right
Sun Jan 27, 2019 10:13 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Calculating Enthalpy
Replies: 2
Views: 84

### Re: Calculating Enthalpy

The enthalpies of the reactants and the enthalpies of the products.
Mon Jan 21, 2019 1:36 pm
Forum: Administrative Questions and Class Announcements
Replies: 179
Views: 12688

Can someone explain how to do Worksheet 1 #4d? My friend did it with initial concentration of NH3 as 0 and she got the right answer. Why doesn't the initial concentration of NH3=5.82*10^-3 ?
Sun Jan 20, 2019 9:36 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: 5I.13
Replies: 2
Views: 117

### Re: 5I.13

What does the question say?
Sun Jan 20, 2019 9:33 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Inert Gases
Replies: 7
Views: 290

### Re: Inert Gases

What is an inert gas?
Sun Jan 20, 2019 9:25 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: pressure and volume
Replies: 5
Views: 192

### Re: pressure and volume

As pressure increases, volume decreases, which causes the concentration of reactants and products to change. This change makes the system not in equilibrium, and therefore causes movement towards equilibrium.
Sun Jan 20, 2019 9:09 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K and Kc (Section 5H.3 7th Edition)
Replies: 2
Views: 81

### Re: K and Kc (Section 5H.3 7th Edition)

I think one of the TAs said that we won't need to know it. I think if it's on the test we'll probably be given the equation and the important values?
Sun Jan 20, 2019 9:03 pm
Forum: Ideal Gases
Topic: pH and pOH
Replies: 18
Views: 881

### Re: pH and pOH

What does the problem say? I think generally it tells you which to solve for.
Thu Jan 17, 2019 10:05 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Constants
Replies: 5
Views: 180

### Re: Equilibrium Constants

Also, Kp=Kc*RT^[(moles of products)-(moles of reactants)]
Sat Dec 08, 2018 5:37 pm
Forum: Lewis Acids & Bases
Topic: 6th edition 12.17
Replies: 5
Views: 193

### Re: 6th edition 12.17

I think BaO is basic because the O will have 3 lone pairs which will allow it to donate an electron pair?
Sat Dec 08, 2018 5:36 pm
Forum: Lewis Acids & Bases
Topic: 6th edition 12.17
Replies: 5
Views: 193

### Re: 6th edition 12.17

Can someone also explain why SO3 is acidic?
Fri Dec 07, 2018 3:53 pm
Forum: Administrative Questions and Class Announcements
Replies: 135
Views: 31332

For Week 9 worksheet #5, why cant H3O+ and H2O neutralize an added base? And why cant H2O neutralize an acid and be potentially amphoteric?
Wed Dec 05, 2018 5:48 pm
Forum: Amphoteric Compounds
Topic: Amphoteric compounds
Replies: 1
Views: 85

### Re: Amphoteric compounds

An amphoteric compound can act as both an acid and a base, so it can donate and accept protons.
Wed Dec 05, 2018 5:45 pm
Forum: Naming
Topic: 9C3 7th Edition
Replies: 1
Views: 89

### Re: 9C3 7th Edition

There are 3 Br because one bromide ion has a charge of -1, and since the compound is neutral, you need to balance out the +3 charge on the Cobalt. Therefore you need 3 Bromide ions 3*(-1)=-3 to balance out the +3 charge of the Cobalt.
Wed Dec 05, 2018 5:40 pm
Forum: Naming
Topic: Naming Coordination Compounds
Replies: 4
Views: 184

### Re: Naming Coordination Compounds

I think we're supposed to memorize the ligand names.
Wed Nov 28, 2018 12:04 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: London forces vs. Dipole-Dipole Importance
Replies: 1
Views: 139

### London forces vs. Dipole-Dipole Importance

On Hannah Chew's Week 6 Worksheet #4a [Rank the following from weakest intermolecular forces to strongest a) H2S, H2Te, H2Se] why is the strength of london dispersion forces more important than the dipole-dipole forces? Doesn't H2S have the strongest dipole-dipole forces of the three molecules?
Tue Nov 27, 2018 10:56 pm
Forum: Administrative Questions and Class Announcements
Topic: Step Up Session Worksheet (Monday + Friday, Hannah) [ENDORSED]
Replies: 37
Views: 2082

### Re: Step Up Session Worksheet (Monday + Friday, Hannah)[ENDORSED]

On the Week 6 Worksheet #4a [Rank the following from weakest intermolecular forces to strongest a) H2S, H2Te, H2Se] why is the strength of london dispersion forces more important than the dipole-dipole forces? Doesn't H2S have the strongest dipole-dipole forces of the three molecules?
Mon Nov 26, 2018 9:58 pm
Forum: Octet Exceptions
Topic: Tin with only 6 electrons
Replies: 4
Views: 362

### Re: Tin with only 6 electrons

I thought that completing the octet was more important than minimizing formal charges?
Mon Nov 26, 2018 9:27 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Most Favorable Placement of Formal Charges
Replies: 2
Views: 374

### Most Favorable Placement of Formal Charges

is it more favorable to have formal charges spread out or to have them concentrated? For example, for N3- is it more favorable for one of the formal charges to be [2-, 1+, 0] or [1-, 1+, 1-]? or are neither of them the best one?
Sun Nov 25, 2018 2:52 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Sigma and Pi bonds
Replies: 6
Views: 195

### Re: Sigma and Pi bonds

If there is a double bond will there always be 1 sigma and 1 pi bond?
Sun Nov 25, 2018 2:46 pm
Forum: Hybridization
Topic: SeF3+
Replies: 2
Views: 2377

### Re: SeF3+

The shape is trigonal pyramidal and the lewis structure is
'''''''''''F
'''''''''''|
F — Se — F
'''''''''''. .
Thu Nov 15, 2018 11:14 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Repulsion Strength
Replies: 2
Views: 99

### Re: Repulsion Strength

A lone pair is also more delocalized than a bonding pair, so it will have greater ability to move around and repel other electrons.
Thu Nov 15, 2018 11:12 am
Forum: SI Units, Unit Conversions
Topic: VSEPR model
Replies: 5
Views: 433

### Re: VSEPR model

The VSEPR model is the Valence-Shell Electron-Pair Repulsion model, which explains experimentally observed shapes of molecules.
Thu Nov 15, 2018 11:11 am
Forum: SI Units, Unit Conversions
Topic: lewis structure shape
Replies: 6
Views: 504

### Re: lewis structure shape

I think there are 11 we need to know:
linear, trigonal planar, angular, tetrahedral, trigonal pyramidal, trigonal bipyramidal, see-saw, t-shaped, octahedral, square pyramidal, square planar
Sun Nov 04, 2018 11:31 pm
Forum: Lewis Structures
Topic: ClO4- 7 bonds
Replies: 1
Views: 109

### ClO4- 7 bonds

Why can the Cl in ClO4- have 7 bonds? I thought that 6 was the limit for Cl? Can it access more than the 4s and 3d orbitals?
Fri Nov 02, 2018 2:32 pm
Forum: Resonance Structures
Topic: 6th edition 3.57 which resonance structures do we draw?
Replies: 1
Views: 77

### Re: 6th edition 3.57 which resonance structures do we draw?

Also, in 3.57b) the solutions show a perchlorate ion where Chlorine has 7 bonds. How/why can Chlorine have 7 bonds?
Fri Nov 02, 2018 2:30 pm
Forum: Resonance Structures
Topic: 6th edition 3.57 which resonance structures do we draw?
Replies: 1
Views: 77

### 6th edition 3.57 which resonance structures do we draw?

The question asks: 3.57 Write the Lewis structure, including typical contributions to the resonance structure (where appropriate, allow for the possibility of octet expansion, including double bonds in different positions)... and the solutions include the Lewis structure that obeys the octet rule, b...
Fri Nov 02, 2018 2:14 pm
Forum: Lewis Structures
Topic: 6th edition 3.35b Lewis Structure of BrO-
Replies: 1
Views: 61

### 6th edition 3.35b Lewis Structure of BrO-

For the Lewis Structure of BrO-, does O carry the formal charge because it's more electronegative?
Thu Nov 01, 2018 2:44 pm
Forum: Lewis Structures
Topic: Drawing Lewis Structures
Replies: 14
Views: 677

### Re: Drawing Lewis Structures

How do we know how many resonance structures to draw?
Thu Nov 01, 2018 2:42 pm
Forum: Trends in The Periodic Table
Topic: Trends in first ionization energies
Replies: 3
Views: 128

### Re: Trends in first ionization energies

Across a period (from left to right), first ionization energy increases. This makes sense since across a period, the number of protons are increasing while the valence electrons are being added to the same energy shell (so they aren't further from the nucleus). This means the nucleus can hold onto t...
Thu Nov 01, 2018 2:35 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Oxidation Numbers
Replies: 3
Views: 214

### Re: Oxidation Numbers

When and why does hydrogen exist as hydride?
Wed Oct 24, 2018 12:38 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: How do I identify excited state through the electronic configuration
Replies: 5
Views: 1484

### Re: How do I identify excited state through the electronic configuration

Is there a specific way that the electron configuration will change when the electron is excited?
Tue Oct 23, 2018 7:36 pm
Forum: Administrative Questions and Class Announcements
Replies: 135
Views: 31332

For question 7 on worksheet 2, why is it not possible to use the eqn in the book that says v= R(1/ni ^2 - 1/nf^2). I tried this just to see if I got the same answer and I didn't. Why doesn't this work as well, because we are using frequency to get n initial? I think that it works as long as you add...
Tue Oct 23, 2018 2:46 pm
Forum: Administrative Questions and Class Announcements
Replies: 135
Views: 31332

Can someone explain what the statement in #9 of worksheet 3 means? "It is impossible to determine both the speed and position of an electron with absolute uncertainty." Why is it absolute uncertainty and not absolute certainty?
Sun Oct 21, 2018 12:15 pm
Forum: SI Units, Unit Conversions
Topic: Remembering Unit Conversions
Replies: 5
Views: 444

### Re: Remembering Unit Conversions

I think we do need to memorize the prefixes and be able to convert between them.
Thu Oct 18, 2018 11:41 pm
Forum: Photoelectric Effect
Topic: units
Replies: 12
Views: 441

### Re: units

do we need to memorize the conversion factor between Joules and eV?
Wed Oct 17, 2018 5:43 pm
Forum: General Science Questions
Topic: Midterm
Replies: 6
Views: 391

### Re: Midterm

Mon Oct 15, 2018 1:18 am
Forum: General Science Questions
Topic: Uncertainty Principle Problem
Replies: 1
Views: 194

### Uncertainty Principle Problem

Here is the problem (6th edition Example 1.7): Estimate the minimum uncertainty in (a) the position of a marble of mass 1.0 g given that its speed is known to within ±1.0 mm s^-1

In the solution, the speed is multiplied by 2. Is it because of the ±? Can someone please explain this!!!
Mon Oct 15, 2018 1:03 am
Forum: General Science Questions
Topic: Workshops
Replies: 3
Views: 229

### Re: Workshops

I would recommend going to the workshops! They help you a lot with foundational skills and are very helpful if you are totally lost on a particular concept. I think that they are just as helpful as TA office hours and that I feel more comfortable asking really basic clarifying questions during the w...
Tue Oct 09, 2018 11:19 pm
Forum: General Science Questions
Topic: Rydberg Equation n
Replies: 1
Views: 285

### Rydberg Equation n

When doing problems using the Rydberg Equation, how do you know which energy level is n1 and which is n2?

Sample question -- 6th Edition Chapter 1 #13: Use the Rydberg formula for atomic hydrogen to calculate the wavelength of radiation generated by the transition from n=4 to n=2.
Sun Oct 07, 2018 1:24 pm
Forum: General Science Questions
Topic: Problem solving, intermediate steps
Replies: 2
Views: 170

### Problem solving, intermediate steps

For the test, do we only have to show the amount of intermediate steps shown in the solutions manual?
Sun Oct 07, 2018 1:21 pm
Forum: Administrative Questions and Class Announcements
Replies: 135
Views: 31332