## Search found 50 matches

Sat Mar 17, 2018 4:27 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Q7b Lyndon's Review
Replies: 6
Views: 299

### Re: Q7b Lyndon's Review

Unique rate is 1/a*(d[A]/dt)
Fri Mar 16, 2018 12:17 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.103
Replies: 1
Views: 203

### 9.103

In question 9.103 it asks A scientist proposed the following two reactions to produce ethanol, a liquid fuel: C2H4 (g) + H20 (g) -> CH3CH2OH (l) C2H6 (g) + H20 (g) -> CH3CH2OH (l) + H2 (g) Assume standard-state conditions and determine if either reaction is thermodynamically spontaneous. Does anyone...
Wed Mar 14, 2018 1:11 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: question 15.79 b
Replies: 1
Views: 241

### question 15.79 b

Can anyone explain why kinetics controls reactions at lower temperatures, but not higher ones? The explanation doesn't make sense in the book (reference 15.79).
Sun Mar 11, 2018 7:13 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: SN2
Replies: 3
Views: 184

### Re: SN2

It's a good example of a substitution reaction.
Sun Mar 11, 2018 7:12 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius equation for 2 temperatures
Replies: 2
Views: 155

### Re: Arrhenius equation for 2 temperatures

Probably just with one temperature since that's all we've discussed in class (and that's all that's on the constants sheet now).
Sun Mar 11, 2018 7:10 pm
Forum: Second Order Reactions
Topic: Half life of second order reactions
Replies: 8
Views: 702

### Re: Half life of second order reactions

Either way, I'm pretty sure the 2nd order half life equation is on the constants and equations sheets on our tests.
Fri Mar 02, 2018 1:19 pm
Forum: General Rate Laws
Topic: Determining Order [ENDORSED]
Replies: 8
Views: 343

### Re: Determining Order[ENDORSED]

The first few homework problems are also solid practice for determining reaction order.
Fri Mar 02, 2018 1:17 pm
Forum: First Order Reactions
Topic: After Integration [ENDORSED]
Replies: 3
Views: 217

### Re: After Integration[ENDORSED]

Also you can think about k as the slope of the graph for (in this case) ln[A] vs t. The slope of the line will be -k.
Fri Mar 02, 2018 1:14 pm
Forum: Zero Order Reactions
Topic: Units of k [ENDORSED]
Replies: 13
Views: 525

### Re: Units of k[ENDORSED]

For a 1st order reaction, k units = s^-1
2nd order reaction, k units = L/(mol*s)
and increasing the powers of L and mol as you go up in reaction order so that rate will be in unit of mol/(L*s)
Fri Mar 02, 2018 1:11 pm
Forum: General Rate Laws
Topic: Question 15.39 [ENDORSED]
Replies: 4
Views: 231

### Re: Question 15.39[ENDORSED]

Any of the integrated rate laws relate reaction rate to time.
Fri Mar 02, 2018 1:10 pm
Forum: First Order Reactions
Topic: First Order Graph
Replies: 11
Views: 497

### Re: First Order Graph

Josh Moy 1H wrote:A proper first order graph is just a straight decreasing line?

Yes, if you're graphing ln[A] vs time. All the "proper" graphs are going to look like straight lines, but the order depends on what's on the y-axis.
Fri Mar 02, 2018 1:08 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Average rate [ENDORSED]
Replies: 6
Views: 543

### Re: Average rate[ENDORSED]

^And because we assume this, we also assume that products are being removed from the system in order to ignore the reverse reaction.
Mon Feb 19, 2018 3:06 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 14.9
Replies: 1
Views: 144

### Re: 14.9

Half reactions have 6 electrons, which is 6 mols of electrons, so n=6.
Red: 6Fe3+ + 6e- --> 6Fe2+
Ox: 2Cr3+ --> Cr2O7 2- + 6e-
Mon Feb 19, 2018 3:04 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.13 part D
Replies: 2
Views: 161

### 14.13 part D

The skeleton equation was Au+(aq) + --> Au(s) + Au3+(aq). Can someone explain why the the anode half reaction is Au3+(aq) + 3e- -> Au(s)?
Sun Feb 18, 2018 9:28 pm
Forum: Balancing Redox Reactions
Topic: Skeletal equation
Replies: 2
Views: 120

### Re: Skeletal equation

Seems like it. In the textbook when they give us skeletal equations, they're also not balanced for atoms.
Sun Feb 11, 2018 8:30 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: q vs delta H
Replies: 2
Views: 167

### Re: q vs delta H

They're different -- q is heat, and deltaH is change in enthalpy, so they shouldn't be interchangeable.
Sun Feb 11, 2018 8:29 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Which is more stable: Fe3O4 or Fe2O3?
Replies: 2
Views: 222

### Re: Which is more stable: Fe3O4 or Fe2O3?

Not sure what you mean by "stable", but larger compounds are typically heavier, which means they'd have a larger degeneracy and therefore more entropy. So Fe3O4 should have a higher entropy.
Sun Feb 11, 2018 8:26 pm
Forum: Phase Changes & Related Calculations
Topic: calculating a phase change in a reaction
Replies: 5
Views: 322

### Re: calculating a phase change in a reaction

If you're calculating heat, I think you're always supposed to include the phase change?
Sun Feb 04, 2018 6:12 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.35 [ENDORSED]
Replies: 5
Views: 245

### Re: 9.35[ENDORSED]

It is saying a has more molecules, and more molecules in a container means more entropy change.
Sun Feb 04, 2018 6:06 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.35
Replies: 4
Views: 153

### Re: 9.35

If there are more molecules, there can be more movement, so more entropy change.
Mon Jan 29, 2018 10:40 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: 9.23 Determining what has higher entropy state
Replies: 4
Views: 263

### 9.23 Determining what has higher entropy state

Which would you expect to have a higher molar entropy at T = 0, single crystals of BF3 or of COF2? Why?
I don't really understand the explanation at the back of the book for this one.
Sun Jan 28, 2018 11:54 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: The second law ?
Replies: 3
Views: 163

### Re: The second law ?

The 2nd law of thermodynamics relates entropy change to heat and temperature, and part of what we now know is that if heat is constant, entropy change will be greater at lower temperatures than at higher ones.
Sun Jan 28, 2018 11:49 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.7
Replies: 2
Views: 148

### Re: 9.7

Example 9.2 on page 322 of the textbook also talks about this if you want a textbook reference!
Mon Jan 22, 2018 11:02 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: HW 8.99
Replies: 2
Views: 205

### HW 8.99

For 8.99, why do we have to calculate the limiting reagent? The problem is as follows: Hydrochloric acid oxidizes zinc metal in a reaction that produces hydrogen gas and chloride ions. A piece of zinc metal of mass 8.5 g is dropped into an apparatus containing 800.0 mL of 0.500 m HCl(aq). If the ini...
Mon Jan 15, 2018 3:57 pm
Forum: Phase Changes & Related Calculations
Replies: 3
Views: 156

Also, when we discuss enthalpies, we're talking about heat released or absorbed in chemical reactions.
Mon Jan 15, 2018 3:51 pm
Forum: Phase Changes & Related Calculations
Topic: Types of Systems
Replies: 10
Views: 633

### Re: Types of Systems

Also for reference, an open system can exchange both matter and energy with its surroundings (e.g. a car engine).
Mon Jan 15, 2018 3:49 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Units of Pressure
Replies: 3
Views: 251

### Re: Units of Pressure

In 14A the conversions were on the constants sheet given to us on tests, though I can't say whether we'll have to memorize them for this class.
Sat Jan 13, 2018 5:06 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond enthalpies
Replies: 2
Views: 129

### Re: Bond enthalpies

We can use bond enthalpies to calculate the deltaH of a reaction as well.
Sat Jan 13, 2018 5:03 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Specific Heat
Replies: 2
Views: 130

### Re: Specific Heat

Also if you find that you're missing more than one variable, it's possible that the specific heat value can be found in a table in the reading (possibly 8.2).
Sat Jan 13, 2018 5:01 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Closed System
Replies: 7
Views: 352

### Re: Closed System

Another example of an isolated system from the textbook is a hot liquid poured into a thermos/container with insulated walls.
Sat Dec 09, 2017 5:16 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 12.33 question
Replies: 1
Views: 190

### Re: 12.33 question

Because it's asking for the [OH-] after the person diluted the 5.00mL of the stock solution to 500 mL.
Sat Dec 09, 2017 5:10 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Remembering VSEPR
Replies: 3
Views: 514

### Remembering VSEPR

Does anyone have any tricks for remembering VSEPR shapes?
Sat Dec 09, 2017 12:50 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: mole ratio with solids
Replies: 2
Views: 303

### Re: mole ratio with solids

Do I use mole ratio when solids are in equation to determine which way it will favor. Example, A(s) <--> B(g) + C(g) If volume is decreased, would I say the reaction favors reactants because mole ratio is (0:2) I would say that if the volume is decreased, it means the molarity of the products goes ...
Sat Dec 09, 2017 12:40 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: calculating pH
Replies: 3
Views: 265

### Re: calculating pH

I recall in Friday lecture, Dr.Lavelle was talking about how if the concentration of H3O+ is less than 10^-7, the solution then the solution is considered neutral. He brought up numbers like 0.0000001 M H3O+ and 0.0000000001 M H3O+ and he said that if you take the negative log of the smaller number...
Sun Dec 03, 2017 4:23 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Notes on 11.37
Replies: 3
Views: 342

### Notes on 11.37

In question 11.37, eq.3 = 1/2eq1, and the K of eq.3 = (K of eq.1)^1/2. Eq.4 = 2eq.1, and K of eq. 4 = (K of eq. 1)^2. Is this pattern actually a rule?
Sun Dec 03, 2017 4:11 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Graphing
Replies: 1
Views: 134

### Re: Graphing

In lecture we learned that K remains constant unless the temperature changes, so its graph would look like a straight line. You might be able to plot Q over time and compare the values to K at each given time.
Sat Nov 25, 2017 11:07 am
Forum: Naming
Topic: Naming (steps)
Replies: 6
Views: 363

### Re: Naming (steps)

The roman numeral is the oxidation state of the transition metal. You determine that based on the overall charge of the compound, and on the individual charges of everything else in the compound.
Sat Nov 25, 2017 11:04 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Question about ATP lecture example
Replies: 1
Views: 133

### Question about ATP lecture example

In class we assumed that the initial ADP and Pi concentrations were ≈0, and ignored the sig figs. How would taking the initial concentrations into account change the way we did the problem?
Thu Nov 16, 2017 3:49 pm
Forum: Dipole Moments
Topic: 4.29b
Replies: 2
Views: 162

### 4.29b

The question asks out of 3 sample molecules which one has the largest dipole moment. How do we determine relative dipole magnitudes based on structure without numbers?
Wed Nov 15, 2017 10:36 pm
Forum: Photoelectric Effect
Topic: Midterm question [ENDORSED]
Replies: 6
Views: 456

### Re: Midterm question[ENDORSED]

@Leah No, it's not. So it's asking us to consider that the work functions of metal are unique to each metal, and that increasing the frequency still may not overcome that specific metal's work function.
Sun Nov 12, 2017 4:27 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Textbook Problem Chp 4 #9
Replies: 3
Views: 191

### Re: Textbook Problem Chp 4 #9

The shape is trigonal planar because you determine molecular shape by the number of bonding pairs on the central atom. When you then factor in the lone pairs, they bonded e- and lone pair e- repel each other and the molecular shape becomes T-shaped, changing the angle to less than 90º.
Wed Nov 08, 2017 9:07 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Nodes on the Midterm?
Replies: 4
Views: 326

### Re: Nodes on the Midterm?

Not sure about the types of nodes, but in one of the review sessions I remember one of the TAs saying something about just knowing what the electron density around a node is.
Sun Nov 05, 2017 8:50 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angle of OCLO
Replies: 2
Views: 229

### Re: Bond Angle of OCLO

I think trigonal planar
Sun Nov 05, 2017 8:48 pm
Forum: Empirical & Molecular Formulas
Topic: textbook problem M.22
Replies: 1
Views: 201

### textbook problem M.22

In the 9/4 Fundamentals review session, we went over problem M.22 from the textbook, which reads: A compound produced as a by-product in an industrial synthesis of polymers was found to contain carbon, hydrogen, and iodine. A combustion analysis of 1.70 g of the compound produced 1.32 g of CO2 and 0...
Fri Oct 27, 2017 3:58 pm
Forum: Resonance Structures
Topic: Formal charge question
Replies: 3
Views: 296

### Formal charge question

In class today, we said the sulfate ion with the double bonds was the best representation based on formal charge. Why was this?
Sun Oct 22, 2017 3:14 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: nodal planes [ENDORSED]
Replies: 3
Views: 475

### nodal planes[ENDORSED]

What is important/what do we need to know about nodal planes in the atomic orbitals?
Sun Oct 22, 2017 3:07 pm
Forum: Trends in The Periodic Table
Topic: Atomic Size Trend [ENDORSED]
Replies: 4
Views: 266

### Re: Atomic Size Trend[ENDORSED]

As you go down and left across the periodic table, atomic radius will increase. I think the reason the radius increases as you go down is because quantum numbers increase, and therefore valence electrons will begin to occupy higher levels. As the quantum number increases, electrons are held further ...
Sun Oct 15, 2017 5:45 pm
Forum: Properties of Electrons
Topic: De Broglie Equation
Replies: 3
Views: 288

### De Broglie Equation

Would anyone be able to explain/go through the derivation of the De Broglie equation? I know we don't necessarily need to know it but it would help my understanding.
Sat Oct 14, 2017 5:29 pm
Forum: Quantum Numbers and The H-Atom
Topic: Photoelectric effect post assessment problem 34 [ENDORSED]
Replies: 1
Views: 169

### Photoelectric effect post assessment problem 34[ENDORSED]

If molybdenum is irradiated with 194 nm light, what is the maximum possible kinetic energy of the emitted electrons? We're given in the last problem that that Molybdenum metal absorbs radiation with minimum frequency of 1.09x10^15 s^-1. I also calculated the minimum energy (E=hv) is 7.22 x 10^-9 J. ...
Wed Oct 11, 2017 12:19 pm
Forum: Properties of Light
Topic: Rydberg's Formula
Replies: 4
Views: 343

### Rydberg's Formula

The numbers involved in Rydberg's formula v = R{(1/n1^2)-(1/n2^2)} make sense to me, but, in words, what does the formula tell you?