Search found 61 matches

by Christine Wastila 1H
Fri Mar 16, 2018 3:03 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Collision Theory
Replies: 3
Views: 180

Re: Collision Theory

Lecture outline 4 says that we need to be able to explain how the collision model and activated complex model account for the temperature dependence of reactions.
by Christine Wastila 1H
Thu Mar 15, 2018 5:19 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: emf
Replies: 3
Views: 147

Re: emf

Remember also that emf represents the maximum potential difference.
by Christine Wastila 1H
Sun Mar 11, 2018 2:52 pm
Forum: *Organic Reaction Mechanisms in General
Topic: HW 15.67
Replies: 1
Views: 301

Re: HW 15.67

This ratio determines the factor by which the catalyst increases the rate of reaction.
by Christine Wastila 1H
Sun Mar 11, 2018 2:43 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: HW 15.45
Replies: 2
Views: 105

Re: HW 15.45

Yes, AB is is the intermediate because it is produced in one reaction and consumed in another. It is completely consumed.
The overall reaction is: 2AC+B -> A2B+2C. Therefore, A2B is not formed using AB as a reactant.
by Christine Wastila 1H
Sat Mar 10, 2018 1:13 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediate and rate law [ENDORSED]
Replies: 3
Views: 138

Re: Intermediate and rate law [ENDORSED]

If a compound or element is both produced and used up, it is an intermediate regardless of how reactive it may be. Most intermediates are very reactive, which is why they are typically short-lived molecules that quickly convert to a more stable form. In other words, they are used up fast.
by Christine Wastila 1H
Sat Mar 10, 2018 1:02 pm
Forum: *Enzyme Kinetics
Topic: Chapter 15 [ENDORSED]
Replies: 3
Views: 163

Re: Chapter 15 [ENDORSED]

Yes. Although test 3 only went to 15.6, the final will cover the rest (except 15.9).
by Christine Wastila 1H
Fri Mar 09, 2018 9:03 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: Negative k? [ENDORSED]
Replies: 4
Views: 299

Re: Negative k? [ENDORSED]

I don't think so. Rate is always a positive value, and since rate=k[A], then k cannot be negative.
by Christine Wastila 1H
Fri Mar 09, 2018 9:00 am
Forum: Zero Order Reactions
Topic: Half Lives? [ENDORSED]
Replies: 7
Views: 428

Re: Half Lives? [ENDORSED]

Yes because that would indicate that the species has undergone two half-lives.
by Christine Wastila 1H
Thu Mar 08, 2018 1:30 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Homework Problems
Replies: 3
Views: 183

Re: Homework Problems

The test covers 15.1-15.6, which corresponds with homework problems up to 45 (and some integrated exercises).
by Christine Wastila 1H
Thu Mar 08, 2018 1:28 pm
Forum: Second Order Reactions
Topic: Half Life for First Order vs Second Order
Replies: 5
Views: 373

Re: Half Life for First Order vs Second Order

1st order reaction: t1/2=0.693/k
2nd order reaction: t1/2=1/(k[A]0)

both can be found on the constants and equations sheet :)
by Christine Wastila 1H
Wed Mar 07, 2018 6:16 pm
Forum: Student Social/Study Group
Topic: Test 3
Replies: 3
Views: 328

Re: Test 3

The other two responses are correct, but check the integrated exercises as well if you want some more practice.
by Christine Wastila 1H
Wed Mar 07, 2018 6:11 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Elementary Steps for Reaction Mechanisms
Replies: 2
Views: 109

Re: Elementary Steps for Reaction Mechanisms

I think we would be given the steps and asked to analyze whether the proposed mechanism is valid (i.e. whether or not it agrees with the experimentally determined rate law). The example from lecture today is probably a good indication of what future problems will be like.
by Christine Wastila 1H
Tue Mar 06, 2018 5:23 pm
Forum: *Enzyme Kinetics
Topic: Catalyst
Replies: 6
Views: 406

Re: Catalyst

I assume you mean in a chemical equation. In this case, since catalysts are neither reactants nor products, they are written above the arrow. If that's not given, I think it would have to be stated in the problem.
by Christine Wastila 1H
Tue Mar 06, 2018 5:17 pm
Forum: General Rate Laws
Topic: Coefficients
Replies: 6
Views: 202

Re: Coefficients

They do not affect the rate law as written: rate=k[A]order (i.e. you would not input different values than those given for concentration or oder because of the stoichiometric coefficients).
by Christine Wastila 1H
Tue Mar 06, 2018 12:08 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Determining Reaction Mechanism
Replies: 2
Views: 100

Re: Determining Reaction Mechanism

Also remember that the rate law is determined by the slow step, so if the rate law is given, you know which one is the slow step because they have to correspond.
by Christine Wastila 1H
Tue Mar 06, 2018 12:05 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: reaction mechanism
Replies: 1
Views: 75

Re: reaction mechanism

We may not always be told explicitly, but it will be obvious by the information given. For example, if we are told the rate law, than we know which one is the slow step because they have to correspond.
by Christine Wastila 1H
Tue Feb 27, 2018 4:47 pm
Forum: Administrative Questions and Class Announcements
Topic: Test 3
Replies: 6
Views: 291

Test 3

I saw on Dr. Lavelle’s website that test 3 will cover 15.1-15.6. Which homework problems does this material align with? I think I have an idea, but I just want to be sure I don’t leave anything out.
by Christine Wastila 1H
Mon Feb 26, 2018 5:59 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Activation Energy???
Replies: 7
Views: 256

Re: Activation Energy???

Both of the other replies are correct, but I have one thing to add for clarity. The source of activation energy is usually heat, so reactions with a higher activation energy have a slower rate because it takes longer for the reactant molecule(s) to absorb enough heat in order to form products.
by Christine Wastila 1H
Sat Feb 24, 2018 8:11 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cells
Replies: 5
Views: 186

Re: Galvanic Cells

If E is negative, then the process is called electrolysis, which is where an electric current is used to drive a non-spontaneous reaction. In a Galvanic cell, chemical energy is converted to electrical energy. The opposite is true of electrolysis.
by Christine Wastila 1H
Sat Feb 24, 2018 8:05 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Trends in Increasing Reducing Ability
Replies: 5
Views: 251

Re: Trends in Increasing Reducing Ability

I think you would want to compare using two equations where the amount of electrons transferred is the same.
by Christine Wastila 1H
Sat Feb 24, 2018 7:58 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Calculating n in the Nernst Equation
Replies: 2
Views: 366

Re: Calculating n in the Nernst Equation

Since you have different amounts of electrons being transferred, you want to find the least common multiple of those two coefficients. In the case of 3 and 2, the least common multiple is 6. So multiply the reaction with 3 electrons on the reactant side by 2 and multiply the reaction with 2 electron...
by Christine Wastila 1H
Thu Feb 22, 2018 1:17 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cathode vs Anode
Replies: 4
Views: 178

Re: Cathode vs Anode

The anode is on the left and the cathode is on the right. Solids are always on the outside (add Pt if none) and aqueous are closest to the salt bridge (I don’t think order matters if there are multiple).
by Christine Wastila 1H
Sat Feb 10, 2018 9:49 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Homework problem 9.25: orientations of a molecule
Replies: 2
Views: 104

Re: Homework problem 9.25: orientations of a molecule

You don't necessarily have to draw out each form, but having a model of at least one of them will help you visualize how many different arrangements the molecule has. Drawing all of them can check your answer if you have time.
by Christine Wastila 1H
Sat Feb 10, 2018 9:32 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Third law
Replies: 3
Views: 129

Re: Third law

The third law states that at 0K, the entropy of a perfect crystal is 0. Therefore, as T approaches 0, entropy also approaches 0. limT->0S=0.
by Christine Wastila 1H
Sat Feb 10, 2018 9:27 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Commas in Cell Diagram
Replies: 2
Views: 108

Re: Commas in Cell Diagram

Just to add on, notation for the salt bridge would be ||
by Christine Wastila 1H
Sat Feb 03, 2018 12:31 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Problem 9.13
Replies: 4
Views: 177

Re: Problem 9.13

9.13 is listed in the solution manual errors page on the class website. It should be C instead of R for calculating entropy change due to a change in temperature.
by Christine Wastila 1H
Sat Feb 03, 2018 12:24 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Question 3b on the test
Replies: 4
Views: 197

Re: Question 3b on the test

The question asked if work was done. We know this is true for this situation because W=-PdeltaV. Since the volume of the balloon decreased, deltaV is negative, which shows that work was done on the system (the balloon).
by Christine Wastila 1H
Sat Feb 03, 2018 12:07 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: deltaG at equilibrium
Replies: 5
Views: 128

Re: deltaG at equilibrium

If given concentration or pressure, you could calculate Q and compare it to K if that value is given.
by Christine Wastila 1H
Thu Jan 25, 2018 3:17 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: constant pressure
Replies: 5
Views: 187

Re: constant pressure

That statement refers to the enthalpy of a reaction.
by Christine Wastila 1H
Thu Jan 25, 2018 3:10 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: exothermic vs endothermic [ENDORSED]
Replies: 7
Views: 323

Re: exothermic vs endothermic [ENDORSED]

Calorimeters are not isolated systems. Bomb calorimeters are able to exchange heat with the surroundings, therefore classifying them as closed systems.
by Christine Wastila 1H
Thu Jan 25, 2018 3:07 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: Molar Entropy vs Residual molar entropy
Replies: 2
Views: 113

Re: Molar Entropy vs Residual molar entropy

The Boltzmann equation relates entropy to the number of microstates. A microstate is one of many possible molecular arrangements for a given substance. More of these microstates indicate higher entropy.
by Christine Wastila 1H
Sat Jan 20, 2018 11:46 am
Forum: Calculating Work of Expansion
Topic: What exactly is reversible expansion?
Replies: 2
Views: 133

Re: What exactly is reversible expansion?

Just so you know, this won't be on the first test, and Dr. Lavelle said we would cover this topic in week 3.
by Christine Wastila 1H
Sat Jan 20, 2018 11:42 am
Forum: Administrative Questions and Class Announcements
Topic: Week 3 Test Topic is endorsed
Replies: 37
Views: 1807

Re: Week 3 Test Topic is endorsed

In terms of numbered problems, the only ones I see that have isothermal reversible expansion are 8.11 part B and 8.12 part B, so just omit those.
by Christine Wastila 1H
Sat Jan 20, 2018 11:38 am
Forum: Calculating Work of Expansion
Topic: 8.13 - Understanding the Solution
Replies: 2
Views: 126

Re: 8.13 - Understanding the Solution

The answer, 1626 kJ refers to how much work can be done by the fuel in the cylinder. You subtract 947 kJ because this amount of energy was lost to the surroundings as heat.
by Christine Wastila 1H
Fri Jan 12, 2018 4:07 pm
Forum: Administrative Questions and Class Announcements
Topic: Homework grading
Replies: 6
Views: 279

Re: Homework grading

Sara Varadharajulu wrote:I think what she means (as this was the same for me too), if you do you homework in pencil for example, get something wrong and correct it in pen, and turn in that marked up homework, you still get full credit.

Yes, this is what I meant :)
by Christine Wastila 1H
Fri Jan 12, 2018 3:48 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Different Molar Heat Capacities For Gases
Replies: 5
Views: 218

Re: Different Molar Heat Capacities For Gases

Cv denotes the heat capacity of a gas at a constant volume while Cp denotes the heat capacity of a gas at constant pressure. We have two values because, when heating takes place at constant pressure, some of the heat is used to do expansion work rather than raise the temperature of the system. For a...
by Christine Wastila 1H
Fri Jan 12, 2018 3:29 pm
Forum: Administrative Questions and Class Announcements
Topic: Homework grading
Replies: 6
Views: 279

Re: Homework grading

It's ok if you try one and get it wrong as long as you correct your answer. Last quarter, I would do my corrections in another color if needed, which earned me full credit.
by Christine Wastila 1H
Thu Dec 07, 2017 10:29 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: pKb and pKa
Replies: 1
Views: 156

Re: pKb and pKa

Lower values of pKa or pKb relate to stronger acids and stronger bases, respectively. So to answer your question, no. An extremely weak base would have a high pKb value.
by Christine Wastila 1H
Wed Dec 06, 2017 11:10 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Factors Affecting K [ENDORSED]
Replies: 2
Views: 148

Re: Factors Affecting K [ENDORSED]

The equilibrium constant is only changed by temperature. However, the reaction quotient Q may be more or less than K depending on if the reaction is at equilibrium or not.
by Christine Wastila 1H
Tue Dec 05, 2017 11:33 am
Forum: Lewis Acids & Bases
Topic: 12.15 part B
Replies: 1
Views: 102

12.15 part B

This is more of a Lewis structure question. Why is the structure for SO2 drawn with a single bond on one of the oxygen + 6 valence electrons and a double bond on the other + 4 valence electrons rather than double bonds on both + 4 valence electrons? I have it with S in the middle + a lone pair and t...
by Christine Wastila 1H
Mon Dec 04, 2017 10:34 am
Forum: Bronsted Acids & Bases
Topic: Bronsted and Lewis acid definitions?
Replies: 3
Views: 232

Re: Bronsted and Lewis acid definitions?

Whether or not something is an acid or base does not change no matter what definition you use, but the Bronsted/Lewis definitions focus on different characteristics. Bronsted acids donate protons while Bronsted bases accept them. Lewis acids accept electron pairs while Lewis bases donate them. Howev...
by Christine Wastila 1H
Thu Nov 30, 2017 9:53 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: drawing coordination compounds
Replies: 5
Views: 235

Re: drawing coordination compounds

I think if the total molecule has a charge, you should bracket it and indicate the charge like you would with any other Lewis structure.
by Christine Wastila 1H
Thu Nov 30, 2017 9:49 pm
Forum: Hybridization
Topic: When?
Replies: 2
Views: 185

Re: When?

To summarize, the number of orbitals should match the regions of electron density. So if you have AX4 or AX3E, it would be sp3 (1 s orbital + 3 p orbitals=4 total) because there are 4 regions of electron density in both cases even though one of those regions is a lone pair in the latter example.
by Christine Wastila 1H
Thu Nov 30, 2017 9:37 pm
Forum: Sigma & Pi Bonds
Topic: Sigma and Pi bonds
Replies: 5
Views: 305

Re: Sigma and Pi bonds

To give you a quick answer:
single bond=1 sigma bond
double bond=1 sigma and 1 pi bond
triple bond=1 sigma and 2 pi bonds
by Christine Wastila 1H
Thu Nov 30, 2017 9:32 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Dipole moments
Replies: 2
Views: 139

Re: Dipole moments

Be sure to make sure that the dipoles do not cancel, though. This can be determined by looking at the VSEPR model. For example, CO2 is nonpolar because of its linear form even though O is more electronegative than C. Since the dipoles are directly across from each other, they cancel.
by Christine Wastila 1H
Thu Nov 30, 2017 9:29 pm
Forum: Dipole Moments
Topic: Determining polar or non polar: 4.27
Replies: 2
Views: 188

Re: Determining polar or non polar: 4.27

Look for sizable differences in electronegativity. For example, C-H bonds do not cause partial charges because there is not a large difference in electronegativity between C and H. However, a C-N bond or a C-Cl bond could cause polarity because N and Cl are more electronegative than C, causing a par...
by Christine Wastila 1H
Wed Nov 29, 2017 10:47 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Change in Equilibrium for Aqueous Solutions
Replies: 2
Views: 167

Re: Change in Equilibrium for Aqueous Solutions

I think since Kp only applies to gaseous equilibria, changes in pressure would not cause changes in aqueous equilibria.
by Christine Wastila 1H
Wed Nov 29, 2017 10:34 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Monodentate vs Bidentate etc. [ENDORSED]
Replies: 7
Views: 1126

Re: Monodentate vs Bidentate etc. [ENDORSED]

Monodentate ligands only have one electron donor atom that binds with the central atom/ion. Thus, they are only attached at one point. Polydentate ligands are able to attach to the central atom/ion multiple times due to the presence of multiple electron donor atoms. In many cases, ligands are monode...
by Christine Wastila 1H
Mon Nov 27, 2017 4:28 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Ligands
Replies: 2
Views: 124

Re: Ligands

Just to add on, ligands can be mono- or polydentate depending on how many donor atoms they have. A ligand with one donor atom can bind to the central atom once, making it monodentate. A ligand with multiple donor atoms can bind with the central atom more then once, making it polydentate.
by Christine Wastila 1H
Mon Nov 27, 2017 4:02 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Q [ENDORSED]
Replies: 7
Views: 488

Re: Q [ENDORSED]

Q is the reaction quotient. By comparing this value to K, we can determine how the reaction will progress. If Q<K, the formation of products will be favored. If Q>K, the formation of reactants will be favored. If Q=K, then the reaction is at equilibrium.
by Christine Wastila 1H
Mon Nov 20, 2017 10:31 am
Forum: Naming
Topic: Oxidation State vs. Formal Charge
Replies: 3
Views: 215

Re: Oxidation State vs. Formal Charge

In response to the previous comment, yes, that is possible. A positive oxidation number represents how many electrons an atom can accept, while a negative oxidation number represents how many electrons an atom can donate.
by Christine Wastila 1H
Mon Nov 20, 2017 10:27 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Why do lone pairs take up more space than bonds?
Replies: 5
Views: 1868

Re: Why do lone pairs take up more space than bonds?

Just to add on, because lone pairs have a stronger negative charge than bonding pairs, they cause a higher degree of repulsion, which is why they appear to take up more space.
by Christine Wastila 1H
Mon Nov 20, 2017 10:24 am
Forum: Naming
Topic: Anionic Ligand Naming
Replies: 2
Views: 122

Re: Anionic Ligand Naming

I believe Dr. Lavelle said that the book uses a newer convention, but both are correct.
by Christine Wastila 1H
Wed Nov 01, 2017 8:25 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Quantum Number m
Replies: 1
Views: 113

Re: Quantum Number m

There are two m values: ml and ms (l and s are subscripts). ml describes which orbital in a subshell an electron occupies and ms describes the spin. Depending on which orbital and which subshell the electron is in, ml will have one of these values. s: ml=o (one possible orbital) p: ml=-1,0,+1 (px, p...
by Christine Wastila 1H
Wed Nov 01, 2017 8:05 pm
Forum: Quantum Numbers and The H-Atom
Topic: Multiple Electron Atoms
Replies: 2
Views: 182

Re: Multiple Electron Atoms

Effective nuclear charge is the net charge an electron experiences in a multiple electron atom. Shielding occurs when electrons in the inner shells prevent electrons in the outer shells from feeling the full positive charge of the nucleus. Thus, electrons closer to the nucleus have a higher effectiv...
by Christine Wastila 1H
Fri Oct 20, 2017 6:22 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Orbital Energy Levels
Replies: 3
Views: 181

Re: Orbital Energy Levels

The 4s orbital is lower energy than the 3d orbital for Ca and K because they do not have electrons in the 3d state. However, after the 4s orbital is occupied and electrons enter the 3d state, 3d is then lower energy than 4s. For example, the electron configuration for Scandium is Sc: [Ar] 3d1 4s2.
by Christine Wastila 1H
Fri Oct 20, 2017 6:15 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 3d And 4s Orbital Energy Levels [ENDORSED]
Replies: 3
Views: 279

Re: 3d And 4s Orbital Energy Levels [ENDORSED]

4s is lower energy than 3d for Ca and K because they do not have any electrons in the d block. After the 4s orbital is occupied and electrons enter the 3d state, 3d is then lower energy than 4s. That is why electrons in the 3d block are listed before those in 4s when writing the electron configurati...
by Christine Wastila 1H
Fri Oct 13, 2017 6:40 pm
Forum: Photoelectric Effect
Topic: Lyman Series v Balmer series
Replies: 2
Views: 213

Re: Lyman Series v Balmer series

Just to add on, since the Lyman series have a shorter wavelength, they indicate that a greater amount of energy is being absorbed (because E=hv, v=c/wavelength). If you recall the model from lecture, this means the electrons are making a bigger "jump", such as from the first level to the s...
by Christine Wastila 1H
Fri Oct 13, 2017 6:30 pm
Forum: Photoelectric Effect
Topic: Post Assessment #28 [ENDORSED]
Replies: 4
Views: 254

Re: Post Assessment #28 [ENDORSED]

You need to divide the work function by Avogadro's number (6.022x10^23) because the it was given in kJ/mol and the question asks about the energy needed to remove one electron from ONE sodium atom, not a mole of them. I got confused on that, too! Hope this helps.

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