## Search found 51 matches

Mon Mar 12, 2018 11:35 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Chapter 14 #117
Replies: 1
Views: 163

### Re: Chapter 14 #117

I believe nF = -deltaG/E is derived from the equation deltaG = -nFE. However, I am not sure how we are supposed to know that It = nF. I think we would be given this equation if needed on an exam.
Mon Mar 12, 2018 11:27 pm
Forum: General Rate Laws
Topic: 15.99 (e)(f)
Replies: 3
Views: 235

### Re: 15.99 (e)(f)

I think this is because k and temperature are not directly proportional (they change at different rates), whereas rate and concentration are directly proportional for a reaction that is first order in A (rate = k[A]).
Mon Mar 12, 2018 11:09 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.49
Replies: 1
Views: 149

### Re: 8.49

I think we always assume standard conditions (298K, 1atm) unless stated otherwise.
Sun Mar 11, 2018 8:20 pm
Forum: Reaction Mechanisms, Reaction Profiles
Replies: 2
Views: 226

Hi,

The steady state approximation method assumes that one of the intermediates in the reaction method is consumed as quickly as it is generated. Its concentration remains the same throughout the reaction.
Sun Mar 11, 2018 8:18 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Proposed Reaction Mechanisms
Replies: 1
Views: 153

### Proposed Reaction Mechanisms

How do we know if our proposed reaction mechanism is the correct one?
Sun Mar 11, 2018 8:05 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediates
Replies: 3
Views: 267

### Intermediates

How do we determine the best species to propose as an intermediate?
Sun Mar 04, 2018 8:58 pm
Forum: General Rate Laws
Topic: Instantaneous Rate
Replies: 3
Views: 278

### Re: Instantaneous Rate

Hi,

I believe the rate of reaction is used to calculate the speed at which the concentration changes over a period of time (delta[A] / delta t), while the instantaneous rate of change is used to calculate the rate of reaction at a single point.
Sun Mar 04, 2018 8:54 pm
Forum: Zero Order Reactions
Topic: Initial concentrations
Replies: 2
Views: 230

### Re: Initial concentrations

Hi,

I believe zero order, first order, and second order all depend on initial concentration when calculating rate laws.
Sun Mar 04, 2018 8:49 pm
Forum: First Order Reactions
Topic: Derivations
Replies: 6
Views: 426

### Re: Derivations

Hello,

So far, Dr. Lavelle has never asked for derivations on our exams, so I do not expect that he will for this week's test.
Thu Feb 22, 2018 11:22 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Current
Replies: 2
Views: 180

### Re: Current

The formula for the current (I) is:

I = deltaG / -(Et)
Thu Feb 22, 2018 11:13 pm
Forum: Balancing Redox Reactions
Topic: 14.5a
Replies: 2
Views: 231

### Re: 14.5a

Hi,

I think this may actually be a typo in the solutions manual. If I am not mistaken, they should have used the same phase (aq) for both.

Please correct me if I'm wrong!
Thu Feb 22, 2018 11:09 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams [ENDORSED]
Replies: 7
Views: 474

### Cell Diagrams[ENDORSED]

What is the purpose of inert electrodes in galvanic cells? (i.e. Pt)

Thanks!
Fri Feb 16, 2018 9:39 pm
Forum: Balancing Redox Reactions
Topic: Oxidizing vs. Reducing Agent
Replies: 7
Views: 451

### Oxidizing vs. Reducing Agent

How do we determine which species is the oxidizing / reducing agent?
Fri Feb 16, 2018 9:35 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.9
Replies: 1
Views: 176

### Re: 14.9

I believe we have to balance the redox reaction and see how many moles of electrons are transferred in the equation.
Fri Feb 16, 2018 9:25 pm
Forum: Balancing Redox Reactions
Topic: 14.3 Balancing redox reactions
Replies: 2
Views: 233

### Re: 14.3 Balancing redox reactions

The last step is to balance the charges. You currently have a charge of -2 on the left side of the reaction, and a charge of 2(-2) + 10 = +6 on the right side of the reaction. Adding 8 electrons to the products side will balance the charges. Your final balanced reaction will be: S2O3(2-) + 5H2O -> 2...
Sun Feb 11, 2018 11:21 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Entropy
Replies: 6
Views: 424

### Re: Entropy

The vibrational motion causes disorder, so entropy increases. Diatomic molecules would cause greater entropy because the dissolution of polyatomic molecules results in a greater number of particles than the dissolution of monatomic molecules.
Sun Feb 11, 2018 11:07 pm
Forum: Van't Hoff Equation
Topic: Different versions of van't Hoff
Replies: 2
Views: 313

### Re: Different versions of van't Hoff

Hi,

I think we would determine which equation to use based on the information we are given and what we are trying to solve for.
Sun Feb 11, 2018 10:59 pm
Forum: Calculating Work of Expansion
Topic: different ways to calculate w
Replies: 4
Views: 294

### Re: different ways to calculate w

Hi,

I believe the first equation is used when the system is at equilibrium (constant pressure) and the second is used when the pressure is changing.
Sun Feb 04, 2018 11:24 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Test 1 Question
Replies: 4
Views: 365

### Re: Test 1 Question

Hi,

The system is isolated because the question states that the cooler is "ideal." An IDEAL cooler would be perfectly insulated and would not exchange any matter or energy with its surroundings (we would not find such a cooler in the real world).
Sun Feb 04, 2018 11:15 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Calculations on Internal Energy
Replies: 4
Views: 411

### Re: Calculations on Internal Energy

Hi,

The midterm will most likely cover everything we've learned so far, so that would include internal energy and work calculations.
Sun Feb 04, 2018 11:13 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta S vs Delta U [ENDORSED]
Replies: 5
Views: 1206

### Re: Delta S vs Delta U[ENDORSED]

Hi,

Delta S is the change in entropy and delta U is the change in internal energy.
Sun Feb 04, 2018 11:12 pm
Forum: Van't Hoff Equation
Topic: Friday Lecture:
Replies: 2
Views: 379

### Re: Friday Lecture:

Hello, In Friday's lecture, Dr. Lavelle went over the derivation of the formula delta G (standard) = -RTlnK. He then discussed the values of K that make delta G positive, negative, and equal to zero. He also taught us how to derive the equation lnK = (-deltaH/RT) + (deltaS/R) by manipulating formula...
Sun Jan 28, 2018 3:01 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Distribution
Replies: 3
Views: 220

### Re: Distribution

It is important to consider the different possible microstates when determining degeneracy (w) because degeneracy is defined as the number of different arrangements that allow for a given energy state.
Sun Jan 28, 2018 2:57 am
Forum: Calculating Work of Expansion
Topic: The integral equation
Replies: 8
Views: 410

### Re: The integral equation

We used integrals to derive the work equations because when systems are at equilibrium, changes within them occur infinitesimally. The integral allows us to sum together all of these small steps to calculate the total work. As mentioned above, the integrals were only used for the formula derivations...
Sun Jan 28, 2018 2:32 am
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: Positional Entropy
Replies: 2
Views: 996

### Re: Positional Entropy

Hello!

Positional entropy refers to the number of molecular positions or arrangements that a system can have, whereas thermal entropy refers to the amount of thermal energy that is not available for any useful work.
Sun Jan 21, 2018 1:37 am
Forum: Calculating Work of Expansion
Topic: Lecture notes , work eqn
Replies: 3
Views: 196

### Re: Lecture notes , work eqn

Yes, I think we only use this equation when the system is at constant pressure (delta P = 0)!
Sun Jan 21, 2018 1:14 am
Forum: Phase Changes & Related Calculations
Topic: Equations to know
Replies: 6
Views: 270

### Re: Equations to know

Hello,

Based on my experience in Lavelle's 14A class, we will be provided with what we need to know.
Sun Jan 21, 2018 12:56 am
Forum: Calculating Work of Expansion
Topic: Reversible vs Isothermal
Replies: 3
Views: 290

### Reversible vs Isothermal

Can someone please clarify the definitions of and differences between reversible and isothermal expansion? Thanks!
Sun Jan 14, 2018 2:10 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Reaction Enthalpy vs. Enthalpy of Formation
Replies: 2
Views: 186

### Reaction Enthalpy vs. Enthalpy of Formation

Hello,

Can someone please clarify the differences between reaction enthalpy and enthalpy of formation? Thanks!
Sun Jan 14, 2018 2:06 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Internal Energy
Replies: 2
Views: 131

### Internal Energy

Hello,

I am having difficulty understanding the concept of internal energy and its importance in determining enthalpy. Can someone please clarify this for me? Thanks!
Sun Jan 14, 2018 1:34 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Extensive vs Intensive Property
Replies: 3
Views: 153

### Re: Extensive vs Intensive Property

Hi,

Extensive properties depend on the amount of matter in a sample, whereas intensive properties do not. For example, volume is an extensive property and density is an intensive property. Hope this helps!
Fri Dec 08, 2017 10:35 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Determining Denticity
Replies: 2
Views: 731

### Determining Denticity

Hi, I know this question has already been asked, but I am still unsure about this topic. How do we determine whether a molecule is monodentate, bidentate, etc. based on its formula? The examples given in review session were solved using Lewis structures, but I do not understand how we can know the s...
Fri Dec 08, 2017 10:21 pm
Forum: Hybridization
Topic: Bond Notation
Replies: 3
Views: 301

### Re: Bond Notation

Hi,

If I remember correctly, it was said in a review session today that that number indicates the row on the periodic table. C is in the second row, so a 2 is placed in front of the hybridization. Please correct me if I'm wrong!
Sun Nov 26, 2017 6:54 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: 11.13 Part C
Replies: 2
Views: 247

### Re: 11.13 Part C

Hi,

For reactions in the gas phase I think it is better to write Q in terms of partial pressures.
Sun Nov 26, 2017 6:44 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angle
Replies: 2
Views: 167

### Re: Bond Angle

Hi,

Unless we are given this information, we cannot know the exact angles. It is enough to say that the angle is slightly less than 109.5.

Hope this helps!
Sun Nov 19, 2017 4:10 pm
Forum: Lewis Structures
Topic: Lewis Structure of CO
Replies: 2
Views: 216

### Re: Lewis Structure of CO

Hi,

Adding onto the previous reply, you have to find the structure with formal charges closest to zero while also obeying the octet rule. Simply positioning the electrons in a way to get the charges to zero is incorrect. I hope this helps.
Sun Nov 19, 2017 4:01 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Listing all Bond Angles
Replies: 2
Views: 207

### Re: Listing all Bond Angles

Hi,

I think we should list all of the bond angles present in the molecule.
Wed Nov 08, 2017 9:08 pm
Forum: Resonance Structures
Topic: Resonance Structures for the Midterm
Replies: 3
Views: 404

### Re: Resonance Structures for the Midterm

I think we just draw the most stable structure based on formal charge unless the problem specifically asks for resonance structures. I am not entirely sure, though.
Wed Nov 08, 2017 8:57 pm
Forum: Octet Exceptions
Topic: 3.55
Replies: 3
Views: 257

### Re: 3.55

Hi,

Radicals have unpaired electrons. To determine which of these species are radicals, we simply calculate the number of valence electrons that each has; those with an odd number of electrons will have an unpaired electron and therefore be a radical species. Answer choices b and c are radicals.
Wed Nov 08, 2017 8:54 pm
Forum: Lewis Structures
Topic: Polyatomic Ions
Replies: 1
Views: 146

### Polyatomic Ions

Just to confirm, we are not expected to have polyatomic ions memorized for the midterm, correct? Thank you!
Fri Nov 03, 2017 10:04 pm
Forum: Lewis Structures
Topic: 33 Part C
Replies: 1
Views: 128

### Re: 33 Part C

Hi,

I believe the central atom is the one with the lowest electronegativity, not the lowest ionization energy. In this case, the least electronegative element is nitrogen.

Hope this helps.
Fri Nov 03, 2017 9:51 pm
Forum: Quantum Numbers and The H-Atom
Topic: Angular Momentum Quantum Number
Replies: 1
Views: 249

### Re: Angular Momentum Quantum Number

The g subshell is simply the next subshell and it has nine orbitals for a total of eighteen electrons. I think that there aren't currently any known elements whose ground-state configurations reach the g subshell.
Fri Oct 27, 2017 11:38 pm
Forum: Trends in The Periodic Table
Topic: Metals, Nonmetals, and Semimetals/Metalloids
Replies: 2
Views: 284

### Re: Metals, Nonmetals, and Semimetals/Metalloids

Most of the periodic tables I've seen are color coded for these categories. I believe this is just something we memorize or will have given to us.
Fri Oct 27, 2017 9:10 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Tl3+ electron configuration
Replies: 2
Views: 2336

### Re: Tl3+ electron configuration

Hello!

I think this is because the three electrons removed from Tl to form Tl3+ are taken from the highest energy orbitals 6s and 6p. Therefore, the Tl configuration [Xe]4f14 5d10 6s2 6p1 will become [Xe]4f14 5d10.

Someone please correct me if I'm wrong!
Fri Oct 20, 2017 4:31 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Orbital Energy Levels
Replies: 3
Views: 259

### Re: Orbital Energy Levels

Hello! Yes, the 4s orbital has a higher energy than the 3d orbital.
Fri Oct 20, 2017 12:41 am
Forum: Photoelectric Effect
Topic: Textbook 1.38
Replies: 1
Views: 177

### Re: Textbook 1.38

Hello! For this problem, we use the de Broglie equation lambda = h/(mv). If the distance travelled in one second is equal to wavelength, this means that the velocity is equal to wavelength. We figure this out using the formula d = vt (distance = velocity x time): d = vt = v(1 s) = lambda -> v = lamb...
Fri Oct 13, 2017 5:17 pm
Forum: General Science Questions
Topic: What is Rydberg's Constant?
Replies: 1
Views: 845

### Re: What is Rydberg's Constant?

I believe these different values for the Rydberg's Constant are equivalent, simply differing in their units. The 3.28 x 10^15 value is in Hz, and the 1.09 x 10^7 is in m-1. We use the first value for the equation E = -hR/n^2.
Fri Oct 13, 2017 5:08 pm
Forum: Properties of Light
Topic: Exited state
Replies: 5
Views: 496

### Re: Exited state

Yes; the electron must gain energy in order to jump up an energy level (i.e. by absorbing light).
Thu Oct 05, 2017 9:10 pm
Forum: Empirical & Molecular Formulas
Topic: Caproic Acid Question
Replies: 3
Views: 2688

### Re: Caproic Acid Question

I converted the 0.512g of CO2 to moles of CO2, converted the moles of CO2 to moles of C, and the moles of C to grams of C. I then calculated the mass of H by going through these same steps for the H2O. This gave me 0.140g C and 0.0234g H. I then calculated for the mass of O by subtracting the masses...
Thu Oct 05, 2017 4:58 pm
Forum: Empirical & Molecular Formulas
Topic: Mass Percent Composition
Replies: 4
Views: 373

### Re: Mass Percent Composition

It is not necessary to calculate the percent compositions or use a 100g sample. After converting the given masses to moles, you will then divide each one by the smallest value. This will give you a ratio of the atoms relative to each other, which is all you need to write an empirical formula. Hope t...
Wed Oct 04, 2017 7:41 pm
Forum: Empirical & Molecular Formulas
Topic: Molarity and Dilution (G25)
Replies: 3
Views: 496

### Re: Molarity and Dilution (G25)

My approach for this problem utilized the key concept that dilutions do not change the number of moles of solute in a solution. Assuming that the amount of X will remain the same after the 90 dilutions, I simply calculated for moles by multiplying the starting 0.10M molarity by the starting .010L vo...