## Search found 58 matches

Fri Mar 16, 2018 9:03 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: Degeneracy
Replies: 1
Views: 208

### Degeneracy

How do you find total degeneracy? And what does that tell you about the system?
Fri Mar 16, 2018 9:00 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: S and delta S
Replies: 4
Views: 381

### S and delta S

Can someone tell me the difference between S (like in the Boltzmann equation) and delta S besides the fact that delta S is the change in entropy? How would we find S?
Wed Mar 14, 2018 8:37 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Oxidation Power
Replies: 3
Views: 183

### Oxidation Power

Does a large value for oxidation power mean a more positive reduction potential or is it the other way around?
Wed Mar 14, 2018 8:36 pm
Forum: Phase Changes & Related Calculations
Topic: Test 1 Question 7
Replies: 1
Views: 169

### Test 1 Question 7

In order to make iced-tea a 50g ice cube at 0C is added to 500mL of tea at 20C. What is the final temperature of the iced tea once it has reached thermal equilibrium. Assume that no heat is transferred to or from the surroundings. The density of water (and iced tea) is 1g/mL over the range 0C-20C. C...
Wed Mar 14, 2018 8:20 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Midterm Question 6A
Replies: 2
Views: 235

### Midterm Question 6A

For question 6A on the midterm, are answers A and B both correct? If so, could someone explain why A is valid?
Wed Mar 14, 2018 8:18 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Positive or Negative Entropy
Replies: 2
Views: 264

### Positive or Negative Entropy

On the midterm for question 2B, I know that the entropy would be positive but can someone explain the actual reasoning behind that?
Wed Mar 14, 2018 8:15 pm
Forum: General Rate Laws
Topic: Test 3 Question 6
Replies: 1
Views: 127

### Test 3 Question 6

A 1st order reaction is allowed to proceed for 2 hours. Then it is determined that at this time that 76.6% of the initial concentration of reactants remain. Determine what chemical reaction is occurring and at what temperature the reaction is occurring. (There is a table included in the test if you ...
Wed Mar 14, 2018 8:13 pm
Forum: General Rate Laws
Topic: Test 3 Question 8
Replies: 1
Views: 138

### Test 3 Question 8

In a 2nd order reaction, a reactant has a known half-life of 3 minutes and an initial concentration of 5M. How much time will it take for the concentration of this reactant to drop to 2M? Could someone explain each step to solve this problem?
Wed Mar 14, 2018 7:54 pm
Forum: General Rate Laws
Topic: Unimolecular
Replies: 5
Views: 456

### Unimolecular

Could someone explain the uni- bi- molecular concept again? Does unimolecular have to be first order and bimolecular, second order?
Tue Mar 13, 2018 10:00 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate Determining Step
Replies: 2
Views: 193

### Rate Determining Step

If a reaction has multiple mechanisms which means multiple slow steps, would the rate determining step be the whole mechanism or just the slow step of that particular mechanism depending on the rates given?
Tue Mar 13, 2018 9:45 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pre-Equilibirum Approach
Replies: 1
Views: 68

### Pre-Equilibirum Approach

I'm still a little unclear about the pre-equilibirum approach so could anyone explain this simply?
Tue Mar 13, 2018 9:43 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Energy Diagrams
Replies: 1
Views: 142

### Energy Diagrams

When looking at energy diagrams, how would you know which peak is the rate-determining step? Is it the highest peak because that's the highest activation energy?
Tue Mar 13, 2018 9:41 pm
Forum: *Alkanes
Topic: Multiple Functional Groups [ENDORSED]
Replies: 2
Views: 687

### Multiple Functional Groups[ENDORSED]

So my TA mentioned that one element could be involved in multiple functional groups at the same time. Is there an example of this?
Tue Mar 13, 2018 9:27 pm
Forum: Reaction Mechanisms, Reaction Profiles
Replies: 2
Views: 189

Could someone explain steady state approximation and in what scenarios it would be used?
Tue Mar 06, 2018 12:35 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Which compound to use
Replies: 3
Views: 190

### Which compound to use

If you're given and end reaction and told to find the individual steps, how would you know what compound to use as the intermediate? Or would you be given that information already?
Mon Mar 05, 2018 11:17 pm
Forum: General Rate Laws
Topic: Concentration and Rate Relationship
Replies: 4
Views: 277

### Concentration and Rate Relationship

In a second order reaction, if one reactant alone is doubled does that mean the rate is quadrupled? What happens if two reactants in a second order reaction are both doubled?
Wed Feb 28, 2018 1:41 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: Dependence on Concentration
Replies: 2
Views: 186

### Dependence on Concentration

So I know that the rate constant and equilibrium constant both depend on the concentrations, but what is the relationship between the two besides that? If we have one, can we calculate the other?
Wed Feb 28, 2018 1:39 am
Forum: General Rate Laws
Topic: Orders of Reactions
Replies: 1
Views: 143

### Orders of Reactions

What information does the order of a reaction give us? Can someone give me a rundown of the context?
Tue Feb 20, 2018 1:18 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Hydrogen Electrode
Replies: 1
Views: 72

### Re: Standard Hydrogen Electrode

I believe it's used as a standard to compare electron transfer. Since we can not measure electron transfer of one cell, we compare the electron transfer of all cells through half-reactions with respect to the standard hydrogen electrode.
Tue Feb 20, 2018 1:12 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Max Potential
Replies: 1
Views: 99

### Max Potential

Can someone explain why max potential is when there is very little current flow?
Tue Feb 20, 2018 1:11 am
Forum: Balancing Redox Reactions
Topic: Oxidation Agents
Replies: 4
Views: 198

### Re: Oxidation Agents

Oxidizing agents are being reduced and reducing agents are being oxidized because if the substance is being reduced, that must mean its gaining electrons from somewhere which means it's causing another substance to lose electrons. This is why the one being reduced is called an oxidizing agent. Just ...
Tue Feb 13, 2018 10:33 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Endothermic Favorable?
Replies: 2
Views: 775

### Endothermic Favorable?

Why are endothermic reactions not favorable at high temperatures?
Tue Feb 13, 2018 10:27 pm
Forum: Calculating Work of Expansion
Topic: Free Expansion
Replies: 1
Views: 168

### Free Expansion

When you have expansion in a vacuum, is it always free expansion and no work is being performed?
Tue Feb 06, 2018 10:36 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: monatomic ideal gasses
Replies: 2
Views: 229

### Re: monatomic ideal gasses

To my knowledge, the only monoatomic gases that are stable in ideal conditions are the noble gases.
Tue Feb 06, 2018 10:34 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: W
Replies: 3
Views: 193

### Re: W

W is the number of ways of achieving a given energy state, aka the number of possible microstates. Consider two elements with the same energy in a flask, the microstates could be AB on one side, BA on one side, A on the left and B on the right, or B on the left and A on the right. This makes W=4 bec...
Wed Jan 31, 2018 3:08 pm
Forum: Phase Changes & Related Calculations
Topic: Example in Lecture
Replies: 4
Views: 256

### Example in Lecture

In the example during lecture (at what temp is Br(l) to Br(g) spontaneous at 1 atm), why do we ask the question at what temp is deltaG negative? And then why do we find the temperature when deltaG=0 later on if we're trying to make deltaG negative?
Mon Jan 29, 2018 11:28 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Perfect Crystal in terms of Entropy
Replies: 2
Views: 104

### Re: Perfect Crystal in terms of Entropy

I think that in terms of entropy, a perfect crystal has entropy=0 because all the molecules are lined up perfectly. All the molecules are uniform and no matter how you arrange the molecules, they'll still fit perfectly. Since this is true, there is no "disorder" and this foundation makes u...
Mon Jan 29, 2018 11:22 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: unit of entropy
Replies: 11
Views: 557

### Re: unit of entropy

The units are Joules per Kelvin (J/K).
Tue Jan 23, 2018 3:51 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Mean Bond Enthalpy
Replies: 2
Views: 183

### Mean Bond Enthalpy

Would the difference between using the average bond enthalpies to calculate enthalpy of reaction and using specific bond enthalpies be significant? Or would they give nearly the same result in calculation?
Tue Jan 23, 2018 12:03 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Work Done On or By System
Replies: 1
Views: 164

### Work Done On or By System

How do you differentiate between whether work is done ON a system or BY the system?
Fri Jan 19, 2018 12:02 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy [ENDORSED]
Replies: 3
Views: 119

### Re: Enthalpy[ENDORSED]

Enthalpy is a way to measure energy in a thermodynamic system, it's the total heat content of a system or the internal energy of the system plus the product of pressure and volume. It's also a state function which means it does not depend on the pathway. When a reaction occurs, heat is either releas...
Thu Jan 18, 2018 9:41 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.67
Replies: 3
Views: 155

### Re: 8.67

We know that the products are all in the liquid state, so now we consider the states of the reactants needed to make those products. For example, we get liquid H2O from O2 and H2. Both of these diatomic elements are in the gaseous state because elements like to be in the most stable phase at 1 atm a...
Fri Jan 12, 2018 5:56 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity vs Specific Heat
Replies: 2
Views: 164

### Heat Capacity vs Specific Heat

I know that the Specific Heat Capacity is the one used in calculations because it's intensive, but would there be any occasion we would use the Heat Capacity for calculations instead?
Fri Jan 12, 2018 5:54 pm
Forum: Phase Changes & Related Calculations
Topic: Heating Curve
Replies: 3
Views: 205

### Heating Curve

Could some please clarify why there are plateaus in a heating curve when there is a phase change? Heat is being added so why isn't there a china in temperature represented until the next phase is reached?
Sat Dec 09, 2017 1:59 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Polarity
Replies: 2
Views: 210

### Re: Polarity

For example, if there is a positive charge on the central atom, and a negative charge on one bonded atom does that mean those charges cancel each other regardless of another atom attached to the central atom without a pull on it?
Sat Dec 09, 2017 1:56 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Polarity
Replies: 2
Views: 210

### Polarity

If a compound has a linear shape, how do you determine polarity or non-polarity? Is there a sure fire method?
Sat Dec 09, 2017 1:31 am
Forum: Ionic & Covalent Bonds
Topic: Ionic Character
Replies: 2
Views: 244

### Ionic Character

Why does CO2 have a greater ionic character than CS2?
Tue Dec 05, 2017 11:42 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Bond Length
Replies: 1
Views: 164

### Bond Length

I know that longer bonds mean weaker bonds and more acidity. In the course reader it says that H2O is less acidic than H2Te because H2O has a shorter bond since it's in period 2 and Te is in period 5. Does H2Te have a weaker bond because Te is not as electronegative as O?
Mon Nov 27, 2017 11:03 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Chemical Equilibrium True/False
Replies: 2
Views: 749

### Chemical Equilibrium True/False

Determine whether the following statements are true or false:
a. When chemical equilibrium is reached, the composition of the reaction mixture remains constant.
b. If we make a reaction go faster, we can increase the amount of product at equilibrium.
Mon Nov 27, 2017 10:57 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Chemical Equlibrium
Replies: 1
Views: 163

### Re: Chemical Equlibrium

A. One number that gives us information about the relative concentrations of reactant and product.
Tue Nov 21, 2017 7:34 pm
Forum: Naming
Topic: HW 17.31 b
Replies: 4
Views: 287

### Re: HW 17.31 b

I think the (III) refers to the Cobalt and not the chloride. So your formula is correct, just take out the subscript 3 on the Cl.
Tue Nov 21, 2017 7:30 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Chelate
Replies: 1
Views: 153

### Re: Chelate

I believe that's usually true but there are exceptions. For example a bidentate ligand such as ethylenediamine can bind to a metal such as Ni^2+ to form a five-membered ring with is a chelate ring. But complexes that contain polydentate ligands are called chelate complexes. Polydentate ligands are s...
Sun Nov 19, 2017 6:42 pm
Forum: Coordinate Covalent Bonds
Topic: Quiz 4 and Final [ENDORSED]
Replies: 1
Views: 302

### Quiz 4 and Final[ENDORSED]

Will we need to know how to name complex coordinate compounds or just be able to recognize them? If yes, is there any simple way to remember all the IUPAC prefixes and rules?
Sun Nov 19, 2017 6:39 pm
Forum: Lewis Structures
Topic: Lewis Structures
Replies: 3
Views: 333

### Re: Lewis Structures

My logic with how to place the atoms was that C likes to have four bonds, Oxygen likes to have two, and Hydrogen likes to have one bond (this is what I learned as the HONC guideline in high school chemistry). With this in mind, if you put the two O's and the H around the C, then the number of bonds ...
Thu Nov 09, 2017 2:07 am
Forum: Lewis Acids & Bases
Topic: Lewis Acid or Base: AlCl3 [ENDORSED]
Replies: 3
Views: 2865

### Lewis Acid or Base: AlCl3[ENDORSED]

How would you know the Al atom in aluminum chloride is a Lewis Acid? I read somewhere else that if you calculate the formal charge and it's positive, then it's a Lewis acid because it wants to accept electrons. But when I calculated the formal charge for Al, I got 0 so how would you know if Al was a...
Wed Nov 08, 2017 12:37 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Bond Length Order [ENDORSED]
Replies: 1
Views: 199

### Bond Length Order[ENDORSED]

If you're given B2^+, B2, B2^-, and B2^2- how would you know how to order them from shortest bond length to longest bond length using the molecular orbital theory?
Mon Nov 06, 2017 11:21 am
Forum: Determining Molecular Shape (VSEPR)
Topic: For the test vsepr and lewis
Replies: 3
Views: 230

### Re: For the test vsepr and lewis

Tetrahedral named molecules do not have lone pairs on the central atom which means there are four electron density regions and all four of those regions are occupied by atoms. In trigonal pyramidal molecules, there is one lone pair on the central atom which means only 3 out of the 4 regions are occu...
Fri Nov 03, 2017 12:24 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Problem for a Peer Learning Session
Replies: 3
Views: 278

### Re: Problem for a Peer Learning Session

Yes, you're correct. The electron configuration would be 1s^2 2s^2 2p^6 3s^2 3p^6 3d^8 because of the absence of 4s^2 due to the 2+ charge.
Fri Nov 03, 2017 12:21 pm
Forum: Lewis Structures
Topic: Midterm
Replies: 4
Views: 231

### Re: Midterm

Yes, that is correct. All material up until October 25th will be covered so basically Fundamentals up until the end of Chapter 3.
Fri Nov 03, 2017 12:16 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: For the test vsepr and lewis
Replies: 3
Views: 230

### Re: For the test vsepr and lewis

The VSEPR name of CH4 is tetrahedral where there are all bonded pairs. Trigonal pyramidal would be three bonded pairs and one lone pair of electrons such as NH3. A lewis structure is a representation of the structure but I do not think they have names if that's what you're asking. Hope this helped!
Fri Oct 27, 2017 9:58 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Stable Lewis Structures
Replies: 1
Views: 197

### Stable Lewis Structures

We talked about the different ways to draw SO4^2- and worked out how the structure with double bonds was more stable than the structure with only single bonds. But are both technically correct Lewis structures?
Fri Oct 27, 2017 9:55 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Formal Charge [ENDORSED]
Replies: 1
Views: 227

### Formal Charge[ENDORSED]

I know formal charge indicates the gain or loss of electrons while forming covalent bonds but does that mean it indicates the gain/loss of electrons in the molecule as a whole or each atom separately?
Tue Oct 17, 2017 1:24 am
Forum: Einstein Equation
Topic: Chapter 1 Question 25 [ENDORSED]
Replies: 4
Views: 478

### Chapter 1 Question 25[ENDORSED]

Sodium vapor lamps, used for public lighting, emit yellow light of wavelength 589 nm. How much energy is emitted by (a) an excited sodium atom when it generates a photon (b) 5.00 mg of sodium atoms emitting light at this wavelength (c) 1.00 mol of sodium atoms emitting light at this wavelength So fo...
Tue Oct 17, 2017 1:08 am
Forum: *Shrodinger Equation
Topic: Upcoming Test
Replies: 4
Views: 451

### Upcoming Test

Should we know how to do Shrodinger Equation problems for the upcoming test? Or do we just need the De Broglie Equation and the Heisenberg Uncertainty principle?
Fri Oct 13, 2017 10:52 am
Forum: Photoelectric Effect
Topic: Kinetic energy equal to zero?
Replies: 4
Views: 954

### Re: Kinetic energy equal to zero?

Hi! From what I know, if the work function (threshold energy to remove electrons) is equal to the energy of the photon then no electrons are ejected which means there’s no excess energy and kinetic energy equals 0. I believe that the problems will usually tell you that no electrons were ejected or t...
Wed Oct 11, 2017 9:51 pm
Forum: Properties of Electrons
Topic: Series
Replies: 6
Views: 567

### Series

For series problems on tests like Lyman, Balmer, etc. do we need to know the exact wavelengths each series corresponds to or do we just need to remember what n-levels they are associated with?
Thu Oct 05, 2017 1:57 pm
Forum: Empirical & Molecular Formulas
Topic: Mass Percent Composition
Replies: 4
Views: 339

### Re: Mass Percent Composition

How I approached F13 was to find the mass percent composition first. So 4.14g P/27.8g solid * 100 comes out to be 14.89% which means Cl makes up 85.11% of the compound. With this you can assume, 100 grams and find the moles and then the atomic ratio from there. Finding empirical formulas almost alwa...
Tue Oct 03, 2017 12:59 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Fundamentals E Question 35 [ENDORSED]
Replies: 2
Views: 382

### Fundamentals E Question 35[ENDORSED]

The decay of teeth can be slowed by the use of fluoridated toothpaste. The fluoride ions convert the hydroxyapatite, Ca5(PO4)3OH, in tooth enamel into fluorapatite, Ca5(PO4)3F. If all the hydroxyapatite is converted into fluorapatite, by what percentage does this conversion increase the mass of the...