## Search found 69 matches

Sat Mar 16, 2019 8:31 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalyst effect on activation energy
Replies: 1
Views: 69

### Catalyst effect on activation energy

If a catalyst doubles the reaction rate, what's the new activation energy? Would it be half?
Sat Mar 16, 2019 8:15 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Frequency factor units
Replies: 2
Views: 356

### Frequency factor units

What would the units of the frequency factor be?
Sat Mar 16, 2019 7:53 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Collision model
Replies: 3
Views: 105

### Collision model

What is the collision model and activated complex model?
Sat Mar 16, 2019 7:32 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pre-equilibrium approach q
Replies: 3
Views: 349

### Pre-equilibrium approach q

Given general reaction mechanism like

Step 1 (Fast): 2A + B -> C
Step 2 (Slow): C + D -> 2E

Would the expression for the rate of formation of the product E using the pre-equilibrium approach be equal to (2k1k2/k1')[A]^2[B][D] ?

This is question 12 from Lyndon's practice final btw
Sat Mar 16, 2019 7:08 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Determining catalysts
Replies: 2
Views: 84

### Determining catalysts

If given a general reaction mechanism like

Step 1 (Fast): 2A + B -> C
Step 2 (Slow): C + D -> 2E

How do we determine what the intermediates and catalysts are?

This is question 12a on Lyndon's practice final btw
Sat Mar 16, 2019 1:03 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic cells and K
Replies: 3
Views: 116

### Re: Galvanic cells and K

Joon Chang 2F wrote:You can use the equation $ln K=\frac{nFE^{\circ}}{RT}$

Would that be the same if you're asked to find Ka?
Sat Mar 16, 2019 12:55 pm
Forum: Balancing Redox Reactions
Topic: Acidic v basic conditions
Replies: 3
Views: 130

### Acidic v basic conditions

If you're balancing redox reactions, does it matter if it's acidic or basic conditions?
Sat Mar 16, 2019 12:40 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic cells and K
Replies: 3
Views: 116

### Galvanic cells and K

If we're just given a galvanic cell with the cell potential, how do we find K for the cell?
Sat Mar 16, 2019 12:15 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Porous disk
Replies: 1
Views: 54

### Porous disk

What's the purpose of the porous disk in a concentration cell?
Fri Mar 15, 2019 9:32 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Test 2 Q 7 [ENDORSED]
Replies: 5
Views: 545

### Test 2 Q 7[ENDORSED]

Why is the change in Gibbs free energy negative when ice melts? Isn't it gaining heat or in other words, isn't delta H positive?
Fri Mar 15, 2019 9:21 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Delta G of galvanic cells
Replies: 2
Views: 280

### Delta G of galvanic cells

Why do we know that the delta G of galvanic cells will always be less than 0?
Fri Mar 15, 2019 9:08 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: When to use Nernst
Replies: 3
Views: 148

### When to use Nernst

I'm confused as to when the Nernst equation would be applicable? When do we know to use it?
Fri Mar 15, 2019 8:27 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Q6 on the midterm
Replies: 3
Views: 289

### Q6 on the midterm

For question 6 on the midterm, how do you know that the reaction will do expansion work?
Thu Mar 14, 2019 3:46 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction mechanisms and slowest step
Replies: 1
Views: 90

### Reaction mechanisms and slowest step

How do you determine which step is the fastest and which is the slowest? I'm specifically asking for the pre-equilibrium approach. Are we usually given that information? Or is there a way to figure it out with the information we're given? Like in class we were given 2NO + O2 -> 2 N02 with the observ...
Wed Mar 13, 2019 10:36 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Reducing power
Replies: 4
Views: 144

### Reducing power

How do you determine reducing and oxidation power?
Wed Mar 13, 2019 9:02 pm
Forum: Administrative Questions and Class Announcements
Replies: 7
Views: 429

When is the last day to finish posting on Chemistry Community? For it to count for points this quarter.
Mon Feb 25, 2019 10:49 pm
Forum: Balancing Redox Reactions
Topic: Solution to balancing this redox reaction
Replies: 1
Views: 84

### Solution to balancing this redox reaction

Balance the following redox reactions in acidic solution.

Br–(aq) + MnO4–(aq) -> Br2(l) + Mn2+(aq)

I got 5Br- + Mn04- + 8H+ -> 5/2(Br2) + Mn^2+ + 4H2O and I just want to know if it's correct
Mon Feb 25, 2019 10:20 pm
Forum: Balancing Redox Reactions
Topic: Oxidation number calculation
Replies: 1
Views: 63

### Oxidation number calculation

How do you find the oxidation number of certain atoms in a molecule? Are there just some oxidation numbers that are certain?
Mon Feb 25, 2019 8:17 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Vant Hoff Equation
Replies: 3
Views: 132

### Vant Hoff Equation

Will we be given the Vant Hoff equation for the test? I can't find it on the posted equation sheet
Mon Feb 25, 2019 7:55 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Value of K in Gibbs free energy equation
Replies: 3
Views: 176

### Value of K in Gibbs free energy equation

In the equation delta G = -RT*ln(K), K is the equilibrium constant right? But it's stated that a reaction is at equilibrium when delta G equals zero or when K equals 1. There are many reactions that have an equilibrium constant that is not equal to one but is in equilibrium. So I'm confused with thi...
Mon Feb 25, 2019 7:42 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs free energy at equilibrium
Replies: 2
Views: 89

### Gibbs free energy at equilibrium

Why is delta G 0 at equilibrium? I don't understand conceptually why that's the case
Mon Feb 25, 2019 7:28 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta S in relation to Gibbs free energy
Replies: 1
Views: 111

### Delta S in relation to Gibbs free energy

Why does a positive delta S favor the forward process in a reaction?
Wed Feb 13, 2019 1:03 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Practice problem help
Replies: 2
Views: 197

### Practice problem help

I was wondering if my answers are correct for this practice problem. Specifically a and c. The exothermic reaction of carbon disulfide with chlorine is as follows: CS2 (g) + 3Cl2 (g) ⇋ CCl4 (g) + S2Cl2 (g) delta H = -238 kJ Predict the effect of the following changes to the system on the direction o...
Wed Feb 13, 2019 12:20 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Delta S equations
Replies: 3
Views: 295

### Delta S equations

I'm confused about the different delta S equations. When does delta S equal q/t vs nRln(V2/V1) vs nCln(T2/T1)?
Wed Feb 13, 2019 12:11 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isothermal work
Replies: 2
Views: 1949

### Isothermal work

What does it mean that an isothermic reaction has maximum work? Why is that the maximum?
Tue Feb 12, 2019 11:18 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: When a system can only be prepared in one way
Replies: 2
Views: 375

### When a system can only be prepared in one way

What does it mean that a system can only be prepared in one way? And why does that mean S=0?
Tue Feb 12, 2019 10:51 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: n in degeneracy
Replies: 8
Views: 871

### n in degeneracy

When calculating degeneracy, does the number of available particles mean the number of UNIQUE available particles? For example would n=2 or 1 if the molecule is 02?
Tue Feb 12, 2019 10:47 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: Difference in entropy: N2 or CO
Replies: 1
Views: 320

### Difference in entropy: N2 or CO

My TA was talking about the difference in entropy when comparing N2 and CO. Why does CO have more positive entropy? N2 also has two atoms so wouldn't they be able to take up the same amount of states?
Tue Feb 12, 2019 10:36 pm
Forum: Calculating Work of Expansion
Topic: delta U = 3/2nR(delta T)
Replies: 2
Views: 579

### delta U = 3/2nR(delta T)

I have the equation delta U= 3/2 nR delta T = 0 written in my notes and I can't remember what that's in reference to. When does that equation apply?
Tue Feb 12, 2019 10:17 pm
Forum: Calculating Work of Expansion
Topic: Uses of different formulas
Replies: 3
Views: 174

### Uses of different formulas

How do I know when to use w=-pv vs w= -nrT ln(V2/V1) ?
Tue Feb 12, 2019 9:27 pm
Forum: Phase Changes & Related Calculations
Topic: Phase Change and Temperature
Replies: 3
Views: 145

### Phase Change and Temperature

Why doesn't temperature change during a phase change? I understand how to interpret the heating curve for water but why is a substance able to absorb so much heat without changing temperature?
Tue Feb 12, 2019 9:25 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 at its max
Replies: 2
Views: 330

### Degeneracy at its max

What does it mean that entropy is a maximum at equilibrium? Why is it at its maximum?
Tue Feb 12, 2019 9:24 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible v irreversible
Replies: 4
Views: 448

### Reversible v irreversible

What does it mean when an expansion is isothermal/reversible? What would be an example of an irreversible expansion?
Mon Jan 21, 2019 2:18 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: pKa confusion
Replies: 2
Views: 107

### pKa confusion

So when Ka is less than 10^-3, it is a weak acid right? So how does pKa work and what's the scale? If pKa is small, then is it a strong acid? And is it the same for pKb?
Mon Jan 21, 2019 1:32 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Strong acids and bases
Replies: 4
Views: 187

### Strong acids and bases

Are we supposed to just know the list of strong acids and bases? Or is there a way to figure out if the acid/base is strong and completely dissociates based on the chemical equation we're given?
Mon Jan 21, 2019 12:32 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Change in temperature's effect on K
Replies: 4
Views: 158

### Change in temperature's effect on K

I'm confused as to why heating will favor R formation if the reaction is exothermic. If the reaction releases heat, wouldn't the extra heat favor P formation?
Mon Jan 21, 2019 10:55 am
Forum: Administrative Questions and Class Announcements
Topic: TA posted slides (dis 1B)
Replies: 1
Views: 142

### TA posted slides (dis 1B)

So I'm in discussion 1B and my TA (Wang) posts his slides on here and I don't know how to access them. Does anyone knows what I'm supposed to specifically search for or where I can find them?
Mon Jan 21, 2019 10:43 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Pure substances
Replies: 3
Views: 125

### Pure substances

Why aren't solids and liquids included in K expression? Wouldn't it significantly change K?
Mon Jan 21, 2019 10:35 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kp vs Kc
Replies: 7
Views: 267

### Kp vs Kc

When you're calculating K and all the R and P are gases, does it really matter whether or not you use partial pressure or molar concentrations? You would get the same calculation right?
Fri Dec 07, 2018 6:49 pm
Forum: Lewis Acids & Bases
Topic: Lewis v Bronsted
Replies: 2
Views: 75

### Lewis v Bronsted

How do the different definitions of Lewis acids and Bronsted acids help us conceptualize acids and bases? Would each term be applicable in different problems?
Fri Dec 07, 2018 6:36 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: TM and oxidation states
Replies: 1
Views: 100

### TM and oxidation states

Why are transition metals able to have many oxidation states?
Fri Dec 07, 2018 5:41 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Oxidation state
Replies: 1
Views: 86

### Oxidation state

I'm confused about how to calculate the oxidation state of a molecule. I don't know if we went over rules in lecture and I just missed it? But when we were talking about the coordination number of the molecule [Fe(CN)6]^4- he mentioned that the oxidation state is +2 and I have no clue where he got t...
Fri Dec 07, 2018 5:15 pm
Forum: Sigma & Pi Bonds
Topic: Rotation
Replies: 5
Views: 442

### Rotation

What does it mean that sigma bonds allow bound atoms to rotate? What are they rotating between and why don't pi bonds allow rotation of bound atoms?
Fri Dec 07, 2018 5:01 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Hydrogen bonding
Replies: 1
Views: 115

### Hydrogen bonding

Why is hydrogen bonding one of the strongest types of intermolecular forces?
Fri Dec 07, 2018 4:49 pm
Forum: Bond Lengths & Energies
Topic: Shape of molecule
Replies: 4
Views: 353

### Shape of molecule

Why are the instantaneous dipoles in rod-shaped molecules stronger than those in spherical molecules?
Fri Dec 07, 2018 12:22 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: Interaction potential energy [ENDORSED]
Replies: 1
Views: 216

### Interaction potential energy[ENDORSED]

When would we need to calculate this on an exam? And what useful information does it provide?
Fri Dec 07, 2018 12:05 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: Induced dipole-induced dipole
Replies: 1
Views: 142

### Induced dipole-induced dipole

How does dispersion work? How can a dipole be induced then induce another?
Thu Dec 06, 2018 11:41 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polarizing power
Replies: 1
Views: 257

### Polarizing power

Which ions cause large distortions? Do the ions increase in polarizing power as they increase in atomic radius?
Thu Dec 06, 2018 11:30 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Distorted electrons
Replies: 2
Views: 352

### Distorted electrons

What does it mean that highly distorted electrons are highly polarizable?
Thu Dec 06, 2018 11:04 pm
Forum: Octet Exceptions
Replies: 2
Views: 340

So I understand that a radical is a compound with an unpaired electron but I don't understand how this occurs. Why would a radical form? Are there few compounds that can support an unpaired electron? And when Lavelle says that they only exist for a short time, what happens to them?
Thu Dec 06, 2018 10:50 pm
Forum: Trends in The Periodic Table
Topic: Expanded Valence Shells
Replies: 3
Views: 311

### Expanded Valence Shells

Which atoms accommodate more than 8 valence electrons? And why? I know that P, S, and Cl have expanded valence shells but why? And what are the others that have expanded valence shells?
Fri Nov 09, 2018 12:00 am
Forum: Trends in The Periodic Table
Replies: 3
Views: 272

Why does the atomic radius decrease across a period and increase down a group? I'm confused about the relationship between electrons/shells and size.
Thu Nov 08, 2018 11:52 pm
Forum: Ionic & Covalent Bonds
Topic: Proportionality of bond strength
Replies: 3
Views: 255

### Proportionality of bond strength

Why isn't a double bond twice as strong as a single bond? It seems like there isn't a linear relationship between the amount of bonds and bond strength. Why is that?
Thu Nov 08, 2018 11:49 pm
Forum: Ionic & Covalent Bonds
Topic: Bond strength and state of matter
Replies: 2
Views: 145

### Bond strength and state of matter

Is there an explicit relationship between the strength of a bond and whether it's a solid, liquid, or gas?
Fri Nov 02, 2018 12:54 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Probability of finding an electron
Replies: 1
Views: 107

### Probability of finding an electron

I don't quite understand how you would calculate the probability of finding an electron. I understand that it's psi squared but what does that mean exactly? What would you need to know to calculate that?
Fri Nov 02, 2018 12:51 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Ionization energy
Replies: 1
Views: 179

### Ionization energy

Why is removing a second electron always harder than the first? Does this logic apply to the third electron, meaning the third is even harder to remove than the second?
Fri Nov 02, 2018 12:47 am
Forum: Formal Charge and Oxidation Numbers
Topic: 6th edition: 3.23
Replies: 1
Views: 99

### 6th edition: 3.23

How can chlorine exist in both positive and negative oxidation states? And how do you find the maximum and negative oxidation number that chlorine can have?
Fri Nov 02, 2018 12:32 am
Forum: Trends in The Periodic Table
Topic: Group 13 elements
Replies: 1
Views: 66

### Group 13 elements

In lecture, Lavelle said that group 13 elements need 5 electrons to complete their octet. What does this mean? They only need 5 electrons in total or need 5 more to complete an octet?
Fri Nov 02, 2018 12:28 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Degenerate orbitals
Replies: 3
Views: 175

### Degenerate orbitals

Can someone explain the definition of degenerate orbitals? How do you find how many degenerate orbitals a specific orbital has?
Fri Oct 26, 2018 1:06 am
Forum: *Shrodinger Equation
Topic: Schrodinger and quantum numbers
Replies: 3
Views: 455

### Schrodinger and quantum numbers

How does Schrodinger's equation related to orbitals and quantum numbers?
Fri Oct 26, 2018 12:01 am
Forum: DeBroglie Equation
Topic: Measurable wavelength properties
Replies: 5
Views: 285

### Measurable wavelength properties

Lavelle worked through an example in class about the wavelength of a car moving at a certain velocity. He asked if the car has "any measurable wavelength properties." What does that mean and how do you determine if there are measurable wavelength properties?
Thu Oct 25, 2018 10:56 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: H spectrum
Replies: 3
Views: 204

### H spectrum

What does it mean that the empirical equation En= -hr/n^2 only works for the H spectrum?
Thu Oct 25, 2018 10:54 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Bohr frequency condition v empirical equation for H atom
Replies: 1
Views: 197

### Bohr frequency condition v empirical equation for H atom

I'm confused in regard to the connection between the Bohr frequency condition and the empirical equation for H-atom. Do they give you the same solution? The change in energy? And you just use either one depending on what information you're given? Or are they two separate, unconnected formulas?
Fri Oct 12, 2018 3:35 am
Forum: Significant Figures
Topic: sig figs urgent question!
Replies: 12
Views: 928

### Re: sig figs urgent question!

Zeros between non zero digits are always significant
Fri Oct 12, 2018 3:31 am
Forum: Significant Figures
Topic: Atlantic Pacific Rule
Replies: 2
Views: 942

### Re: Atlantic Pacific Rule

If there's a decimal point, start counting digits from the left starting with the first non-zero digit. If there isn't a decimal point, start counting digits from the right side starting with the first non-zero digit. Just think of a map: Pacific = left, Atlantic = right.
Fri Oct 12, 2018 3:28 am
Forum: Empirical & Molecular Formulas
Topic: F13
Replies: 3
Views: 323

### F13

F 13 asks for the name of the compound for which we find the empirical and molecular compound. Are we expected to know how to determine the name of compounds given this information? If so, what are the rules for the nomenclature?
Fri Oct 05, 2018 3:04 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: 6th edition: E15
Replies: 2
Views: 125

### 6th edition: E15

E. 15 asks "The molar mass of the metal hydroxide M(OH)2 is 74.10 g*mol-1. What is the molar mass of the sulfide of this metal?"

I'm confused by the term "sulfide" in this question. Is there a typo in the book or can a sulfide refer to something other than the anion of sulfur?
Fri Oct 05, 2018 2:20 am
Forum: Significant Figures
Topic: Scientific Notation
Replies: 7
Views: 247

### Scientific Notation

How do we know when to write solutions using scientific notation? I usually do so as a default but when checking the solutions manual, I noticed that sometimes answers like (for example) .0623 is left just like that and not written as 6.23 * 10^2. Is there a reason for that? Are there specific rules...
Fri Oct 05, 2018 2:15 am
Forum: SI Units, Unit Conversions
Topic: E23 (6th Edition)
Replies: 4
Views: 137

### Re: E23 (6th Edition)

Yes, you're right. You would only have to use Avagadro's number if it asked you to calculate the number of molecules or formula units as it did in question E21. In this case, the question is just asking for the number of moles so no need to use Avagadro's number.