## Search found 61 matches

Sun Mar 17, 2019 3:12 pm
Forum: Calculating Work of Expansion
Topic: Work in a System
Replies: 4
Views: 304

### Work in a System

Under what conditions is work equal to 0? What is delta U in this case?
Tue Mar 12, 2019 1:34 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow Step
Replies: 6
Views: 169

### Slow Step

Are we going to be asked to identify the slow step in a given reaction, or will this information be given to us in the problem?
Tue Mar 12, 2019 1:31 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Frequency Factor
Replies: 1
Views: 64

### Re: Frequency Factor

I think orbital shapes come into it, but it gets more complex after the s orbital. Basically a frequency factor refers to collisions between molecules that will have the correct angle to cause a reaction, like the example in class with bromine. They have to line up in the right orientation, but sinc...
Tue Mar 12, 2019 12:05 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Electrolysis
Replies: 1
Views: 96

### Re: Electrolysis

I don't believe we've covered overpotential yet.
Sun Mar 10, 2019 2:58 pm
Forum: General Science Questions
Topic: Math question
Replies: 2
Views: 291

### Re: Math question

To get something out of a log, you use the base of the log for each side and raise to the power of each side of the equation. So for log base ten, you would make each side an exponent with base 10. For your example, you would get 10^(logx) = 10^8. Since the base and the log base are the same, everth...
Sun Mar 10, 2019 2:54 pm
Forum: General Rate Laws
Topic: Units pseudo rate law
Replies: 2
Views: 99

### Re: Units pseudo rate law

I believe it depends on the order of the reaction. For example, for a second order rate constant rate = k[A][B], if we assume B is in large excess, then we can say rate = k'[A] where k' = k[B]. In this case, the units of k are 1/M*s, so when we multiply this by the concentration of B we get 1/s as t...
Sun Mar 10, 2019 2:44 pm
Forum: Zero Order Reactions
Topic: Zero Order Reactions
Replies: 1
Views: 85

### Zero Order Reactions

Since a zero order reaction implies that the rate is not dependent on the concentration of reactants, can any reaction be a zero order reaction in the presence of a catalyst, regardless of how many reactants there are?
Tue Feb 26, 2019 4:03 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Standard Reduction Potential
Replies: 2
Views: 95

### Re: Standard Reduction Potential

Are we allowed to sum E?
Tue Feb 26, 2019 3:19 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Standard Reduction Potential
Replies: 2
Views: 95

### Standard Reduction Potential

When calculating for the Eo of a cell do we add the Eo of each half reaction with the corresponding sign the same way we did in class? Someone mentioned during review that this was incorrect because E is not a state function.
Tue Feb 26, 2019 9:27 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Reduction Potential of Cathodes and Anodes
Replies: 1
Views: 87

### Standard Reduction Potential of Cathodes and Anodes

I understand that to calculate the standard cell potential, we subtract the standard reduction potential of the oxidation half reaction from the standard reduction potential of the reduction half reaction. How do we find these values? Are they given?
Mon Feb 25, 2019 3:41 pm
Forum: Balancing Redox Reactions
Topic: Water in Redox Reactions [ENDORSED]
Replies: 3
Views: 134

### Water in Redox Reactions[ENDORSED]

Does anyone know how we know when to add water to balance our redox reaction? How do we know how much to add?
Sun Feb 24, 2019 11:44 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Adding an inert electrode? 6L.5b
Replies: 1
Views: 66

### Re: Adding an inert electrode? 6L.5b

I know that the reason you need an inert electrode is so you can have an electron transfer between the reactants and products without affecting the overall reaction. I think you might just need to recognize inert conductors (like platinum) because the notation looks the same.
Sun Feb 24, 2019 11:41 pm
Forum: Student Social/Study Group
Topic: Test 2
Replies: 3
Views: 128

### Test 2

Will the second test cover any topics outside of Gibbs free energy and electrochemistry?
Sun Feb 24, 2019 11:38 pm
Forum: Balancing Redox Reactions
Topic: Balancing redox reactions
Replies: 1
Views: 62

### Re: Balancing redox reactions

When the original equation has water in the products, it just means that water was created from the reaction. However, it does not directly contribute to the reaction in the same way an ion does.
Sun Feb 17, 2019 11:08 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: HW for W7
Replies: 7
Views: 237

### Re: HW for W7

Yes, we are supposed to do homework from those sections.
Sun Feb 17, 2019 11:06 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Polyprotic Acids
Replies: 5
Views: 197

### Polyprotic Acids

When writing out K for a polyprotic acid, do we include both versions of the conjugate base in the expression or just one?
Sun Feb 17, 2019 10:49 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Battery
Replies: 5
Views: 182

### Re: Battery

I'm not sure, but since batteries can heat up, I would say they are a closed system.
Sun Feb 10, 2019 7:59 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: U = (3/2)nRT
Replies: 2
Views: 118

### Re: U = (3/2)nRT

This is the formula calculating for work of a monatomic gas
Sun Feb 10, 2019 7:56 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: Irr vs Rev Graphs and Work
Replies: 1
Views: 94

### Re: Irr vs Rev Graphs and Work

So the negative sign on work indicates that the system is losing energy by doing work on the surroundings (there is an output of work). So the larger the negative number, the more work is being done on the surroundings. Reversible reactions always do more work than irreversible reactions. We can see...
Sun Feb 10, 2019 7:45 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Kinetic Energy P(U)
Replies: 2
Views: 63

### Kinetic Energy P(U)

I understand how to use U in formulas, but under what circumstances would we need to use potential energy P?
Sun Feb 03, 2019 11:14 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Closed Systems
Replies: 6
Views: 178

### Closed Systems

How does a closed system differ from an isolated system?
Sun Feb 03, 2019 11:10 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Types of calorimetry
Replies: 1
Views: 87

### Re: Types of calorimetry

Constant P calorimetry refers to keeping a constant pressure while constant V calorimetry refers to keeping a constant volume. For example, a container with gas inside with a movable piston vs. with a fixed piston would be one example of the different types of calorimetry.
Wed Jan 23, 2019 11:49 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Solubility
Replies: 1
Views: 101

### Re: Solubility

I don't think the two concepts are directly related, equilibrium is more about determining which way a reaction will run, concentrations of species and things like that. Solubility has to do with specific species involved in reactions, while equilibrium constants relate more to the ratio of species ...
Wed Jan 23, 2019 11:44 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Reactions at Equilibrium
Replies: 1
Views: 81

### Reactions at Equilibrium

If we are given a reaction, but we are not told which way it runs, what should we choose as the reactants and products?
Wed Jan 23, 2019 11:37 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K for gaseous equations
Replies: 2
Views: 113

### K for gaseous equations

If we are asked to calculate the equilibrium constant for an equation involving only gases, and it lists the constant as being K without a subscript, should we calculate using partial pressures or molar concentration?
Sun Jan 20, 2019 7:11 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: ICE Table Calculations
Replies: 4
Views: 187

### ICE Table Calculations

Will we ever be required to do a problem involving an ICE table with more than three species?
Sun Jan 20, 2019 7:08 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Replies: 1
Views: 105

One way you could do this is by looking at the species involved in the reaction and estimating a pH based on how you think the reaction will affect the pH of solution. For example, if the reaction involves a strong acid, you should expect a relatively low pH, etc.
Sun Jan 20, 2019 7:05 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE calculation sig figs
Replies: 5
Views: 161

### Re: ICE calculation sig figs

I'm not sure, but I've heard from several TA's that it is important not to round any answers until the end because this is how they calculate the test answers. I'm not sure why they would round before getting the final answer, but to be safe I would complete the entire problem and only take sig figs...
Sun Jan 13, 2019 11:12 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Solids and Liquids in Equilibrium [ENDORSED]
Replies: 2
Views: 96

### Re: Solids and Liquids in Equilibrium[ENDORSED]

I believe aqueous species can be included, since they are technically neither solid nor liquid.
Sun Jan 13, 2019 11:11 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Question 11.11
Replies: 2
Views: 55

### Re: Question 11.11

In order to start doing part c, find the percentages for both the products and the reactants (#molecules in question/# total molecules) the multiply these fractions by .10 bar. These should give you the partial pressures needed to solve the problem.
Sun Jan 13, 2019 11:07 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Equilibrium in relation to K and Q
Replies: 5
Views: 164

### Re: Equilibrium in relation to K and Q

Solving for Q and solving for K are the same, K just indicates that the reaction is at equilibrium.
Wed Dec 05, 2018 2:23 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Ligands
Replies: 4
Views: 238

### Ligands

How do we know how many ligands will bind to a particular transition metal?
Wed Dec 05, 2018 2:19 am
Forum: Naming
Topic: Charge of Ligands
Replies: 1
Views: 98

### Re: Charge of Ligands

If you mean the overall charge, that can be done by drawing the Lewis structure, finding the formal charge for each atom, and finding the overall charge for the molecule. It might also be helpful to look for how many areas of electron density there are, and that will determine if the ligand is monod...
Wed Dec 05, 2018 2:11 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: unit
Replies: 3
Views: 115

### Re: unit

I believe it is M, or molarity (moles/liter).
Fri Nov 30, 2018 5:45 pm
Forum: Lewis Acids & Bases
Topic: Mixing up Lewis and Bronsted
Replies: 3
Views: 184

### Re: Mixing up Lewis and Bronsted

When he said general, he meant that all substances can be categorized as a Lewis acid or base based on whether they donate or accept electrons in a reaction. The Bronsted definition of acids and bases is much narrower because it only looks at substances that donate or accept protons, so many substan...
Fri Nov 30, 2018 5:41 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Pentagonal bipyramidal
Replies: 4
Views: 399

### Re: Pentagonal bipyramidal

Any molecule with the VSEPR formula AX7 will be pentagonal bipyramidal. I don't know whether or not it's rare, but we definitely haven't covered it in class, so I would guess it's not super common.
Fri Nov 30, 2018 5:37 pm
Forum: Sigma & Pi Bonds
Topic: Drawing out Sigma and Pi Bonds
Replies: 1
Views: 129

### Re: Drawing out Sigma and Pi Bonds

I believe the way a sigma bond for a d orbital would work is that two adjacent d-orbitals would join to make a bond on the internuclear axis. I don't think it really matters which orbitals, so long as they are directly adjacent. After the first sigma bond is formed, any additional bonds will have to...
Sun Nov 25, 2018 1:55 pm
Forum: Lewis Structures
Topic: Central atom of CNO-
Replies: 2
Views: 80

### Re: Central atom of CNO-

Nitrogen should be the central atom
Sun Nov 25, 2018 12:08 pm
Forum: Dipole Moments
Topic: convention used
Replies: 1
Views: 107

### Re: convention used

During class, Dr. Lavelle mentioned that in physics, the dipole arrow points towards the positive dipole, because it relates to the electric field. However, in chemistry, he explained that the arrow will point towards the negative dipole. I'm not sure about the convention used in the book, but the o...
Sun Nov 25, 2018 12:03 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: Distinguishing between the different intermolecular forces
Replies: 9
Views: 416

### Re: Distinguishing between the different intermolecular forces

Generally you can tell which forces are present in a molecule by looking at its overall polarity. For example, if a molecule is polar, it can have dipole-dipole interactions. Molecules which have a hydrogen bonded to a highly electronegative atom, such as water, will have hydrogen bonding. All molec...
Wed Nov 14, 2018 1:07 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 3
Views: 137

### Bond Angles

When looking at molecular shape, is there a difference in bond angles if the area of electron density is caused by a lone pair or a bond? Does one have a stronger pull?
Wed Nov 14, 2018 12:58 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Isobal Analogy
Replies: 1
Views: 112

### Re: Isobal Analogy

I think the term might be isolobal? It has to do with the energy of molecular fragments, and it basically just means that their energy, shape, and structure are about the same. But Dr. Lavelle hasn't mentioned it in class, so I don't think it will come up on tests or anything.
Wed Nov 14, 2018 12:52 pm
Forum: Resonance Structures
Topic: Formal Charge
Replies: 13
Views: 760

### Formal Charge

When making a Lewis structure for an ion, does it matter what atom the formal charge is on, or the structure is valid as long as the overall formal charge is correct?
Sun Nov 11, 2018 10:58 pm
Forum: Bond Lengths & Energies
Topic: hydrogen bonds
Replies: 3
Views: 138

### Re: hydrogen bonds

All bonds are associated melting points; it just refers to the amount of energy required to break the bond. All bonds have an energy associated with them, so the stronger the bond, the higher the melting point.
Sun Nov 11, 2018 10:54 pm
Forum: Dipole Moments
Topic: How do you draw dipole moments
Replies: 6
Views: 197

### Re: How do you draw dipole moments

In chemistry we draw it towards the more electronegative atom, but I believe it is the opposite in physics.
Sun Nov 11, 2018 10:52 pm
Forum: Lewis Structures
Topic: Poly-atomic Ions
Replies: 2
Views: 172

### Poly-atomic Ions

When drawing the Lewis structure for a poly-atomic ion, is there a preferred place to put the charge? Is it better to have the formal charge on a central atom or on peripheral atom?
Sun Nov 04, 2018 10:39 pm
Forum: Octet Exceptions
Topic: Expanded Octet [ENDORSED]
Replies: 5
Views: 143

### Expanded Octet[ENDORSED]

Which atoms are allowed to have an expanded octet? Where do these extra electrons go?
Sat Nov 03, 2018 11:00 pm
Forum: Octet Exceptions
Topic: Copper ion electron structure
Replies: 3
Views: 240

### Copper ion electron structure

Cu2+ ends up having the electron structure [Ar] 3d9. Why would this be, since filling the d orbital in this way does not result in a fully filled d orbital? Why is the structure not [Ar]3d7 4s2?
Sat Nov 03, 2018 10:56 pm
Forum: Octet Exceptions
Topic: Ions and Exceptions to the Octet Rule
Replies: 3
Views: 138

### Ions and Exceptions to the Octet Rule

For some of the answers on the homework, it seemed like ions sometimes used the exception to the octet rule, even when they were not copper, silver, etc. For example, on question 13 in the 6th edition, Zn+ had one electron removed from the 4s orbital and not the 3d orbital. Can anyone explain why th...
Mon Oct 22, 2018 1:54 pm
Forum: Trends in The Periodic Table
Topic: Ionic trends
Replies: 2
Views: 61

### Ionic trends

I understand the trends for the periodic table, but why do the trends for ions not behave in the same way? For example, for phosphorous, sulfur, and chlorine, the order of increasing atomic size would go Cl, S, P, but for the ionized forms of these elements, the order is reversed. Why is this?
Mon Oct 22, 2018 1:47 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 4s and 3d Orbitals [ENDORSED]
Replies: 3
Views: 103

### 4s and 3d Orbitals[ENDORSED]

I remember from lecture that the 4s orbital has more energy than the 3d orbital, but if this is the case, why is the 4s orbital filled first?
Mon Oct 22, 2018 1:45 pm
Forum: Properties of Light
Topic: Light Intensity
Replies: 2
Views: 70

### Light Intensity

I know that the intensity of a light source does not have to do with it's frequency, but what exactly does intensity or brightness mean in the context of photons?
Fri Oct 19, 2018 5:20 pm
Forum: Photoelectric Effect
Topic: The Photoelectric Effect
Replies: 3
Views: 113

### Re: The Photoelectric Effect

I believe it is an experimental way to test the relative strength of electron attraction in different metals. The higher the frequency of light needed to eject electrons, the stronger the forces binding the electrons to the atoms of the metal.
Fri Oct 19, 2018 5:15 pm
Forum: Properties of Electrons
Topic: Heisenberg uncertainty principle
Replies: 1
Views: 99

### Heisenberg uncertainty principle

Does anyone know why psi by itself represents the height of the wave, but psi squared represents the probability of finding an electron? Thanks
Fri Oct 19, 2018 5:05 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Equation
Replies: 1
Views: 50

### Rydberg Equation

Is E = -hR/n^2 the Rydberg equation? My TA said that we shouldn't use the Rydberg equation in our calculations, but I've been using this one and I know it has the Rydberg constant in it.
Thu Oct 11, 2018 12:10 pm
Forum: Limiting Reactant Calculations
Topic: Limiting Reagent
Replies: 10
Views: 872

### Limiting Reagent

If you were given a limiting reagent question with three reagents, how would you solve it? Would you see which one was limiting between two of the reagents, and then check if the third reagent was more limiting than the first limiting reagent?
Tue Oct 09, 2018 9:37 pm
Forum: Balancing Chemical Reactions
Topic: Homework question M9
Replies: 1
Views: 168

### Homework question M9

Do we need to know how to write net ionic equations for the test? This problem asks for one, but I don't think Dr. Lavelle has said anything about it in class.
Tue Oct 09, 2018 4:17 pm
Forum: General Science Questions
Topic: First Quiz
Replies: 1
Views: 179

### Re: First Quiz

The quiz should take 40 minutes, and discussion is only 50 minutes long, so I'm not sure that we would have time to go over it.
Thu Oct 04, 2018 11:25 pm
Forum: SI Units, Unit Conversions
Topic: Reaction Stoichiometry Unit Conversion
Replies: 2
Views: 116

### Re: Reaction Stoichiometry Unit Conversion

Just to add, answers might be expected to be in SI units if the question requires you to use a derived unit (like g/mol) since you have to convert mass into grams in order for the answer to be correct. However, the units of the final answer shouldn't matter as long as the calculation was correct.
Thu Oct 04, 2018 4:47 pm
Forum: Empirical & Molecular Formulas
Topic: Molecular Formulas
Replies: 5
Views: 338

### Re: Molecular Formulas

For this problem, at least in my 6th edition textbook, you only need to provide the ratio of the atoms, which essentially means the empirical formula. In order to calculate the molecular formula, we would need the molar mass of the compound, which is not given.
Wed Oct 03, 2018 10:07 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Accuracy vs Precision
Replies: 23
Views: 1342

### Re: Accuracy vs Precision

How can values be accurate but not precise? If all the values are accurate (close to the true value) how can they still be not precise in relation to each other?