Search found 61 matches
- Sun Mar 17, 2019 3:12 pm
- Forum: Calculating Work of Expansion
- Topic: Work in a System
- Replies: 4
- Views: 598
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: 506
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: 233
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: 234
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: 474
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: 270
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: 227
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: 256
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: 256
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: 199
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: 405
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: 203
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: 335
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: 158
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: 650
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: 511
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: 494
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: 681
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: 295
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: 204
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: 454
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: 248
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: 217
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: 232
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: 277
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: 457
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
- Topic: Checking answers
- Replies: 1
- Views: 229
Re: Checking answers
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: 425
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: 121
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: 134
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: 391
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: 523
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: 189
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: 233
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: 483
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: 1292
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: 282
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: 164
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: 233
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: 820
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: 311
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: 225
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: 1370
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: 344
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: 987
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: 346
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: 490
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: 781
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: 701
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: 117
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: 295
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: 156
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: 188
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: 230
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: 119
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: 1580
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: 211
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: 218
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: 280
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: 964
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: 2601
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?