Search found 51 matches
- Fri Mar 16, 2018 2:30 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Saying Thank You to Dr. Lavelle
- Replies: 490
- Views: 504249
Re: Saying Thank You to Dr. Lavelle
I don't know if people are still posting these, but I want to thank Dr. Lavelle for being an encouraging and dynamic professor; his courses really helped me to gain confidence and proficiency in chemistry. I can now firmly say that I like chemistry more than I do physics. Before, they were sort of t...
- Fri Mar 16, 2018 2:27 pm
- Forum: *Electrophiles
- Topic: what is going to be on the final? [ENDORSED]
- Replies: 12
- Views: 2629
Re: what is going to be on the final? [ENDORSED]
I asked my TA and he said we only needed to be able to identify the functional groups that Dr. Lavelle went over in class.
- Wed Mar 14, 2018 1:38 am
- Forum: General Science Questions
- Topic: Rusty on High School Chem [ENDORSED]
- Replies: 347
- Views: 410750
Re: Rusty on High School Chem [ENDORSED]
Hi! I totally understand your rustiness. I took a basic chem class in my sophomore year of high school and then never again. I feel that even though AP Chem would have better prepared me for a lot of 14A and B, I was able to understand the concepts by paying attention in class and going to review se...
- Wed Mar 14, 2018 1:35 am
- Forum: First Order Reactions
- Topic: 15.85
- Replies: 3
- Views: 559
Re: 15.85
The complex refers to the thing formed as the intermediate between reaction and product. It's also used when referring to the form that enzymes take when they bind with substrates.
- Mon Mar 05, 2018 10:11 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: k'
- Replies: 4
- Views: 520
Re: k'
I think in class today, Dr. Lavelle used k and k' to denote the rate constants for the forward and backwards reactions of a reaction at equilibrium.
- Mon Mar 05, 2018 10:03 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: "Slow" Step Only?
- Replies: 4
- Views: 634
Re: "Slow" Step Only?
Dr. Lavelle gave a baking example today. If it takes 30 minutes for all the other steps of cookie-making but 45 minutes to bake the cookies, then no matter how much dough you prepare you can only make cookies as fast as the oven will bake them.
- Mon Mar 05, 2018 10:00 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Molecularity and the Coefficient of an Elementary Step
- Replies: 2
- Views: 351
Re: Molecularity and the Coefficient of an Elementary Step
Yes, I believe that's correct. Molecularity is the number of reactants in a particular step, so for example a reaction that requires 2 molecules of one compound and 1 molecule of another would be 2A+B--->product, and it should be termolecular.
- Mon Mar 05, 2018 9:58 pm
- Forum: First Order Reactions
- Topic: Order Reactions
- Replies: 3
- Views: 444
Re: Order Reactions
I don't think we will need to do anything too difficult in regards to derivations. Maybe we will need to manipulate some equations or combine them, like we have done on tests or midterms, but I don't think we will need to completely derive anything.
- Wed Feb 28, 2018 12:53 am
- Forum: Balancing Redox Reactions
- Topic: Oxidation state
- Replies: 4
- Views: 527
Re: Oxidation state
Yes. Two molecules of a +2 molecule would have a total +4 effect, so you would need to evaluate the amount of negative charge needed accordingly.
- Wed Feb 28, 2018 12:51 am
- Forum: Balancing Redox Reactions
- Topic: H+ or H3O+ [ENDORSED]
- Replies: 3
- Views: 616
Re: H+ or H3O+ [ENDORSED]
I think the H+ is the part that matters if its taking place in an acidic solution, but H30 is the technical substance that is being formed.
- Wed Feb 28, 2018 12:50 am
- Forum: Balancing Redox Reactions
- Topic: Can the Hydroxide ion ever be reduced/oxidized?
- Replies: 3
- Views: 1061
Re: Can the Hydroxide ion ever be reduced/oxidized?
I think I've only ever seen hydroxide used to balance the charges, hydrogens, and oxygens.
- Wed Feb 28, 2018 12:45 am
- Forum: First Order Reactions
- Topic: Ways of determining what order reactions are
- Replies: 2
- Views: 386
Re: Ways of determining what order reactions are
Also looking at a graph of the data will give you an idea of what order a reaction is. For example, if the data looks linear, its first order.
- Wed Feb 21, 2018 1:57 am
- Forum: Balancing Redox Reactions
- Topic: Determining acidic or basic solution
- Replies: 3
- Views: 499
Re: Determining acidic or basic solution
So we don't ever have to assume a default of either acidic or basic?
- Wed Feb 21, 2018 1:16 am
- Forum: Balancing Redox Reactions
- Topic: redox agent
- Replies: 5
- Views: 647
Re: redox agent
They are opposites of each other! The oxidizing agent is the one DOING the oxidizing, which means that it is oxidizing the other agent, so the oxidizing agent itself is reduced.
- Wed Feb 21, 2018 1:11 am
- Forum: Balancing Redox Reactions
- Topic: OH/H20
- Replies: 4
- Views: 440
Re: OH/H20
I feel like acidic seems to be the standard, based on the problems I've done. I feel like whether the solution is acidic or basic should be given in the problem or the skeletal equation though.
- Thu Feb 15, 2018 3:02 am
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Is spontaneity determined by entropy or free energy?
- Replies: 9
- Views: 1856
Re: Is spontaneity determined by entropy or free energy?
Is it because the ΔS in the Gibbs free energy equation is only for the system, and not the total?
- Thu Feb 15, 2018 3:01 am
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Relative entropy levels
- Replies: 2
- Views: 515
Re: Relative entropy levels
Also, as per the third law of thermodynamics, a perfectly organized crystal will have 0 entropy. Otherwise, I would look at the state of the substance in question, because there is a big difference between liquid and gas, but not between solid and liquid. I am not sure, however, if a complex molecul...
- Thu Feb 15, 2018 2:58 am
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Units of S and H
- Replies: 4
- Views: 799
Re: Units of S and H
I think the per mole part can be omitted, at least that's what I recall Dr. Lavelle saying. At least for this class.
- Wed Feb 07, 2018 10:39 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Needing a conductor or not?
- Replies: 2
- Views: 354
Re: Needing a conductor or not?
I'm piggybacking onto this post, but I was just wondering if the substance is solid, does it extend into both containers? Because the way that Professor Lavelle described it in lecture, I thought that if one side had a solid reactant and the other didn't, the side without solid reactant would use pl...
- Wed Feb 07, 2018 10:17 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Calculating Potential Difference between Electrodes
- Replies: 3
- Views: 433
Re: Calculating Potential Difference between Electrodes
Yeah, I don't think it makes sense logically if we try to calculate the potential when it equals zero because wouldn't that mean that there was no difference? Haha, I don't know if I'm expressing myself clearly.
- Tue Feb 06, 2018 3:07 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: molar entropy
- Replies: 3
- Views: 418
Re: molar entropy
Is there sort of a "hierarchy" regarding which trait we should consider first when determining molar entropy?
- Sun Jan 28, 2018 11:33 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Self-Test 9.2 B
- Replies: 2
- Views: 315
Re: Self-Test 9.2 B
I agree. Also, since the specific heat is given per gram, then that means the more grams of substance there are, the more C there must be. Thus, multiplying by grams makes sense.
- Sun Jan 28, 2018 11:32 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Relationship between entropy and volume in liquids
- Replies: 5
- Views: 574
Re: Relationship between entropy and volume in liquids
I don't think you can really compress or expand a liquid's volume, but you can increase its entropy by mixing it with another substance or increasing its temperature.
- Sun Jan 28, 2018 11:30 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Work done by Reversible vs. Irreversible Reactions
- Replies: 4
- Views: 609
Re: Work done by Reversible vs. Irreversible Reactions
Dr. Lavelle gave the example of a piston weighed down by sand. The reversible reaction would occur if the weight was removed, grain by grain, slowly. This way, there wouldn't be energy lost as heat.
- Sat Jan 20, 2018 9:25 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Open systems
- Replies: 6
- Views: 718
Re: Open systems
yeah, i think a lot of the problems I saw in the hw deal with closed systems.
- Sat Jan 20, 2018 7:15 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Heating/Cooling A System
- Replies: 4
- Views: 578
Re: Heating/Cooling A System
Then how would you be able to add energy to an open system?
- Wed Jan 17, 2018 10:02 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 8.31
- Replies: 4
- Views: 355
Re: 8.31
Which gas constant R do we use, and how do we choose?
- Fri Jan 12, 2018 7:13 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Delta H for H2
- Replies: 2
- Views: 6401
Re: Delta H for H2
enthalpy of formation is related to the formation of the compound at hand. H2 making H2 doesn't require any extra heat because hydrogen just prefers to stay in H2 form naturally without any other factors influencing it.
- Fri Jan 12, 2018 7:04 pm
- Forum: Phase Changes & Related Calculations
- Topic: Expansion and change in pressure
- Replies: 4
- Views: 359
Re: Expansion and change in pressure
I think the answer is saying that with the expansion, the molecules have more room to move around and thus are less likely to collide with each other or the container. Thus their kinetic energy decreases. Collisions with the container create the pressure exerted on the container, so with less collis...
- Fri Jan 12, 2018 6:53 pm
- Forum: Phase Changes & Related Calculations
- Topic: Heat and work not state functions
- Replies: 7
- Views: 870
Re: Heat and work not state functions
Another way of thinking about it is by using the mountain climbing metaphor Dr. Lavelle went over in class. The change in altitude would be a state function but the distance traveled by foot of the hiker would not be, because the hiker's distance could vary based on the nature of the path he took. I...
- Sat Dec 09, 2017 9:09 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Practice Test Fall 2017 [ENDORSED]
- Replies: 19
- Views: 3317
Re: Practice Test Fall 2017 [ENDORSED]
Thank you for the worksheets and practice exams! Is there any way I could get the answers to the first practice midterm?
- Sat Dec 02, 2017 4:29 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Oxidation States: How to derive [ENDORSED]
- Replies: 3
- Views: 726
Re: Oxidation States: How to derive [ENDORSED]
so we would list all possible oxidation states, even if some are more or less likely than others? Also, would it be possible to do something like this for the transition metals (like in coordination complexes) without having to refer to the charges of the other elements and molecules involved?
- Sat Dec 02, 2017 3:19 pm
- Forum: Sigma & Pi Bonds
- Topic: Notation for sigma and pi bonds [ENDORSED]
- Replies: 1
- Views: 318
Notation for sigma and pi bonds [ENDORSED]
Could someone explain the notation for writing out and describing sigma and pi bonds, and how we know which orbitals are involved?
- Sat Dec 02, 2017 3:17 pm
- Forum: Sigma & Pi Bonds
- Topic: # of sigma and pi bonds [ENDORSED]
- Replies: 4
- Views: 569
Re: # of sigma and pi bonds [ENDORSED]
So basically, the first bond formed is always a sigma bond, and the second or third bond, if there is one, is always a pi bond?
- Sat Dec 02, 2017 3:13 pm
- Forum: Lewis Acids & Bases
- Topic: Chemical Equilibrium [ENDORSED]
- Replies: 2
- Views: 511
Re: Chemical Equilibrium [ENDORSED]
I think in general, yes you always subtract from reactant and add to product. The thing to keep and eye out for is the relative amount to add/subtract. I always double check my equation to make sure that it's balanced, and I try to pick a reactant with a stoichiometric coefficient of one to set as m...
- Tue Nov 21, 2017 12:58 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: HW question 11.7
- Replies: 2
- Views: 308
Re: HW question 11.7
Hey! Sorry I don't have an answer to your question, but I was wondering if you could walk me through how you got the 0.17 number. I was a little confused about that. Thanks!
- Mon Nov 20, 2017 9:33 pm
- Forum: Ideal Gases
- Topic: Chemical equilibrium [ENDORSED]
- Replies: 9
- Views: 1783
Re: Chemical equilibrium [ENDORSED]
In the case of adding more reactant or product, would we then be able to say that the equilibrium has "shifted"? What effect does that have on K?
- Mon Nov 20, 2017 9:01 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Can the equilibrium constant be calculated using both concentration and partial pressure?
- Replies: 2
- Views: 350
Can the equilibrium constant be calculated using both concentration and partial pressure?
Self-test 11.2A asks for the equation for the equilibrium constant for the reaction between atmospheric oxygen and oxygen dissolved in water. The solution given is K = [O2 ]/PO. Can someone explain to me how this is ok? I thought the entire equation had to be written either in terms of concentration...
- Mon Nov 20, 2017 8:08 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Homework Question 11.7 [ENDORSED]
- Replies: 4
- Views: 554
Re: Homework Question 11.7 [ENDORSED]
Basically, when the amount of diatomic molecules stays the same between flasks that's when equilibrium has been reached. I have another question regarding 11.7. For the part that asks you to calculate K but only gives you the partial pressure of the diatomic molecules, how do you figure out the pres...
- Thu Nov 09, 2017 4:39 pm
- Forum: Octet Exceptions
- Topic: Noble gas exception
- Replies: 4
- Views: 797
Re: Noble gas exception
To add on to what is being discussed, a UA in a midterm review today said that the maximum amount of electrons an expanded valence shell can have is 12.
- Thu Nov 09, 2017 12:07 pm
- Forum: Electronegativity
- Topic: ELECTRON AFFINITY
- Replies: 7
- Views: 1516
Re: ELECTRON AFFINITY
In response to Shannon's question, I think that in general, the noble gases should have an electron affinity of basically 0 because they already have a full valence shell and thus would not tend to try to gain or lose electrons. Halogens would have a high electron affinity because they really want t...
- Thu Nov 02, 2017 7:45 pm
- Forum: Ionic & Covalent Bonds
- Topic: Homework 3.5 part c [ENDORSED]
- Replies: 3
- Views: 508
Re: Homework 3.5 part c [ENDORSED]
For trickier problems, I like to write out the neutral atom's electron configuration first, putting all the orbitals in their proper order by the amount of energy they have. Then, to form ions, specifically anions, I would remove the specified number starting from the outermost, highest-energy elect...
- Thu Nov 02, 2017 7:42 pm
- Forum: Ionic & Covalent Bonds
- Topic: Cations and Anions [ENDORSED]
- Replies: 12
- Views: 2047
Re: Cations and Anions [ENDORSED]
Cations and anions have positive and negative charges respectively, but why do they have those charges? Imagine a neutral atom like Silver. In its zero-charge state it has 79 electrons and thus it must also have 79 protons to cancel those charges out so we end up with a net zero. If one electron is ...
- Tue Oct 24, 2017 9:50 pm
- Forum: Trends in The Periodic Table
- Topic: Atomic Size Trend [ENDORSED]
- Replies: 4
- Views: 493
Re: Atomic Size Trend [ENDORSED]
As you move down the periods, electrons start to occupy higher-level orbitals, so the shielding effect Dr. Lavelle mentioned goes into effect. The outermost electrons are shielded from the full attractive force of the positive nucleus, so there isn't as strong of a pull on the outer layers of electr...
- Tue Oct 24, 2017 9:37 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: unpaired electrons [ENDORSED]
- Replies: 4
- Views: 1277
Re: unpaired electrons [ENDORSED]
One trick that makes figuring out unpaired electrons easier is if you write your configuration starting from the last noble gas above the period with the element you are working on. Since noble gases have a full valence electron shell, we know that their orbitals are all full. Thus, you only have to...
- Thu Oct 19, 2017 11:51 am
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Orbitals as Probability
- Replies: 2
- Views: 433
Re: Orbitals as Probability
Basically, since electrons are in constant, random motion, you cannot pinpoint where a single electron is at any given moment. However, since electrons have different levels of energy and are all attracted to the positive charges in the nucleus, you know that the electrons must occupy a certain area...
- Thu Oct 19, 2017 11:46 am
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Test 2
- Replies: 5
- Views: 693
Re: Test 2
I took it today and can confirm: the test is just 1.1-1.5.
For those of you taking it on Friday, good luck!
For those of you taking it on Friday, good luck!
- Thu Oct 12, 2017 1:13 am
- Forum: Properties of Light
- Topic: Speed of Light [ENDORSED]
- Replies: 8
- Views: 1193
Re: Speed of Light [ENDORSED]
If I need a precise answer, I use as many significant digits as I am given. However, if I am solving something for a ratio or something where rounding does not change the final outcome, I will use a more general number and save some time.
- Thu Oct 12, 2017 1:11 am
- Forum: Properties of Light
- Topic: Photo electric effect
- Replies: 3
- Views: 412
Re: Photo electric effect
I'll just add some things that Dr. Lavelle covered in lecture today. The photoelectric experiments showed that light can behave like a wave, and the properties of light, specifically the effects of increasing its intensity, change when light is thought of as particles. In wave form, light's energy i...
- Wed Oct 04, 2017 10:21 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Molarity and Dilution
- Replies: 11
- Views: 4377
Re: Molarity and Dilution
Molarity is moles of solute/volume of solution. The Mi*Vi = Mf*Vf is dilution, which is not what this particular problem is asking. To solve this problem, you first convert grams of KCl to moles by dividing the mass by the molar mass. Then, you divide the number of moles by the volume in liters, whi...
- Wed Oct 04, 2017 10:12 pm
- Forum: SI Units, Unit Conversions
- Topic: Base Units
- Replies: 6
- Views: 760
Re: Base Units
Additionally, a lot of formulas are given in specific, usually SI units. For example, temperature is usually in Kelvins in formulas, but it is in Celsius when you measure it. In that case, to use the formula correctly, you have to convert Celsius to Kelvin.