Search found 51 matches

by Yixin Angela Wang 2H
Fri Mar 16, 2018 2:30 pm
Forum: Administrative Questions and Class Announcements
Topic: Saying Thank You to Dr. Lavelle
Replies: 209
Views: 101106

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...
by Yixin Angela Wang 2H
Fri Mar 16, 2018 2:27 pm
Forum: *Electrophiles
Topic: what is going to be on the final? [ENDORSED]
Replies: 12
Views: 841

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.
by Yixin Angela Wang 2H
Wed Mar 14, 2018 1:38 am
Forum: General Science Questions
Topic: Rusty on High School Chem [ENDORSED]
Replies: 166
Views: 100946

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...
by Yixin Angela Wang 2H
Wed Mar 14, 2018 1:35 am
Forum: First Order Reactions
Topic: 15.85
Replies: 3
Views: 231

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.
by Yixin Angela Wang 2H
Mon Mar 05, 2018 10:11 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: k'
Replies: 4
Views: 139

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.
by Yixin Angela Wang 2H
Mon Mar 05, 2018 10:03 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: "Slow" Step Only?
Replies: 4
Views: 181

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.
by Yixin Angela Wang 2H
Mon Mar 05, 2018 10:00 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Molecularity and the Coefficient of an Elementary Step
Replies: 2
Views: 94

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.
by Yixin Angela Wang 2H
Mon Mar 05, 2018 9:58 pm
Forum: First Order Reactions
Topic: Order Reactions
Replies: 3
Views: 171

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.
by Yixin Angela Wang 2H
Wed Feb 28, 2018 12:53 am
Forum: Balancing Redox Reactions
Topic: Oxidation state
Replies: 4
Views: 183

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.
by Yixin Angela Wang 2H
Wed Feb 28, 2018 12:51 am
Forum: Balancing Redox Reactions
Topic: H+ or H3O+ [ENDORSED]
Replies: 3
Views: 174

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.
by Yixin Angela Wang 2H
Wed Feb 28, 2018 12:50 am
Forum: Balancing Redox Reactions
Topic: Can the Hydroxide ion ever be reduced/oxidized?
Replies: 3
Views: 195

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.
by Yixin Angela Wang 2H
Wed Feb 28, 2018 12:45 am
Forum: First Order Reactions
Topic: Ways of determining what order reactions are
Replies: 2
Views: 111

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.
by Yixin Angela Wang 2H
Wed Feb 21, 2018 1:57 am
Forum: Balancing Redox Reactions
Topic: Determining acidic or basic solution
Replies: 3
Views: 151

Re: Determining acidic or basic solution

So we don't ever have to assume a default of either acidic or basic?
by Yixin Angela Wang 2H
Wed Feb 21, 2018 1:16 am
Forum: Balancing Redox Reactions
Topic: redox agent
Replies: 5
Views: 177

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.
by Yixin Angela Wang 2H
Wed Feb 21, 2018 1:11 am
Forum: Balancing Redox Reactions
Topic: OH/H20
Replies: 4
Views: 146

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.
by Yixin Angela Wang 2H
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: 4
Views: 317

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?
by Yixin Angela Wang 2H
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: 250

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...
by Yixin Angela Wang 2H
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: 400

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.
by Yixin Angela Wang 2H
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: 128

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...
by Yixin Angela Wang 2H
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: 128

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.
by Yixin Angela Wang 2H
Tue Feb 06, 2018 3:07 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: molar entropy
Replies: 3
Views: 116

Re: molar entropy

Is there sort of a "hierarchy" regarding which trait we should consider first when determining molar entropy?
by Yixin Angela Wang 2H
Sun Jan 28, 2018 11:33 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Self-Test 9.2 B
Replies: 2
Views: 107

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.
by Yixin Angela Wang 2H
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: 173

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.
by Yixin Angela Wang 2H
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: 190

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.
by Yixin Angela Wang 2H
Sat Jan 20, 2018 9:25 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Open systems
Replies: 6
Views: 254

Re: Open systems

yeah, i think a lot of the problems I saw in the hw deal with closed systems.
by Yixin Angela Wang 2H
Sat Jan 20, 2018 7:15 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Heating/Cooling A System
Replies: 4
Views: 227

Re: Heating/Cooling A System

Then how would you be able to add energy to an open system?
by Yixin Angela Wang 2H
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: 159

Re: 8.31

Which gas constant R do we use, and how do we choose?
by Yixin Angela Wang 2H
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: 221

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.
by Yixin Angela Wang 2H
Fri Jan 12, 2018 7:04 pm
Forum: Phase Changes & Related Calculations
Topic: Expansion and change in pressure
Replies: 4
Views: 190

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...
by Yixin Angela Wang 2H
Fri Jan 12, 2018 6:53 pm
Forum: Phase Changes & Related Calculations
Topic: Heat and work not state functions
Replies: 7
Views: 352

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...
by Yixin Angela Wang 2H
Sat Dec 09, 2017 9:09 pm
Forum: Administrative Questions and Class Announcements
Topic: Practice Test Fall 2017 [ENDORSED]
Replies: 19
Views: 2070

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?
by Yixin Angela Wang 2H
Sat Dec 02, 2017 4:29 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Oxidation States: How to derive [ENDORSED]
Replies: 3
Views: 300

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?
by Yixin Angela Wang 2H
Sat Dec 02, 2017 3:19 pm
Forum: Sigma & Pi Bonds
Topic: Notation for sigma and pi bonds [ENDORSED]
Replies: 1
Views: 173

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?
by Yixin Angela Wang 2H
Sat Dec 02, 2017 3:17 pm
Forum: Sigma & Pi Bonds
Topic: # of sigma and pi bonds [ENDORSED]
Replies: 4
Views: 291

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?
by Yixin Angela Wang 2H
Sat Dec 02, 2017 3:13 pm
Forum: Lewis Acids & Bases
Topic: Chemical Equilibrium [ENDORSED]
Replies: 2
Views: 230

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...
by Yixin Angela Wang 2H
Tue Nov 21, 2017 12:58 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: HW question 11.7
Replies: 2
Views: 215

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!
by Yixin Angela Wang 2H
Mon Nov 20, 2017 9:33 pm
Forum: Ideal Gases
Topic: Chemical equilibrium [ENDORSED]
Replies: 9
Views: 782

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?
by Yixin Angela Wang 2H
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: 166

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...
by Yixin Angela Wang 2H
Mon Nov 20, 2017 8:08 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homework Question 11.7 [ENDORSED]
Replies: 4
Views: 246

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...
by Yixin Angela Wang 2H
Thu Nov 09, 2017 4:39 pm
Forum: Octet Exceptions
Topic: Noble gas exception
Replies: 4
Views: 381

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.
by Yixin Angela Wang 2H
Thu Nov 09, 2017 12:07 pm
Forum: Electronegativity
Topic: ELECTRON AFFINITY
Replies: 7
Views: 576

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...
by Yixin Angela Wang 2H
Thu Nov 02, 2017 7:45 pm
Forum: Ionic & Covalent Bonds
Topic: Homework 3.5 part c [ENDORSED]
Replies: 3
Views: 235

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...
by Yixin Angela Wang 2H
Thu Nov 02, 2017 7:42 pm
Forum: Ionic & Covalent Bonds
Topic: Cations and Anions [ENDORSED]
Replies: 12
Views: 931

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 ...
by Yixin Angela Wang 2H
Tue Oct 24, 2017 9:50 pm
Forum: Trends in The Periodic Table
Topic: Atomic Size Trend [ENDORSED]
Replies: 4
Views: 228

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...
by Yixin Angela Wang 2H
Tue Oct 24, 2017 9:37 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: unpaired electrons [ENDORSED]
Replies: 4
Views: 358

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...
by Yixin Angela Wang 2H
Thu Oct 19, 2017 11:51 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbitals as Probability
Replies: 2
Views: 178

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...
by Yixin Angela Wang 2H
Thu Oct 19, 2017 11:46 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Test 2
Replies: 5
Views: 366

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!
by Yixin Angela Wang 2H
Thu Oct 12, 2017 1:13 am
Forum: Properties of Light
Topic: Speed of Light [ENDORSED]
Replies: 8
Views: 454

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.
by Yixin Angela Wang 2H
Thu Oct 12, 2017 1:11 am
Forum: Properties of Light
Topic: Photo electric effect
Replies: 3
Views: 221

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...
by Yixin Angela Wang 2H
Wed Oct 04, 2017 10:21 pm
Forum: Molarity, Solutions, Dilutions
Topic: Molarity and Dilution
Replies: 10
Views: 2304

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...
by Yixin Angela Wang 2H
Wed Oct 04, 2017 10:12 pm
Forum: SI Units, Unit Conversions
Topic: Base Units
Replies: 6
Views: 422

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.

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