## Search found 51 matches

Sun Mar 11, 2018 3:21 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction Too Slow to Include in Mechanism
Replies: 1
Views: 151

### Re: Reaction Too Slow to Include in Mechanism

I think the problem will usually just let you know!
Sun Mar 11, 2018 3:20 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate-determining slowest step
Replies: 5
Views: 402

### Re: Rate-determining slowest step

I think the problem will usually tell you which is slower on the side in parentheses or something. If not it will give you the experimental rate law and you can tell from which reactants are included in the rate law which step is the slow step
Sun Mar 11, 2018 3:19 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Elementary Step
Replies: 4
Views: 237

### Re: Elementary Step

I like to think of elementary steps as straight forward steps so what you see is what you get. While the overall reaction may contain intermediates that aren’t included, the elementary step contains the exact reactants and products and so we can derive the rate law for the elementary step right from...
Mon Mar 05, 2018 10:53 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Unique rates
Replies: 4
Views: 360

### Re: Unique rates

Dr. Lavelle just mentioned unique rates last week. Whereas average rate is the change in concentration over the change in time, and is different for each product and reactant, unique rate is the same for every product and reactant in that specific, or "unique", reaction. To find unique rat...
Mon Mar 05, 2018 10:48 pm
Forum: General Rate Laws
Topic: 15.3 Rate Laws Depending on concentrations of products
Replies: 3
Views: 198

### Re: 15.3 Rate Laws Depending on concentrations of products

In the homework, there were a couple problems on rate law and proposing mechanisms. Only one of them had an elementary step that had a significant reverse reaction, and it was given to you in the problem that that was the case, so I don't think you need to worry about it too much!
Mon Mar 05, 2018 10:44 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8017
Views: 1402206

### Re: Post All Chemistry Jokes Here

What did atom A say to the atom B who was telling this joke?
You're such a Boron
Mon Feb 26, 2018 6:21 pm
Forum: First Order Reactions
Topic: Equation in the Book vs. in Lecture
Replies: 2
Views: 205

### Re: Equation in the Book vs. in Lecture

They include both in the book. It just depends on the problem and what you are solving for. Like, if you are solving for time t or k, the equation with ln would be better. If you are solving for concentration, the exponential form would be easier to use
Mon Feb 26, 2018 6:18 pm
Forum: Second Order Reactions
Topic: 15.19
Replies: 2
Views: 174

### Re: 15.19

You divide out the number. So [B] goes from 1.25 to 3.02 which means it increased by a factor of 2.416. The rate goes from 8.7 to 50.8, so it increased by a factor of 5.839. Since everything else in the rate law is the same, you can set the factor by which [B] increased ^c equals the factor by which...
Mon Feb 26, 2018 6:13 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Units for Concentration
Replies: 4
Views: 257

### Re: Units for Concentration

I don't think it matters, you should just know which ones u were working with to match the units!
Sun Feb 18, 2018 10:26 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Determining Q when only one element is involved
Replies: 1
Views: 109

### Re: Determining Q when only one element is involved

You would not cancel out the aqueous Ag+ and treat each molarity of Ag separately. Therefore, for Q, you would have Ag+ of .005M on top and .15M on the bottom.
Sun Feb 18, 2018 10:23 pm
Forum: Balancing Redox Reactions
Topic: HW 14.11 d
Replies: 1
Views: 157

### Re: HW 14.11 d

I'm not sure if this is what you're asking, but the OH- is just included in the half-reaction in the table at the back of the book already. They just took the equation straight as it was out of the appendix
Sun Feb 18, 2018 10:21 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Example 14.8 (pg 586)
Replies: 1
Views: 134

### Re: Example 14.8 (pg 586)

It seems like they did switch it. Or rather, you are mixing up the two methods. One method is to reverse the sign for the oxidation half reaction and then add it to the reduction half reaction. The other is to keep the signs as they are and subtract the potential of the oxidation half reaction from ...
Sun Feb 11, 2018 4:40 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: signs
Replies: 3
Views: 191

### Re: signs

I don't think you ever actually have to put +. It's probably just for emphasis/clarity
Sun Feb 11, 2018 4:38 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: equilibrium
Replies: 3
Views: 232

### Re: equilibrium

at equilibrium Ecell should equal 0 V
Sun Feb 11, 2018 4:37 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: Orientations for Boltzmann Formula
Replies: 1
Views: 190

### Re: Orientations for Boltzmann Formula

I don't think we would be given anything too crazy. Just like CO would have 2 positions and N2would only have 1. I think they would be easy enough that we could visualize it or draw it out which is what i did for one of the homework problems. There was also a hw problem that told you the number of p...
Sun Feb 04, 2018 6:46 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Example 9.5 (page 325)
Replies: 2
Views: 154

### Re: Example 9.5 (page 325)

tl;dr LOL
BaSically you do the change in volume first and then do the change in temperature so when you’re calculating the temperature, the volume has already changed and is now constant.

Don’t use pressure bc it is not specified what is happening with that so it is better to avoid dealing with it
Sun Feb 04, 2018 6:42 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: conceptual question about change in entropy due to both temp and vol [ENDORSED]
Replies: 3
Views: 214

### Re: conceptual question about change in entropy due to both temp and vol[ENDORSED]

We are assuming, by using the two step process, that first the volume increases and then the temperature increases(or decreases whatever the problem says) so when the temperature is changing, the volume has already changed and is now constant
Sun Feb 04, 2018 6:40 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: ΔS of vaporization
Replies: 2
Views: 164

### Re: ΔS of vaporization

They explain this in the book. I’m not sure but off the top of my head I think the reason for this is that gas molecules of different substances behave in the same way so when liquids become gases they kind of change in the same way (so entropy change is the same). The only reason the change in entr...
Mon Jan 29, 2018 10:49 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.15a [ENDORSED]
Replies: 2
Views: 149

### Re: 9.15a[ENDORSED]

delta H fus is 6.01 for melting so for freezing you would have to reverse the sign and make it -6.01 kJ/mol!
Mon Jan 29, 2018 10:46 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Temperature units for Entropy [ENDORSED]
Replies: 2
Views: 189

### Re: Temperature units for Entropy[ENDORSED]

It does make a difference since the temperatures are being divided you would get different answers for Kelvins vs Celsius. I think you should be using Kelvins but Im not sure why. might be in the derivation of the formula!
Mon Jan 29, 2018 10:42 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy in Relation to Temp [ENDORSED]
Replies: 1
Views: 139

### Re: Entropy in Relation to Temp[ENDORSED]

The equation is actually deltaS = q/T. When temperature is lower, then deltaS will be more. It makes sense if you think about it, although I'm not sure why. If we have one system that is at a lower temperature and one that is at a higher temperature but we input the same amount of heat, the heat wil...
Sun Jan 21, 2018 1:32 pm
Forum: Phase Changes & Related Calculations
Topic: Calculating the Initial Temperature Of An Object
Replies: 3
Views: 395

### Re: Calculating the Initial Temperature Of An Object

You would find the q of the water using the change in temperature and q=mC(deltaT). Then set the negative that equal to the amount of heat the copper lost (they should give you the specific heat capacity of copper) and solve for delta T. Use delta T to then find initial temperature. (the final tempe...
Sun Jan 21, 2018 1:29 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.57
Replies: 1
Views: 119

### Re: 8.57

I think you're talking about Hess's Law right? The equations would have to be given, but it some cases, the question just says "the combustion of" and so you would have to write the equation yourself with your knowledge of combustion (i.e. compound + O2--> CO2 + H2O
Sun Jan 21, 2018 1:26 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Wed 01/17 Lecture
Replies: 1
Views: 126

### Re: Wed 01/17 Lecture

The density of water is 1g/ml. I think what you're referring to is that Lavelle said to assume the density of the solution is like water (~1 g/mL) because it is dilute enough to do so. I may be wrong, but I think the importance of knowing the density is just so we can covert from volume (mL) to mass...
Tue Jan 16, 2018 4:17 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Finding change in enthalpy of a rxn
Replies: 3
Views: 212

### Re: Finding change in enthalpy of a rxn

For problems in the textbook I believe they are in a table in the appendix of the book
Tue Jan 16, 2018 4:12 pm
Forum: Phase Changes & Related Calculations
Topic: question 8.41
Replies: 5
Views: 321

### Re: question 8.41

You might also be using the wrong C for the ice. It should be 4.184, the liquid form, because the ice has melted into liquid before it rises in temperature. (I did this and couldn't figure out the problem for a while lol but you might have done what the above person stated, I don't remember the answ...
Tue Jan 16, 2018 4:09 pm
Forum: Phase Changes & Related Calculations
Topic: Homework Problem 8.41
Replies: 1
Views: 178

### Re: Homework Problem 8.41

To start this problem, realize that the heat the ice cube gains is equal to the heat the surrounding water loses. First, take into account the energy needed to melt the ice (deltaH fusion=6.01kJ/mol) and add it to the amount of energy needed to raise the ice cube x degrees (using q=mCdeltaT). Then s...
Thu Jan 11, 2018 4:28 pm
Forum: Phase Changes & Related Calculations
Topic: ∆Hsub= ∆Hfus+ ∆Hvap
Replies: 4
Views: 862

### Re: ∆Hsub= ∆Hfus+ ∆Hvap

enthalpy is a state function which makes it additive. Sublimation is a solid going to a vapor and fusion is a solid to a liquid and vaporization is a liquid to a vapor. So if you take out the middle step, it becomes solid to vapor. Basically, the same amount of energy goes into converting a solid di...
Thu Jan 11, 2018 4:20 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Why is fusion another name for melting?
Replies: 4
Views: 250

### Re: Why is fusion another name for melting?

Abel Thomas 2C wrote:It may have to do with the fact the etymology of the word fusion comes from the Latin "fundere" which means "melting together".

I think this is correct. That's what my TA said during discussion
Thu Jan 11, 2018 4:18 pm
Forum: Phase Changes & Related Calculations
Topic: Hess Law [ENDORSED]
Replies: 5
Views: 325

### Re: Hess Law[ENDORSED]

yup basically multiply by (-)
Sun Dec 03, 2017 11:52 pm
Forum: Sigma & Pi Bonds
Topic: Pi bonds
Replies: 3
Views: 379

### Re: Pi bonds

pretty much! the leftover unhybridized orbitals just overlap as pi bonds
Sun Dec 03, 2017 11:50 pm
Forum: Resonance Structures
Topic: Naming coordination compounds [ENDORSED]
Replies: 3
Views: 358

### Re: Naming coordination compounds[ENDORSED]

Yes! One of them is just an updated way. I remember Lavelle saying he will accept either :)
Sun Nov 26, 2017 10:41 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.45 Equilibrium in terms of stability
Replies: 1
Views: 164

### Re: 11.45 Equilibrium in terms of stability

In this question if you complete steps a and b you will see that the value of x for Cl2 is less than that for F2. That means less Cl2 was converted to Cl than F2 was converted to F--hence, Cl2 is more stable than F. There may be more underlying the answer but that's what makes sense to me :)
Sun Nov 26, 2017 10:36 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Aqueous and Gaseous Phases
Replies: 3
Views: 240

### Re: Aqueous and Gaseous Phases

It depends what is given in the problem. If the concentrations of all the reactants, whether gaseous or aqueous, are given, then it is safe to use Kc. If the pressure is given for the gaseous phases, then you would need to use pv=nrt to find the concentrations by first finding n (the number of moles...
Tue Nov 21, 2017 8:14 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: HW question 11.7
Replies: 2
Views: 248

### 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! Hey yeah I can tell you how the solutions manual did it! The chemical equation for this problem is X2->2X so K=(p of products...
Mon Nov 20, 2017 10:42 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Reaction arrows
Replies: 3
Views: 287

### Re: Reaction arrows

The double arrows are used to express the state of dynamic equilibrium--both reactions are occurring at the same time at stable rates so that the concentrations/pressures of each do not change. From what I remember from high school I believe the reverse reaction is not always happening (if there are...
Mon Nov 20, 2017 10:33 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: HW question 11.7
Replies: 2
Views: 248

### HW question 11.7

So I was doing the homework and for 11.7 part c, the value of K turned out to be .17. However, at equilibrium the reactant had become more product (6 out of 11 X2 decomposed). Shouldn't K be larger than 1 then? Also, Avogadro's law states that, "equal volumes of all gases, at the same temperatu...
Mon Nov 13, 2017 3:43 pm
Forum: Lewis Structures
Topic: Midterm Question CH3SH
Replies: 5
Views: 484

### Re: Midterm Question CH3SH

Yup that's what I got too! It works out very neatly with every atom having a formal charge of 0 :)
Mon Nov 13, 2017 3:36 pm
Forum: Bond Lengths & Energies
Topic: Bond Length
Replies: 8
Views: 1794

### Re: Bond Length

All three of the examples come from an H bonded with a halogen so the structure of the bond is pretty much the same--H single bonded to the halogen. The difference in bond length comes from the size of the atom. Bond length is the measure of the center of one atom to the other, and since I has the b...
Mon Nov 06, 2017 11:17 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Which one do I draw?
Replies: 5
Views: 453

### Re: Which one do I draw?

I think Professor Lavelle said we would pretty much never have to draw the 3D vsepr model. For vsepr, we will probably only be asked to name the structure, bond angles, and to give the vsepr formula, which would be in the form AXE
Mon Nov 06, 2017 11:08 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Xenon Tetrafluoride?
Replies: 4
Views: 699

### Re: Xenon Tetrafluoride?

Usually noble gases would not form any bonds but since xenon is such a heavy noble gas with valence electrons so far away from the nucleus and experiencing very little attraction that it can be forced to make bonds with very electronegative elements such as fluorine. As stated above, you probably d...
Tue Oct 31, 2017 12:12 am
Forum: Octet Exceptions
Topic: Octet Exceptions
Replies: 3
Views: 454

### Re: Octet Exceptions

I think you can figure it out using formal charge and electronegativity. For instance, in SO4 2- the S has a formal charge of 0 when there are 2 double bonded O's which is more favorable than having only one double bonded O. However, it cannot have 3 double bonded O's because then it would have a FC...
Tue Oct 31, 2017 12:09 am
Forum: Lewis Structures
Topic: Lewis Structures
Replies: 10
Views: 580

### Re: Lewis Structures

You probably won't have to worry I think they usually will ask for it
Fri Oct 27, 2017 1:19 am
Forum: Quantum Numbers and The H-Atom
Topic: P-Orbitals (x,y,z) [ENDORSED]
Replies: 3
Views: 2433

### Re: P-Orbitals (x,y,z)[ENDORSED]

Same with above. In my lecture, I remember Professor Lavelle saying that we only use Px Py Pz when we want to accentuate that the electrons are occupying separate orbitals. Other than that, it is fine to just use p1 p2 p3
Fri Oct 27, 2017 1:17 am
Forum: Quantum Numbers and The H-Atom
Topic: Magnetic Quantum Number
Replies: 4
Views: 720

### Re: Magnetic Quantum Number

Catherine Yang 3G wrote:
Do the ml values correspond to a specific orientation? Like do px orbitals correspond to ml=-1 for example? Thanks!

Yes I'm pretty sure that the ml values correspond to a specific orientation, but I'm also pretty sure that we won't need to know the content that specifically :)
Tue Oct 17, 2017 9:11 pm
Forum: Properties of Electrons
Topic: Energy Level Change
Replies: 5
Views: 430

### Re: Energy Level Change

To add, is there any specific reason an electron wouldn't automatically just jump back to level one? is it random? I went to office hours and Lavelle answered a similar question someone had. The question was "why do some electrons go from n=4 to n=2 while others go straight down to n=1?" ...
Tue Oct 17, 2017 9:06 pm
Forum: Properties of Light
Topic: Color of visible light
Replies: 11
Views: 750

### Re: Color of visible light

I have seen a homework question that asked for the color of the visible light. However, I don't think that Professor Lavelle would expect us to know it aside from that violets and blues have the shorter wavelengths and reds and oranges the longer. In fact, the spectrum is much like a rainbow in the ...
Thu Oct 12, 2017 8:46 pm
Forum: Properties of Light
Topic: Prefix Conversion
Replies: 12
Views: 731

### Re: Prefix Conversion

I would convert in the beginning or right when you are doing the problem. It would be best to have the same units so that they can properly cancel out. Doing so, you will be seeing that you end up with the right units in your answer.
Thu Oct 12, 2017 8:38 pm
Forum: Ideal Gases
Replies: 147
Views: 104528

I think reading the textbook would be helpful even if you don't understand it. That way you get a taste of the material so during class the lecture will flow better.
Wed Oct 04, 2017 11:11 pm
Forum: Significant Figures
Topic: All students read this sig fig post [ENDORSED]
Replies: 131
Views: 17033

### Re: All students read this sig fig post[ENDORSED]

What are the subtraction/addition/multiplication/division rules for sig figs? I understand the concept of using the numbers given but don't know what you're referring to with the "rules" For multiplication and division, the rule is to end up with an answer with sig figs equivalent to the ...
Mon Oct 02, 2017 3:48 pm
Forum: Significant Figures
Topic: All students read this sig fig post [ENDORSED]
Replies: 131
Views: 17033

### Re: All students read this sig fig post[ENDORSED]

During the calculations I would just keep a long string of numbers after the decimal until I come to the answer and then apply sig fig rules to get 3 sig figs cuz 4 sig figs might not be enough to avoid round off error. I'm not sure what's meant by "inconsistent." As long as you avoid roun...