## Search found 52 matches

Wed Mar 14, 2018 11:05 pm
Forum: Balancing Redox Reactions
Topic: Balancing in a basic solution
Replies: 4
Views: 2608

### Balancing in a basic solution

For the final, do we need to know how to balance redox equations in basic conditions? Or should we just focus on acidic?

Thanks!
Wed Mar 14, 2018 5:18 pm
Forum: First Order Reactions
Topic: Psuedo-Order Rate Laws
Replies: 1
Views: 236

### Psuedo-Order Rate Laws

Do we need to be able to use/apply the pseudo-first- or pseudo-second-order rate laws for the final?

Thanks!
Tue Mar 13, 2018 6:21 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Question 9.20
Replies: 1
Views: 257

### Question 9.20

Did anyone do question 9.20? I want to check my answers. :)

Thanks!
Sun Mar 11, 2018 12:18 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: Finding n
Replies: 4
Views: 407

### Re: Finding n

When using experimental data, answers will not always be exact. However, they should be close enough to where you can assume 1.9 or 2.1 is 2, but not assuming the answer is 2 if you have, for example, 2.5.
Tue Mar 06, 2018 8:33 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.20
Replies: 1
Views: 145

### 15.20

Thanks!
Tue Mar 06, 2018 8:19 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.18
Replies: 1
Views: 146

### 15.18

Did anyone do 15.18? If you did, can you post your answers here? I want to check if I got them right.

Thanks!
Sun Mar 04, 2018 9:33 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Homework 15.19
Replies: 3
Views: 289

### Re: Homework 15.19

On a test, I'm sure they'd still give you the points as long as all of the conversions match up (as long as it doesn't ask for a specific unit). My TA said if the question doesn't ask specifically for moles, then you can leave it in mmol if you are not confident that your conversions will be correct!
Sun Mar 04, 2018 9:28 pm
Forum: First Order Reactions
Topic: 15.23
Replies: 4
Views: 289

### Re: 15.23

For product to form, there must be something taken from the reactant. Therefore, you take the initial concentration of A and subtract the concentration that has been used to create B at time t.
Sat Mar 03, 2018 5:51 pm
Forum: General Rate Laws
Topic: Test 3 - Derivations
Replies: 4
Views: 325

### Test 3 - Derivations

Do we need to know how to derive all of the differential/integral rate laws for the upcoming test?

Thanks!
Mon Feb 19, 2018 9:09 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Water in cell diagrams
Replies: 1
Views: 116

### Water in cell diagrams

Is H20(l) never included in cell diagrams?
If so, are H20(g) and H20(s) included?
Also, are there any other molecules that will never be included in a cell diagram?

Thanks!
Mon Feb 19, 2018 8:12 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Platinum in Cell Diagrams
Replies: 1
Views: 160

### Platinum in Cell Diagrams

When writing out the cell diagrams, how do we know when to put Pt(s) on it? And if its applicable, will it be on both sides? Or is it possible to have Pt(s) just on one side?

Thanks!
Mon Feb 19, 2018 7:46 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.15a
Replies: 1
Views: 226

### 14.15a

For the half-equations Ag+(aq) + e- -> Ag(s) (cathode) and Ag(s) + Br-(aq) -> AgBr(s) + e- (anode) the cell diagram in the solutions says Ag(s)|AgBr(s)|Br-(aq)||Ag+(aq)|Ag(s) Why are the Ag(s) and AgBr(s) in the left half separated by a vertical line instead of a comma, even though they are in the s...
Sun Feb 18, 2018 3:50 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.11d
Replies: 1
Views: 127

### 14.11d

Can someone walk me through writing the half-equations and balanced equation for this problem?

Pt(s)|O2(g)|H+(aq)||OH-(aq)|O2(g)|Pt(s)
Sun Feb 18, 2018 3:14 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 14.9
Replies: 2
Views: 207

### 14.9

For all of the answers, I got my answers in Joules, but the solutions manual answers are in J/mol. Is there a reason for this, & will there be a difference between the two on the test?
Thu Feb 15, 2018 11:38 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation 2.303RT/F = .059V
Replies: 4
Views: 3283

### Re: Nernst Equation 2.303RT/F = .059V

A follow up: I'm not sure if we went over the 2.303RT/F in class but I was watching videos on the Nernst equation & it talked about this.

I think it may just be a conversion factor if you want to use log instead of ln.
Thu Feb 15, 2018 9:23 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation 2.303RT/F = .059V
Replies: 4
Views: 3283

### Nernst Equation 2.303RT/F = .059V

Can someone explain where the 2.303 comes from in the Nernst Equation when
(2.303RT)/F = .059 V
so
E°= - (.0592)/n log(Q)

Thanks!
Sat Feb 10, 2018 5:58 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: When to use Cv and Cp with entropy
Replies: 1
Views: 315

### When to use Cv and Cp with entropy

Can someone explain in which situations we use Cv and Cp? I think I remember my TA saying with entropy Cv is actually used when the volume and temperature are changing, but I don't know if I heard that correctly, since last chapter we used it when the volume was constant.
Sat Feb 10, 2018 5:29 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.13
Replies: 4
Views: 231

### 9.13

In the solutions manual, it uses 1 mol of nitrogen gas in calculations. How do we know that there is 1 mol? Is this just something we assume if not given a molar amount?
Sat Feb 10, 2018 4:52 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.5
Replies: 3
Views: 202

### 9.5

I just wanted to double check if my train of thought was correct on this one:

Is the heat negative on the 800K reservoir because the process is taking heat from that reservoir and giving it to the 200K reservoir?
If not, why is it negative?

Thanks!
Fri Feb 02, 2018 1:57 pm
Forum: Phase Changes & Related Calculations
Replies: 2
Views: 280

### Re: Adding Delta H(Fusion/Vaporization )

It takes heat to change the phase, so basically if you have ice and put it in water, it is first going to take the heat away from the water to melt the ice, and THEN the water will lose more heat to in turn heat up the "ice water." Therefore you add the heat required to melt and the heat t...
Fri Feb 02, 2018 1:54 pm
Forum: Phase Changes & Related Calculations
Topic: Phase change
Replies: 4
Views: 256

### Re: Phase change

You'll know to do a phase change when it hits the temperature for fusion or vaporization. I think normally these questions will have to do with ice/water because the melting point is 0 degrees Celsius and boiling is 100 degrees, and so its a pretty straightforward/easy one to remember. If it is ice ...
Fri Feb 02, 2018 1:39 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Steps to getting equations
Replies: 1
Views: 123

### Steps to getting equations

On tests, are we going to need to know all of the steps that Dr. Lavelle went over in class, or do we just need to know the final form of the equations?

Thanks!
Mon Jan 29, 2018 1:26 am
Forum: Phase Changes & Related Calculations
Topic: 8.21
Replies: 3
Views: 272

### Re: 8.21

Did you set the negative q of copper to the positive q of water? The copper is losing heat so you have to account for that by putting -q.
Mon Jan 29, 2018 1:23 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.57 Hess's Law [ENDORSED]
Replies: 3
Views: 530

### Re: 8.57 Hess's Law[ENDORSED]

In a simple form, you write out the reactions for combustion for those given enthalpies (add + O2 to all of them, reactants will be CO2 & H2O, except for with H2, then all you get as a product is H20). Then you just proceed as normal by multiplying/adding the equations together to cancel things ...
Sat Jan 27, 2018 9:35 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Question 8.31
Replies: 7
Views: 500

### Re: Question 8.31

Because getting from Celsius to Kelvin is just adding 273.15, the difference between T2 and T1 in Celsius is going to be just the same as between T2 and T1 in Kelvin. For example: If the initial temp is 20 degrees Celsius, that is 293.15 K. If the final temp is 40 degrees Celsius, that is 313.15 K. ...
Sun Jan 21, 2018 10:57 pm
Forum: Phase Changes & Related Calculations
Topic: ΔU vs. ΔH
Replies: 10
Views: 1275

### ΔU vs. ΔH

Can someone explain more in-depth the difference between ΔU & ΔH? I have a general understanding, but I’d like to have a more solid knowledge for the test. (for ex: in which circumstances do we use which one?)

Thanks!
Sun Jan 21, 2018 10:52 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Memorizing Enthalpies [ENDORSED]
Replies: 5
Views: 233

### Memorizing Enthalpies[ENDORSED]

Do we need to memorize common enthalpies for elements that are not on the constants/equations sheet or will they be provided on the exam?
Sat Jan 20, 2018 3:58 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard State [ENDORSED]
Replies: 2
Views: 105

### Standard State[ENDORSED]

How do we know if a substance is in its standard state? I know its the most stable form, but is there a way to tell if it is in that form? Or do we just have to memorize the standard states for common substances?

Thanks!
Sat Jan 20, 2018 1:53 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: J vs. kJ [ENDORSED]
Replies: 4
Views: 223

### J vs. kJ[ENDORSED]

Is there a certain time we should use joules vs using kilojoules (& vice versa)?

Thanks!
Sat Jan 13, 2018 5:12 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Question 8.41
Replies: 2
Views: 110

### Question 8.41

When you set the heat in ice and water equal to each other, why is there a negative sign in front of heat(water)?

Thanks!
Wed Jan 10, 2018 8:29 pm
Forum: Administrative Questions and Class Announcements
Topic: Constants & Equations Sheet
Replies: 3
Views: 217

### Constants & Equations Sheet

Do we still get the paper with all of the constants & equations on it for tests in this class?

Thanks!
Sat Dec 09, 2017 12:57 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: 12.45 Help
Replies: 1
Views: 327

### 12.45 Help

For question 45, the question asks about a pattern that can be drawn from the strengths. The answer says "aryl amines<ammonia<alkylamines" and "methyl<ethyl<etc." Where do these come from?

Thanks!
Thu Dec 07, 2017 1:26 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.89
Replies: 4
Views: 354

### Re: 11.89

100 kPa=1 bar, so to go from 1kPa you multiply each by 1/100 bar.
Sun Dec 03, 2017 6:18 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 11.73 Concept Question
Replies: 3
Views: 218

### Re: 11.73 Concept Question

If there are more moles of reactant, then an increase in pressure and decrease in volume makes the equation shift to the right. If there are more moles of product, increased pressure and decreased volume will mean a shift to the right. However, make sure you note that if pressure is increased becaus...
Sun Dec 03, 2017 6:02 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: P4
Replies: 2
Views: 251

### Re: P4

Nonpolar; there is no difference in electronegativity between the atoms since they are all the same element.
Sun Nov 26, 2017 7:36 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.45 part c
Replies: 1
Views: 126

### 11.45 part c

For part C, it asks whether Cl2 or F2 is more thermodynamically stable relative to its atoms at 1000. K. How exactly do we figure out which is more stable?

I got that the concentration for each is:
Cl2 .001 mol/L
Cl 1.1x10^-5 mol/L
F2 8x10^-4 mol/L
F 3.2x10^-4 mol/L

Thanks!
Sat Nov 25, 2017 10:31 pm
Forum: Naming
Topic: 17.31 -- Adding molecules before/after complex
Replies: 1
Views: 141

### 17.31 -- Adding molecules before/after complex

In 17.31, when you add an element before or after the complex in brackets, how do you know how much of it to add?
For example, on A the answer for potassium hexacyanidochromate (III)
K3[Cr(CN)6]
How do you know that there are 3 potassium?

Thanks!
Sat Nov 25, 2017 8:08 pm
Forum: Hybridization
Topic: 4.43 - "s-character"
Replies: 1
Views: 142

### 4.43 - "s-character"

Can someone explain the answer to this question to me? It asks: "Do you expect the bond angle between two hybrid orbitals to increase or decrease as the s-character of the hybrids is increased?" The correct answer is increase. Also, what exactly do they mean by "s-character"? Tha...
Fri Nov 24, 2017 5:15 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Shape Memorization
Replies: 6
Views: 560

### Molecular Shape Memorization

For the upcoming test, the shapes/angles are just something to know by memory, correct? Also, does anyone know if there are there specific ones we need to have memorized or just all of them that are mentioned in the textbook?

Thanks!
Tue Nov 14, 2017 4:48 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Most Favorable Formal Charge
Replies: 5
Views: 2534

### Re: Most Favorable Formal Charge

In general, the central element should not be negative, and the outer should not be positive. As long as that is followed, you just want to have the lowest overall charge & for the most part try not to have any charges on a single element above +1 or below -1.
Tue Nov 07, 2017 6:35 pm
Forum: Electronegativity
Topic: "Higher" Electron Affinity
Replies: 4
Views: 727

### Re: "Higher" Electron Affinity

For the most part, electron affinity increases going upwards and to the right. There are a few exceptions (like nitrogen, for example), so the trend is not always exact. If you look at the 3rd photo on this website, it shows the EA's of each element with a corresponding color that makes some of the ...
Tue Nov 07, 2017 6:13 pm
Forum: Ionic & Covalent Bonds
Topic: Order of Electrons Lost by Ions
Replies: 2
Views: 367

### Re: Order of Electrons Lost by Ions

The 4s energy level is higher than 3d (and 5s higher than 4d, etc.), and you remove electrons from the highest energy level first, therefore you remove from the 4s first. You remove from the higher energy levels so that the ion is more stable.
Tue Oct 31, 2017 1:41 pm
Forum: Trends in The Periodic Table
Replies: 4
Views: 371

It goes from 1s to 2p in the question, and as you go down the periodic table it increases. In this case the increase downwards must be greater than the decrease to the right.
Tue Oct 31, 2017 1:16 pm
Forum: Trends in The Periodic Table
Topic: Negative Electron Affinity
Replies: 2
Views: 329

### Re: Negative Electron Affinity

Electron affinity is the energy released when an electron is added to a gas phase atom, so when it attaches, energy is is given off.When EA is negative, there is no excess energy to give off and actually more must be provided to attach it, and therefore EA is considered low. High electron affinity w...
Thu Oct 26, 2017 1:06 am
Forum: Quantum Numbers and The H-Atom
Topic: P-Orbitals (x,y,z) [ENDORSED]
Replies: 3
Views: 2564

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

What exactly is the significance of the Px Py and Pz for the P-orbitals? Do we ever need to write these when writing electron configurations?

Thanks!
Thu Oct 26, 2017 1:00 am
Forum: Quantum Numbers and The H-Atom
Topic: Homework Question 2.17 part d
Replies: 5
Views: 387

### Re: Homework Question 2.17 part d

There are 2(l)+1 orbitals in a subshell of quantum number l. So for D, when l=3, 2(3)+1=7
Tue Oct 17, 2017 4:48 pm
Forum: DeBroglie Equation
Topic: Help with #1.33 part C
Replies: 1
Views: 211

### Help with #1.33 part C

When you have
E(photon)=1.66x10^-17 +(1/2)mv^2
why do they plug in (3.6x10^6) as v in the solution manual, when the given value in the problem is 3.6x10^3?

Thanks!
Tue Oct 17, 2017 4:26 pm
Forum: Properties of Electrons
Topic: Hydrogen Series
Replies: 4
Views: 381

### Re: Hydrogen Series

It may be important to remember that the Lyman is UV & Balmer is visible, because I noticed that in one textbook problem it says "in the UV region" but never says Lyman or n1=1, but the problem solution requires you to recognize that UV means n1=1. However, I can't see the other two be...
Mon Oct 16, 2017 2:19 pm
Forum: Properties of Light
Topic: Homework Week of 10/16 [ENDORSED]
Replies: 2
Views: 259

### Re: Homework Week of 10/16[ENDORSED]

Just chapter 1. We haven't covered anything from chapter 2 in class yet.
Thu Oct 12, 2017 11:29 am
Forum: Properties of Electrons
Topic: Series
Replies: 6
Views: 588

### Re: Series

According to my TA, we don't need to know the exact wavelengths that go with each, but we do need to know which series n=1=1, n1=2, etc. go with.
Thu Oct 05, 2017 12:48 pm
Forum: Molarity, Solutions, Dilutions
Topic: G25
Replies: 4
Views: 462

### Re: G25

I don't believe so, its just the mathematical way to solve it because of the exponent on (1/2) being a variable. If there was another way I'd imagine it would be pretty complicated!
Mon Oct 02, 2017 10:23 pm
Forum: Molarity, Solutions, Dilutions
Topic: Help with G9 [ENDORSED]
Replies: 2
Views: 309

### Help with G9[ENDORSED]

So for question G9 I'm using the formula M(I) x V(I) = M(F) x V(F)
I got
M(I)=.179mol/L
V(I)=.5L

but I can't figure out M2 and V2? or am I possibly mixing up which ones are the initial and which are final?
This might actually turn out to be simple, but I'm stuck! Help!

Thanks :)