## Search found 53 matches

Fri Mar 16, 2018 3:12 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Midterm #6A
Replies: 2
Views: 407

### Re: Midterm #6A

I believe they said that due to the wording, the point was given to both A & B, but A was the correct answer.
Fri Mar 16, 2018 3:10 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Example 15.7
Replies: 1
Views: 145

### Example 15.7

This asks to derive the rate law implied by the mechanism, and confirm that it matches the observed rate law for the rate of decomposition of O3. I understand up to the substitution of [O], but can someone explain how they got the 2? -- Edit: I understand how that they got 2 by multiplying by the co...
Thu Mar 15, 2018 10:08 pm
Forum: First Order Reactions
Topic: Exam 3: Question 6
Replies: 2
Views: 269

### Re: Exam 3: Question 6

You would use ln([A]t/[A]0)=-kt with [A]t=.719[A]0

Then, you would can cancel out [A]0 in ln(.719[A]0/[A]0)=-k(10 minutes) and solve for k from there.
Thu Mar 15, 2018 6:44 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Midterm #2b
Replies: 1
Views: 266

### Re: Midterm #2b

Because liquids have more entropy, detS for the reaction is positive as it goes from a lower entropy (solids) to higher entropy (liquids).
Wed Mar 14, 2018 12:36 pm
Forum: *Enzyme Kinetics
Topic: Catalyst and equilibrium constant
Replies: 3
Views: 1019

### Re: Catalyst and equilibrium constant

Yes, K doesn't change when a catalyst is added.
Tue Mar 13, 2018 8:04 pm
Forum: Administrative Questions and Class Announcements
Topic: Organic Chem on Final
Replies: 9
Views: 769

### Re: Organic Chem on Final

Wayland Leung wrote:So we would need to know all the functional groups and their line diagrams and how to draw them?

Yes. He introduced it to us in Monday lecture and will continue to go over more examples on Wednesday.
Tue Mar 13, 2018 8:02 pm
Forum: Administrative Questions and Class Announcements
Replies: 4
Views: 489

### Re: Test Grading

I don't remember him saying that either! Plus, Lavelle usually doesn't drop tests.
Tue Mar 13, 2018 8:00 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Test 1 #3
Replies: 4
Views: 424

### Re: Test 1 #3

I had written the equation, w=-pdetV, and then noted that there was a change in volume at a constant pressure.
Tue Mar 13, 2018 7:52 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Identifying highest reducing/oxidizing power
Replies: 3
Views: 234

### Re: Identifying highest reducing/oxidizing power

(If reduction potentials are given--) A higher reduction potential means a higher oxidizing power (as it's more likely to reduce), and a lower reduction potential means a higher reducing power (as its more likely to oxidize).
Tue Mar 13, 2018 7:47 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Test 2 Calculating standard potential #7
Replies: 2
Views: 320

### Re: Test 2 Calculating standard potential #7

You're trying to find the standard potential for the whole reaction using the reduction potentials given. You can set it up by saying detG(3)=detG(1)+detG(2) with 3 being the whole reaction, and 1 and 2 being the parts of the reaction with the reduction potential given. You then plug in -nFE for eac...
Thu Mar 08, 2018 12:36 am
Forum: First Order Reactions
Topic: Question 15.23
Replies: 3
Views: 266

### Re: Question 15.23

Why would you multiply [B] by 2 and not divide?
Wed Mar 07, 2018 11:49 am
Forum: First Order Reactions
Topic: Integrated Rate Laws
Replies: 1
Views: 131

### Integrated Rate Laws

Will we have to know exactly how to integrate the rate laws or can we just memorize the equations?
Wed Mar 07, 2018 10:57 am
Forum: First Order Reactions
Topic: Example 15.3
Replies: 2
Views: 222

### Example 15.3

What concentration of N2O5 remains 10.0min (600 s) after the start of its decomposition at 65 C (in reaction A) when its initial concentration was .040 mol/L? See Table 15.1 for the rate law.

Where did they find k which equals 5.2 x 10^-3? Why isn't it 3.7x10^-5?
Tue Mar 06, 2018 5:48 pm
Forum: General Rate Laws
Topic: Specification of Reactant/Product
Replies: 3
Views: 165

### Specification of Reactant/Product

If we were to forget the species to which the rate refers for average reaction rate, would the answer be incorrect?
Mon Feb 12, 2018 9:11 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Example 9.5
Replies: 3
Views: 243

### Re: Example 9.5

But why would you use argon when the question is asking about oxygen?
Mon Feb 12, 2018 4:05 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Example 9.5
Replies: 3
Views: 243

### Example 9.5

In one experiment, 1.00 mol O2(g) was compressed suddenly (and irreversibly) from 5.00 L to 1.00 L by driving in piston, and in the process its temperature was increased from 20.0 C to 25.2 C. What is the change in entropy of the gas? In Step 2, why did they use the heat capacity of argon in deltaS=...
Mon Feb 12, 2018 3:59 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Self Test 9.2
Replies: 1
Views: 168

### Self Test 9.2

Self-Test 9.3A Calculate the change in molar entropy of an ideal gas when it is compressed isothermally to one-third its initial volume.

So far, I can see that you use the equation deltaS=nRln(V2/V1), but what would you use for n in this case?
Mon Feb 12, 2018 2:57 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Derivations of Equations
Replies: 5
Views: 348

### Re: Derivations of Equations

The Van't Hoff equation isn't on the equation sheet, so that derivation would probably be nice to remember.
Mon Feb 12, 2018 2:49 am
Forum: Calculating Work of Expansion
Topic: When to use this equation
Replies: 4
Views: 283

### Re: When to use this equation

w = -nRT ln (Vfinal/Vinitial) is also used when the pressure is not kept at a constant.
Mon Feb 12, 2018 2:46 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Practice Midterm [ENDORSED]
Replies: 5
Views: 564

### Re: Practice Midterm[ENDORSED]

If you go to "Administrative Questions and Class Announcements," it's the second post!
Mon Feb 12, 2018 2:43 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Midterm Practice #2C
Replies: 1
Views: 183

### Midterm Practice #2C

How do you know to add the standard enthalpy of sublimation of carbon rather than subtracting it?
Mon Feb 12, 2018 2:37 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Test #1 Question 1B
Replies: 3
Views: 255

### Re: Test #1 Question 1B

For bonds broken, it's C=C and H-H. For bonds formed, it's C-C, C-H, and C-H.
Mon Feb 12, 2018 2:29 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Enthalpy of fusion [ENDORSED]
Replies: 4
Views: 356

### Re: Enthalpy of fusion[ENDORSED]

You set it up as q=mcdeltaT + deltaH(fusion)(1/2m), which becomes deltaH(fusion)=((2)(q-mcdeltaT))/(m). Then you just plug in the numbers and you end up getting 3.7 kJ/g.
Mon Feb 12, 2018 2:26 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Test #1 Question 6
Replies: 2
Views: 182

### Re: Test #1 Question 6

I solved this by changing the reaction so that I would have 4 moles of C instead. I multiplied the entire reaction by 4/3 to get 4 C (graphite) + 16/3 H2 (g) --> 4/3 C3H8 (g). And then I did Hess's Law according to the new equation with the 4 moles of C.
Mon Feb 12, 2018 2:22 am
Forum: Phase Changes & Related Calculations
Topic: Test #1 Question 7
Replies: 1
Views: 168

### Re: Test #1 Question 7

The answer given at review session was 16 degrees.
Mon Feb 12, 2018 2:21 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs = 0
Replies: 2
Views: 198

### Re: Gibbs = 0

deltaG=0 when the reaction is at equilibrium, so for that problem, it's because it's at a phase change.
Sun Feb 11, 2018 12:54 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Test #7
Replies: 7
Views: 434

### Test #7

For #7, I understand that we have to include deltaH(fusion) into the calculations, but can someone explain where and how? And when calculating q(ice), would we be using the specific heat for ice in this case?
Sun Feb 11, 2018 12:12 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Sig Figs in 11.19
Replies: 2
Views: 240

### Re: Sig Figs in 11.19

I feel like it should be 2 sig figs as well given the 25 degrees.
Fri Feb 02, 2018 5:15 am
Forum: Phase Changes & Related Calculations
Topic: Adding Delta H(Fusion/Vaporization )
Replies: 2
Views: 282

### Adding Delta H(Fusion/Vaporization )

In terms of calculating things such as the iced tea problem on the previous test, can someone explain conceptually why you have to add delta H fusion/vaporization on top of calculating the Q=-Q ?
Fri Feb 02, 2018 4:48 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.43
Replies: 3
Views: 238

### Re: 9.43

I believe you use 75.3 J/(molxK) which is the molar heat capacity.
Thu Jan 25, 2018 3:23 am
Forum: Phase Changes & Related Calculations
Topic: Self Test 8.7A
Replies: 2
Views: 138

### Self Test 8.7A

In an exothermic reaction at constant pressure, 50 kJ of energy left the system as heat and 20 kJ of energy left the system as expansion work. What are the values of (a) deltaH and (b) delta U for this process? Answer: (a) 50 kJ (b) 70 kJ Why don't you include the energy that left the system as expa...
Tue Jan 23, 2018 10:09 pm
Forum: Administrative Questions and Class Announcements
Topic: Week 3 Test Topic is endorsed
Replies: 37
Views: 3001

### Re: Week 3 Test Topic is endorsed

how similar are the homework questions to lavelle's test questions? On the syllabus, it says, "Homework problems will be included in tests and exams"! And I believe I saw somewhere that said at least 1 homework problem will be on the test? Either way, doing the homework always helps for L...
Mon Jan 22, 2018 10:32 pm
Forum: Phase Changes & Related Calculations
Topic: Self Test 8.1
Replies: 1
Views: 149

### Self Test 8.1

Self-Test 8.1 Water expands when it freezes. How much work does 100g of water do when it freezes at 0.0 C and pushes back the metal wwall of a pipe that exerts an opposing pressure of 1070 atm? The densities of water and ice at 0.0 C are 1.00gcm3 and .92 gcm3, respectively. [Answer: w=.86kJ] How wou...
Thu Dec 07, 2017 5:53 am
Forum: Bronsted Acids & Bases
Topic: Definition clarity
Replies: 1
Views: 306

### Re: Definition clarity

I found this on the bottom of page 464: "In Fundamentals, Section J, we saw that an Arrhenius acid is a compound that produces hydronium ions in water and an Arrhenius base is a compound that produces hydroxide ions in water. The Brønsted definition is more general because it includes the possi...
Thu Dec 07, 2017 4:50 am
Forum: Conjugate Acids & Bases
Topic: Strong Acids/Bases [ENDORSED]
Replies: 5
Views: 409

### Re: Strong Acids/Bases[ENDORSED]

For strong acids, it's best to memorize the seven (HCl, HBr, HI, HNO₃, H₂SO₄, HClO3, HClO₄), and I believe it's usually assumed all other acids are weak acids.
Thu Dec 07, 2017 4:39 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculations using ice box
Replies: 4
Views: 369

### Re: Calculations using ice box

Usually just seeing if K < 10-3 is sufficient, but if you want to be extra certain, you can use the 5% rule. I think either works.
Wed Dec 06, 2017 8:33 am
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Reason for not including water
Replies: 6
Views: 436

### Re: Reason for not including water

Yeah, you don't include water because it is a liquid. Liquids and solids aren't included in the constants because they don't affect the reactant amount at equilibrium.
Wed Dec 06, 2017 8:04 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Using The Equilibrium Arrow
Replies: 5
Views: 1374

### Re: Using The Equilibrium Arrow

Is there every an instance where there's both a strong acid and a weak base reacting together? And if so, would you still use the equilibrium arrow or would you use a regular chemical reaction arrow in that case?
Wed Dec 06, 2017 7:52 am
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Ka and Concentration
Replies: 3
Views: 427

### Re: Ka and Concentration

No, Ka is [H3O+][A-]/[HA-], so the products divided by the reactants for K!
Wed Dec 06, 2017 7:48 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: ICE Chart [ENDORSED]
Replies: 9
Views: 602

### ICE Chart[ENDORSED]

When using an ICE chart, do you only you use it for weak acids/bases where there's an equilibrium reaction? Why?
Wed Dec 06, 2017 7:45 am
Forum: Lewis Acids & Bases
Topic: 12.53
Replies: 2
Views: 267

### Re: 12.53

Here's a thread with the explanation of the question: https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=8795 In terms of memorization of strong acids/bases, I believe we just have to (or it would be helpful to) memorize the common ones, like the "strong six" acids (HCl, HBr, HI, HNO₃, H₂...
Wed Dec 06, 2017 7:31 am
Forum: Bronsted Acids & Bases
Topic: 12.25
Replies: 2
Views: 272

### Re: 12.25

The equation is

Ba(OH)2 ---> Ba2+ + 2 OH-

So for every mole of Ba(OH)2, you have 2 moles of OH-, so you multiply the concentration by 2.
Wed Dec 06, 2017 7:28 am
Forum: Lewis Acids & Bases
Topic: Memorizing Acids and Bases
Replies: 7
Views: 566

### Re: Memorizing Acids and Bases

I think it would probably be helpful to know the "strong six" (HCl, HBr, HI, HNO₃, H₂SO₄, HClO₄) for acids, and the rules for strong bases (Group 1 Hydroxides, Group 1&2 Oxides).
Wed Dec 06, 2017 7:25 am
Forum: Lewis Acids & Bases
Topic: 12.49
Replies: 2
Views: 252

### Re: 12.49

Not sure if we'll have the pKb/pKa provided but based on the tables in the text, the pKb of the hypobromite ion is 5.31 and the pKb for C17H19O3N is 5.79. Since the pKb of hypobromite is smaller, it's the stronger base.
Wed Dec 06, 2017 7:18 am
Forum: Conjugate Acids & Bases
Topic: Strong Acids/Bases [ENDORSED]
Replies: 5
Views: 409

### Strong Acids/Bases[ENDORSED]

During review session yesterday, they mentioned that strong acids/bases don't have conjugate bases/acids? Can someone explain this?
Wed Dec 06, 2017 7:17 am
Forum: Naming
Topic: Memorization [ENDORSED]
Replies: 1
Views: 227

### Memorization[ENDORSED]

For the final, will we have to memorize the whole table of ligands? or just the more common ones?
Mon Dec 04, 2017 6:43 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Using The Equilibrium Arrow
Replies: 5
Views: 1374

### Using The Equilibrium Arrow

How do we know when to use the equilibrium arrow when writing reactions with acids and bases? Do you do it whenever there's weak acids and bases? I was reading through Fundamentals J, and I noticed on F84 that they wrote a net ionic equation for the neutralization of the weak acid/base but they used...
Thu Nov 30, 2017 3:53 am
Forum: Lewis Structures
Topic: 4.9
Replies: 1
Views: 201

### 4.9

4.9 (a) What is the shape of an ICl3 molecule (iodine is the central atom)? (b) What value is expected for the ClICl bond angle?

When we finish filling up the octet, we can just put the extra electrons on the central atom? How does this work?
Thu Nov 30, 2017 3:38 am
Forum: Lewis Structures
Topic: 4.7A Homework
Replies: 3
Views: 741

### 4.7A Homework

4.7 (a) What is the shape of the thionyl chloride molecule, SOCl2? Sulfur is the central atom. (b) How many different OSCl bond angles are there in this molecule? (c) What values are expected for the OSCl and ClSCl bond angles? For A, I'm not sure if I drew it correctly. Is it supposed to be single ...
Thu Nov 30, 2017 2:29 am
Forum: Naming
Topic: HW 29 part C
Replies: 4
Views: 319

### Re: HW 29 part C

Does anyone know why cyanido is written before cobalt even though that's not alphabetical?
Thu Nov 30, 2017 2:21 am
Forum: Naming
Topic: Homework 17.29(B)
Replies: 1
Views: 157

### Homework 17.29(B)

17.29 Name each of the following complex ions and determine the oxidation number of the metal: (b) [Co(NH3)6]3+

Can someone explain why cobalt has a +3 oxidation number? or how we know the oxidation number of NH3?
Mon Oct 16, 2017 2:06 am
Forum: Properties of Light
Topic: Quiz #2 References [ENDORSED]
Replies: 4
Views: 316

### Quiz #2 References[ENDORSED]

What functions/constants/equations will we be given for the quiz?
Sun Oct 15, 2017 11:38 pm
Forum: Properties of Light
Topic: Homework Week 3
Replies: 3
Views: 244

### Homework Week 3

For the homework this week, will it be including Chapter 2? Or is it still just Chapter 1 #3-41?

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