## Search found 57 matches

Fri Mar 16, 2018 11:44 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cp or Cv??
Replies: 1
Views: 218

### Cp or Cv??

I'm still uncertain when to use Cv or Cp in finding the entropy. I've seen some threads saying that they will explicitly say which variable is constant in the question. But im looking at question 2part B on the winter 2014 Final where the volumes are changing, yet they still used Cv?
Fri Mar 16, 2018 11:38 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation
Replies: 2
Views: 100

### Nernst Equation

In the equation sheet in the test they use E= standard E - 0.05916/n(logQ). But in some cases ive seen the numerator to be 0.0257. Is there a difference between the two?
Thu Mar 15, 2018 1:12 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.29
Replies: 2
Views: 123

### 14.29

The question says: Suppose that each of the following pairs of redox couples is joined to form a galvanic cell that generates a current under standard conditions. Identify the oxidizing agent and the reducing agent, write a cell diagram, and 2 calculate the standard cell potential. (a) Co /Co and Ti...
Sun Mar 11, 2018 2:05 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.117
Replies: 1
Views: 88

### 8.117

The question says: one step in the production of hydrogen as fuel is the reaction of methane with water vapor: CH4(g)+H2O(g) --> CO2(g)+3H2(g). deltaH=-318KJ. What is the change in internal energy for the production of 1.00 mol H2? I understand that the formula delta U= delta H - P delta V must be u...
Sun Mar 11, 2018 2:01 pm
Forum: Balancing Redox Reactions
Topic: 15.114
Replies: 2
Views: 93

### Re: 15.114

OMG lol I meant question #115 on chapter 14.
Sat Mar 10, 2018 5:08 pm
Forum: Balancing Redox Reactions
Topic: 15.114
Replies: 2
Views: 93

### 15.114

How did they come up with the half reactions in the solutions manual?
Sat Mar 10, 2018 4:37 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 823889

### Re: Post All Chemistry Jokes Here

Q: What is "HIJKLMNO"?
A: H2O.
Sat Mar 10, 2018 4:37 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 823889

### Re: Post All Chemistry Jokes Here

Q: If H20 is water, what is H204?
A: Drinking, bathing, washing, swimming, etc.
Fri Mar 09, 2018 3:28 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: formula on 15.61
Replies: 3
Views: 125

### formula on 15.61

Anyone know how they got the formula in the solutions manual for #61? Is it somehow related to the slope of an Arrhenius graph?
Fri Mar 02, 2018 10:09 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 823889

### Re: Post All Chemistry Jokes Here

Q: What do you do with a sick chemist?
A. First you try to helium, then you try to curium, but if this fails then you have to barium.
Fri Mar 02, 2018 10:08 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 823889

### Re: Post All Chemistry Jokes Here

I told a chemistry joke once, but there was no reaction. :(
Thu Mar 01, 2018 4:08 pm
Forum: General Rate Laws
Topic: self test 15.2A
Replies: 1
Views: 71

### self test 15.2A

The average rate of the reaction N2(g) + 3 H2(g) --> 2 NH3(g) over a certain period is reported as 1.15 (mmol NH3) L -1 h -1. (a) What is the average rate over the same period in terms of the consumption of H2?
Tue Feb 20, 2018 11:40 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Example 14.3
Replies: 1
Views: 60

### Example 14.3

In this example the molarity of the reaction was given as 1.00 mol/L. They want to know what deltaG is. I understand that you can find deltaG with -nFE. My question is how they found the number of mol as 2.00 mol?
Tue Feb 20, 2018 1:01 am
Forum: Balancing Redox Reactions
Topic: oxidation states
Replies: 4
Views: 132

### oxidation states

How do you find the oxidation state of an element/molecule? Is it just something you memorize?
Fri Feb 09, 2018 3:32 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Self test 8.14A
Replies: 2
Views: 113

### Self test 8.14A

The question says: " Calculate the standard enthalpy of combustion of glucose from the standard enthalpies of formation in Table 8.4 and Appendix 2A." I used the formula standard deltaH= [sigma n(deltaH)formation of products] - [sigma n(deltaH)formation of reactants]. I got the same magnit...
Fri Feb 09, 2018 1:48 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Self test 8.12A
Replies: 1
Views: 132

### Self test 8.12A

The question says: " The thermochemical equation for the combustion of cyclohexane, C6H12, is C6H12(l) + 9 O2(g) -> 6 CO2(g) + 6 H2O(l), deltaH = - 3920 kJ at 298 K. What is the change in internal energy for the combustion of 1.00 mol C6H12(l) at 298 K?" I used the formula deltaU= deltaH-d...
Mon Feb 05, 2018 2:59 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Evaluation 9.3A
Replies: 2
Views: 119

### Evaluation 9.3A

The question says: "Calculate the change in molar entropy of an ideal gas when it is compressed isothermally to one-third its initial volume." They got an answer of 9.13J/K.mol. Can someone please explain how they got that?
Mon Feb 05, 2018 2:50 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Evaluation 9.2B
Replies: 1
Views: 75

### Evaluation 9.2B

The question says: "The temperature of 5.5 g of stainless steel is increased from 20 C to 100 C. What is the change in the entropy of the stainless steel? The specific heat capacity of stainless steel is 0.51 J /( C)(g)." I'm not entirely sure how to go about this problem, is it okay if I ...
Thu Feb 01, 2018 3:21 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: reversible vs irreversible
Replies: 3
Views: 138

### reversible vs irreversible

im still confused as to how reversible and irreversible process work in thermodynamics? can someone please explain the concepts and how they relate with entropy?
Tue Jan 30, 2018 9:00 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: heat capacity and entropy
Replies: 2
Views: 80

### heat capacity and entropy

just a bit confused as to why the entropy increases if the heat capacity is greater?
Sun Jan 28, 2018 11:24 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 823889

### Re: Post All Chemistry Jokes Here

im running out of chemistry jokes i should zinc of new ones :(
Sun Jan 28, 2018 11:24 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 823889

### Re: Post All Chemistry Jokes Here

Neon was cracking up so much he was like
"That was sodium funny. I slapped my neon that one!"
Tue Jan 23, 2018 7:09 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: units of enthalpy
Replies: 1
Views: 83

### units of enthalpy

when is the unit for the standard enthalpy of formation just kJ and when is it kJ/mol? i noticed in 8.65 that the reactants and products' enthalpy of formation are in kJ/mol, but the enthalpy for the reaction is just in kJ.
Tue Jan 23, 2018 4:54 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.57
Replies: 1
Views: 76

### 8.57

in 8.57, it says-- Determine the reaction enthalpy for the hydrogenation of ethyne to ethane, C2H2(g) + 2 H2(g) --> C2H6(g), from the following data: deltaHc (C2H2, g) =-1300. kJ·mol 1, deltaHc (C2H6, g)=- 1560. kJ·mol 1, deltaHc (H2, g)=- 286 kJ·mol . Can someone explain how to go about this proble...
Sun Jan 21, 2018 12:09 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 823889

### Re: Post All Chemistry Jokes Here

A neutron walked into a bar and asked how much for a drink. The bartender replied, "for you, no charge."
Thu Jan 18, 2018 9:09 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: open system
Replies: 6
Views: 236

### open system

so in lecture today dr. lavelle talked about how you can change the energy of a system if you add or subtract substance from the system. how so?
Thu Jan 18, 2018 4:34 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: enthalpy of formation
Replies: 2
Views: 106

### enthalpy of formation

why is the standard enthalpy of formation of an element in its most stable form zero? does that mean it doesn't release energy when it is formed?
Sat Jan 13, 2018 11:04 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: enthalpy
Replies: 2
Views: 114

### enthalpy

so the formula for enthalpy is internal energy + pressure(volume). why is pressure and volume need to be accounted for when calculating enthalpy?
Sat Jan 13, 2018 9:44 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 823889

### Re: Post All Chemistry Jokes Here

The optimist sees the glass half full. The pessimist sees the glass half empty. The chemist sees the glass completely full, half with liquid and half with air.
Fri Jan 12, 2018 12:53 pm
Forum: Administrative Questions and Class Announcements
Topic: HW for week 2 disc
Replies: 5
Views: 217

### HW for week 2 disc

so i know the hw for this week is on ch 8. but for wk 2 do we answer ch 9 questions? or just the stuff that prof lavelle lectured on?
Thu Jan 11, 2018 9:39 pm
Forum: Phase Changes & Related Calculations
Topic: constant pressure
Replies: 3
Views: 145

### constant pressure

The book says: "In chemistry, though, we are more concerned with heat transfers at constant pressure: most chemical reactions take place in containers open to the atmosphere and therefore take place at a constant pressure of about 1 atm. Such systems are free to expand or contract. If a gas is ...
Sun Dec 10, 2017 11:02 pm
Forum: Administrative Questions and Class Announcements
Topic: Saying Thank You to Dr. Lavelle
Replies: 200
Views: 45352

### Re: Saying Thank You to Dr. Lavelle

Hello Dr. Lavelle, Wow! What a quarter! This Chemistry class was definitely a great experience. I never liked Chemistry before because I can never understand it... until I got into your class. It's amazing how one's perspective can instantly change once a great teacher comes along -- and in just a s...
Sat Dec 09, 2017 3:43 pm
Forum: Bronsted Acids & Bases
Topic: 12.131
Replies: 1
Views: 152

### 12.131

12.131 Recall from Section 11.13 that hemoglobin (Hb) molecules in blood carry O2 molecules from the lungs, where the concentration of oxygen is high, to the tissues where it is low. In the tissues the equilibrium H3O (aq) + HbO2 (aq) <-> HHb(aq) + H2O(l) + O2(aq) releases oxygen. When muscles work ...
Thu Dec 07, 2017 11:02 pm
Forum: Lewis Structures
Topic: HClO Lewis Structure
Replies: 1
Views: 198

### HClO Lewis Structure

Why is the Oxygen the central atom when it is more electronegative than Cl?
Thu Dec 07, 2017 10:30 pm
Forum: Administrative Questions and Class Announcements
Topic: Formula Sheet
Replies: 1
Views: 103

### Formula Sheet

Just wanted to make sure if we will be given the formula sheet on the final?
Sat Dec 02, 2017 11:56 am
Forum: Lewis Acids & Bases
Topic: Lewis acid and Bronsted acid confusion?!
Replies: 2
Views: 187

### Lewis acid and Bronsted acid confusion?!

Hey all, I was reading the chapter and stumbled upon this sentence: "In other words, a Brønsted acid is a supplier of one particular Lewis acid, a proton." can someone please tone it down for me because I am just confused with what the relation between a Bronsted acid and Lewis acid is?
Fri Dec 01, 2017 12:20 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 823889

### Re: Post All Chemistry Jokes Here

Q: What do you call a tooth in a glass of water?
A: One molar solution
Mon Nov 27, 2017 9:51 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Diethylenediamine
Replies: 2
Views: 154

### Re: Diethylenediamine

Whoops I made a mistake, I thought it was -diamine instead of -triamine. Thank you so much!
Mon Nov 27, 2017 9:15 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Diethylenediamine
Replies: 2
Views: 154

### Diethylenediamine

How many binding sites does dien have? Would it be just multiplying 2 by 2 because en has 2 binding sites?
Sat Nov 25, 2017 11:51 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 823889

### Re: Post All Chemistry Jokes Here

Q: Why does hamburger yield lower energy than steak?
A: Because it's in the ground state.
Sat Nov 25, 2017 11:50 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.1 part a.
Replies: 1
Views: 94

### 11.1 part a.

Hey all,

Just a bit confused and can't really wrap my head around the idea that in equilibrium, the reaction will still happen and the concentrations of the products and reactants will be constant? How does that happen?
Fri Nov 17, 2017 3:49 pm
Forum: Administrative Questions and Class Announcements
Topic: Homework for Week 8 [ENDORSED]
Replies: 2
Views: 163

### Homework for Week 8[ENDORSED]

is the hw for week 8 on ch 4 or 5?
Mon Nov 13, 2017 9:45 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 823889

### Re: Post All Chemistry Jokes Here

"The name's bond. Sigma bond."
-007
Wed Nov 08, 2017 9:53 am
Forum: Bond Lengths & Energies
Topic: Bond Strength In Same Group
Replies: 6
Views: 619

### Re: Bond Strength In Same Group

Tue Nov 07, 2017 9:50 pm
Forum: Ionic & Covalent Bonds
Topic: #25 on Chapter 3
Replies: 6
Views: 308

### Re: #25 on Chapter 3

Correct me if I'm wrong but I'm inferring you determine the charge based on how many electrons it needs to take out/it needs to add in order to attain a noble gas electron configuration? So for example for Mg, since it is in the 3rd period s-block, it is easier for it to take out 2 electrons (and th...
Thu Nov 02, 2017 9:42 pm
Forum: Ionic & Covalent Bonds
Topic: Chemical bonds create lower energy?
Replies: 4
Views: 177

### Chemical bonds create lower energy?

Hey all,

Why is it that there is less energy when atoms are bonded as compared to when they were separated?
Wed Nov 01, 2017 4:37 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm Review [ENDORSED]
Replies: 4
Views: 327

### Re: Midterm Review[ENDORSED]

Will there be a review session beside the UA sessions? Like a session wherein it's not just for student questions but also going over all the past topics?
Tue Oct 24, 2017 9:39 pm
Forum: Trends in The Periodic Table
Topic: Electron Affinity
Replies: 1
Views: 131

### Electron Affinity

Hey all,

In which scenario would there be a negative/positive electron affinity? I just can't visualize why there needs to be more energy /release of energy when attaching an electron to an atom.
Mon Oct 23, 2017 10:57 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Energy level for n=3 and n=4?
Replies: 3
Views: 265

### Energy level for n=3 and n=4?

Hey all,

So for electron configuration I know we fill in 4s first before 3d. Does that mean that 3d has higher energy level than 4s? If yes/no, please help me understand why/why not. Thanks!
Mon Oct 16, 2017 9:31 pm
Forum: DeBroglie Equation
Topic: Post Module #34
Replies: 1
Views: 159

### Post Module #34

Hey all, I figured out the first part of the question, but I'm having troubles finding what makes the speed a reasonable amount. 34. If an electron (mass 9.11 x 10-31 kg) has an associated wavelength of 7.28 x 10-9 m, what is its speed? Is your answer reasonable, why? A. 1.00 x 10-5 m.s-1. Yes. 1.00...
Mon Oct 16, 2017 9:09 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra Module Q 29
Replies: 2
Views: 239

### Re: Atomic Spectra Module Q 29

Hi!

So basically what I did here is I divided the Total number of Energy released in 1 sec, which is 11J, by the energy per photon, which is the answer you got from part a. After that, you should get the number of photons.
Mon Oct 16, 2017 7:59 pm
Forum: Photoelectric Effect
Topic: Post Module #24
Replies: 3
Views: 189

### Post Module #24

Hey all, can someone tell me what the right answer and why fro #24? I tried answering visible light but it was incorrect. Thanks! In photoelectric experiments, typically what part of the electromagnetic spectrum is the incoming light? A. Ultraviolet B. Infrared C. Visible light D. Gamma rays E. None...
Wed Oct 11, 2017 6:51 pm
Forum: Administrative Questions and Class Announcements
Replies: 3
Views: 265

Does anyone know where I can buy a course reader for this class? I already checked the bookstore and it appears that they don't carry it.

Thanks.
Tue Oct 10, 2017 6:55 pm
Forum: Administrative Questions and Class Announcements
Topic: UA Peer Learning Sessions [ENDORSED]
Replies: 1
Views: 103

### UA Peer Learning Sessions[ENDORSED]

Hi there,

Just wondering if the UA Peer Learning Sessions are specific for Chem 14A students only or are there also students/concepts discussed from higher Chem classes?

Thanks
Fri Oct 06, 2017 7:07 pm
Forum: Empirical & Molecular Formulas
Topic: Friday Oct 6 Test
Replies: 7
Views: 450

### Re: Friday Oct 6 Test

Taylor 1F wrote:Also, are we supposed to do the pre-modules for week 2 before next week?

I think the pre-modules are just optional stuff and not graded. :)
Fri Oct 06, 2017 12:10 pm
Forum: Significant Figures
Topic: Sig Fig in final answer [ENDORSED]
Replies: 3
Views: 247

### Sig Fig in final answer[ENDORSED]

Hi, just wanted some clarification regarding significant figures.
For example the two given numbers for a problem are as follows: 5.43 and 5.9.
How many significant figures should the final answer be in?