## Search found 30 matches

Sun Mar 19, 2017 12:45 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: The different Nernst equations
Replies: 2
Views: 509

### The different Nernst equations

When do I use which equation? How do I know which one to use?

E_cell = E˚_cell - 0.0592/n * logQ

or

E_cell = E˚_cell - RT/nF ln Q??
Sun Mar 19, 2017 10:49 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 2016 Final Question 4a
Replies: 2
Views: 347

### 2016 Final Question 4a

Overall rxn is 2Fe + 2H20 + 02 --> 2Fe(OH)2 Estandard = .840 Droplet 1: [O2] = .00117, E= 0.796V after 100s What is the reaction quotient for droplet 1? Answer: n = 4 plug into E=Estandard -RT/nFlnQ Q = 942.23 I understand the plugging part, but I have two questions. How are the number of moles foun...
Mon Mar 06, 2017 12:18 pm
Forum: *Nucleophiles
Topic: 2-bromobutane reacts with cyanide
Replies: 1
Views: 1019

### 2-bromobutane reacts with cyanide

In the equation

CH3CHBRCH2CH3 + CN(-) ---> CH3CNCHCH2CH3 + Br(-),

which I'm guessing the naming would be 2-bromobutane + cyanide yields 2-cyanobutane + bromide,

specifically which atom in the cyanide ion is the nucleophile? Is it the carbon or the nitrogen and why?
Sun Feb 26, 2017 5:51 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Midterm 2017 Q2
Replies: 1
Views: 301

### Midterm 2017 Q2

Q2 A) A system consists of two glass vessels and a valve connecting them. During the following process this system is maintained at 25 degrees Celsius. Initially the valve is closed. Container A (0.24L) has 2.0 mol ) O_2. Container B (0.24L) has 8.0 mol N_2. Now we open the valve and wait until the ...
Wed Feb 15, 2017 4:24 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Molar Entropies
Replies: 4
Views: 509

### Re: Molar Entropies

thanks so much! But what do you mean by thermal energy?
Wed Feb 15, 2017 4:18 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Molar Entropies
Replies: 4
Views: 509

### Molar Entropies

When deciding which has the higher molar entropy, I understand that it depends on molar mass and residual energy. Which trumps which? In other words if one compound had a greater mass but less residual energy and the other compound a lower mass and more residual energy which molecule would have the ...
Wed Feb 15, 2017 4:13 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Quiz Prep 1, #8
Replies: 3
Views: 390

### Re: Quiz Prep 1, #8

Wed Feb 15, 2017 4:11 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Winter Midterm 2014 QB
Replies: 3
Views: 521

### Winter Midterm 2014 QB

Which has a higher molar entropy value at 25 degrees C benzene or hexane? Why is the answer hexane?
Tue Feb 14, 2017 6:21 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: Midterm Winter 2013 problem 5B
Replies: 10
Views: 1118

### Re: Midterm Winter 2013 problem 5B

I'm also very confused why that is the correct order!! What is the explanation?
Sun Feb 12, 2017 7:41 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Midterm winter 2013 question #4
Replies: 3
Views: 379

### Re: Midterm winter 2013 question #4

Not the same part of Question 4, but still about question 4. In finding the mass of water- where does the equation qwater +qboiling = m_water * C_water * ∆T + m_water * ∆H_vap come from?? I understand how it is related to q = mc∆T but where does the ∆H_vap come from?
Sun Feb 12, 2017 7:23 pm
Forum: Calculating Work of Expansion
Topic: Practice Midterm Q3A Winter 2013
Replies: 5
Views: 539

### Re: Practice Midterm Q3A Winter 2013

The answers explain that q_katana = (1.45kg)(473 J/kg*K)(289˙C). Why isn't 289˙C converted to Kelvin?
Sun Feb 12, 2017 7:04 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Winter 2013 Midterm Q2A
Replies: 10
Views: 932

### Re: Winter 2013 Midterm Q2A

I still don't understand where the equation q(ice) = n*∆H + m*C_sp * ∆T comes from?? Also what is C_sp?
Mon Jan 30, 2017 3:02 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Chapter 9, Question 9.3
Replies: 1
Views: 254

### Chapter 9, Question 9.3

When a system gains heat is the formula ∆S_sys = ∆Hsys/T applicable? With the outcome being a positive number?
Mon Jan 30, 2017 2:47 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Question 9.1
Replies: 1
Views: 243

### Question 9.1

A human body generates heat at a rate of 100W. At what rate does your body heat generate entropy in your surroundings taken at 20 degrees C? How much entropy do you generate each day? Woudl the entropy generated be greater of less if you were ni a room kept at 30 degrees C? What equations would I us...
Mon Jan 23, 2017 3:38 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Quiz Prep 1, #8
Replies: 3
Views: 390

### Quiz Prep 1, #8

A sample of 1mol of gas at 1atm and 298K is heated at a constant pressure to 350K, then the gas is compressed isothermally to its initial volume and finally cooled to 298K at a constant volume. Which of the following values is zero? ∆S_surr and ∆G ∆S_sys and ∆S_surr q and w W ∆G and ∆S_sys So I calc...
Mon Jan 23, 2017 3:20 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Quiz 1 Prep, #8
Replies: 4
Views: 556

### Quiz 1 Prep, #8

For the reaction 2C (s) + 2H2 (g) --> C2H4(g) ∆Hr is 52.3kJ/mol and ∆S = -53.07J/Kmol at 298K At what temperature will this reaction be spontaneous? I set the ∆G to zero, and got T + ∆H/∆S which = 52300/-53.07, the calculated temperature I got was -985K. So for the reaction to be spontaneous does T ...
Sun Jan 22, 2017 7:19 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Manipulating Enthalpy Reactions [ENDORSED]
Replies: 1
Views: 295

### Manipulating Enthalpy Reactions[ENDORSED]

When manipulating reactions to calculate the standard reaction enthalpy, if i divide an equation by two would I also divide the standard reaction enthalpy? For example if the equation produced 2 moles of gas and I only needed one mol of gas. Does the ∆H remain constant even if I divide an equation o...
Sun Jan 22, 2017 6:51 pm
Forum: Calculating Work of Expansion
Topic: Reversible and Isothermal
Replies: 4
Views: 485

### Re: Reversible and Isothermal

When calculating the work of a reversible or isothermal system, do we use different equations. Basically if its a reversible system do we use w= -P∆V or w = -nRTln(V2/V1)??
Sat Jan 14, 2017 2:42 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: HW 8.7
Replies: 1
Views: 267

### HW 8.7

Use the information in tables 8.3 and 8.6 and 8.7 to estimate the enthalpy of formation of each other following compounds in the liquid state. The standard enthalpy of sublimation of carbon in 717kJ/mol. a) H20 b) methanol c)benzene without resonance d) benzene with resonance How would I even go abo...
Thu Jan 12, 2017 6:28 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Cha. 8 HW Problem #57
Replies: 7
Views: 868

### Re: Cha. 8 HW Problem #57

do you always need to go through the process of canceling out or can you stop before that?
Thu Jan 12, 2017 6:11 pm
Forum: Calculating Work of Expansion
Topic: Problem 8.3
Replies: 3
Views: 408

### Problem 8.3

I can't figure out why I have my conversions wrong for this problem. The correct answer is 28J but I keep getting 287763J. Here is my work- 1) u = - (Pev)(change in volume) change in volume = -1.42 m^3 3cm= .03m 20cm=.2m pi(.2)(.015^2) Pev = 2atm 2) 1m^3 = 1000L 1.42m^3 = 1420L u = (-2atm)(-1420L)= ...
Thu Jan 12, 2017 5:33 pm
Forum: Calculating Work of Expansion
Topic: Problem 8.3
Replies: 3
Views: 330

### Problem 8.3

I can't figure out why I have my conversions wrong for this problem. The correct answer is 28J but I keep getting 287763J. Here is my work- 1) u = - (Pev)(change in volume) change in volume = -1.42 m^3 3cm= .03m 20cm=.2m pi(.2)(.015^2) Pev = 2atm 2) 1m^3 = 1000L 1.42m^3 = 1420L u = (-2atm)(-1420L)= ...
Sun Nov 08, 2015 11:28 pm
Forum: Administrative Questions and Class Announcements
Topic: Next Quarter Classes
Replies: 1
Views: 465

### Next Quarter Classes

Is it required that we have completed LS30A or Math3A before we can take Chem 14B? First quarter they told us, we could take LS30A or Math3A while taking Chem 14B... has policy changed?
Sun Nov 01, 2015 5:11 pm
Forum: Photoelectric Effect
Topic: Question 6, Quiz 1, Section 3F
Replies: 1
Views: 413

### Question 6, Quiz 1, Section 3F

The Photoelectric effect is the observation that many metal emit electrons when light shines upon them. Given the threshold energy of copper (7.53x10^-19J), calculate the velocity in (m/s) of an electron that is emitted when electromagnetic radiation with a wavelength of 161nm is shone on the surface.
Sun Oct 25, 2015 10:13 pm
Forum: Hybridization
Topic: hybridization exceptions
Replies: 1
Views: 330

### hybridization exceptions

Are there any special or unique hybridizations? For example how chromium and copper have unique electron configurations, are there unique hybridizations that are crucial to know?
Fri Oct 23, 2015 3:50 pm
Forum: Hybridization
Topic: Chapter 3.5
Replies: 4
Views: 733

### Re: Chapter 3.5

thanks so much
Tue Oct 20, 2015 10:37 pm
Forum: Hybridization
Topic: Chapter 3.5
Replies: 4
Views: 733

### Re: Chapter 3.5

similiarly in 3.21 part d, why is Ag+:[Kr]4d10 as opposed to Ag+:[Kr]4d95s1
Tue Oct 20, 2015 10:08 pm
Forum: Hybridization
Topic: Chapter 3.5
Replies: 4
Views: 733

### Chapter 3.5

I'm not sure if this is because of hybridization, but why is the electron configuration of Ga3+: [Ar]3d10. I thought it would be Ga3+:[Ar]3d84s2?
Sun Oct 18, 2015 10:16 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Carbamate ion
Replies: 1
Views: 263

### Carbamate ion

Describe as completely as you can the structure and bonding in a carbamate ion. The C-O bond lengths are both 128pm and C-N bond length is 136pm.
Sun Oct 04, 2015 7:45 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra Question 1.15
Replies: 2
Views: 320

### Atomic Spectra Question 1.15

In the ultraviolet spectrum of atomic hydrogen, a line is observed at 102.6nm. Determine the values of n for the beginning and ending energy levels of the electron during the emission of energy that leads to this spectral line. How is it possible to know which energy levels are the beginning and end...