## Search found 22 matches

Mon Mar 07, 2016 12:20 pm
Forum: *Cyclohexanes (Chair, Boat, Geometric Isomers)
Topic: Chair conformation
Replies: 2
Views: 423

### Re: Chair conformation

You are correct in that if all substituents were the same it would not matter which chair orientation you drew because both have energies of 0 kJ/mol. Hope that helped!
Mon Mar 07, 2016 12:16 pm
Forum: Administrative Questions and Class Announcements
Topic: Video Competition
Replies: 66
Views: 25157

### Re: Video Competition

Chem 14B Mathematical Rhapsody! :)

Fariha Hameed (Lecture 1)
Whitney LaValle (Lecture 3)
Rachel Tat (Lecture 3)

Mon Feb 29, 2016 2:39 pm
Forum: *Free Energy of Activation vs Activation Energy
Topic: Measuring Gibbs Free Energy and Activation Energy On Graph
Replies: 1
Views: 339

### Measuring Gibbs Free Energy and Activation Energy On Graph

Hello! On Self-Test 4.4A in the organic textbook, we are given a reaction profile diagram with two bumps/steps. Starting with a baseline from the reactants, we get that ΔG o ‡ is larger for step 2. If we change the y-axis to potential energy and start with a baseline from the reactants and then anot...
Mon Feb 22, 2016 3:05 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Pre-equilibrium approach
Replies: 3
Views: 825

### Re: Pre-equilibrium approach

For the pre-equilibrium approach you want your observed rate to match the rate of your slow step. You find the rate equation of your rate determining/slow step, but since there can be an intermediate, you want a way to rewrite the rate so there is no intermediate and the rate equations matches that ...
Tue Feb 16, 2016 3:57 pm
Forum: First Order Reactions
Topic: Half Life Graph
Replies: 1
Views: 357

### Re: Half Life Graph

The graph would be the same as the 1st, 2nd, or 0th order graph with time on the x-axis, ln[A], 1/[A], or [A] on the y-axis, and slope of -k, k, or -k, respectively. Half life is just the point on the graph at the time at which [A] is one half its original concentration. Hope this helps!
Mon Feb 08, 2016 12:25 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Using ∆Go to Find Eo
Replies: 2
Views: 503

### Using ∆Go to Find Eo

Hi! Question 14.27 from homework asks us to calculate the standard potential for the half-reaction U 4+ (aq) +4e - -->U (s) . You use the half-reactions U 4+ +e - -->U 3+ with E o = -0.61V and U 3+ +3e - -->U with E o = -1.79V and want to find E o for the desired half-reaction. Why c...
Mon Feb 01, 2016 12:20 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Potential Difference CR pg. 49
Replies: 1
Views: 242

### Re: Potential Difference CR pg. 49

You would plug the -0.76 V into the equation to get +1.1 V. The reason the equation is E o cell = E o cathode - E o anode is that all E o values are written as reductions, but since the anode (Zn in this case) is oxidized, the equation accounts for reversing the E o value by subtracting it from the ...
Mon Jan 25, 2016 12:25 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: calculating standard gibbs free energy of reation
Replies: 1
Views: 905

### Re: calculating standard gibbs free energy of reation

You make the value positive because you are not forming HgO but rather doing the reverse, which is decomposing 2HgO to make 2Hg and O2. Hope this helps!
Wed Jan 20, 2016 2:10 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: Third Law of Thermodynamics
Replies: 1
Views: 396

### Re: Third Law of Thermodynamics

There can only be 0 entropy at 0 Kelvin. When temperatures are above 0 K, particles start to move, generating some disorder or entropy. So only a perfect crystal with no movement at absolute 0 can have 0 entropy. Hope this helps!
Mon Jan 11, 2016 3:50 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Enthalpy of Formation of NO2
Replies: 1
Views: 4496

### Standard Enthalpy of Formation of NO2

Hi! In the course reader we used Hess's Law to find the ΔH for NO 2 formation with the net reaction N 2 (g) + O 2 (g) --> 2NO 2 (g). If we instead wanted to know the value of the standard enthalpy of formation for NO 2 , would we take the net enthalpy (which was 68 kJ) and divide it by the 2 moles o...
Fri Jan 08, 2016 3:25 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Breaking and Forming Bonds
Replies: 1
Views: 275

### Re: Breaking and Forming Bonds

Hi! Breaking bonds would require an input of energy and be endothermic, and forming bonds would release energy and be exothermic. Atoms usually prefer to form bonds to get them to a more stable, lower energy state, and energy would then be released. Hope this helps!
Thu Dec 03, 2015 2:42 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: When K=1
Replies: 3
Views: 4086

### Re: When K=1

Oh yes sorry about that! We know that neither products nor reactants are favored at K=1 , but we would not know if it is at equilibrium. We would have to be given value of the equilibrium constant for that particular reaction to find out.
Mon Nov 30, 2015 2:51 pm
Forum: Significant Figures
Topic: Significant Figures given Kc
Replies: 1
Views: 815

### Significant Figures given Kc

Hi! If we are given initial concentrations all with 4 significant figures and an equilibrium constant with 3 significant figures, should our final answer have 4 or 3 significant figures? Does the number of sig figs of the given constant affect how accurately our final concentration should be measure...
Mon Nov 23, 2015 3:18 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: When K=1
Replies: 3
Views: 4086

### Re: When K=1

Hi! When K=1 the reaction is definitely still occurring but has reached equilibrium. In the equilibrium equation aA+bB<-->cC+dD, the value of [C]cx[D]d would equal the value of [A]ax[B]b, and neither the reactant nor product would be favored. Hope this helps!
Mon Nov 16, 2015 3:21 pm
Forum: Ideal Gases
Topic: Question about Kp vs Kc
Replies: 2
Views: 656

### Re: Question about Kp vs Kc

You can convert the pressures into concentrations by rearranging the ideal gas equation PV=nRT to get n/V (which is concentration) equal to P/RT. Make sure to use the R constant with the same unit of pressure given and to use T in Kelvin. Hope this helps!
Wed Nov 11, 2015 3:37 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Changes in Volume
Replies: 1
Views: 332

### Changes in Volume

Hi! Why is it that a decrease in volume shifts the reaction to the side with fewer moles and vice versa? Thank you!
Mon Nov 02, 2015 3:05 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Quiz 1 uncertainty question
Replies: 1
Views: 510

### Re: Quiz 1 uncertainty question

It would be the electron because the neutron would have a greater delta p (which is equal to mass times velocity.) Since certainty in momentum and certainty in position are inversely related, the greater the certainty in momentum, the lower the certainty in position. Hope that answered your question!
Mon Oct 26, 2015 2:41 pm
Forum: Lewis Structures
Topic: Lewis Structure for CH2
Replies: 1
Views: 4047

### Lewis Structure for CH2

Hi! What would the Lewis Structure for CH2 be? Would you put a lone pair on the C atom or put two unpaired electrons, making it biradical? How would you know which to do? Thank you!
Mon Oct 19, 2015 3:00 pm
Forum: Octet Exceptions
Topic: Incomplete Octets
Replies: 1
Views: 377

### Incomplete Octets

Hello! Why is it that Boron and Aluminum can have incomplete octets? Is it to maintain a formal charge of 0? Thank you!
Mon Oct 12, 2015 3:51 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration for Fe2+
Replies: 1
Views: 2549

### Electron Configuration for Fe2+

Hi! Would the electron configuration for Fe2+ be [Ar]3d6 by removing the two electrons from the outermost 4s orbital or [Ar]3d54s1 and isoelectronic with chromium? Thank you!
Wed Oct 07, 2015 2:53 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 4s Before 3d
Replies: 1
Views: 403

### 4s Before 3d

Hello! Why do we first fill the 4s orbital before the 3d orbital if 3d is a lower energy level? Doesn't this defy the Aufbau principle? Thank you!
Wed Sep 30, 2015 4:19 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Number of Energy Levels
Replies: 1
Views: 292

### Number of Energy Levels

Hi! To how high an energy level (n=1,2,3...) can an electron jump? And does an atom of any element have the same number of available energy levels? Thank you!