Search found 23 matches

by Reem Abu-Shamma 2H
Fri Mar 17, 2017 8:57 pm
Forum: Administrative Questions and Class Announcements
Topic: Saying Thank You to Dr. Lavelle
Replies: 202
Views: 70166

Re: Saying Thank You to Dr. Lavelle

Dear Professor Lavelle, Thank you for finally making me feel confident with chemistry. I have a feeling that the material you've taught me for both Chem 14A and 14B will continue to stick in my mind for years to come. I've enjoyed your classes (especially the last 2 mins of chemistry jokes). Wish yo...
by Reem Abu-Shamma 2H
Mon Mar 13, 2017 6:52 pm
Forum: *Cyclohexanes (Chair, Boat, Geometric Isomers)
Topic: bond angles
Replies: 2
Views: 267

Re: bond angles

If you recall from Chem 14A, when we discussed shapes of molecules and hybridization, we said that any molecule with 4 bonds (and therefore sp3 hybridization) would prefer to have a bond angle of 109.5. This is due to the valence shell electron pair repulsion theory which basically states that elect...
by Reem Abu-Shamma 2H
Thu Mar 09, 2017 10:10 pm
Forum: *Cycloalkanes
Topic: Priority
Replies: 1
Views: 278

Re: Priority

The molecule would be called: 2-isopropyl-1,1-dimethylcyclopentane because lower numbers always get priority. So overall, we would rather have: 2,1,1 than 1,2,2 when numbering the substituents because the former (2,1,1) has a greater amount of smaller numbers.
by Reem Abu-Shamma 2H
Mon Feb 27, 2017 6:04 pm
Forum: Administrative Questions and Class Announcements
Topic: Friday Review Session Broadcast
Replies: 3
Views: 319

Friday Review Session Broadcast

Will the review session on friday be broadcasted? I would love to attend but the timing conflicts with my shift for volunteering at the hospital.
by Reem Abu-Shamma 2H
Thu Feb 23, 2017 7:19 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.89
Replies: 1
Views: 221

Re: 15.89

The activation energy is the distance between the peak and the horizontal line corresponding to the reactants and/or intermediates (for a 3 step reaction) as shown in the attachment below The reaction is exothermic when the reactants have a greater energy than the products (reactants are above produ...
by Reem Abu-Shamma 2H
Sat Feb 18, 2017 10:43 am
Forum: General Rate Laws
Topic: Difference Between K and Kprime [ENDORSED]
Replies: 1
Views: 246

Re: Difference Between K and Kprime [ENDORSED]

k is the rate constant for the forward reaction while k' is the rate constant for the reverse reaction
by Reem Abu-Shamma 2H
Wed Feb 08, 2017 8:23 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Q=What is "i"?
Replies: 1
Views: 246

Q=What is "i"?

On page 45 of the course reader it says that "in the limit as i -->0, potential difference is called the electromotive force of the cell"
What does "i" refer to?

Thanks in advance.
by Reem Abu-Shamma 2H
Sat Feb 04, 2017 10:41 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Example on page 50 in course reader (Gold)
Replies: 1
Views: 257

Re: Example on page 50 in course reader (Gold)

For a spontaneous process E must be positive; since it's negative for the oxidation of gold from solid to aqueous (dissolving gold), the reaction is unfavourable.
Also delta G should be negative for a reaction to be favourable.
by Reem Abu-Shamma 2H
Sun Jan 29, 2017 8:01 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpy [ENDORSED]
Replies: 2
Views: 331

Re: Bond Enthalpy [ENDORSED]

Draw out the lewis structures for each of the molecules in the products and reactants and it'll make it easier to visualise which bonds break and which bonds form
by Reem Abu-Shamma 2H
Sat Jan 21, 2017 10:23 pm
Forum: Calculating Work of Expansion
Topic: Work Equation, changing V and P
Replies: 2
Views: 301

Re: Work Equation, changing V and P

Yes, that reasoning makes sense.
by Reem Abu-Shamma 2H
Sat Jan 21, 2017 10:14 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Calculating work of isothermal expansion [ENDORSED]
Replies: 1
Views: 281

Re: Calculating work of isothermal expansion [ENDORSED]

Calculate the work done for each process and compare them: 1) use: w= -Pex * delta V (because external pressure is constant) so w= -(1 atm) * (4 L) = -4 L*atm which is -405 J 2) use: w= -nRT ln(Vfinal/Vinitial) (because it is the reversible isothermal path) so w= -(1 mole) * (8.3145JKMol) *(303 K)*(...
by Reem Abu-Shamma 2H
Fri Dec 02, 2016 1:51 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Why aqua is monodentate?
Replies: 2
Views: 352

Re: Why aqua is monodentate?

When you decide whether a ligand is a monodentate or a polydentate you need to look at the number of ATOMS with lone pairs, not the number of lone pairs only. Since only ONE atom (Oxygen) in aqua has lone pairs, then the ligand is a monodentate.
by Reem Abu-Shamma 2H
Thu Nov 24, 2016 2:24 pm
Forum: Lewis Acids & Bases
Topic: Determining which compound is stonger
Replies: 2
Views: 358

Re: Determining which compound is stonger

Yes, trichloroacetic acid is a stronger acid than acetic acid because Cl is more electronegative than H. Recall that the more electronegative the element is, the more electron withdrawing occurs, and therefore the negative charge is more delocalised. The greater the delocalisation, the more stable a...
by Reem Abu-Shamma 2H
Thu Nov 17, 2016 7:14 pm
Forum: Naming
Topic: Polydentates
Replies: 4
Views: 501

Re: Polydentates

Carbonato does have 4 oxygen atoms with lone pairs but only 2 of them are attached to the C with single bonds. The single bonds allow the ligand to rotate and adjust around the transition metal to form coordinate bonds. The remaining 2 oxygens bind to the Carbon with double bonds and therefore don't...
by Reem Abu-Shamma 2H
Fri Nov 11, 2016 7:34 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K and Q calculations
Replies: 1
Views: 243

Re: K and Q calculations

Kc and Kp are both gas equilibrium constants. Which one you need to find depends on what is given in the question. If the concentration of the reactants and products is given then you find Kc. If partial pressure is given then you find Kp.
by Reem Abu-Shamma 2H
Fri Oct 28, 2016 9:39 pm
Forum: General Science Questions
Topic: Hybridization
Replies: 1
Views: 460

Re: Hybridization

Think of the word "Hybrid" to remember the concept of hybridization (hybrid: something made by the combination of two different things). In this case, these "two different things" are the "s" and "p" orbitals, combining to form a new set of orbitals (either sp...
by Reem Abu-Shamma 2H
Fri Oct 28, 2016 9:12 pm
Forum: Hybridization
Topic: Hybridization of Benzene
Replies: 1
Views: 1180

Re: Hybridization of Benzene

Each carbon atom has 3 regions of electron density (the shape is a trigonal planar). The carbon forms 2 single bonds and 1 double bond. Each single bonds form 1 sigma bonds and the double bond forms one sigma bond and one double bond (total of 3 sigma and 1 pi). The hybridized orbitals are the 2sp2 ...
by Reem Abu-Shamma 2H
Fri Oct 28, 2016 8:59 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Sigma/Pi Bonds
Replies: 1
Views: 274

Re: Sigma/Pi Bonds

1) all single bonds are sigma bonds
2) all double bonds have one sigma bond and one pi bond
3) all triple bonds have one sigma bong, and two pi bonds
by Reem Abu-Shamma 2H
Sun Oct 23, 2016 9:25 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Charge Distribution in Molecules
Replies: 1
Views: 245

Re: Charge Distribution in Molecules

The concept of electric dipole moment explains how one part of the molecule is slightly more negative than the other part of the molecule. This occurs due to the difference in electronegativity (the ability to pull on the electrons more) between the atoms in the covalent bond. So in the example in t...
by Reem Abu-Shamma 2H
Sun Oct 23, 2016 9:07 pm
Forum: Dipole Moments
Topic: Polar vs. Nonpolar Covalent Bonds
Replies: 1
Views: 642

Re: Polar vs. Nonpolar Covalent Bonds

When determining if a covalent molecule is polar or non-polar, there are more factors to take into consideration (not just difference in electronegativity). The shape of a molecule is very important. For example, let's consider BeCl2 (which has a linear shape). Despite the relatively high difference...
by Reem Abu-Shamma 2H
Sat Oct 15, 2016 5:43 pm
Forum: Resonance Structures
Topic: Breaking the Octet Rule
Replies: 6
Views: 839

Re: Breaking the Octet Rule

There are some cases in which an atom can have more than 8 valence electrons. These atoms are known to have an "expanded octet". This happens for some atoms in the third period and for atoms in periods below that. Some common examples are Phosphorous in PCL5 (which has 10 valence electrons...
by Reem Abu-Shamma 2H
Sat Oct 01, 2016 4:25 pm
Forum: Photoelectric Effect
Topic: Question 18 Part B on Photoelectric Post Assessment [ENDORSED]
Replies: 3
Views: 502

Re: Question 18 Part B on Photoelectric Post Assessment [ENDORSED]

The work function is also known as the threshold energy (the energy required to remove the electrons from a metal surface). Since the value for work function is given in Joules per moles and the question asks how much energy is needed to remove an electron from ONE sodium atom, you need to divide th...

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