Search found 22 matches

by Jessica Chern 1H
Wed Mar 15, 2017 4:55 pm
Forum: *Cyclohexanes (Chair, Boat, Geometric Isomers)
Topic: Eclipsed Hydrogens for Boat Conformation of Cyclohexanes
Replies: 1
Views: 236

Eclipsed Hydrogens for Boat Conformation of Cyclohexanes

On page 113 of the Intro to Organic Chemistry book, when talking about the boat conformation for cyclohexane, it says that "the four C-H bonds on the sides are eclipsed." Which C-H bonds is this referring to? It says "side," but looking at the diagram of the molecule, I would hav...
by Jessica Chern 1H
Sun Mar 05, 2017 4:30 pm
Forum: *Alkanes
Topic: Naming Organic Molecules
Replies: 5
Views: 474

Re: Naming Organic Molecules

Yes, the longest chain is the parent chain (it can bend around when drawing the structure).
by Jessica Chern 1H
Sun Feb 26, 2017 5:44 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7610
Views: 1020535

Re: Post All Chemistry Jokes Here

Prostitute Teacher: Describe hydrogen.
Student: It is a prostitute element.
Teacher: Who taught you that?
Student: You said it does not belong to a particular group and it reacts with almost all the elements in the periodic table.
by Jessica Chern 1H
Tue Feb 21, 2017 12:27 am
Forum: General Rate Laws
Topic: Hw 15.27 and 15.35
Replies: 2
Views: 315

Re: Hw 15.27 and 15.35

Also another note, since I got tripped up here, with a first-order reaction, t = ln[A 0 /A] / k. If A = 1/8 A 0 , the equation would be t = ln[A 0 / (1/8 * A 0 )] / k, so the A 0 would cancel out. With a second-order reaction however, you need to include the initial concentration in your calculation...
by Jessica Chern 1H
Sun Feb 12, 2017 1:57 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: E and E°, G and G°
Replies: 3
Views: 512

Re: E and E°, G and G°

Well generally, ° means it's under standard conditions. So for example, E is different from E° when the concentrations of the products and reactants are not the same.
by Jessica Chern 1H
Sun Feb 05, 2017 3:54 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7610
Views: 1020535

Re: Post All Chemistry Jokes Here

What do you call a periodic table with gold missing?

Au revoir!
by Jessica Chern 1H
Sat Jan 28, 2017 10:07 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: HW 9.13
Replies: 3
Views: 416

Re: HW 9.13

I thought that the equation using R was only for volume or pressure (ΔS = nR ln(V2/V1)). Is it the same for temperature too? Where did that equation come from?
by Jessica Chern 1H
Sat Jan 28, 2017 5:03 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy Change Relating to Temperature
Replies: 1
Views: 234

Entropy Change Relating to Temperature

I know that ΔS = q/T, so I understand (using the equation) that the entropy change is smaller at higher temperatures. But why is this so, conceptually?
by Jessica Chern 1H
Fri Jan 27, 2017 11:24 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Calculating delta H of a reaction
Replies: 2
Views: 361

Re: Calculating delta H of a reaction

That's because the enthalpy of formation for elements in their most stable form equals 0. O2 is the most stable form for oxygen.
by Jessica Chern 1H
Thu Jan 19, 2017 4:14 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 1
Views: 201

Re: Bond Enthalpies

You would have to draw out the Lewis structures for each compound in order to determine the bonds between certain atoms. But I just assume all bonds in the structures are broken and then reformed in my calculations (because any that weren't actually broken would just cancel out since you subtract th...
by Jessica Chern 1H
Sat Jan 14, 2017 10:16 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Standard Reaction Enthalpy Property
Replies: 2
Views: 330

Re: Standard Reaction Enthalpy Property

Standard reaction enthalpies refer to the changes in enthalpy for an entire reaction when the reactants change into products. Standard enthalpies of formation refer to the change in enthalpy for a particular substance (e.g. one particular reactant or one particular product) which are then added/subt...
by Jessica Chern 1H
Wed Nov 30, 2016 4:10 pm
Forum: *Titrations & Titration Calculations
Topic: Weak base-strong acid
Replies: 1
Views: 227

Re: Weak base-strong acid

It's basically showing why the stoichiometric point is not exactly at ph7 for weak acids or bases. NH 3 + HCl + H 2 O <-> H 2 O + NH 4 + + Cl - ^This part shows how the salt donates its proton to the base, forming a conjugate acid (NH 4 + ). Since it's a weak base, it's at an equilibrium, so that so...
by Jessica Chern 1H
Wed Nov 30, 2016 3:59 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Hydronium and Hydroxide
Replies: 2
Views: 337

Re: Hydronium and Hydroxide

I think we usually consider the solvent to be water, so it shows the transfer of the proton from the acid to water to produce the hydronium ion. Not sure if that answered your question.
by Jessica Chern 1H
Mon Nov 14, 2016 4:45 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Quiz #3 [ENDORSED]
Replies: 7
Views: 809

Re: Quiz #3 [ENDORSED]

There are some practice questions from the Quiz 2 preparations that actually covered MOs.
by Jessica Chern 1H
Tue Nov 01, 2016 1:18 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Molecular Orbitals between Two Atoms that are Different Elements
Replies: 1
Views: 301

Molecular Orbitals between Two Atoms that are Different Elements

This is based off homework question 4.57. I understand why the bonding orbitals would be closer to the more electronegative atom in energy (because of the greater pull on electrons), but why are the antibonding orbitals closer to the less electronegative atom in energy?
by Jessica Chern 1H
Tue Nov 01, 2016 12:25 pm
Forum: Hybridization
Topic: s-character of hybrids
Replies: 1
Views: 283

s-character of hybrids

This is referring to the homework question 4.43. What does it mean by the s-character of the hybrids?
by Jessica Chern 1H
Tue Oct 25, 2016 11:00 pm
Forum: Ionic & Covalent Bonds
Topic: Lewis Structure of Ionic vs. Covalent
Replies: 3
Views: 343

Re: Lewis Structure of Ionic vs. Covalent

What about for compounds like potassium phosphide or sodium hypochlorite? (textbook exercise 3.39)
by Jessica Chern 1H
Tue Oct 25, 2016 10:14 pm
Forum: Ionic & Covalent Bonds
Topic: Lewis Structure of Ionic vs. Covalent
Replies: 3
Views: 343

Lewis Structure of Ionic vs. Covalent

Based on the name of the compound itself (e.g. ammonium chloride), how do you know if the compound is ionically or covalently bonded when drawing the Lewis Structure?
by Jessica Chern 1H
Sat Oct 22, 2016 6:27 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic Radii Trends
Replies: 1
Views: 285

Re: Ionic Radii Trends

The s-block forms cations (with a positive charge), so the loss of an electron/electrons causes a smaller radius. However, the radii also decreases due to the increasing nuclear charge. The p-block forms anions (with a negative charge), so the addition of an electron/electrons causes a larger radius...
by Jessica Chern 1H
Sat Oct 22, 2016 6:22 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Determining Resonance
Replies: 3
Views: 530

Re: Determining Resonance

Also, if an atom is double bonded to one atom of a certain element X as well as single bonded to more atoms of that same element X (that aren't also bonded to anything else), there will be resonance.
by Jessica Chern 1H
Sat Oct 08, 2016 9:27 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty of Momentum and Position [ENDORSED]
Replies: 1
Views: 356

Uncertainty of Momentum and Position [ENDORSED]

Can't you not know with zero uncertainty either the momentum or position since that would effectively make Heisenberg's Indeterminacy Equation 0 = h/4π, which is not true? (As in, shouldn't there be at least some uncertainty in both the momentum and position?)
by Jessica Chern 1H
Thu Oct 06, 2016 11:39 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Why h/4π?
Replies: 2
Views: 640

Why h/4π?

Where does the h/4π in Heisenberg's Indeterminacy Equation come from? Was it found experimentally? What determined that value?

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