Search found 21 matches

by Peiliang Zhou 3K
Sat Mar 12, 2016 3:33 pm
Forum: *Constitutional and Geometric Isomers (cis, Z and trans, E)
Topic: EZ naming vs Cis/Trans naming
Replies: 1
Views: 432

EZ naming vs Cis/Trans naming

Under what conditions do E and Z work and cis and trans don't? I understand they can be interchangeable for some molecules, but when can you use only one of the two? Can all cis and trans in names be replaced with E and Z, or are there also some conditions where only cis and trans can be used?
by Peiliang Zhou 3K
Sun Mar 06, 2016 5:31 pm
Forum: *Alkanes and Substituted Alkanes (Staggered, Eclipsed, Gauche, Anti, Newman Projections)
Topic: Cycloalkanes and there conformations
Replies: 2
Views: 425

Re: Cycloalkanes and there conformations

Yes, the cycloalkanes with more than 3 carbons are indeed non-planar due to staggered conformation. However, there is more to it than that. The reasoning behind why cyclopropane can only be in planar formation is because none of the carbon-carbon single bonds can spin due to being stuck in a triangu...
by Peiliang Zhou 3K
Sun Feb 28, 2016 11:46 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Difference between equations for calculating Ecell
Replies: 3
Views: 590

Re: Difference between equations for calculating Ecell

E = E standard - (0.0592/n)(logQ) is the equation used when you know the system is under standard conditions. It is essentially the same as E = E standard - ((RT)/(nF))(lnQ) except T will be constant at 25 o C, and thus the calculation RT/F is a constant itself and is already done for you, and all ...
by Peiliang Zhou 3K
Sun Feb 21, 2016 9:18 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalyst vs. Intermediate
Replies: 2
Views: 1039

Re: Catalyst vs. Intermediate

A species is an intermediate if it is formed in an earlier reaction, and then used up in a later reaction. In other words, if a species is on the product side of a reaction and then on the reactant side of a later reaction, that species can be cancelled out when writing the overall reaction and can ...
by Peiliang Zhou 3K
Sun Feb 14, 2016 11:27 pm
Forum: First Order Reactions
Topic: The dependancy on initial concentration
Replies: 1
Views: 500

The dependancy on initial concentration

Why is the half-life equation for a first order reaction independent of the initial concentration, unlike the half-life for a 2nd or zero order reaction? Is it simply because the values cancel out mathematically? What is the chemical basis?
by Peiliang Zhou 3K
Sun Feb 07, 2016 10:17 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Formula for heat
Replies: 1
Views: 294

Re: Formula for heat

q=nC (delta)t is for situations where the molar heat capacity is used, so that the mol in Cm=J/K/mol can be cancelled, and the K is cancelled out by the delta T. Similarly, q=mC (delta)t is used for specific heat capacity (where Cs=kJ/ o C/g). q=C (delta)t is used when only the heat capacity (C=kJ/K...
by Peiliang Zhou 3K
Sun Jan 31, 2016 11:33 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electromotive force
Replies: 1
Views: 190

Re: Electromotive force

"i" should represent electric current with unit A as in Amperes (Coulomb/second). Limit as i--->0 means that the current is becoming infinitely smaller and smaller, but never reaching zero. This is the point where max potential E is reached, also known as the cell potential or electromotiv...
by Peiliang Zhou 3K
Sun Jan 24, 2016 10:19 pm
Forum: Calculating Work of Expansion
Topic: Irreversible vs. Reversible Expansion - HW 8.11
Replies: 2
Views: 411

Re: Irreversible vs. Reversible Expansion - HW 8.11

Questions should tell you if an expansion was done reversibly or not, since it means the act of performing a process very slowly so that it is possible to be reversed. I think the reason reversible expansions do more work is because the process is performed with the maximum possible energy as it is ...
by Peiliang Zhou 3K
Sun Jan 17, 2016 6:56 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Water Evaporation Explanation
Replies: 1
Views: 335

Re: Water Evaporation Explanation

Since temperature is the average kinetic energy of molecules, the kinetic energy of the molecules themselves can vary greatly. There are a lot of random collisions of molecules in a body of water, which will vary the speed at which each molecule travels. As a result, there will always be some molecu...
by Peiliang Zhou 3K
Sun Jan 17, 2016 6:39 pm
Forum: Phase Changes & Related Calculations
Topic: Selecting the Correct Heating Curve
Replies: 3
Views: 495

Re: Selecting the Correct Heating Curve

You can tell C is the right answer by eliminating the other answers step-by-step. First of all, (d) can be eliminated right away as the parts where the compound is changing state should be completely flat, since all the energy is used to convert the physical state. Second of all, since the delta H(f...
by Peiliang Zhou 3K
Sun Jan 10, 2016 10:59 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Standard Enthalpy of formation of an element
Replies: 1
Views: 322

Re: Standard Enthalpy of formation of an element

When an element is in its most stable form, it means that it no longer needs to change, and can exist by itself in a sealed container. For example, O 2 (g) is in its most stable form when it is a gas. Thus, its formation equation is O 2 (g) ---> O 2 (g). No heat is absorbed or emitted in this reacti...
by Peiliang Zhou 3K
Sat Dec 05, 2015 5:16 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Valence e- configuration in 2011 Final
Replies: 1
Views: 296

Re: Valence e- configuration in 2011 Final

Yes, I'm pretty sure that's fine. They are both in the same energy level and electrons are interchangeable between the two orbitals. For example, it wouldn't matter if you put (∏2px) 2 (∏2py) 1 or (∏2px) 1 (∏2py) 2 , so it probably wouldn't matter if you combined them and put ∏2p 3 . Same goes for ∏...
by Peiliang Zhou 3K
Sun Nov 29, 2015 9:46 pm
Forum: Bronsted Acids & Bases
Topic: Clarification on Oxides
Replies: 1
Views: 380

Clarification on Oxides

Is it safe to assume that all metal oxides are basic oxides and all nonmetal oxides are acidic oxides? Also, in the course reader, it is stated that (presumably all) "metal oxides" react with water to form strong bases, while "many nonmetal oxides" react with water to form acids....
by Peiliang Zhou 3K
Mon Nov 23, 2015 5:08 pm
Forum: Lewis Acids & Bases
Topic: Strong vs Weak Acids and Bases
Replies: 3
Views: 631

Re: Strong vs Weak Acids and Bases

I would say it has to do with both memorization and objectivity. Strong acids are usually species that can easily give off protons (H+), and are completely dissociated when they react with water. Strong acids are HCl, HBr, HI, H 2 SO 4 , etc. It's good to memorize these so as to more quickly identif...
by Peiliang Zhou 3K
Sun Nov 15, 2015 9:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homework Question 11.63: a question on assuming
Replies: 1
Views: 269

Re: Homework Question 11.63: a question on assuming

According to my TA, first you have to continue the calculation based on the assumption that x=0. After you get a value for x based on that assumption, find the % dissociation of the chemical species from its initial concentration, and if that dissociation is less than 5%, your assumption is justifie...
by Peiliang Zhou 3K
Sun Nov 08, 2015 10:14 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Q vs K
Replies: 4
Views: 1222

Re: Q vs K

Q represents the ratio of [Product]/[Reactant] at any point of a reaction. K represents this ratio when the reaction is at equilibrium, meaning the ratio between the product and reactant when the reaction is most stable. In chemistry, reactions strive to maintain balance and low energy, and equilib...
by Peiliang Zhou 3K
Sun Nov 01, 2015 9:38 pm
Forum: Hybridization
Topic: Unhybridized orbitals
Replies: 1
Views: 333

Re: Unhybridized orbitals

The role of unhybridized orbitals is mainly to create the pi bonds for the double and triple bonds that the situation calls for. Depending on the atom, types of bonds, and number of electron groups, unhybridized p bonds will create the p-orbital overlaps, or pi bonds. For example, in CH4, carbon has...
by Peiliang Zhou 3K
Sun Oct 25, 2015 7:11 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: HW 4.19 (c)
Replies: 1
Views: 259

Re: HW 4.19 (c)

The total number of electrons of BH2- is 6e- (3e- in B + 2*1e- in H + 1e-). After you draw the lewis structure, you should have a Boron as the central atom with the two hydrogens bonded with single bonds and a lone electron pair on the central B atom. It should look like this: . . B / \ H H Because ...
by Peiliang Zhou 3K
Sun Oct 18, 2015 10:06 pm
Forum: Resonance Structures
Topic: What is a resonance structure?
Replies: 1
Views: 318

Re: What is a resonance structure?

Your second explanation is the more correct one. Resonance simply means that a molecule can be any of the resonance structures at the same time. Essentially, if a double bond is in one location in one of the structures, and a second location in another structure, the electrons of that double bond ar...
by Peiliang Zhou 3K
Sun Oct 11, 2015 11:45 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: The d-block in electron configurations
Replies: 1
Views: 349

The d-block in electron configurations

Since the number before the letter in an electron configuration refers to the row or period, why do electron configurations for the d-block start with 3d, even though the d-block begins on the 4th period? Is it due to the nature and/or size of the electron sub-shells? Or is it due to differences in ...
by Peiliang Zhou 3K
Sun Oct 04, 2015 8:07 pm
Forum: Molarity, Solutions, Dilutions
Topic: Titration
Replies: 2
Views: 606

Re: Titration

Second Question When calculating the concentration of the analyte (the solution with unknown concentration) after performing the titration, you will use the volume of titrant (the solution with known concentration) that was used to reach the equivalence point by looking at the change in volume in t...

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