Search found 22 matches

by Joyce Xiong 4C
Sun Mar 13, 2016 12:25 pm
Forum: Balancing Redox Reactions
Topic: Winter Final 2015
Replies: 1
Views: 298

Re: Winter Final 2015

Hey Susanna, The cell potential of a reaction does not change when you multiply/divide the reaction by a certain number; it remains the same. The only time it changes is when you flip it, changing the reaction from a reduction to oxidation reaction or from an oxidation to reduction reaction. Further...
by Joyce Xiong 4C
Sun Mar 06, 2016 10:11 pm
Forum: *Calculations Using ΔG° = -RT ln K
Topic: lnk=G/-RT
Replies: 1
Views: 889

Re: lnk=G/-RT

Hey there! As temperature decreases, Keq will increase, and when the temperature increases, Keq will decrease. The Keq tells you the ratio between two conformations (how many of the molecules in one conformation vs how many will be in the second/other conformation). In the example Dr. Lavelle gave u...
by Joyce Xiong 4C
Thu Mar 03, 2016 8:56 pm
Forum: *Alkanes
Topic: Common Names
Replies: 1
Views: 208

Re: Common Names

Hey there!

I think its really helpful to just know what they look like. Here are the pictures from Wednesday's lecture

Hope this helps
by Joyce Xiong 4C
Sun Feb 28, 2016 10:17 pm
Forum: *Organic Reaction Mechanisms in General
Topic: Kinetically Controlled
Replies: 1
Views: 243

Re: Kinetically Controlled

Hey there! I don't think there a specific cut-off for how big the Gibbs free energy must be for a molecule to be kinetically controlled, but it must be high enough to be an energy barrier that prevents the molecule from going from one state to another. In other words, so much energy is required to b...
by Joyce Xiong 4C
Sun Feb 21, 2016 1:06 am
Forum: Second Order Reactions
Topic: Deriving the Second Order Equation
Replies: 1
Views: 224

Re: Deriving the Second Order Equation

Hey there!

To get the equation, you don't need to multiple both sides by [A]t or [A]o, its a lot more simpler than that! I derived it for you on paper- you can see my work on the photo attached. Hope it helps!
by Joyce Xiong 4C
Sun Feb 21, 2016 12:37 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Pre-Equillibrium Use
Replies: 1
Views: 263

Re: Pre-Equillibrium Use

Hey there! The pre-equilibrium approach is used to verify a proposed reaction mechanism and see if it agrees with the experimental data (if they agree, two conditions must be met 1) the sum of elementary steps creates the overall reaction and 2) the rate law of the proposed mechanism matches the exp...
by Joyce Xiong 4C
Sun Feb 07, 2016 10:22 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Porous Pot- Daniell cell
Replies: 2
Views: 4162

Re: Porous Pot- Daniell cell

Hey there! For the cell structure, the porous barrier is necessary because it allows only sulfate ion to diffuse across from the cathode side to the anode side to make sure there is no charge build up caused from the flow of electrons from the anode to the cathode. By sending sulfate over the porous...
by Joyce Xiong 4C
Fri Jan 29, 2016 2:38 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isothermal, Delta U = 0
Replies: 2
Views: 568

Re: Isothermal, Delta U = 0

Hey there! There is no difference between q=-w and -q=w: they are the same thing, and both are saying that when delta U is 0, the work leaving the system is replaced by the q entering in the system, or vice versa, work done on the system results in the loss of heat. The value of w and q are the same...
by Joyce Xiong 4C
Sun Jan 24, 2016 5:15 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Why does isothermal mean no change in internal energy?
Replies: 2
Views: 384

Re: Why does isothermal mean no change in internal energy?

Hey there!

When the system is isothermal, the internal energy doesn't change because of the ideal gas law. For reversible expansion, change in U= 3/2nrt. Since T=0. the change in U (internal energy) is 0 too.
by Joyce Xiong 4C
Sun Jan 17, 2016 12:42 pm
Forum: Phase Changes & Related Calculations
Topic: Temperature as a state property?
Replies: 2
Views: 360

Re: Temperature as a state property?

Hi there! From what I know, what you said was correct, that temperature is a state property and heat is only sometimes a heat property. The reason why heat is only sometimes a state property is because heat, when the pressure of the system is constant (enthalpy), is a state property, but is not a st...
by Joyce Xiong 4C
Sat Jan 09, 2016 4:17 pm
Forum: Phase Changes & Related Calculations
Topic: Open, Closed, or Isolated Systems
Replies: 6
Views: 2784

Re: Open, Closed, or Isolated Systems

Hey Susan! So in thermochemistry, heat is exchanged between the system and its surroundings. The system is what you would be studying (an organism, a beaker) and the surrounding is the external environment that this system interacts with (the environment the organism is at, a lab where the beaker is...
by Joyce Xiong 4C
Sun Dec 06, 2015 1:29 am
Forum: Bronsted Acids & Bases
Topic: Acid strength
Replies: 1
Views: 515

Re: Acid strength

Hey there! For the examples where acids with a fluorine atom are stronger than acids with a chlorine atom, it is because chlorine is bigger than fluorine (radius increases down a group). Because the chlorine has a bigger radius than fluorine, its bond with hydrogen is longer, and thus, the bond is w...
by Joyce Xiong 4C
Sun Nov 29, 2015 1:16 pm
Forum: Octet Exceptions
Topic: Having more than 8 valence electrons
Replies: 1
Views: 10999

Re: Having more than 8 valence electrons

Hey there! Some molecules can accommodate more than 8 valence electrons because they have expanded valence shells. These molecules are from periods 3 or higher because starting from n=3, atoms have d-orbitals that can accommodate for more that 9 valence electrons. Unlike atoms from periods one and t...
by Joyce Xiong 4C
Sun Nov 22, 2015 10:04 pm
Forum: *Molecular Orbital Theory Applied To Transition Metals
Topic: Mo Theory
Replies: 1
Views: 572

Re: Mo Theory

Hey there! To fill out a molecular orbital diagram, first you need to find out how many valence electrons there are in the molecule you are drawing the diagram for. You count the electrons like how you would if you weren't doing a molecular orbital diagram, so for the molecule B2, there are 6 valenc...
by Joyce Xiong 4C
Fri Nov 13, 2015 1:37 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Two positives, which is right?
Replies: 1
Views: 190

Re: Two positives, which is right?

Hey there! When you get two positive answers, you look at those numbers and compare it to the initial concentration. The equilibrium concentration (the answer you get from solving the quadratic equation) of a reactant, cannot be larger than the initial concentration. Make sure however, you are looki...
by Joyce Xiong 4C
Fri Nov 13, 2015 1:23 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K equilibrium vs Q equilibrium
Replies: 2
Views: 415

Re: K equilibrium vs Q equilibrium

Hey there! In a chemical equilibrium, K stands for the equilibrium constant of a reaction, and Q stands for the reaction quotient. You calculate Q just like how you would calculate K, but the Q value is different (or else it would be called K). What happens here is that when you haven't waited long ...
by Joyce Xiong 4C
Sun Nov 08, 2015 11:22 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: molecular orbital theory
Replies: 2
Views: 316

Re: molecular orbital theory

I was actually confused about this too so I asked the same question during one of the midterm review sessions. You use (O1s) for 1s shells but you can also use it when a question asks you to "write the whole/complete/full electron configuration" for the molecules. However, when it asks you...
by Joyce Xiong 4C
Thu Oct 29, 2015 2:40 pm
Forum: Resonance Structures
Topic: SO4 2-
Replies: 1
Views: 2429

Re: SO4 2-

Hey there! The two lewis structures you described are indeed resonance structure of SO4 2- because despite there being a difference in how the atoms are bonded, the arrangement of atoms remain the same. Going off from there though, there are actually even more resonance structures that result from t...
by Joyce Xiong 4C
Fri Oct 23, 2015 2:48 am
Forum: Hybridization
Topic: Hybrid Orbitals
Replies: 1
Views: 226

Re: Hybrid Orbitals

Hey there! Hybridization actually does not determine the shape of a molecule (the VSEPR does that), but what it does do, is it helps us explain how our bond order (number of bonds) and geometry is correct, although it doesn't seem correct when we look at the atomic orbitals of the central atom. To i...
by Joyce Xiong 4C
Sun Oct 18, 2015 2:30 pm
Forum: Octet Exceptions
Topic: Radicals
Replies: 1
Views: 339

Re: Radicals

Hi there, Radicals are exceptions to the octet rule that are less common, and they typically occur while a reaction is happening. A radical is a molecule with an unpaired electron and is usually highly reactive, aka, unstable. Because it has an unpaired electron, the number of electrons present is a...
by Joyce Xiong 4C
Sun Oct 11, 2015 3:41 pm
Forum: Lewis Structures
Topic: Xe Lewis Dot Structure
Replies: 2
Views: 2443

Re: Xe Lewis Dot Structure

After finding your question, I researched about the octet rule, and there are actually a lot of exceptions to the octet rule that we have yet to cover. Once we go beyond n=3, there is something called the "expanded octet" that has to do with elements with d orbitals who can have more than ...
by Joyce Xiong 4C
Sun Oct 04, 2015 12:07 pm
Forum: Properties of Light
Topic: Wave Particle Duality
Replies: 1
Views: 303

Re: Wave Particle Duality

Hey Kishan, from my understanding, the orange semi-circles are peaks of the wave. In other words, if the peaks of two waves occur at the same time (when they touch on the diagram), constructive interference occurs. When they touch, it means that the waves are "in phase". That is why the bl...

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