Search found 28 matches

by Annie Qing 2F
Mon Mar 07, 2016 4:16 pm
Forum: *Free Energy of Activation vs Activation Energy
Topic: Is activation energy a constant?
Replies: 3
Views: 1404

Re: Is activation energy a constant?

External factors like pressure and temperature only affect the reaction rate. They do this by increasing the number/energy of collisions, meaning these collisions reach the activation energy more frequently. From my understanding, the only thing that affects activation energy is a catalyst. Hope thi...
by Annie Qing 2F
Mon Mar 07, 2016 3:29 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Reverse Activation Energies
Replies: 1
Views: 838

Re: Reverse Activation Energies

So reverse activation energies are just imagining the reverse reaction occurring. It's easier to visualize it when you think about the graphs of exothermic and endothermic reactions. exothermic.png It makes sense that the reverse activation energy for an exothermic reaction would be ∆H + Ea since th...
by Annie Qing 2F
Mon Mar 07, 2016 3:17 pm
Forum: *Chem3D
Topic: Types of strain
Replies: 3
Views: 1198

Re: Types of strain

Maybe a little more in detail, Torsional strain is the repulsion between electrons of molecules (methyl groups, for example) on neighboring carbons. When you rotate a molecule around a bond (hence torsional, like torque, which is the force to rotate or twist an object), this is the repulsion when gr...
by Annie Qing 2F
Thu Mar 03, 2016 9:45 pm
Forum: Administrative Questions and Class Announcements
Topic: Video Competition
Replies: 66
Views: 25534

Re: Video Competition

Chemistry Extra Credit Video
Thermodynamics - Deriving the Work Equation for a Reversible and Isothermal Process

Created by:
Divya Prajapati and Annie Qing
(Lecture 2)
by Annie Qing 2F
Tue Mar 01, 2016 8:19 am
Forum: *Electrophiles
Topic: Equal sign with a line through it
Replies: 4
Views: 1495

Re: Equal sign with a line through it

Generally, it means "not equal to."
So, for instance, .
by Annie Qing 2F
Tue Feb 23, 2016 1:10 am
Forum: Balancing Redox Reactions
Topic: Redox Reactions
Replies: 1
Views: 412

Re: Redox Reactions

Yes it is different. The reducing agent is oxidized and the oxidizing agent is reduced. If you think about it, oxidation and reduction come in pairs. The oxidizing agent (molecule that causes other molecules to lose electrons) cannot also lose electrons; it must be reduced. The opposite goes for the...
by Annie Qing 2F
Tue Feb 23, 2016 1:08 am
Forum: *Alkanes
Topic: Saturated vs unsaturated fats
Replies: 3
Views: 1755

Re: Saturated vs unsaturated fats

Unsaturated fats are liquids at room temperature because there is at least one double bond. Any non-single bond creates a kink in the structure, not allowing the molecules to crystalize easily.
In contrast, saturated fats are straight chains and pack together much more tightly.
by Annie Qing 2F
Sun Feb 14, 2016 9:33 pm
Forum: General Rate Laws
Topic: Rate laws
Replies: 1
Views: 334

Re: Rate laws

From what I understand, I think for our purposes, yes. While differential rate laws in theory simply is the rate as a function of concentration (and we could experimentally measure how the concentration measures in relation to time), the method of initial rates is the easiest. Because t is very clos...
by Annie Qing 2F
Sun Feb 07, 2016 10:50 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams
Replies: 3
Views: 515

Re: Cell Diagrams

Other than that convention, 1. Put the inert electrodes on the far left and/or far right. (e.g. Pt(s)) 2. Generally, the molecules are put in order of reactants to products on either side of the salt bridge, but I don't think this is a strict rule. *If there's more than one reactant/product, it does...
by Annie Qing 2F
Sun Jan 31, 2016 9:35 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Vacuum Scenario
Replies: 1
Views: 320

Re: Vacuum Scenario

Yes. Since the external pressure is zero, this is free expansion (nothing to expand against) and the work done is also equal to zero.
by Annie Qing 2F
Sun Jan 24, 2016 10:44 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: reversible/irreversible processes
Replies: 1
Views: 336

Re: reversible/irreversible processes

Irreversible processes are ones that happen suddenly (e.g. gas being released into a vacuum) whereas reversible processes are done over a theoretically infinite amount of time because the change happens in infinitesimally small parts. In a reversible process, the system is in equilibrium throughout ...
by Annie Qing 2F
Sun Jan 17, 2016 10:51 pm
Forum: Phase Changes & Related Calculations
Topic: phase changes
Replies: 1
Views: 281

Re: phase changes

I'm not sure if this is exactly what you mean but To change from ice to water (and then heat up the water), you have to calculate the heat required for both parts: changing the phase and then heating up the water. So it's easy to do these in order. First we figure out how much energy we need to put ...
by Annie Qing 2F
Sun Jan 10, 2016 11:09 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Enthalpy
Replies: 1
Views: 325

Re: Standard Enthalpy

Yes. The standard enthalpy of formation for an element in its most stable form is 0 because we define the standard enthalpy of formation as the change in enthalpy between the product and the elements that make it up in its most standard form. Thus in the formation of O2, for example, O2 is both the ...
by Annie Qing 2F
Thu Dec 03, 2015 2:17 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Nominal Concentration
Replies: 1
Views: 6550

Re: Nominal Concentration

So the dissociation reaction is Ba(OH)_{2}\rightarrow Ba^{2+}+2OH^{-} First, calculate the initial molarity of Ba(OH)_{2} : [Ba(OH)_{2}]=\left ( \frac{0.43 g Ba(OH)_{2}}{0.100 L} \right )\left ( \frac{mol Ba(OH)_{2}}{171.342 g Ba(OH)_{2}} \...
by Annie Qing 2F
Tue Nov 24, 2015 12:40 am
Forum: Ideal Gases
Topic: Boiling Point of a Liquid
Replies: 1
Views: 400

Re: Boiling Point of a Liquid

Yes, the boiling point of a liquid is higher at a lower altitude/higher atmospheric pressure. The boiling point is defined as "the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor." As you decrease altitude...
by Annie Qing 2F
Sun Nov 22, 2015 5:17 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Strong Vs. Weak Acids
Replies: 1
Views: 375

Re: Strong Vs. Weak Acids

While it's true that the molecules are becoming less polar as you move from F to I, for example, this also means that the bonds between H and the ion are becoming weaker. Because I is a much larger atom than F, the distance between H and I is also much larger than that between H and F. With a weaker...
by Annie Qing 2F
Mon Nov 16, 2015 12:31 am
Forum: Naming
Topic: Naming [Co (CN)5 (OH2)]^2-
Replies: 1
Views: 559

Re: Naming [Co (CN)5 (OH2)]^2-

So first you list the ligands in alphabetical order by their prefix. We have pentacyano (CN)_{5} and monoaqua ( OH_{2} ), so the first part of the naming will be monoaquapentacyano in alphabetical order. Then you list the central metal atom, which is cobalt. To determine the charge on cobalt...
by Annie Qing 2F
Mon Nov 16, 2015 12:25 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: HW 17.35
Replies: 1
Views: 384

Re: HW 17.35

So, from what I understand, in order for a ligand to be chelating, the "bite angle" or the angle between the two parts of the ligand that will attach to the central metal has to be somewhere around, or less than, 90 degrees. So in 17.35, the NH_{2} parts of the ligand are only less than an...
by Annie Qing 2F
Thu Nov 05, 2015 8:20 pm
Forum: Lewis Structures
Topic: Organic Lewis structures
Replies: 1
Views: 359

Re: Organic Lewis structures

At any end of the line or bend of the structure, we assume there is a carbon atom. We also assume that each carbon atom has four bonds, so hydrogen atoms are assumed to be attached to carbon atoms that don't already have four bonds on it. For example, Organic Chemistry 1.png There are 8 carbon atoms...
by Annie Qing 2F
Sun Nov 01, 2015 8:19 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration for Cr^2+
Replies: 2
Views: 8598

Re: Electron Configuration for Cr^2+

I think the difference with Cr^2+ is that it's an ion so we're technically removing electrons. When removing electrons, we remove from the valence shell first, in this case from n=4. Thus, we remove the first electron from 4s and the second from 3d to create the ion.

Let me know if this makes sense?
by Annie Qing 2F
Sun Nov 01, 2015 8:07 pm
Forum: Photoelectric Effect
Topic: Question 6, Quiz 1, Section 3F
Replies: 1
Views: 467

Re: Question 6, Quiz 1, Section 3F

I would like to preface this with a "sorry the equation editor isn't working for me." Anyways, From E=h(frequency) and c=(wavelength)(frequency), we can get E=h(c/wavelength). Given the wavelength of the emitted light is 161x10^-9 m, c=3.00x10^8 m/s, and h=6.62608x10^-34 J•s, E=h(c/wavelen...
by Annie Qing 2F
Wed Oct 21, 2015 2:49 pm
Forum: Bond Lengths & Energies
Topic: Bond Strength In Same Group
Replies: 6
Views: 1342

Re: Bond Strength In Same Group

I might be wrong but I think to answer your question, the stronger bond is the one with the more electronegative atom involved. For instance, the CCl_{4} bonds are stronger than those of the CBr_{4} molecule because Cl is a more electronegative atom. Electronegative atoms hold electrons more tightly...
by Annie Qing 2F
Mon Oct 12, 2015 5:34 pm
Forum: Properties of Electrons
Topic: Atomic Spectra
Replies: 1
Views: 350

Re: Atomic Spectra

First, solve for the wavelength's frequency by the equation c=\lambda \nu where c is the speed of light. The energy of that frequency can be solved for by the equation E=h\nu where h is Planck's constant. You can then find the principle quantum number (n) that correlates by the equation E_{n}=-\frac...
by Annie Qing 2F
Mon Oct 12, 2015 5:24 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Hydrogen Spectral Series
Replies: 1
Views: 390

Re: Hydrogen Spectral Series

The hydrogen spectral series shows the specific amounts of energy needed to transition between two energy levels within hydrogen and can be observed when electrons fall from higher energy levels and emit photons. We observe specific lines or amounts of energy because electrons do not gradually move ...
by Annie Qing 2F
Sat Oct 10, 2015 4:45 pm
Forum: Student Social/Study Group
Topic: Top of the Hill Study Group
Replies: 5
Views: 1107

Re: Top of the Hill Study Group

I'd be interested! I'm in Hedrick Summit.
by Annie Qing 2F
Sat Oct 10, 2015 4:35 pm
Forum: Properties of Electrons
Topic: Shielding
Replies: 2
Views: 955

Re: Shielding

From what I understand, shielding is not a phenomenon that occurs as orbitals change but as the number of shells (quantum number n) changes. So, as you go down the periodic table, the effective charge on an electron decreases because the shells are increasingly farther away from the nucleus and clos...
by Annie Qing 2F
Fri Oct 02, 2015 11:32 pm
Forum: Balancing Chemical Reactions
Topic: States of Matter In Chemical Equations
Replies: 2
Views: 621

Re: States of Matter In Chemical Equations

I believe since the boiling point for CO_{2} is -78.5°C and reactions generally occur above that temperature, CO_{2} is usually found as a gas. If by some chance the reaction occurred under -78.5˚C, I think CO_{2} would be found as a solid (because CO_{2} sublimates) under normal pressure circumstan...
by Annie Qing 2F
Fri Oct 02, 2015 11:21 pm
Forum: Trends in The Periodic Table
Topic: Atomic radius regarding the bonding of Na and Cl
Replies: 2
Views: 448

Re: Atomic radius regarding the bonding of Na and Cl

Yes, I think you're right with the electrostatic repulsion between electrons. Because the number of protons (and therefore positive charge) stays constant as chlorine gains an electron, the electrons aren't pulled closer in any way and instead spread out within the "shell" as an effect of ...

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