Search found 35 matches

by Shirley_Zhang 3O
Tue Mar 21, 2017 11:18 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7606
Views: 1018749

Re: Post All Chemistry Jokes Here

Why do sodium, carbon, hydrogen, and oxygen taste so good together?
- NaCHOs
by Shirley_Zhang 3O
Sun Mar 12, 2017 11:54 pm
Forum: *Alkanes and Substituted Alkanes (Staggered, Eclipsed, Gauche, Anti, Newman Projections)
Topic: Butane - Gauche formation
Replies: 1
Views: 268

Re: Butane - Gauche formation

The energy is determined by how far the neighboring atoms are spaced out, not how big the angles are.
by Shirley_Zhang 3O
Sun Mar 05, 2017 12:46 pm
Forum: *Free Energy of Activation vs Activation Energy
Topic: exergonic vs exothermic
Replies: 2
Views: 654

Re: exergonic vs exothermic

Exergonic refers to the negative change in Gibbs free energy, whereas exothermic refers to the negative change in enthalpy.
by Shirley_Zhang 3O
Sun Feb 26, 2017 11:47 pm
Forum: *Electrophiles
Topic: Electrophile Vs. Nucleophile
Replies: 3
Views: 410

Re: Electrophile Vs. Nucleophile

I suppose when you say "it is not obvious," you mean that the elements do not have obvious partial charges that are used to classify them as nucleophile or electrophile. In this case, you would need to look at the elements' likelihood of accepting or donating electrons. If the element acce...
by Shirley_Zhang 3O
Sun Feb 19, 2017 9:42 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Unique Rate of A Reaction
Replies: 2
Views: 309

Re: Unique Rate of A Reaction

Some students asked the same question couple years ago, and here is what Dr. Lavelle posted back then: "A unique rate is a rate of appearance/disappearance of any of the species in a reaction divided by its stoichiometric coefficient. A unique rate will be the same for each reactant or product....
by Shirley_Zhang 3O
Sun Feb 12, 2017 7:37 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: constant volume and pressure
Replies: 1
Views: 366

Re: constant volume and pressure

Cv,m stands for the molar specific heat capacity under constant volume, so you use Cv,m when volume is constant. Cv,m = 3R/2 because the object is assumed to behave IDEALLY. This does not mean that Multiplying Cv,m with "n" gives you the specific heat capacity of whatever object you are ca...
by Shirley_Zhang 3O
Wed Jan 25, 2017 1:38 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Calculating Internal Energy Change
Replies: 1
Views: 254

Re: Calculating Internal Energy Change

I am not sure if I am correct, but here is what I think. The heat capacity of the calorimeter remains unchanged regardless of the rxn that takes place inside because heat capacity measures how much heat is needed to rise the temperature of the system by 1 degree. Heat capacity is an intensive proper...
by Shirley_Zhang 3O
Sun Jan 22, 2017 12:19 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy
Replies: 2
Views: 243

Re: Entropy

The two factors that change entropy (the probability of a system being in a particular state) are heat and expansion. The entropy associate with heat is called THERMAL ENTROPY, which is calculated by reversible heat divided by temperature. The entropy associated with expansion is called is RESIDUAL ...
by Shirley_Zhang 3O
Mon Jan 16, 2017 9:36 pm
Forum: Phase Changes & Related Calculations
Topic: Adiabatic
Replies: 1
Views: 265

Re: Adiabatic

Adiabatic means that no heat leaves or enters the system.
by Shirley_Zhang 3O
Sat Dec 03, 2016 11:12 am
Forum: Ideal Gases
Topic: Q and K [ENDORSED]
Replies: 35
Views: 1204

Re: Q and K [ENDORSED]

There is no difference between the two formula.
by Shirley_Zhang 3O
Sun Nov 20, 2016 9:28 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Strong Acid or Weak Acid
Replies: 3
Views: 548

Re: Strong Acid or Weak Acid

the strong acids are usually composed of hydrogen + group 1 or group 2 elements because these compound desolve easily in solvent, thus contributing a large increase to the concentration of hydronium ions. I don't think there's a way in determining the strength of an acid based simply on the chemical...
by Shirley_Zhang 3O
Sun Nov 20, 2016 9:20 pm
Forum: Conjugate Acids & Bases
Topic: pOH from pH [ENDORSED]
Replies: 2
Views: 404

Re: pOH from pH [ENDORSED]

Remember that pOH and pH are reverse of each other.
First, you calculate the "-log[conc. of hydronium]" which gives you pH
Then, from the equation "pH + pOH = 14" that we derived in class, you can plug the pH value and solve the equation.
by Shirley_Zhang 3O
Sun Nov 13, 2016 7:52 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: The difference between K, Kc, and Kp
Replies: 2
Views: 375

Re: The difference between K, Kc, and Kp

"K" does not mean any particular number in chemical equilibrium
"Kc" is the equilibrium concentration
"Kp" is the equilibrium pressure
by Shirley_Zhang 3O
Sun Nov 06, 2016 9:45 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Boron M.O. and Bond Order?
Replies: 1
Views: 293

Re: Boron M.O. and Bond Order?

Bond order explains bond stability. It is not an indication of how many bonds a atom can form.
by Shirley_Zhang 3O
Sun Oct 30, 2016 3:57 pm
Forum: Hybridization
Topic: Lone pairs [ENDORSED]
Replies: 1
Views: 228

Re: Lone pairs [ENDORSED]

Lone pair is considered as an electron density region, so it does affect the number of hybridization orbitals.
The hybridization orbitals for a central atom with three bonds and one lone pair are sp3.
by Shirley_Zhang 3O
Sun Oct 30, 2016 3:50 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Shape and Polarity
Replies: 2
Views: 382

Re: Molecular Shape and Polarity

One general rule to determine the polarity of a molecule is to see whether the bonding electron pairs are scattered evenly around the central atom. If they are evenly scattered, then the molecule is nonpolar. (The idea behind this guideline is that the difference between partial charges of surround...
by Shirley_Zhang 3O
Sat Oct 22, 2016 2:44 pm
Forum: Electronegativity
Topic: HW 3.59
Replies: 2
Views: 306

Re: HW 3.59

After actually doing #59, and I used double bond; I think it would be better to put the extra electron on chlorine because chlorine can have expanded octet.
adding electron to oxygen would give you a final charge of -1 instead of zero
by Shirley_Zhang 3O
Sat Oct 22, 2016 1:14 pm
Forum: Electronegativity
Topic: HW 3.59
Replies: 2
Views: 306

Re: HW 3.59

At this point, I would refer back to the octet rule.
by Shirley_Zhang 3O
Sat Oct 22, 2016 1:10 pm
Forum: Octet Exceptions
Topic: Octet exceptions and double bonds
Replies: 3
Views: 407

Re: Octet exceptions and double bonds

I think it does have to do with the formal charges. The lewis structure for XeOF4 has FC of zero.
One important thing to note is that having a negative partial charge is not preferable because the surrounding atoms have higher electron affinity.
by Shirley_Zhang 3O
Sat Oct 22, 2016 1:00 pm
Forum: Lewis Structures
Topic: When are you supposed to know?
Replies: 1
Views: 288

Re: When are you supposed to know?

You use brackets "[ ]" for ionic bonds.
You use dashes "___" for covalent bonds.

And you use the difference in electronegativity to determine whether a molecule has ionic or covalent bonds.
by Shirley_Zhang 3O
Sat Oct 22, 2016 12:53 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Px, Py, Pz [ENDORSED]
Replies: 5
Views: 9383

Re: Px, Py, Pz [ENDORSED]

I confirmed with Dr. Lavelle that assigning coordinates ( x, y, z, etc) to orbitals is arbitrary. He will not test us on that, so we do not have to worry too much. :)
by Shirley_Zhang 3O
Fri Oct 21, 2016 1:45 pm
Forum: Ionic & Covalent Bonds
Topic: Order or formula
Replies: 2
Views: 261

Re: Order or formula

Also, if you have part of a formula in parenthesis, such as

(NH2) XYZ , where X, Y, and Z represent some random atoms


the 2 hydrogen atoms are attached to the nitrogen atom when drawing Lewis Structure.
by Shirley_Zhang 3O
Fri Oct 21, 2016 1:39 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Px, Py, Pz [ENDORSED]
Replies: 5
Views: 9383

Re: Px, Py, Pz [ENDORSED]

They describe the locations of electrons in a P-orbital. So instead of saying "these electron are in the front and back," we can say "their positions are on the x-axis" since they are in P-orbital, we state their location as "Px" same idea for Py and Pz Do you know how...
by Shirley_Zhang 3O
Fri Oct 21, 2016 1:07 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge Meaning
Replies: 2
Views: 634

Re: Formal Charge Meaning

What is the actual meaning of the formal charge of an atom, and how does it affect the compound? I understand that we want all the atoms to have formal charges of 0 because this indicates that it is the most "stable", but what does this really mean/refer to? You want the formal charge of ...
by Shirley_Zhang 3O
Fri Oct 21, 2016 12:39 pm
Forum: Lewis Structures
Topic: Lewis Structures
Replies: 6
Views: 451

Re: Lewis Structures

Joslyn_Santana_3A wrote:Here is an example of Xe breaking the octet rule.


Yes, you are right that both the S and P orbitals are filled, but Xe also has 5d orbitals that is shown in period 6 on the periodic table, so the extra pairs of bonds occupy the d-orbitals
by Shirley_Zhang 3O
Sat Oct 15, 2016 11:46 pm
Forum: Trends in The Periodic Table
Topic: d-block electron configuraitons
Replies: 4
Views: 534

Re: d-block electron configuraitons

We must note that before atomic number 20, there''s no d-orbitals. The general guideline is that once the d-orbitals at n-th energy level are filled, their energy levels drop below the s-orbitals of n+1st energy level; therefore d-orbitals, if exist, from n-th energy level should be written before s...
by Shirley_Zhang 3O
Sat Oct 15, 2016 11:22 pm
Forum: Resonance Structures
Topic: Electrons in Resonance [ENDORSED]
Replies: 4
Views: 458

Re: Electrons in Resonance [ENDORSED]

The electrons are in the state of somewhere in between.
by Shirley_Zhang 3O
Sun Oct 09, 2016 10:11 am
Forum: DeBroglie Equation
Topic: Question: How should I decide if I use DeBroglie Equation or the equation for Kinetic Energy?
Replies: 4
Views: 418

Re: Question: How should I decide if I use DeBroglie Equation or the equation for Kinetic Energy?

Even thought both equations contain velocity, calculating Ek doesn't help you to solve for wavelength. At least with what we have learned so far, we do not know how to convert Ek to wavelength or frequency.
by Shirley_Zhang 3O
Sun Oct 09, 2016 9:59 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Px, Py, Pz [ENDORSED]
Replies: 5
Views: 9383

Re: Px, Py, Pz [ENDORSED]

They describe the locations of electrons in a P-orbital. So instead of saying "these electron are in the front and back," we can say "their positions are on the x-axis"
since they are in P-orbital, we state their location as "Px"

same idea for Py and Pz
by Shirley_Zhang 3O
Sun Oct 09, 2016 9:51 am
Forum: *Shrodinger Equation
Topic: wavefunction, psi, and orbitals [ENDORSED]
Replies: 1
Views: 636

Re: wavefunction, psi, and orbitals [ENDORSED]

Based on the information given by the following website http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/wvfun.html#c2 It seems to me that: Psi itself gives you a prediction of position and time of an electron. Psi gives you the shape of an orbital Psi square represents to probability of finding a...
by Shirley_Zhang 3O
Fri Oct 07, 2016 7:41 pm
Forum: Properties of Light
Topic: Problem 7 Quiz 1 Preparation in the Workbook [ENDORSED]
Replies: 1
Views: 211

Re: Problem 7 Quiz 1 Preparation in the Workbook [ENDORSED]

Hertz = 1/second or second^-1
so if we ignore the number, the calculation would look like the following:

(meter*second^-1) / (meter) = second^1 = hertz

which corresponds to

speed of light / wavelength = frequency
by Shirley_Zhang 3O
Fri Oct 07, 2016 7:22 pm
Forum: Trends in The Periodic Table
Topic: orbitals
Replies: 2
Views: 415

Re: orbitals

For your second question:
the elements in the s-block go from group(column) 1 to group 2
the elements in the p-block go from group 13 to 18
the elements in the d-block go from group 3-12
f-block would be the last two periods (6 and 7)
by Shirley_Zhang 3O
Wed Sep 28, 2016 9:49 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Equation Post Assessment Problem
Replies: 3
Views: 1100

Re: Rydberg Equation Post Assessment Problem

1.14E14 = -3.29E15 [(1/n^2) - (1/4^2)]

n^2 = 1/(1.14E14/-3.29E15 + 1/16)

square root both sides and you will get an answer that is close to an integer. :)
by Shirley_Zhang 3O
Tue Sep 27, 2016 11:18 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Equation Post Assessment Problem
Replies: 3
Views: 1100

Re: Rydberg Equation Post Assessment Problem

Given the shortcut formula: frequency = -R [(1/n*2) - (1/N*2)] in which "n" is the initial energy level, and "N" is the final energy level. you basically substitute all the values into the formula and solve for "n". if the negative signs are confusing, try to distribute...

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