Search found 103 matches

by Luyan Zhang - 2D
Fri Mar 13, 2020 7:43 pm
Forum: Administrative Questions and Class Announcements
Topic: ENDGAME Review Session
Replies: 71
Views: 1809

Re: ENDGAME Review Session

For number 7, when you flip the second one around, the E value becomes negative. Do you use this negative E value to calculate G? I thought you would still use the standard reduction potential.
by Luyan Zhang - 2D
Thu Mar 12, 2020 4:12 pm
Forum: Student Social/Study Group
Topic: Review Session???
Replies: 3
Views: 53

Review Session???

Ok. I am just very confused about everything (currently sipping tea at home wondering how everything will unfold)

But will there an online review session this Friday led by UAs. Or at least, will the work for ENDGAME be posted on Chemistry Community?
by Luyan Zhang - 2D
Tue Mar 10, 2020 11:13 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: HW 7.1 Kinetic control vs Thermodynamic control
Replies: 2
Views: 32

HW 7.1 Kinetic control vs Thermodynamic control

Is kinetics always controlling the reaction at the lower temperature since it is the reaction with the lower activation energy?
by Luyan Zhang - 2D
Tue Mar 10, 2020 10:34 pm
Forum: General Rate Laws
Topic: Homework 7A.1
Replies: 4
Views: 34

Re: Homework 7A.1

You should rearrange the equation so that rate of NH3 formed is in term of rate of consumption of H2.
by Luyan Zhang - 2D
Tue Mar 10, 2020 7:43 pm
Forum: Biological Examples
Topic: Chem Final Review Worksheet
Replies: 2
Views: 46

Chem Final Review Worksheet

I understand that the review sessions may be cancelled, but is there a UA made worksheet that I can do for extra practice for the final?
by Luyan Zhang - 2D
Tue Mar 10, 2020 7:42 pm
Forum: Biological Examples
Topic: COVID-19
Replies: 6
Views: 104

Re: COVID-19

Does anyone know if the Review session will also be canceled?
by Luyan Zhang - 2D
Sat Mar 07, 2020 11:54 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate Determining Steps in a series of Elementary Steps
Replies: 2
Views: 34

Rate Determining Steps in a series of Elementary Steps

What is the difference if the rate determining step is the first step in a series of elementary steps versus if it is a later step? I remember Dr. Lavelle said something about pre-equilibrium approximation where the steps before the slow step is at equilibrium because the slow step will cause a bott...
by Luyan Zhang - 2D
Sat Mar 07, 2020 11:41 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: What is 'A'?
Replies: 5
Views: 54

Re: What is 'A'?

A is a constant: it is the fraction of molecules that make collisions which are significant to the chemical equation.
by Luyan Zhang - 2D
Sat Mar 07, 2020 11:34 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate-Limiting Step
Replies: 5
Views: 53

Re: Rate-Limiting Step

The one that matches the experimentally derived rate law is the slow step.
by Luyan Zhang - 2D
Fri Mar 06, 2020 7:59 pm
Forum: Second Order Reactions
Topic: Final Exam Equations
Replies: 10
Views: 74

Final Exam Equations

On the final, will the integrated rate laws and half-life equation for zero-order, 1st order, and 2nd order reactions be given on the equation sheet?
by Luyan Zhang - 2D
Tue Mar 03, 2020 7:35 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: HW 6.65 [ENDORSED]
Replies: 3
Views: 62

HW 6.65 [ENDORSED]

Shouldn't pH + pOH be 14?

at pH=7: K= [H+]/[OH-]= 1.0 x 10^-7 mol.L^-1/1.0 x 10^-7 mol.L^-1= 1 and E = 0

at pH=1: RT/nF (lnK)= .025693 V ln(1.0 mol.L^-1/ 1.0 x 10^-13 mol.L^-1)= +.71 V

at pH=14: RT/nF (lnK)= .025693 V ln(1.0 x 10^-14 mol.L^-1/1.0 mol.L^-1)= -.83 V
by Luyan Zhang - 2D
Tue Mar 03, 2020 5:50 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: HW 6.63
Replies: 2
Views: 56

HW 6.63

When a pH meter was calibrated with a boric acid–borate buffer with a pH of 9.40, the cell potential was + 0.060 V. When the buffer was replaced with a solution of unknown hydronium ion concentration, the cell potential was + 0.22 V. What is the pH of the solution? How do you know n = 1? Which redox...
by Luyan Zhang - 2D
Sat Feb 29, 2020 2:55 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Electrolysis
Replies: 1
Views: 29

Electrolysis

In the book, there are two reactions for the reduction of water

2H2O + 2e- ––> H2 + 2OH- E = -0.42V
O2 + 4H+ + 4e- --> 2H2O E = +0.82V

Can someone tell me when to use each one? And how do we know what is reduced or oxidized?
by Luyan Zhang - 2D
Wed Feb 26, 2020 11:23 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Which one is Product? Cathode or Anode?
Replies: 5
Views: 43

Which one is Product? Cathode or Anode?

In a WORKING concentration cell, is the concentration at cathode always going to be the product in K?
by Luyan Zhang - 2D
Tue Feb 25, 2020 10:33 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6M.5
Replies: 4
Views: 72

Re: 6M.5

Kevin Antony 2B wrote:We need a solid to be the electrode. As there is no solid on the right hand side, we use Platinum.


Well, there are no solids on the left either, so wouldn't we need to add Pt on the left too?
by Luyan Zhang - 2D
Sun Feb 23, 2020 8:48 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L.7 c)
Replies: 1
Views: 34

6L.7 c)

for part (c), why is KOH not part of the cell diagram on the right side (cathode)?
by Luyan Zhang - 2D
Sun Feb 23, 2020 7:03 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L.5 b)
Replies: 5
Views: 25

6L.5 b)

For the anode side, the I2 is in solid state, but the solution manual included Platinum on the anode side of the cell diagram too. Why is that?
by Luyan Zhang - 2D
Sun Feb 23, 2020 6:51 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L.1 A
Replies: 2
Views: 18

Re: 6L.1 A

TWO moles of electrons are being transferred. You can see this in both the oxidation and reduction half reactions.
by Luyan Zhang - 2D
Fri Feb 21, 2020 9:16 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: E values
Replies: 2
Views: 25

E values

Where in the textbook can I find standard reduction potential values?
by Luyan Zhang - 2D
Fri Feb 21, 2020 12:02 am
Forum: Balancing Redox Reactions
Topic: 6K.5 part a
Replies: 2
Views: 20

6K.5 part a

Why can't we balance O3(aq) and O2(g) by simply putting coefficient in front of them? Why do we have to balance by putting H2O and OH- on either side?
by Luyan Zhang - 2D
Thu Feb 20, 2020 10:18 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: E cell values
Replies: 3
Views: 19

Re: E cell values

If the E cell value is positive it means that oxidation-reduction reaction is spontaneous. If the E cell value is negative it means that the reverse reaction is spontaneous, which is reduction at anode and oxidation at cathode. I thought the anode always participate in oxidation and cathode always ...
by Luyan Zhang - 2D
Wed Feb 19, 2020 11:26 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode and Cathode
Replies: 6
Views: 20

Re: Anode and Cathode

The anode is always oxidized, so it loses electrons. The cathode is reduced so it gains electrons. Electrons will always move from anode to cathode. The cell potential only switches signs when you are balancing and equation and you flip one of the equations. Thanks! I understood that when you flip ...
by Luyan Zhang - 2D
Wed Feb 19, 2020 10:57 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode and Cathode
Replies: 6
Views: 20

Anode and Cathode

Does electron always move from anode to cathode? I'm not sure if I understood this right: if the positions of the the two electrodes are switched between the solutions, the cell potential would alter in sign?
by Luyan Zhang - 2D
Wed Feb 19, 2020 9:10 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salts used in Salt bridge
Replies: 2
Views: 23

Salts used in Salt bridge

Cl- is a common salt used in a salt bridge. What type of salts would you NOT want to use in a salt bridge? How do you decide what salt to use?
by Luyan Zhang - 2D
Wed Feb 19, 2020 7:15 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge and function
Replies: 4
Views: 25

Salt Bridge and function

Can someone explain how salt bridge functions? What would happen without the salt bridge?
by Luyan Zhang - 2D
Tue Feb 18, 2020 8:55 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 5J.15
Replies: 4
Views: 43

Re: 5J.15

For part a) I got 1.31 * 10^-9?

Did you guys get delta H = 176.01 kJ?
by Luyan Zhang - 2D
Tue Feb 18, 2020 8:00 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 5G. 13
Replies: 6
Views: 86

Re: 5G. 13

Can someone find where my error is? The question is: (a) Calculate the reaction Gibbs free energy of I2(g) -> 2I(g) at 1200. K (K 5 6.8) when the partial pressures of I2 and I are 0.13 bar and 0.98 bar, respectively. (b) Indicate whether this reaction mixture is likely to form reactants, is likely ...
by Luyan Zhang - 2D
Tue Feb 18, 2020 7:48 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 5G.13
Replies: 8
Views: 115

5G.13

(a) Calculate the reaction Gibbs free energy of I2(g) -->2I(g) at 1200. K (K = 6.8) when the partial pressures of I2 and I are 0.13 bar and 0.98 bar, respectively. (b) Indicate whether this reaction mixture is likely to form reactants, is likely to form products, or is at equilibrium. Can someone go...
by Luyan Zhang - 2D
Tue Feb 11, 2020 9:51 pm
Forum: Administrative Questions and Class Announcements
Topic: Pizza Rolls REVIEW Session DOWNLOAD HERE
Replies: 67
Views: 2479

Re: Pizza Rolls REVIEW Session DOWNLOAD HERE

Can someone explain #6 to me? I dont really understand how to calculate each one of them. And is delta U = 0?
by Luyan Zhang - 2D
Mon Feb 10, 2020 10:50 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 4I.9
Replies: 2
Views: 36

4I.9

Initially an ideal gas at 323 K occupies 1.67 L at 4.95 atm. The gas is allowed to expand to 7.33 L by two pathways: (a) isothermal, reversible expansion; (b) isothermal, irreversible free expansion. Calculate delta S(tot), delta S(system), and delta S(surrounding) for each pathway. I understood par...
by Luyan Zhang - 2D
Sat Feb 08, 2020 4:20 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: Temperature and entropy change
Replies: 1
Views: 18

Temperature and entropy change

delta S = q/T

delta S = k*ln(W)

According to the Boltzmann formula, if the temperature of the system increases, W also increases, and there fore S increase. But according to the first one, temperature is inversely proportional. How does that work?
by Luyan Zhang - 2D
Thu Feb 06, 2020 9:44 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: S = q/T
Replies: 1
Views: 22

S = q/T

Why does entropy decrease with an increase in temperature? If the temperature increases, shouldn't the system be more disordered?
by Luyan Zhang - 2D
Thu Feb 06, 2020 9:35 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy and Equations (reversible vs irreversible)
Replies: 2
Views: 20

Entropy and Equations (reversible vs irreversible)

Delta S = q/T is used for reversible process. How do we calculate change in entropy for irreversible processes?
by Luyan Zhang - 2D
Sun Feb 02, 2020 10:33 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 4.15
Replies: 2
Views: 66

4.15

Hydrochloric acid oxidizes zinc metal in a reaction that produces hydrogen gas and chloride ions. A piece of zinc metal of mass 8.5 g is dropped into an apparatus containing 800.0 mL of 0.500 m HCl(aq). If the initial temperature of the hydrochloric acid solution is 25 degrees C, what is the final t...
by Luyan Zhang - 2D
Sun Feb 02, 2020 10:02 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Combustion
Replies: 5
Views: 31

Combustion

For combustion reaction, is the H2O made in liquid form or gas form? One of the HW question asks me to calculate the reaction enthalpy, so I would need the standard enthalpy of formation of H2O. Since it's at 25 degrees Celsius, does that always mean it would be in liquid form?
by Luyan Zhang - 2D
Sun Feb 02, 2020 4:34 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4E.5
Replies: 3
Views: 27

Re: 4E.5

Katherine Wu 1H wrote:For the benzene ring, you are supposed to use the single/double resonance bond enthalpy (518 kJ) for all six of the bonds.


OH ok thank you!
by Luyan Zhang - 2D
Fri Jan 31, 2020 11:09 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Degeneracy
Replies: 3
Views: 30

Degeneracy

Can someone explain what those "dog bones" Dr.Lavelle drew on the slides? Are they just representative of the two states?
by Luyan Zhang - 2D
Fri Jan 31, 2020 11:00 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4E.5
Replies: 3
Views: 27

4E.5

Can anyone help me on a)? I thought of it like this: Breaking 3 mol C-C triple bond: 3(837) Breaking 6 mol C-H single bond: 6(412) Forming 3 mol C-C double bond: 3(-612) Forming 3 mol C-C single bond: 3(-348) Forming 6 mol C-H single bond: 6(-412) When I added all of them up, I got -369 kJ. I think ...
by Luyan Zhang - 2D
Fri Jan 31, 2020 10:30 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 4D.21 c.
Replies: 1
Views: 7

4D.21 c.

For part c., I got -38.72kJ for some reason, but the answer is 15.28kJ? Can someone explain please?
by Luyan Zhang - 2D
Sun Jan 26, 2020 9:03 pm
Forum: Calculating Work of Expansion
Topic: equipartition theorem
Replies: 2
Views: 22

equipartition theorem

Do we need to know equipartition theorem for this class?
by Luyan Zhang - 2D
Sun Jan 26, 2020 7:01 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: hw question 4B.3
Replies: 2
Views: 94

Re: hw question 4B.3

A system's internal energy is increased by 982 J when 492 J of heat was supplied. Because change in energy is equal to the sum of work and heat, it makes sense that work must have been involved for the the change in energy to be that high. Using that equation, it makes sense that 982 J = 492 J + w,...
by Luyan Zhang - 2D
Sun Jan 26, 2020 6:15 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Internal energy = State function
Replies: 4
Views: 23

Internal energy = State function

Why is Internal energy is a state function, but since delta U = heat + work, and neither heat nor work are state functions? Can state functions have non-state function components?
by Luyan Zhang - 2D
Sun Jan 26, 2020 6:13 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: HW 4A.7
Replies: 2
Views: 48

Re: HW 4A.7

For this question, we need to take into account both the mass of the water and copper and calculate the heat required (q) for both of them and add it together. Your equation should be set up as: (400g)(4.18 J/cg)(100-22C)+ (500g) (0.38 J/Cg)(100-22C)= 1.4 x 10^2 KJ. In the solutions manual, they co...
by Luyan Zhang - 2D
Sun Jan 26, 2020 5:10 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: HW 4A.7
Replies: 2
Views: 48

HW 4A.7

a) Calculate the heat that must be supplied to a copper kettle of mass 400.0 g containing 300.0 g of water to raise its temperature from 20.0 degrees C to the boiling point of water, 100.0 degrees C. (b) What percentage of the heat is used to raise the temperature of the water? I got a different ans...
by Luyan Zhang - 2D
Sun Jan 19, 2020 3:45 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: HW 6D.15b
Replies: 1
Views: 24

HW 6D.15b

For problem 6D.15 (b), how do we know what Ka for the chemical reaction is?
by Luyan Zhang - 2D
Thu Jan 16, 2020 10:13 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 6B.9
Replies: 3
Views: 45

Re: 6B.9

Me too! I think the solution manual is wrong. Because taking the negative log of a number greater than one is negative. But the solution has a positive pH
by Luyan Zhang - 2D
Mon Jan 13, 2020 9:45 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: 5.39
Replies: 1
Views: 30

5.39

On the solution manual, the Kc is 6.1*10^-3, but on table 5G.2, the constant is 6.1*10^23.

Is this a type on the textbook?
by Luyan Zhang - 2D
Thu Jan 09, 2020 10:15 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5.35
Replies: 4
Views: 36

Re: 5.35

Do we have to use bar as the unit to calculate equilibrium constant?
by Luyan Zhang - 2D
Thu Jan 09, 2020 8:32 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 5J.13
Replies: 2
Views: 18

5J.13

A gaseous mixture consisting of 2.23 mmol N2 and 6.69 mmol H2 in a 500.-mL container was heated to 600. K and allowed to reach equilibrium. Will more ammonia be formed if that equilibrium mixture is then heated to 700. K? How would we do this problem if we didn't know that this reaction is exothermic?
by Luyan Zhang - 2D
Wed Jan 08, 2020 11:47 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5I.23
Replies: 1
Views: 17

5I.23

do we set the ICE box with concentration or mols? Or does it not matter?
by Luyan Zhang - 2D
Wed Jan 08, 2020 9:28 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5I.13
Replies: 2
Views: 26

5I.13

In the answer for part b, it says that the concentration of F2 is 8*10^-4 M. But since 2.0 mmol of F2 was added into the vessel containing 2.0L, shouldn't the concentration b e 0.001M?

And can somebody also explain why Cl2 would be more stable? Is it because it disassociated less?
by Luyan Zhang - 2D
Wed Jan 08, 2020 9:26 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5I.13
Replies: 1
Views: 40

Re: 5I.13

1.1 * 10^-5 M
by Luyan Zhang - 2D
Wed Jan 08, 2020 5:24 pm
Forum: Ideal Gases
Topic: Q and K
Replies: 7
Views: 53

Re: Q and K

K describes the reaction once it reaches equilibrium. Q is calculated the same way as K, but it is for the reaction at any point in time that is not equilibrium. You can find Q and compare it with K to determine which way the reaction will proceed. Hope this helps.
by Luyan Zhang - 2D
Wed Jan 08, 2020 5:22 pm
Forum: Ideal Gases
Topic: K
Replies: 10
Views: 65

K

For Kc and Kp, would the constant be the same no matter whether you plug in the concentration or the partial pressure?
by Luyan Zhang - 2D
Thu Dec 05, 2019 11:28 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: 6C.17
Replies: 2
Views: 30

6C.17

We went over comparing which substance is more acidic, but this question asks which one is a stronger base. How would you approach this problem?
by Luyan Zhang - 2D
Thu Dec 05, 2019 2:31 pm
Forum: Administrative Questions and Class Announcements
Topic: Final Review Session
Replies: 6
Views: 99

Re: Final Review Session

Andrew F 3B wrote:Yes, Just look up "Marshmallow" in Chemistry Community's search bar and you can find it for the review session


Thank you so much!
by Luyan Zhang - 2D
Wed Dec 04, 2019 11:23 am
Forum: Administrative Questions and Class Announcements
Topic: Final Review Session
Replies: 6
Views: 99

Final Review Session

Will there be another practice packet for the final review session given like the midterm?
by Luyan Zhang - 2D
Wed Dec 04, 2019 10:44 am
Forum: Lewis Acids & Bases
Topic: HCl and HI
Replies: 10
Views: 59

Re: HCl and HI

HI is stronger because Iodine is a larger atom, and therefore the atomic radius is larger. Because the radius is larger, the bond between them is longer and weaker, and H+ is easily lost to surrounding solution.
by Luyan Zhang - 2D
Sun Dec 01, 2019 10:55 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Oxoacids
Replies: 2
Views: 11

Re: Oxoacids

Ok that makes more sense now, thank you!
by Luyan Zhang - 2D
Sun Dec 01, 2019 10:49 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Oxoacids
Replies: 2
Views: 11

Oxoacids

I wasn't able to make it to the lecture on Wednesday, and I was kind of confused by the slides. Why is Cl––O––H a stronger acid than Br––O––H? I thought Br has a longer atomic radius, which means a longer and weaker bond, and therefore it would be easier to strip proton from it. Or is it different f...
by Luyan Zhang - 2D
Sun Dec 01, 2019 8:46 pm
Forum: Naming
Topic: Oxidation number
Replies: 4
Views: 24

Re: Oxidation number

Look at the charges on individual ligands. Make sure everything in the bracket adds up to the overall charge of the complex.
by Luyan Zhang - 2D
Sun Dec 01, 2019 8:30 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: 9C.1
Replies: 1
Views: 22

Re: 9C.1

CN- has a charge of -1, and since there are six of them, it would be -6. BUT the total charge of the complex is a -4, which must mean that Fe has a charge of +2; -6 + 2 = -4.

Hope this helps.
by Luyan Zhang - 2D
Sun Dec 01, 2019 8:27 pm
Forum: Naming
Topic: Table 9C.1
Replies: 1
Views: 42

Table 9C.1

How many of these common ligands should we commit to memory? Or should we just memorize all of it?
by Luyan Zhang - 2D
Wed Nov 27, 2019 10:12 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Lewis bases vs. ligands
Replies: 3
Views: 34

Lewis bases vs. ligands

Are all ligands basically Lewis bases? And do molecules that donate only one electron count as a Lewis base? Or does "Lewis base" only refer to an atom/molecule that donates a pair of electrons?
by Luyan Zhang - 2D
Mon Nov 18, 2019 10:25 pm
Forum: Sigma & Pi Bonds
Topic: HW 2F.3
Replies: 2
Views: 35

Re: HW 2F.3

Cynthia Gong 1L wrote:I think that's because the textbook used the resonance structure where there is one single-bonded O and one double-bonded O, and so as a result there is only one pi bond.


But the formal charges would not be zero...
by Luyan Zhang - 2D
Mon Nov 18, 2019 10:02 pm
Forum: Sigma & Pi Bonds
Topic: HW 2F.3
Replies: 2
Views: 35

HW 2F.3

for 2F.3 a), why does SO2 have two sigma bonds but only one pi-bond? I thought there are two pi-bonds
by Luyan Zhang - 2D
Fri Nov 15, 2019 11:31 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Inter-molecular Electron Repulsion
Replies: 6
Views: 42

Re: Inter-molecular Electron Repulsion

Lone pair-lone pair > Lone pair-bonding pair > bonding pair-bonding pair

I think you will just have to remember this.
by Luyan Zhang - 2D
Fri Nov 15, 2019 11:24 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Lewis structure for 2E23 (a)
Replies: 1
Views: 24

Lewis structure for 2E23 (a)

I thought there should be a double bond between Sb and O, since the formal charge would be zero for both that way. But the answer key depicted it as a single bond? I know it doesn't really matter for the VSEPR shape, but I'm still confused on whether it is the correct lewis structure or not.
by Luyan Zhang - 2D
Fri Nov 15, 2019 11:22 am
Forum: Determining Molecular Shape (VSEPR)
Topic: 2E.19 (b)
Replies: 3
Views: 29

Re: 2E.19 (b)

The bond angle is linear (180 degrees) because the central atom (Be) is bonded with two atoms (both Carbon) with no extra lone pairs to potentially distort the shape of this bond angle. I would assume that the bond angle would be 120 degrees if the central atom was a Boron atom bonded to three Carb...
by Luyan Zhang - 2D
Fri Nov 15, 2019 12:57 am
Forum: Determining Molecular Shape (VSEPR)
Topic: 2E.19 (b)
Replies: 3
Views: 29

2E.19 (b)

For C–Be-C angle, why is it 180 degrees rather than 120 degrees. Is it because the two valence electrons on Be are lone half pairs?
by Luyan Zhang - 2D
Fri Nov 15, 2019 12:41 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bent shape and angles
Replies: 6
Views: 50

Bent shape and angles

Both VSEPR shape with the formula AX2E and AX2E2 have bent shape. What are the differences in their bond angles?
by Luyan Zhang - 2D
Thu Nov 14, 2019 11:07 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Figure 2E.7
Replies: 1
Views: 28

Figure 2E.7

Do we have to have this figure memorized? Or should we just try to figure out the shape based on the lone pair and bonding atoms ourselves?
by Luyan Zhang - 2D
Thu Nov 14, 2019 10:42 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Differences in these shapes
Replies: 1
Views: 27

Differences in these shapes

What are the differences in trigonal bipyramidal and square pyramidal? They both have five atoms attached to the central atom. My thinking is that in square pyramidal, there could be a lone pair on the central atom, so it would have an electron arrangement of a octahedral, but have a shape of square...
by Luyan Zhang - 2D
Wed Nov 13, 2019 10:44 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: dipole moment clarification
Replies: 6
Views: 34

Re: dipole moment clarification

Polar molecules have a permanent dipole moment. Polar just means that there is an unequal sharing of electrons.
by Luyan Zhang - 2D
Fri Nov 08, 2019 8:48 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Interaction potential energy
Replies: 7
Views: 50

Re: Interaction potential energy

I think this is what happens. When alpha increases, that means the polarizability increases, and since polarizability depends on the size of the atom (and how many e- there are), r increases too so the denominator "grows" faster than the alphas in the numerator so even though the numerato...
by Luyan Zhang - 2D
Fri Nov 08, 2019 12:24 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Interaction energy
Replies: 3
Views: 21

Re: Interaction energy

It is how strongly two atoms/molecules are held together. It is proportional to their polarizability and inversely proportional to the distance between them.
by Luyan Zhang - 2D
Fri Nov 08, 2019 12:15 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Interaction potential energy
Replies: 7
Views: 50

Re: Interaction potential energy

Since there's a negative sign in front of the equation, that means that when r increases, the denominator increases meaning it gets closer to 0, which means that Ep actually increases (from more negative to less negative). If that is the case, with higher alpha (polarizability), the interaction wou...
by Luyan Zhang - 2D
Fri Nov 08, 2019 12:11 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Interaction Potential Energy
Replies: 3
Views: 40

Re: Interaction Potential Energy

It is always negative because there is always an attractive force pulling two atoms or molecules together
by Luyan Zhang - 2D
Fri Nov 08, 2019 12:09 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Interaction potential energy
Replies: 7
Views: 50

Interaction potential energy

Professor Lavelle said that larger atoms/molecules have stronger interactions due to their polarizability. But since larger atoms have a larger distance, wouldn't the interaction potential energy be less? I thought that the distance would contribute more to the equation because it is r to the sixth ...
by Luyan Zhang - 2D
Fri Nov 01, 2019 12:12 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Config for Pd versus Nickel
Replies: 2
Views: 34

Electron Config for Pd versus Nickel

Pd and Ni are in the same group, but electron configuration for Nickel is [ ]3d8 4s2, and electron configuration for Pd is [ ]4d10. Why does the electron from the s-orbitals from Pd move to d-orbitals to fill the full-shell, but the electrons in Ni don't?
by Luyan Zhang - 2D
Thu Oct 31, 2019 11:18 pm
Forum: Bond Lengths & Energies
Topic: Lattice Energy
Replies: 9
Views: 53

Re: Lattice Energy

Lattice energy is the energy stored in the bonds of an ionic solid, such as NaCl. This energy is released when Na and Cl come together. This energy is much greater than the energy needed to strip electron off of Na, when shows why NaCl has a lower energy than Na or Cl.
by Luyan Zhang - 2D
Thu Oct 31, 2019 11:14 pm
Forum: Coordinate Covalent Bonds
Topic: Coordinate covalent bond?
Replies: 12
Views: 522

Re: Coordinate covalent bond?

Usually, a bond is composed of two electrons, and one coming from each of the bonded atom. A coordinate covalent bond refers to a bond in which BOTH electrons come from ONE atom, as in the case of BF4, when both electrons came from the fluoride ion.
by Luyan Zhang - 2D
Thu Oct 31, 2019 11:11 pm
Forum: Resonance Structures
Topic: Delocalization vs. Resonance
Replies: 8
Views: 90

Re: Delocalization vs. Resonance

A resonance refers to one structure of many different but equivalent lewis structures of a molecule. The term "delocalization" refers to an electron that doesn't belong to just one single bond. A delocalized electron is spread out over the molecule. Professor Lavelle mentioned that a true ...
by Luyan Zhang - 2D
Thu Oct 31, 2019 11:06 pm
Forum: Resonance Structures
Topic: Resonance
Replies: 5
Views: 53

Re: Resonance

Yes they do, except for the exceptions Lavelle talked in class. Remember that resonance structures have the same position of atoms, but just different arrangement of electrons and bonds.
by Luyan Zhang - 2D
Thu Oct 31, 2019 11:02 pm
Forum: Ionic & Covalent Bonds
Topic: Electrostatic Potential Energy
Replies: 3
Views: 31

Re: Electrostatic Potential Energy

I think he said in class that we don't need to know how to calculate it, and just understand the relationship between the variables.
by Luyan Zhang - 2D
Thu Oct 24, 2019 12:04 pm
Forum: *Particle in a Box
Topic: TEST 2
Replies: 13
Views: 233

TEST 2

Does anyone know when Test 2 is?
by Luyan Zhang - 2D
Thu Oct 24, 2019 12:02 pm
Forum: Trends in The Periodic Table
Topic: Effective Nuclear Charge
Replies: 5
Views: 55

Re: Effective Nuclear Charge

The effective nuclear charge is just the attraction the electrons feels from the nucleus. Since in a multi-electron atoms, there will be electron-electron repulsion from different shells, the effective nuclear charge will always be less than the actual nuclear charge. As the shells increase, the eff...
by Luyan Zhang - 2D
Thu Oct 24, 2019 11:59 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: coulomb potential energy
Replies: 4
Views: 43

Re: coulomb potential energy

What does the infinity-like symbol next to the equation (q1)(q2)/r mean? Also, would we need this equation to do calculations or is it just the concept about like attraction and potential energy that we need to understand? That symbol means that the potential energy is DIRECTLY PROPORTIONAL to (q1)...
by Luyan Zhang - 2D
Thu Oct 24, 2019 11:57 am
Forum: DeBroglie Equation
Topic: Velocity
Replies: 13
Views: 191

Re: Velocity

Yes, this answer is unreasonable, and you should definitely recheck your work. Perhaps you've made a calculator error.
by Luyan Zhang - 2D
Sun Oct 13, 2019 3:16 pm
Forum: Photoelectric Effect
Topic: Differences between Particle and Wave
Replies: 5
Views: 44

Re: Differences between Particle and Wave

On the large scale, light acts like a wave (diffraction). On the small scale, light is composed of photons, or particles (photoelectric effect).
by Luyan Zhang - 2D
Sun Oct 13, 2019 3:14 pm
Forum: Photoelectric Effect
Topic: Classic Wave in Photoelectric effect
Replies: 5
Views: 57

Re: Classic Wave in Photoelectric effect

Increasing intensity means you increase the NUMBER of photons (not the energy each particular photon carries), and to emit e- from metal surface, you need EACH photon to carry a certain amount of energy (threshold energy). In order to do that, you must increase the frequency of the light source
by Luyan Zhang - 2D
Sun Oct 13, 2019 3:12 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Lyman, Balmer, Paschen, & Bracket Series?
Replies: 4
Views: 55

Re: Lyman, Balmer, Paschen, & Bracket Series?

The series refer to the different states electrons start at and return to. For instance, for all of n(final) = 2, the line is in the Balmer series (visible light)
by Luyan Zhang - 2D
Sun Oct 13, 2019 3:08 pm
Forum: DeBroglie Equation
Topic: De Broglie's Equation
Replies: 4
Views: 77

De Broglie's Equation

If the wavelength of something with a large mass cannot be detected by lab equipments, then how did de Broglie come up with this relation? Or is it all theoretical?
by Luyan Zhang - 2D
Tue Oct 08, 2019 3:59 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty of speed
Replies: 5
Views: 51

Re: Uncertainty of speed

LNgo 14A wrote:I believe the uncertainty would be 5.0. The plus and minus signs just mean that the variation can go either direction.


But in the worked example in the textbook, the velocity is plus or minus 1m/s, but in the solution for it, it used 2m/s as the uncertainty for speed
by Luyan Zhang - 2D
Tue Oct 08, 2019 3:40 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty of speed
Replies: 5
Views: 51

Uncertainty of speed

In the practice problem, 1B.27, it states that the velocity of the bowling ball is 5.00 +/- 5.0ms-1,
does this mean that the uncertainty of the velocity is 10m/s because of the plus or minus sign?
by Luyan Zhang - 2D
Tue Oct 08, 2019 3:38 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: heisenberg's
Replies: 5
Views: 367

Re: heisenberg's

The >= sign just means that the uncertainty can be infinitely greater (which makes sense). Usually, I think you would just use it as an equal sign because it is the minimum uncertainty
by Luyan Zhang - 2D
Thu Oct 03, 2019 9:30 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Units in Answer
Replies: 18
Views: 232

Re: Units in Answer

If the question asks for "mass", you should put grams
by Luyan Zhang - 2D
Tue Oct 01, 2019 11:27 am
Forum: SI Units, Unit Conversions
Topic: Unit Conversions
Replies: 11
Views: 146

Re: Unit Conversions

You use the the conversion:

1 mole = 6.022 * 10^23 molecules/atoms
by Luyan Zhang - 2D
Tue Oct 01, 2019 11:24 am
Forum: SI Units, Unit Conversions
Topic: Significant 0’s [ENDORSED]
Replies: 8
Views: 415

Re: Significant 0’s [ENDORSED]

1. Leading zeroes are not significant eg. 0.00007 only has one sf 2. Trailing zeros in decimals are significant eg. 0.0000700 has 3 sig figs 3. Trailing zeroes in whole numbers are not significant eg 7000 only has one sf (If there is a decimal points after 7000, like 7000., then there are 4 sf) 4. T...
by Luyan Zhang - 2D
Sat Sep 28, 2019 4:00 pm
Forum: Empirical & Molecular Formulas
Topic: Empirical Formulas Rounding and Multiplying
Replies: 11
Views: 190

Re: Empirical Formulas Rounding and Multiplying

What should the threshold be for decimals when solving for empirical formulas? I think that if the results are 0.1 away from the nearest whole number, then you round to that whole number. Otherwise, I think you multiply to the nearest whole number. However, I see in some example problems, like one ...

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