Search found 101 matches

by KDang_1D
Tue Feb 11, 2020 9:29 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Pizza Rolls 6 (pt.1)
Replies: 10
Views: 116

Pizza Rolls 6 (pt.1)

"... First you perform an isobaric compression of the container to 10.0L...."

Why is ∆U=0 for the first part of the problem if the process is isobaric, not isothermic?

Also, why is ∆S=0? Wouldn't a decrease in volume cause a decrease in number of possible positions?
by KDang_1D
Tue Feb 11, 2020 9:14 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Pizza Rolls 5A Substituting q and w
Replies: 1
Views: 33

Pizza Rolls 5A Substituting q and w

As used in Pizza Rolls 5, how do you know when you can substitute w=-nRTln(T2/T1) into ∆S=qrev/T? Why is this process considered reversible for you to do this?
by KDang_1D
Tue Feb 11, 2020 6:50 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 4I.9 Irreversible Expansion
Replies: 2
Views: 16

4I.9 Irreversible Expansion

4I.9 Initiallyanidealgasat323Koccupies1.67Lat4.95atm.The gas is allowed to expand to 7.33 L by two pathways: (a) isothermal, reversible expansion; (b) isothermal, irreversible free expansion. Calculate DStot, DS, and DSsurr for each pathway. How do these two processes differ? Why is no work done by...
by KDang_1D
Tue Feb 11, 2020 12:57 am
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: 4G.5 Trans Isomer
Replies: 1
Views: 10

4G.5 Trans Isomer

Why does the trans isomer of a MX2Y4 molecule have 3 different orientations? If the radial atoms are all identical, wouldn't this be the only possible configuration?
by KDang_1D
Tue Feb 11, 2020 12:08 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 4F.3 Reversible Process
Replies: 2
Views: 13

4F.3 Reversible Process

Calculate the change in entropy of a block of copper at 25ºC that absorbs 65J of energy from a heater.


Why can we assume that this is a reversible process?
by KDang_1D
Sun Feb 09, 2020 8:46 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Enthalpy and Temperature
Replies: 1
Views: 23

Enthalpy and Temperature

As applied to ∆S=∆H/T, for example, what does it mean that temperature remains constant as enthalpy changes? Wouldn't an increase/decrease in energy cause the temperature to go up/down?
by KDang_1D
Wed Feb 05, 2020 1:39 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard State of Compounds
Replies: 2
Views: 19

Standard State of Compounds

Our TA explained that substances in their standard state have a standard enthalpy of formation of 0. In lecture, Dr. Lavelle did an example in which we calculated the standard enthalpy of the combustion of methane. He stated that gases are in their standard state at 1atm and pure liquids are always ...
by KDang_1D
Mon Feb 03, 2020 8:56 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 4B.9e
Replies: 1
Views: 7

4B.9e

4B.9 In an adiabatic process, no energy is transferred as heat. Indicate whether each of the following statements about an adia- batic process in a closed system is always true, always false, or true in certain conditions (specify the conditions): (a) ∆U=0; (b) q=0; (c) q<0; (d) ∆U=q; (e) ∆U=w. Why...
by KDang_1D
Mon Feb 03, 2020 8:41 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 4B.5 Conversion
Replies: 4
Views: 17

4B.5 Conversion

As used in 4B.5, how do you convert Torr(mL) to J?
by KDang_1D
Mon Feb 03, 2020 3:35 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isobaric Reversible Expansion
Replies: 4
Views: 22

Re: Isobaric Reversible Expansion

I guess I'm asking, how would this piston function in practice/how could you model this experimentally?
by KDang_1D
Mon Feb 03, 2020 1:06 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isobaric Reversible Expansion
Replies: 4
Views: 22

Isobaric Reversible Expansion

Today (Monday Week 5), Dr. Lavelle talked about isothermic reversible reactions. The external pressure decreases gradually, allowing heat to instantaneously enter the system as it does work. What would this process look like for reversible expansions for which we use the formula -\int_{V_{1}}^{V_{2}...
by KDang_1D
Mon Jan 27, 2020 4:16 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimetry and Mass
Replies: 2
Views: 12

Calorimetry and Mass

Why doesn't the calorimetry formula q=-C∆T include mass like q=mC∆T. And why is the q value negative if the calorimeter is gaining the energy lost by the reaction?
by KDang_1D
Mon Jan 27, 2020 3:38 pm
Forum: Phase Changes & Related Calculations
Topic: Reversible Expansion
Replies: 1
Views: 29

Reversible Expansion

4A.5 A piston confines 0.200 mol Ne(g) in 1.20 L at 25 8C. Two experiments are performed. (a) The gas is allowed to expand through an additional 1.20 L against a constant pressure of 1.00 atm. (b) The gas is allowed to expand reversibly and isothermally to the same final volume. Which process does ...
by KDang_1D
Sun Jan 26, 2020 10:06 pm
Forum: Phase Changes & Related Calculations
Topic: Heat capacities
Replies: 6
Views: 26

Re: Heat capacities

What is heat capacity?
by KDang_1D
Sat Jan 25, 2020 1:41 pm
Forum: Phase Changes & Related Calculations
Topic: Phase Change
Replies: 4
Views: 24

Re: Phase Change

The information should be given, possibly in a phase change graph. I believe it would be the difference in y-value between two of the horizontal lines (the height of the diagonal) as this would be the energy into the system to bring the substance from one state up to the next.
by KDang_1D
Sat Jan 25, 2020 1:28 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy
Replies: 2
Views: 19

Re: Enthalpy

You can think of enthalpy as the energy stored in the bonds (technically there's heat but don't get it mixed up with the T, temperature). So a certain amount of energy is needed to break the energy of bonds (+∆H), and energy is released when energetically favorable bonds are formed (–∆H).
by KDang_1D
Tue Jan 21, 2020 9:06 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: 6A.19c
Replies: 1
Views: 26

6A.19c

6A.19 Calculate the molar concentration of OH2 in solutions with the following molar concentrations of H3O1: (a) 0.020 mol/L-1; (b) 1.0x10^-5 mol/L-1; (c) 3.1 mol/L-1. c. Why do you divide \frac{1.0\times 10^{-14}}{3.1\times 10^{-3}} , not \frac{1.0\times 10^{-14}}{3.1} , since [H3O+] = 3.1 M (like...
by KDang_1D
Tue Jan 21, 2020 7:59 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: When to Use Q
Replies: 3
Views: 25

When to Use Q

5I.25.) A reaction mixture is prepared by mixing 0.100 mol SO2, 0.200 mol NO2, 0.100 mol NO, and 0.150 mol SO3 in a reaction vessel of volume 5.00 L. The reaction SO2(g) 1 NO2(g) ∆ NO(g) 1 SO3(g) is allowed to reach equilibrium at 460 8C, when Kc 5 85.0. What is the equilibrium concentration of each...
by KDang_1D
Sun Jan 19, 2020 11:30 pm
Forum: Ideal Gases
Topic: Partial Pressure
Replies: 4
Views: 33

Re: Partial Pressure

Dr. Lavelle went over it in lecture, so I believe it would be a fair question.

You would need to apply the ideal gas equation: PV=nRT. Divide V over to get P = (n/V)RT. (n/V) is concentration, which should be given, and RT are constant so just solve for P, your partial pressure
by KDang_1D
Sun Jan 19, 2020 11:26 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Different ways to write K
Replies: 3
Views: 15

Re: Different ways to write K

I think we should include the subscript just to be safe! Especially for reactions involving gases. If given a unitless value for K, the reader would need to know if it's for pressure or concentration and they need to convert
by KDang_1D
Sun Jan 19, 2020 11:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Reaction mixture at equilibrium
Replies: 2
Views: 8

Re: Reaction mixture at equilibrium

This state is called a dynamic equilibrium. Even though it seems like the reaction has stopped, the forward and reverse reactions continue to proceed, just at equivalent rates so it is unnoticeable. But why certain reactions favor specific ratios, however, is beyond what we know in 14B
by KDang_1D
Sun Jan 19, 2020 11:19 pm
Forum: Ideal Gases
Topic: Partial Pressures
Replies: 4
Views: 23

Re: Partial Pressures

I'm not sure how it would be possible to increase the pressure of one type of gas in the same reaction vessel as the other. However, assuming that this change in pressure essentially causes a change in concentration, the other reactant would only be affected as a result of LeChatellier's principle. ...
by KDang_1D
Sun Jan 19, 2020 11:11 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5% rule
Replies: 8
Views: 27

Re: 5% rule

Yes, that expression refers to "percent protonation." Take note that these are the concentrations of the "primary" compounds involved in the reaction. For example, regarding NH3 + H2O --> NH4+ + OH-, you would only use [NH4+] formed /[NH3] initial, not including [H2O] and [OH-] A...
by KDang_1D
Sun Jan 19, 2020 11:04 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE tables for reverse rxns
Replies: 4
Views: 13

Re: ICE tables for reverse rxns

For some problems (i.e. 5I.25), you have to calculate the Q value first and then compare it with K. If Q<K, the reaction will move forward, and if the Q>K, the reactions will move in reverse. This is all relative to how the chemical reaction is written. Then, set up your Ka expression and ICE table ...
by KDang_1D
Sun Jan 19, 2020 10:59 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Applying Kw
Replies: 2
Views: 17

Applying Kw

In lecture, Dr. Lavelle did an example using Ba(OH)2 to show that Kw, a special value of Ka, can be used to determine [H3O+]. Why is this possible? Don't all aqueous reactions have different Ka values, so shouldn't Ba2+ affect the value of Ka/Kw?
by KDang_1D
Sun Jan 12, 2020 1:18 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: changing conditions
Replies: 6
Views: 18

Re: changing conditions

Removing some of the product would decrease its concentration/partial pressure value. Mathematically the ratio [P]/[R] would be smaller. Since Q<K, the forward reaction will be favored until Q=K again
by KDang_1D
Sun Jan 12, 2020 1:14 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Significance of principle
Replies: 6
Views: 20

Re: Significance of principle

One of the most well-known applications of Le Chatelier's Principle is the production of NH3 for fertilizer. Dr. Lavelle mentioned it in lecture and one of the TA's talked about it in discussion N2(g) + 3H2(g) --> 2NH3(g) Chemist Fritz Haber highly pressurized the NH3 gas (with a catalyst) so that i...
by KDang_1D
Sun Jan 12, 2020 1:03 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium and Limiting Reagent
Replies: 2
Views: 18

Equilibrium and Limiting Reagent

How does what we're learning about equilibrium relate to what we learned in 14A about limiting reagents? Wouldn't those calculations be invalid since we were assuming that the reactions ran to completion?
by KDang_1D
Sun Jan 12, 2020 12:57 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Write reaction quotient Q
Replies: 2
Views: 8

Re: Write reaction quotient Q

I believe both are correct if not specified. As long as you remember that partial pressure only applies to gases and not aqueous solutions
by KDang_1D
Sun Jan 12, 2020 12:55 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Concentration and partial pressure
Replies: 2
Views: 8

Re: Concentration and partial pressure

Concentration and partial pressure can be converted using a form of the ideal gas equation: PV = nRT --> P = (n/V)R, where n/V is concentration. Equilibrium expressions using concentration (Kc) will contain brackets ("[X]") and expressions using partial pressures (Kp) will contain the vari...
by KDang_1D
Mon Jan 06, 2020 3:58 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: H3O and OH
Replies: 5
Views: 46

H3O and OH

Regarding the Chemical Equilibrium Pt 1B Pre-Assessment, for reactions that involve liquid water as a product and H3O+(aq) or OH-(aq) as a product, are the H3O/OH included in the K calculation?
by KDang_1D
Sat Dec 07, 2019 1:47 pm
Forum: Identifying Acidic & Basic Salts
Topic: HW 6D11
Replies: 7
Views: 90

Re: HW 6D11

How would you know that the coordinator for hydrated Al is 6?
by KDang_1D
Fri Dec 06, 2019 1:07 am
Forum: Biological Examples
Topic: Cisplatin H2O
Replies: 2
Views: 31

Cisplatin H2O

I was wondering how cisplatin binds to DNA since Cl doesn't typically form coordinating covalent bonds. Google says that the Cl is replaced with H2O. What drives this process?
by KDang_1D
Fri Dec 06, 2019 12:20 am
Forum: Naming
Topic: Isocyanido
Replies: 2
Views: 25

Isocyanido

Is it correct to call CN "cyanido" or does it have to be "isocyanido"? (in reference to Table 9C.1)
by KDang_1D
Thu Dec 05, 2019 10:51 pm
Forum: Naming
Topic: (diqaua)
Replies: 1
Views: 26

(diqaua)

For 9C.3d "sodiumbisoxalato(diaqua)ferrate(III)", why is diaqua written in parentheses? Also, why does it come after the bisoxalato?
by KDang_1D
Wed Dec 04, 2019 12:18 am
Forum: Lewis Structures
Topic: 6.5b
Replies: 2
Views: 32

6.5b

Why doesn't H2SO5 have cis/trans isomers?
by KDang_1D
Mon Dec 02, 2019 5:19 pm
Forum: Lewis Structures
Topic: 2.61
Replies: 2
Views: 26

2.61

In the radical HOCO, how do you know that the carbon would have the unpaired electron? Isn't oxygen more electronegative?
by KDang_1D
Mon Dec 02, 2019 5:09 pm
Forum: Hybridization
Topic: Energy Level
Replies: 2
Views: 20

Energy Level

Are all sp(1,2,3) hybridized orbitals in the 2nd energy level?
by KDang_1D
Mon Dec 02, 2019 4:17 pm
Forum: Hybridization
Topic: 2F.3b
Replies: 1
Views: 22

2F.3b

Why does SO2 have two resonance structures? Doesn't the one with two double bonds have formal charges of 0, and the one with only one double bond have formal charges of +/-1?
by KDang_1D
Mon Dec 02, 2019 4:01 pm
Forum: Hybridization
Topic: Lone Pairs
Replies: 2
Views: 19

Lone Pairs

How does hybridization work for atoms with lone pair electrons? For example, HS2
by KDang_1D
Sun Dec 01, 2019 8:44 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: pKa
Replies: 3
Views: 20

Re: pKa

"p" means to take the -log of a value. Just as pH is the -log[H+], pKa is the -log(Ka).

For example, NH4+ has a Ka = 5.6x10^-10
pKa = -log(5.6x10^-10) = 9.25
by KDang_1D
Sun Dec 01, 2019 8:35 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Concentration
Replies: 2
Views: 28

Re: Concentration

I'm sure it would have to be given in the problem. But if, for example, you were given an OH- concentration of 1x10^-8 M, you could calculate that the H3O+ concentration is 1x10^-6 M, since [H3O+] x [OH-] = 1x10^-14. You can also do this using pH values. The pOH for this solution would be 8. pH + pO...
by KDang_1D
Sun Dec 01, 2019 8:29 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: pH scale
Replies: 12
Views: 59

Re: pH scale

Solutions can fall outside the 0-14 range. Dr. Lavelle mentioned "superacids" which have a H3O+ concentration > 1x10^0 M and thus would have a negative pH. However, these are uncommon, especially in biological systems. I'm sure the same is true for bases.
by KDang_1D
Sun Dec 01, 2019 8:25 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: pH Calculation explanation
Replies: 1
Views: 16

Re: pH Calculation explanation

Concentrations for H3O+ (and OH-) are very small, so they will have a negative exponent in their molarity value. For example: [H3O+] = 1x10^-7 M. Since logarithms calculate the value of the exponent, log[H3O+] = -7. Negative numbers aren't as nice to work with as positives, so we just add the negati...
by KDang_1D
Sun Dec 01, 2019 8:22 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Strong Acids
Replies: 3
Views: 24

Re: Strong Acids

Why do the halogens form the strong acids? Why would they have the weakest bonds if they have the smallest atomic radius in each period?
by KDang_1D
Sat Nov 23, 2019 9:05 am
Forum: Naming
Topic: Diethylenetriamine
Replies: 2
Views: 23

Diethylenetriamine

In "diethylenetriamine," why does ethylene come before amine? Not A before E as would be for alphabetical order? In the other example "pentaamminechlorocobalt(II) chloride hydriate," "ammine" comes before "chloro" regardless of the prefix. *Also is NH3 spelled...
by KDang_1D
Sat Nov 23, 2019 8:58 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: [Fe(CN)6]4-
Replies: 5
Views: 34

[Fe(CN)6]4-

In lecture, Dr. Lavelle used the example [Fe(CN)6]4-:

a. How is CN a ligand? Unless it's CN-, it would have an unpaired electron and wouldn't be able to form a coordinate covalent bond?
b. Why is the charge 4-?
by KDang_1D
Tue Nov 19, 2019 10:11 pm
Forum: Bond Lengths & Energies
Topic: Interaction Potential Energy and Radius
Replies: 2
Views: 34

Interaction Potential Energy and Radius

If interaction potential energy is given by the formula: Ep (is proportional to) , then why does attractive force increase as atomic size increases?
by KDang_1D
Tue Nov 19, 2019 12:20 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Pentagonal Bipyramidal
Replies: 8
Views: 67

Re: Pentagonal Bipyramidal

What other VSEPR structures do we need to know that Dr. Lavelle didn't go over in lecture?
by KDang_1D
Tue Nov 19, 2019 12:17 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Pi Bond Rotation
Replies: 2
Views: 23

Pi Bond Rotation

What does the pi bond's inability to rotate mean when determining VSEPR structure? How is this concept applied?
by KDang_1D
Mon Nov 18, 2019 3:28 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Component Orbitals of pi Bonds
Replies: 3
Views: 17

Component Orbitals of pi Bonds

The course outline says we need to be able to "distinguish pi bonds by their component orbitals." What are the component orbitals of pi bonds? Doesn't it depend on each individual molecule's central atom configuration?
by KDang_1D
Mon Nov 18, 2019 3:13 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 2E.25a
Replies: 1
Views: 15

2E.25a

Why is CH2Cl2 a polar molecule? If drawn with the Cl's opposite of each other, wouldn't the dipoles cancel out?
by KDang_1D
Sat Nov 16, 2019 11:20 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Pentagonal Bipyramidal
Replies: 8
Views: 67

Re: Pentagonal Bipyramidal

What is the VSEPR formula (AXE) for this?
by KDang_1D
Fri Nov 15, 2019 3:51 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 6
Views: 55

Re: Bond Angles

109.5 you'll just to memorize, but the others you can tell from their shape. Trigonal planar has three atoms spread out evenly on a single plane. 360/3 = 120 degrees Trigonal bipyramidal has 2 axial elements coming out from both sides of the trigonal planar shape, so you should be able to visualize ...
by KDang_1D
Fri Nov 15, 2019 3:43 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: varying VSEPRs
Replies: 7
Views: 45

Re: varying VSEPRs

No, and even better, the shape of an AXE molecule will always be the same, regardless of the atoms
by KDang_1D
Fri Nov 15, 2019 3:41 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Prefixes
Replies: 2
Views: 36

Re: Prefixes

In today's Friday lecture, we also learned the organic chemistry prefixes cis- and trans-. I don't think we should need to know how to draw organic molecules, but I think we should be familiar with general polarity. "Cis-" means same and "trans-" means opposite, so in general, wh...
by KDang_1D
Fri Nov 15, 2019 3:38 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: T shape
Replies: 7
Views: 48

Re: T shape

Why wouldn't this be a trigonal planar shape with the electron clouds in the axial positions? Didn't we talk about the electron clouds wanting to be as far apart as possible to minimize repulsion and make the molecule more stable?
by KDang_1D
Fri Nov 15, 2019 3:36 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bent shape and angles
Replies: 6
Views: 39

Re: Bent shape and angles

The VSPER theory only gives qualitative, not quantitative descriptions of the shape of molecules, so although we know how the atoms are arranged, we cannot predict exactly what their angles will be. AX2E will be less than 120 degrees, and AX2E2 will be less than 109.5 degrees. Those are the expected...
by KDang_1D
Wed Nov 06, 2019 4:02 pm
Forum: Trends in The Periodic Table
Topic: Electrostatic Forces vs Effective Nuclear Charge
Replies: 1
Views: 37

Electrostatic Forces vs Effective Nuclear Charge

What’s the difference between “electrostatic force/potential energy” and “effective nuclear charge?
by KDang_1D
Tue Nov 05, 2019 11:25 pm
Forum: Lewis Structures
Topic: 2B.11c
Replies: 1
Views: 30

2B.11c

"Draw the complete Lewis structure for glycine, H2C(NH2)COOH." The molecule is drawn H2–N-CH2-CO-OH (if that makes sense). How would you know that the nitrogen is on the end and not in between the two carbons? It's written in the middle of the given formula and usually they give structural...
by KDang_1D
Tue Nov 05, 2019 3:48 pm
Forum: Properties of Electrons
Topic: Schrodinger Equation
Replies: 2
Views: 60

Re: Schrodinger Equation

I think we only need to know the basics that we put the wave function () into the "Hamiltonian operator" and get out energy (E) values that are interpreted to give the shapes of the s, p, d, etc. orbitals that we are familiar with.

by KDang_1D
Tue Nov 05, 2019 3:42 pm
Forum: Properties of Electrons
Topic: Multi-electron atom
Replies: 2
Views: 39

Re: Multi-electron atom

Multi-electron atoms must follow the Aufbau principle, which states that electrons fill the lowest-energy orbitals before the largest. So s<p<d<f within the same energy level. For us, be able to write and interpret quantum numbers (n, l, ml, ms) and electron configurations.
by KDang_1D
Tue Nov 05, 2019 3:23 pm
Forum: Ionic & Covalent Bonds
Topic: 2D.3
Replies: 3
Views: 36

Re: 2D.3

How would we know this without a table with values? I'm pretty sure they've said we shouldn't have to remember specific values.
by KDang_1D
Tue Nov 05, 2019 3:18 pm
Forum: Ionic & Covalent Bonds
Topic: Mini Dino Nuggets 2b
Replies: 6
Views: 59

Mini Dino Nuggets 2b

Which bond has more ionic character, C–F or C–Br? Why?

C-F (look at electronegativity difference)


Why isn't the electronegativity difference greater between C and Br since Br is farther away on the periodic table?
by KDang_1D
Mon Nov 04, 2019 3:39 pm
Forum: Lewis Structures
Topic: 2B.1b
Replies: 3
Views: 26

2B.1b

Why can't the molecule be drawn Cl-C-O-Cl rather than centered around C? The formal charges would all be 0 instead of +1/-1.
by KDang_1D
Sat Nov 02, 2019 4:41 pm
Forum: Ionic & Covalent Bonds
Topic: Homework 2D #15
Replies: 5
Views: 47

Re: Homework 2D #15

This is referencing the concept of bond length that Dr. Lavelle explained during Friday's lecture using the example of the strong acids: HF > HCl > HB > HI. Bond strength decreases as atomic radius of increases because the atoms are farther apart and easier to pull apart. Thus, among CF4, CCl4, CBr4...
by KDang_1D
Sat Nov 02, 2019 4:35 pm
Forum: Ionic & Covalent Bonds
Topic: The net energy decrease when Na and Cl form NaCl
Replies: 2
Views: 24

Re: The net energy decrease when Na and Cl form NaCl

Hmm, I think this is a little more detailed than necessary. I believe it's explaining that all processes require energy, and the formation of ionic bonds is driven by the cation in the compound. More than the electron affinity of the anion, the ionization energy of the cation wanting to lose its ext...
by KDang_1D
Sat Nov 02, 2019 4:25 pm
Forum: DeBroglie Equation
Topic: Dino Nuggets 13a
Replies: 1
Views: 68

Dino Nuggets 13a

Essentially, the question is "what is the kinetic energy of one potassium ion with a wavelength of 11.23 nm?" We used the mass 39.1 g/mol for the potassium ion. Does that mean that the mass of ions and neutral elements are the same? Why wouldn't we have to subtract 9.11x10-31kg from the ma...
by KDang_1D
Wed Oct 30, 2019 7:35 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration of Tungsten
Replies: 1
Views: 28

Electron Configuration of Tungsten

Why does tungsten have 4 electrons in the d-orbital? If element #57 is a lanthanide and the additional electron would go into the f-orbital, wouldn't tungsten have 3 electrons in the d-orbital?
by KDang_1D
Wed Oct 30, 2019 7:27 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Valence-Shell Configuration
Replies: 1
Views: 22

Valence-Shell Configuration

1E.25 Give the notation for the valence-shell configuration (including the outermost d-electrons) of (a) the alkali metals; (b) Group 15 elements; (c) Group 5 transition metals; (d) the "coinage" metals (Cu, Ag, Au). What is the "valence-shell configuration"? What does n and (n-...
by KDang_1D
Wed Oct 30, 2019 7:24 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Expanded Octet
Replies: 2
Views: 17

Re: Expanded Octet

P, S, and Cl are the only elements that we need to know since we will only be covering elements from the first 3 energy levels, I believe.
by KDang_1D
Thu Oct 24, 2019 4:01 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Inverse Relation
Replies: 3
Views: 52

Re: Inverse Relation

It has to do with the impact of detection on the position of the object being detected. When the photons from the measuring device reaches the electron, the electron is pushed off course, altering it's velocity and thus also momentum. Therefore, the more certain we are about the electron's position,...
by KDang_1D
Thu Oct 24, 2019 3:57 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Minimum Uncertainty
Replies: 2
Views: 35

Re: Minimum Uncertainty

The Heisenberg equation is expressed as , meaning that the uncertainty is greater than or equal to that value. Thus, the "minimum uncertainty" would be when the uncertainty is equal to h/(4). So just change >/= to =.
by KDang_1D
Thu Oct 24, 2019 3:45 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Spin Magnetic Quantum #
Replies: 6
Views: 87

Re: Spin Magnetic Quantum #

Yes, the concept of electron spin was discovered through the Stern Gerlach experiment. They fired silver atoms, which have 1 valence electron, through a pair of magnetized plates. The interaction between the local magnetic fields of the individual electrons and the plates' magnetic field caused the ...
by KDang_1D
Thu Oct 24, 2019 3:38 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Lowest Energy for Elements, Compounds, Etc
Replies: 2
Views: 32

Re: Lowest Energy for Elements, Compounds, Etc

Hmm I'm not sure if our class has a detailed answered to why electrons, atoms, etc. tend towards energetically favorable states yet, but on a rudimentary level, think of people standing on a staircase. Unless there were people taking up all the space on the bottom, you wouldn't want to expend any ex...
by KDang_1D
Thu Oct 24, 2019 3:27 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configurations of ions
Replies: 4
Views: 22

Re: Electron Configurations of ions

Yes, in lecture, Prof. Lavelle gave an example with In ions:



by KDang_1D
Thu Oct 24, 2019 3:22 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: subshell or orbital?
Replies: 3
Views: 44

Re: subshell or orbital?

s, p, d, f are all subshells. Then quantum numbers go n then l, so think of these l-values as a "subcategory" for n (energy shells). These subshells then have various bubbles of high probability. They are categorized based on their position in the xyz plane, and each of these regions is ca...
by KDang_1D
Mon Oct 14, 2019 6:02 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Positive and Negative signs?
Replies: 5
Views: 45

Re: Positive and Negative signs?

Positive energy is an increase in the system (coming in), and negative energy is a decrease in the system (going out)

E=hv is positive because you're simply analyzing energy that is already there. E=(-hR)/n^2 is negative because the electron's energy is being emitted as a photon.
by KDang_1D
Mon Oct 14, 2019 5:49 pm
Forum: *Shrodinger Equation
Topic: H=E
Replies: 1
Views: 47

H=E

What is the meaning of the conceptual equation ? What do sin waves, derivatives, and probability have to do with energy?
by KDang_1D
Mon Oct 14, 2019 5:44 pm
Forum: *Shrodinger Equation
Topic: Class Lecture 10/14
Replies: 1
Views: 37

Re: Class Lecture 10/14

Because Schrodinger's equation itself is beyond our level for now, we don't need to go into the specifics, but essentially, the energies of the electrons for various elements matches the energies shown by spectral lines. We haven't covered it in class yet, but the orbitals from \psi^{2} can be assig...
by KDang_1D
Mon Oct 14, 2019 3:43 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty of speed
Replies: 5
Views: 44

Re: Uncertainty of speed

Hmm... the solution manual says that it is actually . I'm not sure why
by KDang_1D
Mon Oct 14, 2019 3:35 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty of speed
Replies: 5
Views: 44

Re: Uncertainty of speed

You are correct, the uncertainty would be 2(5 m/s) = 10 m/s. In his video module, Dr. Lavelle explains that uncertainty should be described as the range. He emphasizes that the uncertainty for +/- 1 would be 2. Additionally, in the problem during lecture that assumes electrons are confined to the nu...
by KDang_1D
Mon Oct 14, 2019 3:26 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Momentum
Replies: 2
Views: 58

Momentum

What is the significance of momentum in the Heisenberg Indeterminacy equation? Why not write the formula in terms of if you can't interpret anything from unless you convert it to velocity using p=mv?
by KDang_1D
Mon Oct 14, 2019 3:22 pm
Forum: *Shrodinger Equation
Topic: Electron Distribution Definition
Replies: 4
Views: 61

Electron Distribution Definition

Prof. Lavelle used the term "e- distribution" to describe . What does mean in this context?
by KDang_1D
Sun Oct 13, 2019 9:07 pm
Forum: DeBroglie Equation
Topic: Rest Mass
Replies: 1
Views: 29

Re: Rest Mass

I don't know what rest mass means as opposed to "moving mass," but particles with a DeBroglie wavelength must have mass because of the inclusion of momentum (p=mv) in the equation: = h/p
by KDang_1D
Sun Oct 13, 2019 7:17 pm
Forum: DeBroglie Equation
Topic: DeBroglie confirmation.
Replies: 2
Views: 41

Re: DeBroglie confirmation.

Yes, an object must have rest mass in order to use the DeBroglie equation. This is shown in the equation, λ = h/p = h/(mv), which needs mass (m) to calculate the momentum.
by KDang_1D
Mon Oct 07, 2019 6:17 pm
Forum: Properties of Light
Topic: Quantum Mechanics Equations
Replies: 2
Views: 41

Re: Quantum Mechanics Equations

Also remember the basic equation . It's useful for converting wavelength and frequency since c is constant for light.
by KDang_1D
Mon Oct 07, 2019 6:13 pm
Forum: Photoelectric Effect
Topic: Potential Difference
Replies: 3
Views: 26

Potential Difference

Professor Lavelle mentioned that the electrons removed from the metal reach the detector by drifting towards it as the result of a "positive potential difference." What does that mean?
by KDang_1D
Mon Oct 07, 2019 6:11 pm
Forum: Photoelectric Effect
Topic: Why do photons not obey the wave equation?
Replies: 6
Views: 91

Re: Why do photons not obey the wave equation?

Yes, the photoelectric effect showed that photons don't always behave as waves. That's part of what made studying atoms at the quantum level so mysterious, light behaved as a wave and as a particle. This became known as the "wave-particle duality" of light. Later on, we would in fact learn...
by KDang_1D
Mon Oct 07, 2019 6:05 pm
Forum: Photoelectric Effect
Topic: How much energy to remove one electron?
Replies: 8
Views: 122

Re: How much energy to remove one electron?

Use the equation for the photoelectric effect:


Rewrite as:

Substitute in the mass of an electron, 9.10938x10^-31 kg. Then solve for E of the photon
by KDang_1D
Sat Oct 05, 2019 12:10 pm
Forum: Properties of Light
Topic: Oscillation
Replies: 1
Views: 35

Oscillation

What does the term "oscillation" mean? What does it mean for EM waves to be "time-varying"?
by KDang_1D
Sat Oct 05, 2019 12:05 pm
Forum: Properties of Light
Topic: E=hv quantization
Replies: 1
Views: 32

E=hv quantization

The textbook explains that E=hv models the quantization of energy. Why is this if frequency (v) varies along the spectrum, not in quantized values like n?
by KDang_1D
Sat Oct 05, 2019 11:55 am
Forum: Photoelectric Effect
Topic: 1B.15 part a
Replies: 1
Views: 38

1B.15 part a

The velocity of an electron that is emitted from a metallic surface by a photon is 3.6x10^3 km/s. What is the wavelength of the ejected electron? The solution manual says to use the de Broglie relationship, \lambda = hp^{-1} = h(mv)^{^{-1}} . Why wouldn't you use the equation the textbook g...
by KDang_1D
Tue Oct 01, 2019 8:30 pm
Forum: Significant Figures
Topic: How Many significant figures to use ?
Replies: 9
Views: 111

Re: How Many significant figures to use ?

Usually you can just use the least number of sig. figs. from the information given in the problem since most calculations involve multiplication and division. However, it is important to remember that when adding and subtracting, sig. figs. are determined by the least number of decimal places. For e...
by KDang_1D
Tue Oct 01, 2019 4:51 pm
Forum: SI Units, Unit Conversions
Topic: SIG FIGS
Replies: 11
Views: 159

Re: SIG FIGS

In calculations involving multiplication and division, the least number of sig. figs. is used in the final answer. So in this example, the answer would only have 1 sig. fig. since 7 is only 1 digit.

3.8*4.25 = 16.15 = 16 (2 sig figs. because of 3.8)
16.15/7 = 2.307 = 2 (1 sig fig. because of 7)
by KDang_1D
Tue Oct 01, 2019 4:45 pm
Forum: Limiting Reactant Calculations
Topic: Aqueous Solutions
Replies: 3
Views: 28

Aqueous Solutions

In reactions including water as a reactant and an aqueous solution as a product, is it safe to assume that water will always be the reactant in excess and the other reactant limiting? Otherwise how would there be enough water for the aqueous solution to dissolve in? ex. 2Na(s) + 2 H2O(l) --> 2NaOH(a...
by KDang_1D
Tue Oct 01, 2019 4:38 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: How was a mole originally determined?
Replies: 3
Views: 54

Re: How was a mole originally determined?

I think, but not certain, that it's an estimate of the number of nucleons in 1g. We know they calculated Avogadro's number using 12 grams of carbon-12, which has 6 protons and 6 neutrons. Thus, 1 gram for each nucleon in the atom. This is why we can use the atomic mass values on the periodic table t...
by KDang_1D
Tue Oct 01, 2019 4:28 pm
Forum: Balancing Chemical Reactions
Topic: Aqueous compounds
Replies: 5
Views: 277

Re: Aqueous compounds

For now, I believe that it's safe to assume that, if not otherwise stated, all compound products will be aqueous, unless it's something obvious like carbon dioxide gas. Also, if one product is a precipitate, I think the other must be aqueous.
by KDang_1D
Tue Oct 01, 2019 4:22 pm
Forum: Balancing Chemical Reactions
Topic: Combustion Reaction Notation
Replies: 6
Views: 71

Combustion Reaction Notation

In combustion reactions, is it necessary to indicate the input in energy (i.e. spark) above the reaction arrow? For example, the use of delta in high temperatures

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