Search found 101 matches

by Andrew Pfeiffer 2E
Sat Mar 14, 2020 7:01 pm
Forum: Calculating Work of Expansion
Topic: work
Replies: 3
Views: 55

Re: work

For a reversible process (with regards to expansion), an infinitesimally small change in external pressure will cuss a change in volume, while in an irreversible process, an infinitesimally small change will not. For an irreversible process, use w=-P(deltaV). For a reversible process, use w=nRT ln V...
by Andrew Pfeiffer 2E
Sat Mar 14, 2020 6:57 pm
Forum: General Rate Laws
Topic: Rate Law
Replies: 2
Views: 50

Re: Rate Law

An integrated rate law will give you the concentration of reactants or products at any time after the start of the reaction, whereas the differential rate law is a general rate law built from the chemical equation like (r=k[A][B]).
by Andrew Pfeiffer 2E
Sat Mar 14, 2020 6:52 pm
Forum: Balancing Redox Reactions
Topic: balancing h and o
Replies: 7
Views: 93

Re: balancing h and o

You should balance the oxygens first with H2O, and then the hydrogens with H+.
by Andrew Pfeiffer 2E
Sat Mar 14, 2020 6:50 pm
Forum: Balancing Redox Reactions
Topic: oh
Replies: 11
Views: 127

Re: oh

No, because adding OH is going to do weird things with the pH of the solution depending on whether or not the reduction reaction happens in an acidic or basic solution.
by Andrew Pfeiffer 2E
Sat Mar 14, 2020 6:49 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: k
Replies: 3
Views: 54

Re: k

From a kinetics standpoint, temperature changes K because temperature affects the forward and reverse rates of the reaction. This is because K=k/k’ where lowercase k is a rate constant. When the temperature is changed, the rate constant is affected. Therefore, K changes with temperature.
by Andrew Pfeiffer 2E
Sat Mar 14, 2020 3:05 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysts on Final
Replies: 6
Views: 88

Catalysts on Final

Do you think we will be tested on our knowledge of catalysts on the final? If so, what are potential questions that could show up?
by Andrew Pfeiffer 2E
Sat Mar 14, 2020 2:58 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Midterm 6B
Replies: 1
Views: 56

Re: Midterm 6B

A is the correct answer because Al and Fe undergo a simple redox reaction, with relatively low values of deltaH nought and deltaG nought. All of the other options have multiple phases or have unbalanced molar distributions, creating variety in the deltaG nought and deltaH nought.
by Andrew Pfeiffer 2E
Sun Mar 08, 2020 9:22 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Electroplating
Replies: 1
Views: 45

Electroplating

If electroplating occurs on the cathode in a Galvanic Cell, why is it introduced in 6O.3, the applications of electrolysis?
by Andrew Pfeiffer 2E
Sun Mar 08, 2020 9:19 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Downs Process
Replies: 4
Views: 44

Downs Process

Will we need to memorize anything about the Downs Process for the final exam?
by Andrew Pfeiffer 2E
Sun Mar 08, 2020 9:12 pm
Forum: Environment, Fossil Fuels, Alternative Fuels
Topic: Gibbs and Environment
Replies: 1
Views: 57

Re: Gibbs and Environment

We'll likely encounter problems of this sort in which we'll need to calculate the molar Gibbs free energy of different alternative fuels and evaluate which fuel will be most useful. We might have to consider the molar mass of the fuel, as the molecular size of the fuel will have implications on how ...
by Andrew Pfeiffer 2E
Sat Mar 07, 2020 5:21 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: the intermediate in a reaction
Replies: 10
Views: 111

Re: the intermediate in a reaction

Because intermediates are by definition produced in one step and consumed in another, they are not actually present in the overall equation or rate law of the reaction.
by Andrew Pfeiffer 2E
Sat Mar 07, 2020 5:15 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Positional Disorder and Thermal Disorder
Replies: 2
Views: 84

Re: Positional Disorder and Thermal Disorder

Thermal disorder has to do with how rapidly the molecules in a substance move. The more the substance is heated, the more quickly the molecules move and bounce off of each other, and the higher the thermal disorder. Increased thermal disorder leads to increased entropy. Positional disorder has to do...
by Andrew Pfeiffer 2E
Sun Mar 01, 2020 7:38 pm
Forum: General Rate Laws
Topic: order of the reactant
Replies: 3
Views: 32

Re: order of the reactant

The order of the reactant indicates how much the rate of the reaction is affected if the concentration of (one of) the reactant(s) is changed.
by Andrew Pfeiffer 2E
Sun Mar 01, 2020 7:36 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: delta G=-nFE
Replies: 7
Views: 66

Re: delta G=-nFE

We can calculate it if we have all the other components of this equation (the standard change in Gibbs free energy, the energy, and Faraday's constant). Otherwise, we must use additional equations and knowledge about the conditions to indirectly solve for n and plug it back in.
by Andrew Pfeiffer 2E
Sun Mar 01, 2020 7:32 pm
Forum: Balancing Redox Reactions
Topic: oxidizing agents
Replies: 11
Views: 78

Re: oxidizing agents

The terminology here appears flipped because of the meaning of the word agent. In general, an agent is a thing that brings about an action. In the case of redox reactions, a reducing agent is the atom or molecule that brings about the oxidization of another, while an oxidizing agent is the atom or m...
by Andrew Pfeiffer 2E
Sun Mar 01, 2020 7:25 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Heat Death
Replies: 2
Views: 111

Re: Heat Death

One implication of the heat death of the universe that I've always wondered about is what it implies about the universe's time frame and origins. If the universe has always existed, then maximum entropy would have already been achieved and no more work could be achieved by the universe. But we have ...
by Andrew Pfeiffer 2E
Sun Mar 01, 2020 7:16 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: intergrated rate law
Replies: 9
Views: 67

Re: intergrated rate law

I think that you'll be okay memorizing it and applying it in problems. That being said, it's always better to understand equations in terms of their derivation, so knowing how to derive the equation certainly would help you. You'll be able to understand conceptual equations better. Hope this helped.
by Andrew Pfeiffer 2E
Sun Feb 23, 2020 11:21 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: G in standard conditions
Replies: 2
Views: 29

Re: G in standard conditions

G in non standard conditions can be calculated by using delta G = delta Go + RT ln Q.

With standard states, it can be calculated delta G = delta H - T delta S.
by Andrew Pfeiffer 2E
Sun Feb 23, 2020 11:10 pm
Forum: Balancing Redox Reactions
Topic: Reduced/Oxidized
Replies: 5
Views: 44

Re: Reduced/Oxidized

You'll have to use your knowledge of valence electrons and charge to determine the charges on individual atoms and ions. From there, use OIL RIG to figure out what's being reduced or oxidized.
by Andrew Pfeiffer 2E
Sun Feb 23, 2020 11:06 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Assuming conditions
Replies: 2
Views: 26

Re: Assuming conditions

Considering most standard values (like enthalpy) are given for standard conditions/STP, maybe when nothing is specified, assume STP.
by Andrew Pfeiffer 2E
Sun Feb 23, 2020 11:04 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isochoric/isometric
Replies: 4
Views: 77

Isochoric/isometric

Is there any meaningful difference between the term isochoric and isometric? When should we use one or the other?
by Andrew Pfeiffer 2E
Sun Feb 23, 2020 10:58 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L.7
Replies: 2
Views: 60

Re: 6L.7

Ag + (aq) + e - --> Ag (s) E cathode = +0.80 V AgBr(s) + e- --> Ag(s) + Br- (aq) E anode = +0.07 80 V - 0.07 V = +0.73 V As far as devising a Galvanic cell goes, think about drawing out the diagram that Dr. Lavelle drew in class. Consider the factors that were present in the example cell (e.g. anode...
by Andrew Pfeiffer 2E
Sun Feb 16, 2020 10:30 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Kirchhoff's Equation? [ENDORSED]
Replies: 2
Views: 101

Kirchhoff's Equation? [ENDORSED]

To what extent do we need to know how to use the Kirchhoff Equation for thermodynamics?
by Andrew Pfeiffer 2E
Sun Feb 16, 2020 10:21 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G equations
Replies: 4
Views: 44

Re: Delta G equations

One of the equations relates delta G to the reaction quotient or equilibrium constant (which we use when equilibrium information is given), and the other relates the Gibbs free energy to change in enthalpy and change in entropy, which we use when we have the delta H and delta S of a reaction.
by Andrew Pfeiffer 2E
Sun Feb 16, 2020 10:17 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: ΔS of Phase Changes
Replies: 5
Views: 121

Re: ΔS of Phase Changes

We do this last step because we want to calculate the entropy of vaporization at that specific temperature. If we didn't do the last step, we would only be calculating the normal entropy of vaporization after heating up the liquid.
by Andrew Pfeiffer 2E
Sun Feb 16, 2020 6:46 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Differences in (delta)G^o equations
Replies: 3
Views: 39

Re: Differences in (delta)G^o equations

As with equilibrium calculations, K is for when the reaction is at equilibrium, and Q (reaction quotient) is for non-equilibrium reactions.
by Andrew Pfeiffer 2E
Sun Feb 16, 2020 6:43 pm
Forum: Calculating Work of Expansion
Topic: Choosing work equation
Replies: 10
Views: 156

Re: Choosing work equation

For an irreversible expansion, use w=-P(deltaX).

For a reversible expansion (isothermal), use w=-nRT(ln deltaV2/deltaV1).
by Andrew Pfeiffer 2E
Sun Feb 09, 2020 8:12 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 6
Views: 52

Re: Bond Enthalpies

Try drawing out the Lewis structures for the molecules that are the reactants. From there, cross out bonds that need to be broken and draw in bonds needed to get your Lewis structures to look like the Lewis structures of the products. Hope this helped!
by Andrew Pfeiffer 2E
Sun Feb 09, 2020 8:08 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Gas Constant
Replies: 3
Views: 19

Re: Gas Constant

Use 8.314 when your units are J/K*mol and use 8.206 x 10-2 when your units are are L*atm/K*mol.
by Andrew Pfeiffer 2E
Sun Feb 09, 2020 8:04 pm
Forum: Phase Changes & Related Calculations
Topic: Phase Change Calculations
Replies: 5
Views: 46

Re: Phase Change Calculations

It is given on our constants and equations sheet!
by Andrew Pfeiffer 2E
Sun Feb 09, 2020 8:02 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Ideal Gas Chart
Replies: 3
Views: 28

Re: Ideal Gas Chart

When you are working with questions where you have to calculate the enthalpy change associated with heating a gas, and the question prompts you to "treat the gas as an ideal", you should refer to the chart.
by Andrew Pfeiffer 2E
Sun Feb 09, 2020 7:50 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 4A.9 Help
Replies: 3
Views: 40

4A.9 Help

I was working on the following homework problem 4A.9: A piece of metal of mass 18.0 g at 100.0 C is placed in a vessel of negligible heat capacity but containing 50.2 g of water at 22.0 C. Calculate the final temperature of the water. Assume that no energy is lost to the surroundings. I ran into tro...
by Andrew Pfeiffer 2E
Sun Feb 02, 2020 9:19 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy
Replies: 7
Views: 45

Re: Enthalpy

If there is no non-expansion work done on the system and the pressure is still constant, then the heat consumed or released by the system will be equal to q.
by Andrew Pfeiffer 2E
Sun Feb 02, 2020 9:11 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 4B.7
Replies: 2
Views: 21

Re: 4B.7

Q is negative because it's about the work that is done by the fuel, not the work done on the cooling chamber. The fuel is combusted and releases energy; therefore it is exothermic.
by Andrew Pfeiffer 2E
Sun Feb 02, 2020 8:54 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Partial Pressure
Replies: 7
Views: 82

Re: Partial Pressure

Partial pressure is calculated by examining a single gas (in a mixture of gases) and identifying what its pressure would be if it occupied its volume on its own. Partial pressure is different from regular pressure, which is simply the pressure generated by all of the gases present in the container.
by Andrew Pfeiffer 2E
Sun Feb 02, 2020 8:43 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Quadratic Equation
Replies: 5
Views: 90

Re: Quadratic Equation

For the general equation: ax2 + bx + c = 0

x = -b +/- sqrt(b2-4ac) / 2a

You use the quadratic equation to solve for x when x is squared.
by Andrew Pfeiffer 2E
Sun Feb 02, 2020 8:33 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: U and H
Replies: 2
Views: 54

Re: U and H

These equations are both related to the first law of thermodynamics. The first equation is relevant when work done in or to the system is provided in the problem. The second equation is better suited for problems with enthalpy like heat transfers at constant pressure.
by Andrew Pfeiffer 2E
Sat Jan 25, 2020 9:12 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Burns: Steam or Water
Replies: 4
Views: 38

Burns: Steam or Water

Can someone please explain why burns from steam are far worse than burns from liquid water? I don't understand how the energy of from the phase change would affect the severity of the burn.
by Andrew Pfeiffer 2E
Sat Jan 25, 2020 8:59 pm
Forum: Ideal Gases
Topic: PV=NRT
Replies: 3
Views: 60

Re: PV=NRT

Roughly 3.34 x 10-9 m
by Andrew Pfeiffer 2E
Sat Jan 25, 2020 8:57 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Energy of the reactants
Replies: 6
Views: 30

Re: Energy of the reactants

The reaction is endothermic, as it has taken in energy in the process of the reaction.
by Andrew Pfeiffer 2E
Sat Jan 25, 2020 5:57 pm
Forum: Phase Changes & Related Calculations
Topic: Heat Capacity
Replies: 2
Views: 20

Re: Heat Capacity

Heat capacity is an extensive property because it is directly proportional to the amount of molecules you have. The more molecules, the more heat energy and the higher the heat capacity.
by Andrew Pfeiffer 2E
Sun Jan 19, 2020 4:20 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 5I.33
Replies: 1
Views: 63

5I.33

Does anyone know how to do 5I.33? Thanks y'all.
by Andrew Pfeiffer 2E
Sun Jan 19, 2020 4:15 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 5I.29
Replies: 1
Views: 44

5I.29

Does anyone know how to do 5I.29? Thanks!
by Andrew Pfeiffer 2E
Sun Jan 19, 2020 3:35 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5H.1 and 5H.3?
Replies: 2
Views: 24

5H.1 and 5H.3?

Can anyone explain the logic behind H.1 and H.3? Thanks y'all.
by Andrew Pfeiffer 2E
Sun Jan 19, 2020 3:28 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Test 1 Acids and Bases Topic
Replies: 9
Views: 78

Re: Test 1 Acids and Bases Topic

As far as acids go for 14B, think of acids as proton donors (H+) and bases as proton acceptors. Strong acids and bases fully dissociate, and memorize the strong acids and bases (they're listed in the book). pH is the negative log of the concentration of the H3O+, and pOH is the negative log of the c...
by Andrew Pfeiffer 2E
Wed Jan 15, 2020 12:05 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: delta H
Replies: 5
Views: 34

Re: delta H

We don't have to be able to calculate delta H yet, but eventually, when we go over enthalpy in more depth, we will learn how to calculate it.
by Andrew Pfeiffer 2E
Tue Jan 14, 2020 4:42 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: volume's effect on K
Replies: 7
Views: 61

Re: volume's effect on K

Recall that volume is integrally related to both concentration and pressure. Decreasing the volume with the same amount of reactants and products is going to increase the pressure and concentration, while increasing the volume with the same amount of reactants and products is going to decrease the p...
by Andrew Pfeiffer 2E
Tue Jan 14, 2020 3:46 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: constant of water
Replies: 3
Views: 37

Re: constant of water

It becomes a little clearer why K w is so small when you consider the autoprotolysis reaction of water. 2 H 2 O (l) -->/<-- H 3 O + (aq) + OH - (aq) Consider several water molecules floating about. Very (and very) occasionally, the attraction of a water molecule's H to the lone pair on another water...
by Andrew Pfeiffer 2E
Tue Jan 14, 2020 3:32 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Lyndon Bui Workshops
Replies: 7
Views: 137

Re: Lyndon Bui Workshops

Hi! While I can't find any of his worksheets on Chem Community, it seems that he'll often use worksheets as the backbone of his workshops. Lyndon has workshops in Covel 210 on Mondays from 6-8. If you attend, I'm sure you will receive some of his practice problems.
by Andrew Pfeiffer 2E
Sun Dec 08, 2019 4:19 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: Hydrogen Bonding
Replies: 2
Views: 92

Re: Hydrogen Bonding

I think so! The oxygens have available lone pairs that could attract the positive dipole of the hydrogens in water. Hydrogen bonding occurs between H and N, O, or F, so I think it's possible.
by Andrew Pfeiffer 2E
Sun Dec 08, 2019 4:10 pm
Forum: Naming
Topic: bis- tris- tetrakis-
Replies: 8
Views: 172

Re: bis- tris- tetrakis-

Another example would be two diethylenetriamine ligands (which are both tridentate). The prefix used would be bis-, resulting in bisdiethylenetriamine.
by Andrew Pfeiffer 2E
Sun Dec 08, 2019 4:04 pm
Forum: Administrative Questions and Class Announcements
Topic: Online Textbook Access Code 14B
Replies: 2
Views: 54

Online Textbook Access Code 14B

For students continuing on to Chem 14B next quarter, does anyone know if the Sapling Access code needs to be renewed in the following quarter, or do we have access to it permanently? Thanks.
by Andrew Pfeiffer 2E
Sun Dec 08, 2019 3:56 pm
Forum: Properties of Light
Topic: Light acting like a wave
Replies: 4
Views: 131

Re: Light acting like a wave

Diffraction patterns when light passes through a small opening (complete with constructive and destructive interference) are evidence for light acting as a wave.
by Andrew Pfeiffer 2E
Sun Dec 01, 2019 10:00 pm
Forum: Lewis Acids & Bases
Topic: Mixing Metal Oxides with H2O
Replies: 1
Views: 24

Re: Mixing Metal Oxides with H2O

When metal oxides mix with H2O, they react to form bases. When nonmetal oxides mix with H2O, acids form.
by Andrew Pfeiffer 2E
Sun Dec 01, 2019 9:57 pm
Forum: Lewis Acids & Bases
Topic: Strong versus weak
Replies: 5
Views: 56

Re: Strong versus weak

Strong acids fully dissociate into its ions in water while weak acids partially dissociate into its ions in water.
by Andrew Pfeiffer 2E
Sun Dec 01, 2019 9:49 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 6B. 1
Replies: 2
Views: 46

Re: 6B. 1

HCl is a strong acid, so it dissociates completely. We know that the change in pH is -log(Mfinal/Minitial), so -log(.12/1) equals .92. Therefore, the pH will change .92. Hope this helped!
by Andrew Pfeiffer 2E
Sun Dec 01, 2019 9:39 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Polydentate
Replies: 5
Views: 54

Re: Polydentate

The molecule in question is a polydentate when

a.) the ligand has at least 2 molecules that have lone pairs and

b.) the atoms have a geometry that enables the transition metal cation to be bound in more than one place at the same time.
by Andrew Pfeiffer 2E
Sun Dec 01, 2019 9:36 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Final
Replies: 3
Views: 143

Re: Final

I would say that any concept and/or equation from the homework would be fair game for the final, including those that didn't show up on the midterm. The midterm is likely a good indicator of difficulty for the quantum world problems. Hope this helped!
by Andrew Pfeiffer 2E
Sun Nov 24, 2019 10:33 pm
Forum: Hybridization
Topic: Why does hybridization occur
Replies: 3
Views: 35

Re: Why does hybridization occur

They hybridize because it lowers the energy of the molecule.
by Andrew Pfeiffer 2E
Sun Nov 24, 2019 10:28 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Drawing molecules
Replies: 7
Views: 75

Re: Drawing molecules

Drawing complete molecules like the one seen on the test will probably come in 14C and 14D, but you will need to know how to analyze central atoms and bond angles.
by Andrew Pfeiffer 2E
Tue Nov 19, 2019 4:13 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: Magnitudes of Intermolecular Forces?
Replies: 1
Views: 19

Re: Magnitudes of Intermolecular Forces?

Ion-ion: -250 kJ/mol
Ion-dipole: -15 kJ/mol
dipole-dipole: -2 kJ/mol
dipole-induced dipole: -2 kJ/mol
induced dipole-induced dipole: -2 kJ/mol
by Andrew Pfeiffer 2E
Tue Nov 19, 2019 3:58 pm
Forum: Hybridization
Topic: When does hybridization not apply?
Replies: 1
Views: 27

Re: When does hybridization not apply?

Hybridization doesn't apply to ionic compounds.
by Andrew Pfeiffer 2E
Sat Nov 16, 2019 10:46 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Pentagonal Bipyramidal
Replies: 8
Views: 83

Pentagonal Bipyramidal

In the textbook, the molecular shape pentagonal bipyramidal (7 regions of high electron concentration) shows up a couple of times. We haven't really discussed this shape in depth in class, so will we be held accountable for it on test 2? Also, what molecules would have this shape?
by Andrew Pfeiffer 2E
Sat Nov 16, 2019 10:37 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: sigma and pi bonds
Replies: 2
Views: 31

Re: sigma and pi bonds

Sigma and pi bonds are chemical covalent bonds that come from overlapping atomic orbitals. Sigma bonds are associated with the "s" orbital, and pi bonds with the "p" orbital. In general, sigma bonds are stronger than pi bonds. They are both important for predicting molecule behav...
by Andrew Pfeiffer 2E
Sat Nov 16, 2019 10:31 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 2
Views: 34

Re: Bond Angles

The size of an atom can affect the molecule by throwing off the distribution of electrons. For example, a bigger molecule with more electrons will repel the other bonding groups, creating a larger bond angle. Electronegativity will attract electrons to certain atoms. With really electronegative elem...
by Andrew Pfeiffer 2E
Sat Nov 16, 2019 10:21 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR
Replies: 4
Views: 29

Re: VSEPR

Because the VSEPR formula is geared towards one central atom surrounded by electron groups, you can only apply it to one of the carbons. Treat the other carbon as a surrounding atom with a bonding group in between. With either of the carbons, you will get the same result. Hope this helped!
by Andrew Pfeiffer 2E
Sat Nov 16, 2019 10:18 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Polarity
Replies: 3
Views: 35

Re: Polarity

In most scenarios, you'll be able to give a good guess right off the bat based on the electronegativity difference between the molecules in question. However, you should always draw the Lewis structure, because dipole moments might cancel out resulting in a non-polar molecule. Hope this helped!
by Andrew Pfeiffer 2E
Mon Nov 11, 2019 7:49 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: Homework 3F.5 Part C
Replies: 2
Views: 36

Re: Homework 3F.5 Part C

It is determined that triiodomethane will have stronger London dispersion forces on the basis of polarizability. Triiodomethane is bigger than trifluoromethane, and its electrons are held more loosely (and can be distorted more easily). Thus, triiodomethane undergoes stronger London dispersion force...
by Andrew Pfeiffer 2E
Mon Nov 11, 2019 7:46 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: 3F.5 [ENDORSED]
Replies: 4
Views: 113

Re: 3F.5 [ENDORSED]

For this type of question, you're going to want to first draw out the Lewis structures of the molecules in the problem. Using the lecture content from this last week, you will determine which intermolecular force applies to the molecules in the question (London dispersion, hydrogen bonding, etc.). A...
by Andrew Pfeiffer 2E
Mon Nov 11, 2019 9:51 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Dimers
Replies: 1
Views: 26

Dimers

I was reading through the textbook, and the subject of dimers briefly came up in 3F.5. The only description of dimers here is "pairs of identical molecules", but this feels a little obscure, since there are lots of pairs of identical molecules. Can someone clear up what a dimer is more spe...
by Andrew Pfeiffer 2E
Mon Nov 11, 2019 9:45 am
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: 1
Views: 29

Re: interaction potential energy

We are not asked in our homework problems to directly use the equation, but it would be used when an exact measurement of the attractive and repulsive forces between molecules is necessary for a calculation or lab procedure.
by Andrew Pfeiffer 2E
Mon Nov 11, 2019 9:37 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: melting points
Replies: 6
Views: 50

Re: melting points

Water molecules undergo intense hydrogen bonding between the oxygen and hydrogen atoms. This makes it significantly harder for the intermolecular forces to be overcome to melt ice. Conversely, H 2 S has dipole-dipole interactions (S being negative and H positive). While these dipole-dipole interacti...
by Andrew Pfeiffer 2E
Sun Nov 03, 2019 11:23 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: rydberg equation
Replies: 2
Views: 53

Re: rydberg equation

During the Dino Nugget Review Session, it was stated that the Rydberg equation can be used for the calculations, but if you get the answer wrong, you will not receive partial credit for your work. Perhaps the best bet is solving the question Dr. Lavelle's way and using the Rydberg equation to check ...
by Andrew Pfeiffer 2E
Sun Nov 03, 2019 11:15 pm
Forum: Resonance Structures
Topic: 2B.15
Replies: 2
Views: 55

Re: 2B.15

For this question, you will have two resonance structures. In both structures the N will have a formal charge of +1 (that is, it will have four shared pairs of electrons with no lone pairs). Cl will always have a formal charge of 0 (that is, it will have a single shared pair of electrons and three l...
by Andrew Pfeiffer 2E
Sun Nov 03, 2019 11:05 pm
Forum: *Shrodinger Equation
Topic: quantization
Replies: 1
Views: 121

Re: quantization

From the Schrodinger equation (which isn't really applied directly in textbook calculations) one can calculate the wave function for any particle, as well as its corresponding energies. Now, the application of the Schrodinger equation to quantization comes from a thought experiment involving a parti...
by Andrew Pfeiffer 2E
Sun Nov 03, 2019 10:45 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Factors affecting energy
Replies: 1
Views: 37

Re: Factors affecting energy

Dr. Lavelle talked about how we will only be responsible for working with elements of the first four periods/rows on the periodic table. If by many-electron atoms you mean atoms of large elements with high energy orbitals, then you shouldn't have to worry about completing big calculations. However, ...
by Andrew Pfeiffer 2E
Sun Nov 03, 2019 10:38 pm
Forum: Trends in The Periodic Table
Topic: Electron affinity vs electronegativity
Replies: 7
Views: 72

Re: Electron affinity vs electronegativity

Electron affinity is the change in energy (in kJ per mole) when an electron is added to a neutral atom (in the gas phase) to make a positive ion. Electronegativity simply is the tendency to attract shared electrons (or a distribution of electrons) toward itself. Both of them share the same trend (in...
by Andrew Pfeiffer 2E
Sun Oct 27, 2019 11:40 pm
Forum: Ionic & Covalent Bonds
Topic: Boron's valence electrons
Replies: 2
Views: 21

Re: Boron's valence electrons

Boron has only 3 valence electrons. In order to satisfy the octet rule, it would have to gain 5 electrons from bonds. However, there are no known compounds where boron bonds with five other atoms. Boron has shown tendencies, thus, to follow the sextet rule: it gains 3 additional electrons through bo...
by Andrew Pfeiffer 2E
Sun Oct 27, 2019 11:29 pm
Forum: Lewis Structures
Topic: 2C15
Replies: 1
Views: 60

Re: 2C15

So in order to calculate the formal charge of a molecule, you need to use the equation FC = (Valence electrons) - (lone pair electrons + (shared electrons/2)) for each atom in the molecule. For example, in the part (a) the formal charge for the oxygen atom on the left of the structure would be solve...
by Andrew Pfeiffer 2E
Sun Oct 27, 2019 10:52 pm
Forum: Ionic & Covalent Bonds
Topic: 2A.23 question
Replies: 5
Views: 49

Re: 2A.23 question

For a further explanation of part A, Magnesium usually gives up 2 valence electrons, while Arsenic usually takes 3 valence electrons. Thus, two Arsenic atoms would take 6 valence electrons, and 3 Magnesium atoms would give 6 valence electrons.
by Andrew Pfeiffer 2E
Sun Oct 27, 2019 10:48 pm
Forum: Ionic & Covalent Bonds
Topic: 2A.23 question
Replies: 5
Views: 49

Re: 2A.23 question

Magnesium arsenide: As2Mg3

Indium III Sulfide: In2S3

Aluminum hydride: AlH3

Aluminum telluride: H2Te

Bismuth III Flouride: BiF3
by Andrew Pfeiffer 2E
Sun Oct 27, 2019 10:36 pm
Forum: Resonance Structures
Topic: Resonance Structures
Replies: 3
Views: 47

Re: Resonance Structures

Resonance structures are necessary when you can draw the same arrangement of atoms with different arrangements of e-. This occurs on account of the number of double bonds and lone pairs on each atom (you can find the best arrangement using formal charge, which we learned about last lecture).
by Andrew Pfeiffer 2E
Sun Oct 27, 2019 10:34 pm
Forum: Resonance Structures
Topic: Resonance
Replies: 3
Views: 61

Re: Resonance

Either of the first two options should suffice. Drawing a resonance hybrid would be the quickest way to display resonance, but drawing all of the structures is helpful in the sense of seeing all the options. Doing both is probably unnecessary, but if specified by the question, would be suggested. Ho...
by Andrew Pfeiffer 2E
Sun Oct 20, 2019 11:44 pm
Forum: DeBroglie Equation
Topic: 1B. 21
Replies: 5
Views: 175

Re: 1B. 21

It does not seem to have an effect on the calculation of the problem. Its inclusion in the problem is more along the lines of a fun fact than a necessity for solving the problem, as they provide the particular weight of the ball used in this problem. If you were able to go through the calculation, s...
by Andrew Pfeiffer 2E
Sun Oct 20, 2019 11:36 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Difference between the electron shell and orbitals
Replies: 4
Views: 55

Re: Difference between the electron shell and orbitals

As succinctly as I can put it, electron shells are made up of orbitals that have the same principal quantum number (n). Orbitals are regions around the nucleus of an atom where one is most likely to find a corresponding electron.

Hope this brief distinction helped!
by Andrew Pfeiffer 2E
Sun Oct 20, 2019 11:29 pm
Forum: Properties of Light
Topic: 1B. 9
Replies: 2
Views: 43

Re: 1B. 9

You were right that 64 J will be emitted! For this question, you need the equation E = (hc)/lambda Plugging in for Planck's constant, the speed of light, and the frequency of violet light, you can find the the energy of the photon to be 4.7 x 10 -19 J/photon. Divide 64 J by this number to get the nu...
by Andrew Pfeiffer 2E
Tue Oct 15, 2019 6:35 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbitals, 1D.11
Replies: 2
Views: 61

Re: Orbitals, 1D.11

We know that the third quantum number m l helps show the individual orbitals within a subshell. We know that m l = 2l + 1 Plug in 0, 2, 1, and 3 for l to get answers one orbital, five orbitals, three orbitals, and seven orbital respectively. See page 34 in the book for a helpful explanation on what ...
by Andrew Pfeiffer 2E
Tue Oct 15, 2019 6:27 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty Measurement Clarification
Replies: 2
Views: 38

Re: Uncertainty Measurement Clarification

Within the examples in the book, it looks as though the uncertainty equation will give you the range of uncertainty (in your example, 10) which can be divided by 2 in order to get the +/- uncertainty (in your example, 5). Hope this helped!
by Andrew Pfeiffer 2E
Sun Oct 13, 2019 11:07 pm
Forum: DeBroglie Equation
Topic: Context for this equation
Replies: 1
Views: 38

Re: Context for this equation

De Broglie's equation is best suited for finding the wavelength for a moving object with mass. If you're working with photons, or things that don't really have mass, use Einstein's equation. Hope this helped!
by Andrew Pfeiffer 2E
Sun Oct 13, 2019 11:01 pm
Forum: Properties of Light
Topic: Homework Problem 1A. 15
Replies: 1
Views: 29

Re: Homework Problem 1A. 15

Start with the equation v = c/lambda. Plug in 2.998 x 10 8 for c and 102.6 x 10 -9 for lambda. This will give us 2.922 x 10 15 seconds -1 . After that, we can use the Rydberg equation to solve for n 2 . Plug all the values into the Rydberg equation (see textbook page 7), and you should end up with n...
by Andrew Pfeiffer 2E
Sun Oct 13, 2019 10:52 pm
Forum: Properties of Light
Topic: Color, Frequency, and Wavelength of Electromagnetic Radiation
Replies: 1
Views: 24

Re: Color, Frequency, and Wavelength of Electromagnetic Radiation

While I'm not sure it'll be required, I am sure memorizing the frequency, color, and wavelength of EM radiation will serve helpful on homework and tests as well! Particularly with UV, visible light, and infrared radiation. Even if you don't memorize the exact ranges, having a ballpark estimation can...
by Andrew Pfeiffer 2E
Sun Oct 13, 2019 10:48 pm
Forum: Photoelectric Effect
Topic: Frequency vs. Amplitude: Intensity?
Replies: 3
Views: 42

Frequency vs. Amplitude: Intensity?

When Dr. Lavelle was lecturing last week on the photoelectric effect, I was a little confused on the distinction between the frequency and amplitude of a wave. I know that frequency is the number of wave cycles per second, and that amplitude is the height of a wave, but which of these two contribute...
by Andrew Pfeiffer 2E
Sun Oct 13, 2019 10:39 pm
Forum: Properties of Light
Topic: Combining Different Equations
Replies: 8
Views: 104

Re: Combining Different Equations

You cannot use the (lambda)(v) = (c) equation or the e = (h)(v) equation for electrons, but you can use them for light!
by Andrew Pfeiffer 2E
Fri Oct 04, 2019 12:16 am
Forum: SI Units, Unit Conversions
Topic: Bond Length
Replies: 5
Views: 101

Re: Bond Length

The length of a bond in a chemical compound depends on the compound at hand. Consider looking up a chart of experimental bond lengths!
by Andrew Pfeiffer 2E
Thu Oct 03, 2019 11:56 pm
Forum: SI Units, Unit Conversions
Topic: scientific notation
Replies: 7
Views: 77

Re: scientific notation

Whenever you're dealing with a number that can't be expressed with a simple decimal (i.e. a single digit followed by a decimal point and the consequent digits), scientific notation can really help clean up messy decimals. That being said, you can use your own judgment as to when numbers need to be c...
by Andrew Pfeiffer 2E
Thu Oct 03, 2019 6:34 pm
Forum: Balancing Chemical Reactions
Topic: Fractions in Balancing Equations
Replies: 11
Views: 195

Re: Fractions in Balancing Equations

Fractions can be used as an intermediate step when balancing equations, but you never want fraction coefficients in your final balanced equation. For example... Given the unbalanced equation C 4 H 10 + O 2 ---> CO 2 + H 2 O. First you would balance H and then balance O. After that, you should have C...
by Andrew Pfeiffer 2E
Thu Oct 03, 2019 6:20 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: mol-1?
Replies: 5
Views: 113

mol-1?

I noticed in lecture that when dealing with the unit of molar mass, grams per mole, Dr. Lavelle writes the unit as g.mol -1 . I've always written the unit simply as g/mol. I know that this is minutia, but wanted to know if I should begin expressing my units the same way, or if the way that I've been...

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