## Search found 102 matches

Tue Mar 10, 2020 9:54 pm
Forum: General Rate Laws
Topic: Determining Rate Laws
Replies: 4
Views: 55

### Re: Determining Rate Laws

You would only use the coefficients of the reactants, not the products, because the rate laws only use the concentrations of the reactants in the reaction.
Tue Mar 10, 2020 9:48 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 7b.3c - where did the ln come from?
Replies: 6
Views: 77

### Re: 7b.3c - where did the ln come from?

You plug the concentrations into the first order integrated rate law equation to find k
ln[A]=-kt+ln[Ainitial]
Tue Mar 10, 2020 12:08 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Developing a Proposed Reaction Mechanism
Replies: 3
Views: 28

### Re: Developing a Proposed Reaction Mechanism

Dr. Lavelle said that we won't have to develop our own reaction mechanism. We just need to be able to decide if a given proposed mechanism supports a rate law, what a rate law would be given a mechanism, etc. But we won't be ask to develop a full mechanism without given much information.
Tue Mar 10, 2020 12:07 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE table
Replies: 5
Views: 57

### Re: ICE table

You can assume x is small when the equilibrium constant (K) is less than 10^-3 as a general rule of thumb. But to test it, after you calculate the equilibrium concentration, you can do the equilibrium concentration of the conjugate base divided by the initial concentration of the weak acid times 100...
Mon Mar 09, 2020 11:48 pm
Forum: General Rate Laws
Topic: Catalysts and Rate Laws
Replies: 2
Views: 34

### Catalysts and Rate Laws

If there is a catalyst in the slow step of a reaction mechanism, is it included in the rate law even if it cancels in the overall reaction?
Thu Mar 05, 2020 10:46 am
Forum: General Rate Laws
Topic: Lecture Question
Replies: 3
Views: 81

### Re: Lecture Question

I think it means that you need in ensure that there isn't product, because if there is then the reverse reaction can occur and you are trying to studying just the rate of the forward reaction with the integrated rate law(which only considers reactant). Therefore, you need to either remove product or...
Thu Mar 05, 2020 10:43 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Cell potential
Replies: 2
Views: 39

### Re: Standard Cell potential

I think it just means that the redox reaction isn't spontaneous (assuming that the cell potential was calculated correctly). A negative cell potential means that there is no energy to do work and the reaction is not spontaneous.
Wed Mar 04, 2020 4:20 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6M.5
Replies: 1
Views: 28

### 6M.5

The question states: For each reaction that is spontaneous under standard conditions (that is, K > 1), write a cell diagram, determine the standard cell potential, and calculate delta G for the reaction. My question is, are we suppose to know if the reaction is spontaneous before calculating the cel...
Tue Mar 03, 2020 7:10 pm
Forum: Van't Hoff Equation
Topic: 5J.15
Replies: 3
Views: 104

### 5J.15

To find the equilibrium constant at 150 Celsius, why can't you use △G=-RTlnK? Why do you need to use the Van't Hoff Equation? For reference: Calculate the equilibrium constant at 25 C and at 150 C for each of the following reactions, using data available in Appendix 2A: NH4Cl(s) --> NH3(g) 1 HCl(g)
Tue Mar 03, 2020 7:09 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: △G=-RTlnK [ENDORSED]
Replies: 1
Views: 129

### △G=-RTlnK[ENDORSED]

Can you use △G=-RTlnK at any temperature or does it need to be at standard conditions (298K)?
Wed Feb 26, 2020 11:10 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Midterm question 4
Replies: 1
Views: 46

### Re: Midterm question 4

The solid isn't included in the equilibrium constant. The salt (C6H5CH2CH(CH3)NH3+Br-) is a solid, but the Br- doesn't affect the solution so in the equilibrium constant, it is only C6H5CH2CH(CH3)NH3+, which is not a solid.
Wed Feb 26, 2020 11:07 pm
Forum: Balancing Redox Reactions
Topic: Coefficient consideration
Replies: 4
Views: 72

### Re: Coefficient consideration

The coefficient matters in terms of redox reactions. For 2Fe2+ you will need 4e- to balance the charge to 0, but for Fe2+ you only need 2e- to balance the charge to 0. However, Fe2+ has a 2+ overall charge regardless of the coefficient and H+ has a +1 charge regardless of the coefficient, etc.
Wed Feb 26, 2020 5:31 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L.3b
Replies: 2
Views: 31

### Re: 6L.3b

They aren't included in the half reactions. In this case, the graphite and platinum are used at inert conductors to allow the flow of electrons in the half reactions.
Wed Feb 26, 2020 4:59 pm
Forum: Balancing Redox Reactions
Topic: 6L.3 d)
Replies: 1
Views: 55

### 6L.3 d)

Write the half-reactions and the balanced equation for the cell reaction for each of the following galvanic cells: Pt(s)|O2(g)|H+(aq)||OH-(aq)|O2(g)|Pt(s) The answer is: 2H2O --> 4H++ O2 + 4e- for the anode and O2 + 2H2O + 4e- --> 4OH- for the cathode How do you know that H+ and O2 are both products...
Wed Feb 26, 2020 4:33 pm
Forum: Balancing Redox Reactions
Topic: 6L.3
Replies: 1
Views: 48

### 6L.3

The question asks: Write the half-reactions and the balanced equation for the cell reaction for each of the following galvanic cells: b) C(gr)|H2(g)|H+(aq)||Cl-(aq)|Cl2(g)|Pt(s) The answer gives the half rxns a: H2(g)-->H+ + 1e- Cl2(g)+2e- --> 2Cl-(aq) My question is how do you know that Cl2 is the ...
Sat Feb 22, 2020 10:21 am
Forum: Balancing Redox Reactions
Topic: Homework 6K.3
Replies: 2
Views: 59

### Re: Homework 6K.3

In some cases, the Cl2 will lose electrons and become oxidized and act as a reducing agent and in other cases the Cl2 will gain electrons and become reduced, acting as an oxidizing agent. It'll just do both in the system since it's the only reactant and it is being both reduced and oxidized in terms...
Sat Feb 22, 2020 10:18 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: n in -nFE
Replies: 12
Views: 113

### Re: n in -nFE

n is the number of moles and it comes from the fact that the value of Faraday's constant is the charge per mole so that's why you have to multiply it by the number of moles.
Thu Feb 20, 2020 2:51 pm
Forum: Balancing Redox Reactions
Topic: Oxidizing/reducing agent
Replies: 7
Views: 79

### Re: Oxidizing/reducing agent

An oxidizing agent does actually gain electrons and becomes reduced. A reducing agent loses electrons and then becomes oxidizes. It is a little weird because it seems backwards but I like to think of it when it's a paired redox reaction and how the oxidizing/reducing agent helps another molecule bec...
Wed Feb 19, 2020 8:28 pm
Forum: Van't Hoff Equation
Topic: Entropy in Van't Hoff Equation
Replies: 3
Views: 51

### Re: Entropy in Van't Hoff Equation

I believe we assume that entropy remains constant because I think we would normally use that equation to find equilibrium constants based on temperature. Also, entropy gets cancelled when you try to find K at two different temperatures if delta H is know
Wed Feb 19, 2020 7:43 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge and function
Replies: 4
Views: 78

### Re: Salt Bridge and function

The salt bridge allows the charges of the two compartments to remain neutral. Without the salt bridge, one compartment would become negatively charged and the other would become positively charged and the battery/galvanic cell would stop working(there would be no flow of electrons)
Tue Feb 11, 2020 9:24 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Intensive and Extensive Properties
Replies: 7
Views: 149

### Re: Intensive and Extensive Properties

Extensive properties depend on the amount of substance (such as heat capacity), but intensive properties don't depend on the amount of substance (such as specific heat capacity)
Tue Feb 11, 2020 9:08 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Question 4J.7
Replies: 5
Views: 91

### Re: Question 4J.7

Enthalpy of formation of O2 is zero because it's in its most stable form of oxygen
Tue Feb 11, 2020 9:07 pm
Forum: Phase Changes & Related Calculations
Topic: Expansion Work
Replies: 6
Views: 143

### Re: Expansion Work

If the volume increases then there is expansion work.
Mon Feb 10, 2020 5:06 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy of System vs Surroundings
Replies: 1
Views: 24

### Entropy of System vs Surroundings

For Question 4I.9, it asks: Initially an ideal gas at 323K occupies 1.67L at 4.95atm. The gas is allowed to expand to 7.33 L by two pathways: (a) isothermal, reversible expansion; (b) isothermal, irreversible free expansion. Calculate deltaStot, deltaS, and deltaSsurr for each pathway. I got the cor...
Mon Feb 10, 2020 5:02 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Double Greater than Sign
Replies: 2
Views: 23

### Re: Double Greater than Sign

I think it just means that the difference in entropy between a gas a liquid is much greater than the difference in entropy between a liquid and a solid because the entropy of gas is a lot of larger since a liquid and solid are still contained to some degree and don't have as many possible positions ...
Wed Feb 05, 2020 6:26 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: 3rd Law
Replies: 4
Views: 30

### Re: 3rd Law

It says that if and object reaches absolute zero temperature (0 Kelvin), then entropy is equal to zero.
Wed Feb 05, 2020 6:22 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy Decreasing, Temperature Increasing
Replies: 6
Views: 57

### Re: Entropy Decreasing, Temperature Increasing

In questions 4F.1 and 4F.3, they are saying that the change in entropy is less when the object is at a higher temperature, not that entropy is decreasing.
Wed Feb 05, 2020 6:19 pm
Forum: Phase Changes & Related Calculations
Topic: ΔH
Replies: 4
Views: 72

### Re: ΔH

ΔH of fusion is the change in enthalpy required for a substance to undergo a phase change from liquid to solid (or solid to liquid) and ΔH of vaporization is the change in enthalpy required for a substance to undergo a phase change from liquid to gas (or gas to liquid). You would use these values to...
Wed Feb 05, 2020 6:04 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Work done on or by the system
Replies: 4
Views: 56

### Re: Work done on or by the system

If work is done by the system then your work value for the system would be negative because the system is losing energy due to work. If the work is done on the system, you work value for the system would be positive because the system is gaining energy.
Wed Feb 05, 2020 6:00 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Max work
Replies: 2
Views: 29

### Re: Max work

A reversible reaction is when you incrementally increase the volume and allow the pressure to come to equilibrium at each small step so because of the infinite small steps, the process is the maximum possible work.
Thu Jan 30, 2020 11:04 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4D19
Replies: 1
Views: 31

### Re: 4D19

In this problem you are using Hess's Law to find the reaction enthalpy. You have to rearrange/multiply the given equations to eventually end up with the equation H2 + Br2 --> 2HBr when you add all of the reactions together. To do this you will need to reverse the first equation and multiply it by a ...
Thu Jan 30, 2020 10:56 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: How are qp and qv different?
Replies: 3
Views: 37

### Re: How are qp and qv different?

qp is enthalpy at constant pressure and qv is at constant volume. They are used when finding enthalpy/delta H but also find change in internal energy which is q + w so q can either be qp or qv depending on the given conditions
Wed Jan 29, 2020 11:16 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4D.7: Finding change in internal energy through ideal gas equation
Replies: 4
Views: 77

### Re: 4D.7: Finding change in internal energy through ideal gas equation

I think it might be because of significant figures
Wed Jan 29, 2020 7:02 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4D.7: Finding change in internal energy through ideal gas equation
Replies: 4
Views: 77

### Re: 4D.7: Finding change in internal energy through ideal gas equation

Because the change in thermal energy is equal to q + w and since there isn't any work being done on the system, I believe that the answer is simply delta U = q and q = delta H so the answer is -320 because that is the value of delta H in the reaction for 1 mol of OF2.
Wed Jan 29, 2020 6:37 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy and Entropy
Replies: 3
Views: 30

### Re: Enthalpy and Entropy

Enthalpy is the change in heat or delta H. Entropy is a measure of randomness/disorder. Enthalpy is used in calculating q, work, and energy due to heat. Entropy can be used to measure delta G which is the change in free energy, but we haven't discussed that yet.
Wed Jan 29, 2020 5:41 pm
Forum: Calculating Work of Expansion
Topic: Converting gas volume to mols
Replies: 2
Views: 29

### Re: Converting gas volume to mols

I think that that conversion factor is only for if the gas is at standard temperature and pressure. Otherwise you can use the ideal gas law to convert from liters to mols at any temperature and pressure.
Thu Jan 23, 2020 12:10 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5% rule
Replies: 13
Views: 131

### Re: 5% rule

You use it to check if you can appropriately approximate x to be a small enough that it would effect the initial concentration that much when using the calculation involving K. You will most likely use this when solving equilibrium equations.
Wed Jan 22, 2020 11:49 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le chatelier and Temperature
Replies: 9
Views: 108

### Re: Le chatelier and Temperature

If delta H is positive (endothermic) and temperature is increased, then the reaction would proceed towards the products. If delta H is negative (exothermic), then the reaction would proceed towards the reactants if temperature is increased.
Wed Jan 22, 2020 11:48 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Problem 5I.13
Replies: 1
Views: 27

### Re: Problem 5I.13

5.5*10^-6 is the value you get for x when you solve for the change in concentration using the equilibrium constant and it's multiplied by 2 because of the stoichiometric ratios in the equation.
Mon Jan 20, 2020 6:22 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: definition of a buffer
Replies: 8
Views: 126

### Re: definition of a buffer

A buffer has a weak acid/base and its conjugate so that it can thus resist a chance in pH. You want to have large enough concentrations of both so that it can react if an acid or base is added to the solution
Mon Jan 20, 2020 6:15 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE tables
Replies: 5
Views: 49

### Re: ICE tables

If you need to find the equilibrium concentration of a reactant of product or need to use the equilibrium concentration in a calculation you generally will need an ICE table. Also if you have to find the pH of the solution given the concentration of reactant, you will also most likely need an ICE ta...
Tue Jan 14, 2020 3:01 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE Table
Replies: 8
Views: 93

### Re: ICE Table

Yes you can. You just have to make sure that all of the values in your ICE tables have the same units (initial, change, and equilibrium) and that if you are going to calculate a Kc or Kp value, that you convert to the proper units.
Tue Jan 14, 2020 2:58 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5G.1 d homework
Replies: 1
Views: 19

### Re: 5G.1 d homework

Yes the statement would be true because if you start with a higher concentration of reactants, you will end up with a higher equilibrium concentration of products since the K stays the same.
Mon Jan 13, 2020 11:16 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6A21
Replies: 2
Views: 40

### Re: 6A21

Temperature just has an affect on the K constant. So in this case, at that temperature, the equilibrium constant Kw is equal to 2.1*10^-14 instead of 1*10^-14 which is Kw at 25 degrees Celsius. From the question you know that the concentration of H3O equals the concentration of OH- because it is a s...
Mon Jan 13, 2020 8:59 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: equilibrium constants and inputs
Replies: 4
Views: 57

### Re: equilibrium constants and inputs

Solids don't have concentrations because it doesn't make sense for it to have one. Liquids/solvents in reaction generally do not change much in terms of concentration so we assume that the value stays the same and will be on both sides of the reaction so it has no effect on the equilibrium constant.
Mon Jan 13, 2020 4:23 pm
Forum: Ideal Gases
Topic: Solids and liquids
Replies: 4
Views: 63

### Re: Solids and liquids

Solids don't have concentrations because it doesn't make sense for solids to have a concentration. The concentration of liquids (which are usually solvents) don't change that much during a reaction so it is therefore not included in the equilibrium expression.
Wed Jan 08, 2020 5:40 pm
Forum: Ideal Gases
Topic: Units for Pressure
Replies: 6
Views: 73

### Re: Units for Pressure

It doesn't matter which unit you use, but you have to make sure the R constant value/units corresponds with that pressure unit to make sure that units cancel.
Wed Jan 08, 2020 5:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: How to find stability based off of equilibrium concentrations
Replies: 2
Views: 50

### Re: How to find stability based off of equilibrium concentrations

I haven't done the exact problem yet but if you know the equilibrium concentrations of dichloride and chlorine or difluorine and fluorine, the one with the higher equilibrium concentration is more stable because the reactions proceeds to the more stable molecules.
Wed Jan 08, 2020 4:51 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Writing K expression with or without aq?
Replies: 5
Views: 64

### Re: Writing K expression with or without aq?

You do include molecules that are in an aqueous solution (aq)
Wed Jan 08, 2020 12:15 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K vs Kp vs Kc
Replies: 9
Views: 99

### Re: K vs Kp vs Kc

K is general term for the equilibrium constant of products over reactants. Kp means that the values in the equilibrium constant are the partial pressures of usually gases. Kc means that the values in the equilibrium constant are concentrations of aqueous solutions
Wed Jan 08, 2020 12:00 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Increasing the concentration of products?
Replies: 3
Views: 26

### Re: Increasing the concentration of products?

Increasing the concentration of the products will cause the reaction to proceed towards the reactants in order to reach equilibrium
Tue Dec 03, 2019 5:22 pm
Forum: Lewis Acids & Bases
Topic: Cations and Anions
Replies: 3
Views: 43

### Re: Cations and Anions

I don't think so because the cations and anions of strong acids and bases are stable so they won't act as acids or bases (ex: Cl- from the dissociation HCl is a stable ion)
Tue Dec 03, 2019 5:13 pm
Forum: Lewis Acids & Bases
Topic: Textbook 6C.17
Replies: 1
Views: 42

### Re: Textbook 6C.17

I think it is because HBrO is a weak acid, which makes BrO- a relatively stronger base than morphine. It also may have to do with nitrogen on the morphine, but I'm not 100% sure.
Tue Dec 03, 2019 4:57 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra
Replies: 3
Views: 132

### Re: Atomic Spectra

Firstly, you would the equation En= -hR/n^2 and the equation △E = Ef-Ei where Ef is for the final state/energy level of the atom and Ei is the initial state where the atom started. Once you find the change in energy, you can use E=hv to find the frequency as the change in energy is the energy of the...
Tue Dec 03, 2019 4:24 pm
Forum: Biological Examples
Topic: Hydrogen Bonding sites
Replies: 8
Views: 88

### Re: Hydrogen Bonding sites

Each lone pair on an oxygen, nitrogen, or fluorine is a potential hydrogen bonding site and each hydrogen that is attached to an oxygen, nitrogen, or fluorine is a potential hydrogen bonding site. For example, water has 4 hydrogen bonding sites (2 lone pairs on oxygen and 2 hydrogens attached to the...
Tue Dec 03, 2019 4:21 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Calculating pH for weak Acids
Replies: 3
Views: 48

### Re: Calculating pH for weak Acids

I think for 14A we only need to know how to calculate pH for strong acids as they 100% dissociate so calculated the pH is straight forward if you're given the concentration. You would just use the pH formula of -log [H30]
Mon Nov 25, 2019 4:05 pm
Forum: Bronsted Acids & Bases
Topic: Weak vs Strong Acid/Bases
Replies: 3
Views: 43

### Re: Weak vs Strong Acid/Bases

I believe you can tell if an acid or base is strong based on the K value, but we haven't learned this. I think we just have to know the main strong acids (HI, HCl, HBr, HClO4, HClO3, etc.) and main strong bases (NaOH, KOH, etc.). The rest are weak that don't 100% deprotonate/protonate. Also, I think...
Mon Nov 25, 2019 3:50 pm
Forum: Naming
Topic: 9C.3 D
Replies: 3
Views: 57

### Re: 9C.3 D

I think that when it comes to the ligands in the coordination complex, the order doesn't matter as much. I think it matters more in actual name.
Mon Nov 25, 2019 3:41 pm
Forum: Naming
Topic: Focus 9C.3
Replies: 4
Views: 36

### Re: Focus 9C.3

The Roman Numeral (III) is for the chromate. There are 3 K so that the charge is neutral. The 6 CN have a total of a 6- charge, the Cr has a 3+ charge, and since each K has a 1- charge, there are 3 of them to make the coordination compound neutral.
Mon Nov 25, 2019 3:39 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: 9C.5
Replies: 1
Views: 40

### 9C.5

The question asks which of the following ligands can be polydentate? CO3 2- was said to be mono or bidentate and oxalate was said to be bidentate. For CO3 2-, why can it be mono or bidentate? For oxalate, where are the two places that the ligand can bind to the central metal? Is it the two oxygens t...
Mon Nov 25, 2019 2:19 pm
Forum: Bronsted Acids & Bases
Topic: Memorizing the Bronsted Acids and Bases
Replies: 4
Views: 59

### Re: Memorizing the Bronsted Acids and Bases

I think it will be helpful at least to know the common ones such as HCl, HBr, and NaOH because I don't think we will be told if the acid or base is strong and weak unless it's one we haven't talked about.
Tue Nov 19, 2019 3:25 pm
Forum: Hybridization
Topic: Sigma and Pi Bond Practice Problems
Replies: 1
Views: 48

### Re: Sigma and Pi Bond Practice Problems

I'm pretty sure 2F.3 is about figuring out the number of sigma and pi bonds!
Tue Nov 19, 2019 3:03 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Seesaw Shape
Replies: 12
Views: 143

### Seesaw Shape

For atoms that have a seesaw molecular shape, I know that you select one of the equatorial angles to be the lone pair. So does that mean that the bond angles for seesaw shaped molecules is 90 degrees, 180 degrees, and <120 degrees? If not, what are the bond angles for a seesaw shaped molecule?
Tue Nov 19, 2019 2:55 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: Differentiating between London Dispersion and Induced-Dipole-Induced-Dipole
Replies: 2
Views: 25

### Re: Differentiating between London Dispersion and Induced-Dipole-Induced-Dipole

I believe they are both the same intermolecular force so they're both the same thing.
Tue Nov 19, 2019 2:42 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Question 2F3 part b
Replies: 3
Views: 43

### Re: Question 2F3 part b

Daria Azizad 1K wrote:I think that both the structure w/ two double bonds and the structure w/ one double bond and one single bond are acceptable, so they are just giving answers for both.

But wouldn't the structure with one double bond and one single bond not be ideal because it doesn't minimize formal charge?
Tue Nov 19, 2019 2:23 pm
Forum: Hybridization
Topic: Degenerate Orbitals
Replies: 1
Views: 28

### Re: Degenerate Orbitals

Yes because when we hybridize orbitals, all of the orbitals become the same level energy, instead of separated by s,p, and d, so they are degenerate.
Wed Nov 13, 2019 3:27 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Ground state?
Replies: 6
Views: 215

### Re: Ground state?

I think ground state refers to the lowest possible energy state of an atom or ion which means that there are no excited electrons in the atom or ion. Charge doesn't impact whether electrons are excited or not so that is why ions have a ground state electron configuration. The ground state configurat...
Wed Nov 13, 2019 3:22 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Shape
Replies: 8
Views: 70

### Re: Shape

Yeah, for the ones we learned today, they all had no lone pairs on the central atom. But there are different shapes when the central atom has lone pairs, which we will probably learn soon.
Wed Nov 13, 2019 2:15 pm
Forum: Administrative Questions and Class Announcements
Replies: 10
Views: 172

### Re: Midterm Answers

Yeah there is. It's on his website under Exam Information and its called "Midterm Solutions". Its on the right hand side if you scroll down.
Wed Nov 13, 2019 2:10 pm
Forum: *Particle in a Box
Topic: Principle quantum number
Replies: 2
Views: 130

### Re: Principle quantum number

The principle quantum number is which shell the electron is in. This is determined by which period the electron of the atom is in. Period 1 has a quantum number of 1, period 2 has a quantum number of 2, etc. For example, an electron is the 2s shell has a principle quantum number of 2.
Wed Nov 13, 2019 2:07 pm
Forum: DeBroglie Equation
Topic: Use
Replies: 4
Views: 126

### Re: Use

The Debroglie equation is used to calculate values for things with a mass (ex: electron, but not a photon). The equation is wavelength = h/mv where h is Planck's constant, m is mass in kg, and and v if speed in m/s.
Tue Nov 05, 2019 5:16 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: van der Waals radius
Replies: 1
Views: 135

### Re: van der Waals radius

Van der Waals are an example of intermolecular forces and during lecture he said it won't be on the midterm.
Tue Nov 05, 2019 5:03 pm
Forum: Trends in The Periodic Table
Topic: Why does having more polar ions create more covalent character?
Replies: 2
Views: 55

### Re: Why does having more polar ions create more covalent character?

A more highly polarizable anion means that the anion's electrons are more likely to be pulled towards the cation because the anion has a relatively low electronegativity. So the bond is considered more covalent because electrons are being distorted and pulled away. A greater difference in electroneg...
Tue Nov 05, 2019 4:45 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Midterm
Replies: 6
Views: 201

### Re: Midterm

I feel like we won't be asked about the specific experiment, but a lot of the experiments relate to concepts or equations that we learned in class like the Photoelectric Experiment and Photoelectric Effect so I think it would be good to know how the concepts and equations were derived from the exper...
Tue Nov 05, 2019 4:43 pm
Forum: Ionic & Covalent Bonds
Topic: 2D.9
Replies: 3
Views: 55

### Re: 2D.9

It's because Be 2+ has a smaller atomic radius so its polarizing power is greater because of more effective nuclear charge so its electronegativity/pulling power is higher than Sr 2+
Tue Nov 05, 2019 4:40 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 1E.25
Replies: 3
Views: 124

### Re: 1E.25

It just means to give the configuration for the outer most shell of electrons (valence electrons) as opposed to the entire electron configuration, in which you would start with 1s2 2s2 etc. Another way of thinking about it is that the valence electron configuration is the configuration from the last...
Fri Nov 01, 2019 11:13 pm
Forum: Sigma & Pi Bonds
Topic: Significance of sigma and pi bonds
Replies: 4
Views: 63

### Re: Significance of sigma and pi bonds

They have to do with double and triple bonds and how many of each are a sigma or pi bond, but I don't think we need to know this for the midterm because we haven't talked about it in class.
Fri Nov 01, 2019 11:03 pm
Forum: Bond Lengths & Energies
Topic: Test?
Replies: 8
Views: 191

### Re: Test?

The last slide of the lecture we had today won't be on the midterm. Bond lengths and energies will probably be on the midterm. The values with either be given to you and you have to use them in a question or you'll have to understand the concept of them to answer a question.
Fri Nov 01, 2019 10:52 pm
Forum: Trends in The Periodic Table
Topic: Periodic Table & Formulas
Replies: 2
Views: 32

### Re: Periodic Table & Formulas

I'm pretty sure it will be the same table! On the midterm review packet, it said to use the Constants and Equations sheet on his website, which I think is similar or exactly the same as the first test.
Fri Nov 01, 2019 10:37 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: manipulating equations
Replies: 3
Views: 60

### Re: manipulating equations

I don't think you need to show every single step, but I think it might be good so you don't mess up and your units match up. However, I don't think it's absolute necessary to show every step to manipulate an equation, as long as you manipulate it correctly.
Fri Nov 01, 2019 6:09 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charges
Replies: 4
Views: 61

### Re: Formal Charges

Formal charge is used to determine which resonance structure is "best" or the most stable. By calculating the formal charge, you can determine which resonance structure is most likely to occur. Ideally, you want the higher electronegative atoms to have the negative charges and you want to ...
Sun Oct 27, 2019 11:50 pm
Forum: Trends in The Periodic Table
Topic: Shielding and Electron Replusion
Replies: 3
Views: 69

### Re: Shielding and Electron Replusion

They are related in a sense. Shielding is when electrons in a lower energy level "shield" electrons in an outer energy level causing them to be less attracted or "pulled" by the nucleus. The example Dr. Lavelle gave in class was your friend blocking you from the heat of a fire by...
Thu Oct 24, 2019 6:04 pm
Forum: Octet Exceptions
Topic: Octet exception examples
Replies: 9
Views: 128

### Re: Octet exception examples

Boron also is an exception at times and there are some elements in the periodic table that can hold more than 8 electrons, but I think we'll talk about these in class at some point.
Thu Oct 24, 2019 4:21 pm
Forum: Trends in The Periodic Table
Topic: Calculated vs Observed Value
Replies: 6
Views: 72

### Re: Calculated vs Observed Value

I think it means that electronegativity is value that is calculated through a formula based on other values, whereas other values such as IE, electron affinity, and atomic radius are already found and don't require a formula for calculation.
Thu Oct 24, 2019 3:18 pm
Forum: Trends in The Periodic Table
Topic: Which element is stronger in IE?
Replies: 2
Views: 31

### Re: Which element is stronger in IE?

Yes, Na has a lower first ionization energy than Mg because of the fact that it has a weaker nuclear pull because it has less protons. Then if both lose one electron, Na+ has a much higher ionization energy than Mg+ because it now has a noble gas electron configuration
Thu Oct 24, 2019 2:16 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configurations of ions
Replies: 4
Views: 37

### Re: Electron Configurations of ions

You would remove from the 4s state first and then from the 3d because the 4s becomes higher in energy once the 3d orbital starts being filled.
Tue Oct 15, 2019 2:30 pm
Forum: DeBroglie Equation
Topic: De Broglie Wavelength
Replies: 7
Views: 116

### Re: De Broglie Wavelength

I think it just means to use the De Broglie equation because the De Broglie equation is derived from the equations E=pc, c= wavelength*frequency, and E=hv which we have learned before. However, this equation only works for any particle with a rest mass, momentum, and wavelength so if it asks for the...
Tue Oct 15, 2019 2:25 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: #20 Post Module
Replies: 3
Views: 50

### Re: #20 Post Module

I think you need to multiply the kinetic energy value you found by Avogadro's number to get the energy per mole of electrons, but I'm not 100% sure.
Tue Oct 15, 2019 2:20 pm
Forum: Properties of Electrons
Topic: Angstrom Conversion
Replies: 12
Views: 174

### Re: Angstrom Conversion

1 Angstrom is equal to 10^-10m so if you have a wavelength, for example, you can convert it from meters to angstroms with that conversion factor.
Tue Oct 15, 2019 1:40 pm
Forum: Properties of Light
Topic: Question 1A.5
Replies: 4
Views: 72

### Re: Question 1A.5

Yes, you write them in order from least to greatest amount of energy
Tue Oct 15, 2019 1:30 pm
Forum: Properties of Light
Topic: Relationships
Replies: 3
Views: 72

### Re: Relationships

Photons are particles of light and they do have energy, which you can calculate using the equation E=h*v. And thus, light is a source of energy.
Thu Oct 10, 2019 2:45 pm
Forum: Significant Figures
Topic: Conflicting Sig Fig Advice
Replies: 3
Views: 95

### Re: Conflicting Sig Fig Advice

For me, I think it's better to round for sig figs at the end of the problem because if you round as you are calculating, your answer is more likely to be more off than if you just round at the end of the problem. Generally, if you are fairly close in terms of sig figs and rounding I think you'll be ...
Thu Oct 10, 2019 2:34 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg vs Balmer Series
Replies: 2
Views: 65

### Re: Rydberg vs Balmer Series

Rydberg is the constant R and it's equal to 3.29x10e-15 Hz. You use this constant in the E= -hR/n^2. The Lyman and Balmer Series are just names for the spectral lines for atomic spectrum for a H atom. Balmer is the visible section and Lyman is the UV section.
Wed Oct 09, 2019 3:02 pm
Forum: Properties of Light
Topic: Kinetic Energy
Replies: 2
Views: 63

### Kinetic Energy

Why does the kinetic energy stay the same, in the photoelectric effect, even with a higher intensity of light?
Wed Oct 09, 2019 2:56 pm
Forum: Properties of Light
Topic: High Intensity
Replies: 5
Views: 68

### High Intensity

When discussing the photoelectric effect, is "high intensity" the same as "increasing the number of photons"? Are they synonymous? If so, does higher intensity just mean more/brighter light?
Wed Oct 09, 2019 2:47 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Positive/ Negative regarding E
Replies: 3
Views: 48

### Re: Positive/ Negative regarding E

The E that you plug into E=hv is the energy for the photon emitted which is why it is positive. The E you find from the problem was the energy of the electron when it moved from n=4 to n=2 which is negative because the energy decreased. The values are equal because the law of conservation of energy,...
Tue Oct 01, 2019 10:09 pm
Forum: Significant Figures
Topic: Rounding
Replies: 3
Views: 84

### Re: Rounding

Yes you're right. Mr. Lavelle's website says that you round to the nearest even digit if the last number if 5 so you are correct for rounding 1.65 to 1.6 and 1.35 to 1.4
Tue Oct 01, 2019 2:42 pm
Forum: Significant Figures
Topic: Could someone please clarify about Sig Figs?
Replies: 4
Views: 77

### Re: Could someone please clarify about Sig Figs?

There is also a document on Mr. Lavelle's website called "Everything you wanted to know about Sig Fig" if you want more clarification, but I think the above replies explains it pretty well. Zeros are only significant if they are between two numbers (ex: 705) or at the end of a number with ...
Tue Oct 01, 2019 2:30 pm
Forum: SI Units, Unit Conversions
Topic: Homework for Week 1
Replies: 16
Views: 362

### Re: Homework for Week 1

The first five homework problems from the textbook are due this Friday (Oct 4th) in lecture. And then starting next week, the five homework problems are due during our discussion sections each week. The five online posts on Chemistry Community are due by Sunday (Oct 6th) and then it's five every week.
Tue Oct 01, 2019 2:26 pm
Forum: Balancing Chemical Reactions
Topic: States of Matter in a Chemical Equation [ENDORSED]
Replies: 11
Views: 161

### Re: States of Matter in a Chemical Equation[ENDORSED]

It doesn't affect the equation itself but it may be good to know so you can visualize the experiment and sometimes elements change states if you have multiple equations that are linked together. Also, as we learn more it may be important when we expand balancing equations into greater concepts that ...

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