Search found 105 matches
- Wed Mar 11, 2020 9:28 pm
- Forum: Administrative Questions and Class Announcements
- Topic: "Open Book" Final?
- Replies: 30
- Views: 2185
Re: "Open Book" Final?
Open book is pretty every resource you can lay your hands on. I don't think he will be using Respondus or another program to record us while taking the exam, so I think textbook, notes, and other instructional notes are all fair game for "open book."
- Wed Mar 11, 2020 9:27 pm
- Forum: Administrative Questions and Class Announcements
- Topic: final
- Replies: 14
- Views: 988
Re: final
Lavelle has not mentioned much about the final, other than the content and the fact that it will be take-home. He did state that he will send out another email and directions soon. I think we'll have more information towards the end of the week and just need to sit tight.
- Wed Mar 11, 2020 9:26 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Format because I posted in 14A by accident
- Replies: 8
- Views: 626
Re: Format because I posted in 14A by accident
He hasn't mentioned the exact format or the directions for the final. Judging from his other tests, I would expect there to be some calculations, but the final may be a similar format to the modules. I honestly have no idea, but he said he would be posting and sending directions in another email thi...
- Wed Mar 11, 2020 9:24 pm
- Forum: General Science Questions
- Topic: Chemistry Final
- Replies: 16
- Views: 1257
Re: Chemistry Final
The format isn't known. From his past tests and exams from Chem 14A and Chem 14B, I don't think so. But he did state that it will be more straightforward and simple.
- Wed Mar 11, 2020 9:23 pm
- Forum: General Science Questions
- Topic: Test 2
- Replies: 3
- Views: 406
Re: Test 2
My TA emailed me about locations and pick-up dates. If he/she hasn't done so yet, it would probably be best to email your TA and ask about it.
- Sun Mar 08, 2020 12:38 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Purpose of Electrode
- Replies: 9
- Views: 730
Re: Purpose of Electrode
An electrode is a metallic conductor that is in the electrolyte solution. This allows electrons to flow between the two solutions. Platinum is really common for this. Graphite is also used, but not nearly as common as Platinum.
- Sun Mar 08, 2020 12:36 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Determining the cathode/anode
- Replies: 9
- Views: 800
Re: Determining the cathode/anode
Use Ecell = Ecathode - Eanode... in a galvanic cell, make sure that Ecell is positive, so the cathode needs to be more positive and the anode more negative.
- Sun Mar 08, 2020 12:35 am
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Calculating ln Q
- Replies: 20
- Views: 1678
Re: Calculating ln Q
Q is the concentration of products divided by the concentration of reactants. Put the coefficient as the exponent for the concentrations of products and reactants.
- Sun Mar 08, 2020 12:33 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: finding n in G=-nFE
- Replies: 15
- Views: 1060
Re: finding n in G=-nFE
n is the number of electrons transferred in a redox reaction.
- Sun Mar 08, 2020 12:32 am
- Forum: Balancing Redox Reactions
- Topic: Half rxns
- Replies: 27
- Views: 1532
Re: Half rxns
When balancing acidic reactions, add H+ and H20. For basic reactions, add H20 and OH-.
- Sun Mar 01, 2020 7:28 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: usage of platinum of cell diagrams
- Replies: 5
- Views: 412
Re: usage of platinum of cell diagrams
Usually you use Pt as an electrode in the diagram if there is no solid present for either the anode reaction or the cathode reaction. Lavelle mentioned that graphite can also be used, but it's not nearly as common as Platinum.
- Sun Mar 01, 2020 7:25 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidizing/reducing agent
- Replies: 18
- Views: 1161
Re: Oxidizing/reducing agent
An oxidizing agent is the thing being reduced, and a reducing agent is the thing being oxidized. I just remember it as the reverse since it can get a little confusing at times.
- Sun Mar 01, 2020 7:24 pm
- Forum: Balancing Redox Reactions
- Topic: H+ or H2O
- Replies: 4
- Views: 323
Re: H+ or H2O
H+ is for acidic reactions, and OH- is for basic reactions. H20 is used in both acidic and basic reactions.
- Sun Mar 01, 2020 7:23 pm
- Forum: Balancing Redox Reactions
- Topic: OH and H
- Replies: 8
- Views: 501
Re: OH and H
OH- and H+ can be added on either side. Remember OH- is for basic solutions and H+ is for acidic solutions.
- Sun Mar 01, 2020 7:22 pm
- Forum: General Rate Laws
- Topic: Integrated Rate Law
- Replies: 5
- Views: 385
Re: Integrated Rate Law
Differential rate laws will show rate as a function (the dependent variable) as a function of the reactant's concentration [R] (independent variable). Integrated rate laws will show reaction rate (dependent variable) as a function of time (independent variable).
- Sun Feb 23, 2020 1:46 pm
- Forum: Balancing Redox Reactions
- Topic: Acidic vs Basic
- Replies: 4
- Views: 388
Re: Acidic vs Basic
In acidic redox reactions, you use H+ to balance the hydrogens in the reaction. In basic redox reactions, you need to use H20 and OH- in a sort of back-and-forth balance. Basic reactions have an "extra step" where you can't just balance O and H with H+ and H2O.
- Sun Feb 23, 2020 1:43 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt bridge
- Replies: 4
- Views: 291
Re: Salt bridge
The salt bridge allows ion transfer across the two solutions. If there is no salt bridge, the reduced and oxidized solutions will continue to get charged as the reaction occurs.
- Sun Feb 23, 2020 1:39 pm
- Forum: Balancing Redox Reactions
- Topic: balancing acidic vs. basic solutions
- Replies: 3
- Views: 330
Re: balancing acidic vs. basic solutions
From what I remember, I think the problem will usually state whether the reaction takes place in basic or acidic solutions.
- Sun Feb 23, 2020 1:38 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Use of Platinum
- Replies: 10
- Views: 621
Re: Use of Platinum
Platinum is an inert conductor used to transfer electrons. It's an electrode that's placed on the reductio side.
- Sun Feb 23, 2020 1:37 pm
- Forum: Balancing Redox Reactions
- Topic: Cell Diagrams
- Replies: 5
- Views: 321
Re: Cell Diagrams
Platinum is the most common electrode used in electrochemical cells. It' resistant to oxidation and won't easily react in redox reactions. Pt is an inert conductor which is used to transfer electrons. Lavelle also stated that graphite can also be used I believe, but is not nearly as common as Platin...
- Sun Feb 16, 2020 4:53 pm
- Forum: Balancing Redox Reactions
- Topic: Number of electrons
- Replies: 5
- Views: 280
Re: Number of electrons
Yes. An oxidation reaction means that there is a loss of electrons, which just be written on the product side.
- Sun Feb 16, 2020 4:52 pm
- Forum: Ideal Gases
- Topic: pv=nrt
- Replies: 19
- Views: 1226
Re: pv=nrt
Yes. Remember STP is standard temperature and pressure, which is temperature (273.15 K) and standard pressure (1 atm).
- Sun Feb 16, 2020 4:50 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Delta s = 0
- Replies: 8
- Views: 724
Re: Delta s = 0
In a reversible isothermal reaction, the total S is zero.
- Sun Feb 16, 2020 4:49 pm
- Forum: Calculating Work of Expansion
- Topic: work = 0
- Replies: 14
- Views: 1365
Re: work = 0
I believe this is because there is no external pressure pushing the piston in, so there is free expansion (the system can do work freely).
- Sun Feb 16, 2020 4:48 pm
- Forum: Balancing Redox Reactions
- Topic: oxidation vs reduction
- Replies: 19
- Views: 1043
Re: oxidation vs reduction
Oxidation is when the reactant will lose an (or more than one) electron. Reduction reactants will gain electrons during the reaction. LEO GRR is really helpful for me.
- Sun Feb 09, 2020 12:03 am
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: q rev
- Replies: 9
- Views: 347
Re: q rev
When Lavelle uses Rev, it means that the reaction is reversible.
- Sun Feb 09, 2020 12:01 am
- Forum: Calculating Work of Expansion
- Topic: Midterm equation sheet
- Replies: 16
- Views: 743
Re: Midterm equation sheet
The equation sheet on the website will be the equation sheet given on the midterm. He also uses the IUPAC periodic table, but it dates back to 2011 or so I believe. The molar masses are slightly different than the ones he uses in class (he uses different periodic tables), so be careful on tests.
- Sun Feb 09, 2020 12:00 am
- Forum: Administrative Questions and Class Announcements
- Topic: Test 1 Distribution
- Replies: 9
- Views: 389
Re: Test 1 Distribution
Lavelle doesn't give out distribution curves for the test. He does provide the average on the midterm and final.
- Sat Feb 08, 2020 11:59 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Grading
- Replies: 7
- Views: 277
Re: Grading
Lavelle does grading on a point system.
Test 1: 50 points
Test 2: 50 points
Midterm: 120 points
Final: 180 points
Homework (5 points per week): 50 points
Chemistry Community (5 points per week): 50 points
Total: 500 points
IF he decides that he is going to scale the class, he does so at the end.
Test 1: 50 points
Test 2: 50 points
Midterm: 120 points
Final: 180 points
Homework (5 points per week): 50 points
Chemistry Community (5 points per week): 50 points
Total: 500 points
IF he decides that he is going to scale the class, he does so at the end.
- Sat Feb 08, 2020 11:57 pm
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: State of molecules
- Replies: 3
- Views: 238
Re: State of molecules
The standard entropy of a substance increases with an increase in the molar mass. But I also think that the standard entropy of a gas at STP takes in a lot of factors of phase change and heat capacities of solids and liquids as well.
- Sun Feb 02, 2020 1:23 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Week 5 Homework
- Replies: 7
- Views: 274
Re: Week 5 Homework
Yes. I also believe you can do the problems from other outlines as well, since the midterm is coming up.
- Sun Feb 02, 2020 1:22 pm
- Forum: Calculating Work of Expansion
- Topic: Equation
- Replies: 4
- Views: 219
Re: Equation
Do we need to know the integral and derivative for the midterm?
- Sun Feb 02, 2020 1:21 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Phase change
- Replies: 20
- Views: 899
Re: Phase change
Delta H should be positive.
- Sun Feb 02, 2020 1:21 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Constant pressure
- Replies: 19
- Views: 716
Re: Constant pressure
Constant external pressure.
- Sun Feb 02, 2020 1:19 pm
- Forum: Calculating Work of Expansion
- Topic: L atm and J
- Replies: 3
- Views: 1058
Re: L atm and J
101.33 Joules converts to 1 atm Liter-atm.
- Sat Jan 25, 2020 11:51 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: state functions?
- Replies: 6
- Views: 769
Re: state functions?
State functions don't depend on the path taken to get to its current state. The formula final - initial works for state functions, meaning that the stuff between final and initial doesn't matter. Enthalpy is a state function.
- Sat Jan 25, 2020 11:50 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Phase Changes
- Replies: 4
- Views: 131
Re: Phase Changes
During a phase change, the temperature doesn't change because the energy (in the form of heat) is being used to either weaken (melting) or break (vaporization) the bonds between molecules.
- Sat Jan 25, 2020 11:48 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Acid and Bases
- Replies: 3
- Views: 214
Re: Acid and Bases
H2SO4 is a strong acid, meaning that we can assume that it dissociates completely. Therefore, we know that the eq concentration of products will be the same as the initial concentration of the reactants (H2SO4). Calculate pH using the formula: -Log[H3)+] = pH.
- Sat Jan 25, 2020 11:47 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Acid and Bases
- Replies: 4
- Views: 214
Re: Acid and Bases
1) ICE Table to determine [H3O+]
2) -log [H3)+] = pH
3) 14 - pH = pOH
2) -log [H3)+] = pH
3) 14 - pH = pOH
- Sat Jan 25, 2020 11:46 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Enthalpy as a state function
- Replies: 4
- Views: 219
Re: Enthalpy as a state function
A state function is determined by the current equilibrium of the reactants and products, meaning that the path taken to reach that current state does not matter. Basically, it means final - initial is a valid calculation for enthalpy.
- Sat Jan 18, 2020 10:26 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Homework Problem Chapter 11 #25
- Replies: 5
- Views: 1242
Re: Homework Problem Chapter 11 #25
The K value you used was probably incorrect. When you look at table 5G.2, there are multiple K and Kc values for each equation. The second column (the first one with the numbers) is the temperature. The K you used, 794, is for the reaction taking place at 298 K. In the problem, it is 500 K and the K...
- Wed Jan 15, 2020 2:09 pm
- Forum: Ideal Gases
- Topic: ICE Table
- Replies: 11
- Views: 852
Re: ICE Table
An ICE table is used for equilibrium concentrations when we are unsure of the amount of change (in molarity) in the reactants as the chemical reaction moves to equilibrium. I stands for initial, which are the molarities that are given. Sometimes, the problem will only provide the moles and the conta...
- Wed Jan 15, 2020 1:56 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: x is small approximation
- Replies: 6
- Views: 559
Re: x is small approximation
When Kc is a very small number, we know that there will be a large amount of reactant and a small amount of product (Kc is products over reactant, so the larger the denominator the smaller Kc). When Kc is 10^-3 or smaller, we can assume that the change (x) is so small that is makes a negligible effe...
- Wed Jan 15, 2020 1:53 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Module 3 #19
- Replies: 2
- Views: 206
Re: Module 3 #19
First, convert moles given to molarity. It's a 10.0 L container, so the molarities of N2 and O2 are .0482 and .0933 respectively. With the equation given, Kc = [NO2]^2/[O2][N2]^2 Create the ICE table. N2 O2 N2O I .0482 .0933 0 C -2x -x 2x E .0482 - 2x .0933 - x 2x Kc = 2.0 x 10^-37 Kc = (2x)^2/(.933...
- Wed Jan 15, 2020 1:48 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Calculating Q
- Replies: 16
- Views: 804
Re: Calculating Q
When you calculate Q, you use the exact same process as if you were calculating for K. This means that you include all aqueous solutions and gases. Do not include solids or liquids in your calculations for Q (or K for that matter).
- Wed Jan 15, 2020 1:46 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Module Part 3, Question 7 (pre-assessment)
- Replies: 4
- Views: 1439
Re: Module Part 3, Question 7 (pre-assessment)
First, you create your ice table. SO2. O2. SO3 I. .522 .633 0 C. - 2x -x 2x E. .522 - 2x .633 - x 2x Then, set up Kc and put in all the numbers/expressions. Kc = 5.66 x 10^-10 Kc = [SO3]^2/[SO2]^2[O2] 5.66 x 10^-10 = ((2x)^2)/(.522-2x)^2(.633-x) *Since Kc is so small, we know that the equilibrium re...
- Fri Jan 10, 2020 11:51 pm
- Forum: Ideal Gases
- Topic: R in PV=nRT
- Replies: 34
- Views: 7119
Re: R in PV=nRT
R is the gas constant. I believe it will be given on the equation/constant sheet on tests.
- Fri Jan 10, 2020 11:50 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Le Chatelier's Principle
- Replies: 7
- Views: 320
Re: Le Chatelier's Principle
Le Chatelier's Principle basically just says that a chemical equation will move to decrease the amount of change as much as possible. So if there is a chemical equation and product has been added, the equation will move "away" from the products and towards the reactants (reverse reaction).
- Fri Jan 10, 2020 11:48 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Using Kc Vs Kp
- Replies: 22
- Views: 1094
Re: Using Kc Vs Kp
Kp is used for gases. Kc can be used for aqueous solutions. It's best to just go by the equation. Remember Kp is in pressure units and Kc is for concentration (M).
- Fri Jan 10, 2020 11:22 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Homework 1
- Replies: 18
- Views: 695
Re: Homework 1
Most TAs correct HW based on correctness and completion. There is the answer solution book to check answers, and just make sure you do five problems a week.
- Fri Jan 10, 2020 11:20 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Homework 1
- Replies: 18
- Views: 695
Re: Homework 1
Homework is usually due during discussion, but for the first week it was due after lecture on Friday.
- Fri Jan 10, 2020 11:18 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE Table Ratios
- Replies: 7
- Views: 275
Re: ICE Table Ratios
As long as the ratio is the same as the ratio of the balanced equation, it doesn't matter what the actual numbers are.
- Sat Dec 07, 2019 8:18 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Equilibrium calculations
- Replies: 6
- Views: 428
Re: Equilibrium calculations
I think we only need to know the concepts and the logistics of Ka, but we won't have to do any calculations since we haven't learned everything about weak acids. We will, however, need to know about strong acids and its dissociation properties.
- Sat Dec 07, 2019 8:15 pm
- Forum: Calculating the pH of Salt Solutions
- Topic: Titrations
- Replies: 6
- Views: 446
Re: Titrations
I think most of it is conceptual. Titrations allow us to find the molarity of an unknown solution using another solution with a known molarity. We use the stoichiometric point/equivalence point to figure out the molarity of the unknown solution.
- Sat Dec 07, 2019 8:10 pm
- Forum: Polyprotic Acids & Bases
- Topic: amphiprotic vs amphoteric
- Replies: 2
- Views: 252
Re: amphiprotic vs amphoteric
Amphiprotic means that the molecule can accept or donate an H+. Amphoteric means that the molecule can can act as a base and an acid. If a molecule is amphiprotic, it's amphoteric, but it doesn't necessarily work the other way (think Lewis acids - relationship with electrons).
- Sat Dec 07, 2019 8:08 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Negative pH
- Replies: 5
- Views: 371
Re: Negative pH
The pH would only be negative if it's a super acid. In these cases, Ka is larger than 1. I don't think we need to know this for the final though.
- Sat Dec 07, 2019 8:06 pm
- Forum: Air Pollution & Acid Rain
- Topic: dirty/clean coal
- Replies: 6
- Views: 448
Re: dirty/clean coal
Dirty coal has a larger amount of S in it. I think that's all we need to know.
- Sat Nov 30, 2019 12:10 pm
- Forum: Student Social/Study Group
- Topic: Preparing for the final
- Replies: 25
- Views: 1316
Re: Preparing for the final
I think practice problems are a really good idea, on top of maybe some reinforcement through the step-up sessions and online videos.
- Sat Nov 30, 2019 12:07 pm
- Forum: Bronsted Acids & Bases
- Topic: Net Ionic Equations
- Replies: 5
- Views: 307
Re: Net Ionic Equations
There are solubility rules that help you identify which ones will dissociate in water and become aqueous, and those that will not. The best way to know is just to memorize the solubility rules. It was mandatory in HS AP Chem to know them, but I'm not sure if Lavelle will have us memorize them too.
- Sat Nov 30, 2019 12:05 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Determining Polarity
- Replies: 10
- Views: 625
Re: Determining Polarity
Drawing net dipoles helps a lot, but you need to make sure that you are not just cancelling dipoles that seem opposite each other. For example, in CHCl3, you can't cancel the dipoles of Cl that are across from each other, because the bond angle is actually 109.5 and not 90/180. Also, when there is a...
- Sat Nov 30, 2019 12:03 pm
- Forum: General Science Questions
- Topic: test taking nervousness
- Replies: 19
- Views: 1130
Re: test taking nervousness
Doing practice problems really help. It's the best way to get used to the types of problems that will be on the test, and it will also reinforce the concepts that you're learning for the test.
- Sat Nov 30, 2019 12:02 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Seesaw Shape
- Replies: 12
- Views: 676
Re: Seesaw Shape
The bond angles for the seesaw molecule will be slightly less than 90 and 120 degrees, since the lone pair affects the bonding angles.
- Sun Nov 24, 2019 5:19 pm
- Forum: Naming
- Topic: using brackets
- Replies: 5
- Views: 452
Re: using brackets
Anything inside the brackets are part of the main coordination compound.
- Sun Nov 24, 2019 5:18 pm
- Forum: Lewis Acids & Bases
- Topic: lewis vs. bronsted
- Replies: 10
- Views: 559
Re: lewis vs. bronsted
A Bronsted acid is a proton donor while a Lewis acid accepts an electron pair.
- Sun Nov 24, 2019 5:16 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Seesaw
- Replies: 23
- Views: 1073
Re: Seesaw
Because there is a lone pair, the angles should be slightly less than 90 and 120.
- Sun Nov 24, 2019 5:16 pm
- Forum: Hybridization
- Topic: Sigma and Pi bonds
- Replies: 13
- Views: 736
Re: Sigma and Pi bonds
When you draw the bonds, you draw them as normal and just label each bond below or beneath the bond with a pi or sigma symbol.
- Sun Nov 24, 2019 5:15 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: AXE Format
- Replies: 34
- Views: 1332
Re: AXE Format
When there is only an X or an E, it is implied that there is one of those.
- Sun Nov 24, 2019 5:14 pm
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: AXE
- Replies: 6
- Views: 566
Re: AXE
It allows you to picture the molecule, allowing you to know how many pairs of lone pair electrons there are and how many atoms the central atom is bonded to.
- Sat Nov 16, 2019 3:18 pm
- Forum: Dipole Moments
- Topic: Hydrogen bonds
- Replies: 17
- Views: 846
Re: Hydrogen bonds
Hydrogen bonds only form between H atoms and N, O, and F.
- Sat Nov 16, 2019 3:17 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Determining if a molecule is polar or non polar
- Replies: 9
- Views: 949
Re: Determining if a molecule is polar or non polar
We don't have to memorize the electronegativity chart. It's easier to use the net dipole to figure out if the molecule is polar or not. For example, for CH3Cl, there is a net dipole towards the chlorine atom, making the whole molecule. However, for CH4, there is no net dipole which makes the molecul...
- Sat Nov 16, 2019 3:15 pm
- Forum: Sigma & Pi Bonds
- Topic: Sigma & Pi Bonds
- Replies: 4
- Views: 993
Re: Sigma & Pi Bonds
Sigma bonds are the first bonds between any two atoms. So, for single bonds, there are only sigma bonds. However, for double and triple bonds, pi bonds are the other bonds (2nd and 3rd bonds) formed between two atoms. So for a double bond, there will be one sigma bond and one pi bond. The pi bonds a...
- Sat Nov 16, 2019 3:14 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: test 2
- Replies: 13
- Views: 764
Re: test 2
If I remember correctly, hybridization will not be on Test 2. The test covers material from the midterm on. The lecture on Monday, about sigma and pi bonds, will be on the test.
- Sat Nov 16, 2019 3:12 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Bond Angles
- Replies: 9
- Views: 562
Re: Bond Angles
The angles for the molecular shapes are all standardized. When a molecule is polar, the bond angles will change, but we do not need to know the exact values. All we need to indicate is that the angles either decrease or increase (i.e. with lone pairs of electrons instead of bonding pairs).
- Sat Nov 09, 2019 4:53 pm
- Forum: Dipole Moments
- Topic: London forces
- Replies: 9
- Views: 562
Re: London forces
London Dispersion Forces (LDF) are classified as universal because any molecule or atom with any number of electrons will experience some kind of movement. Since electrons are not in a "fixed" position (they are in an electron cloud and move around there), there will be some areas that are...
- Sat Nov 09, 2019 4:51 pm
- Forum: General Science Questions
- Topic: Rusty on High School Chem [ENDORSED]
- Replies: 347
- Views: 468368
Re: Rusty on High School Chem [ENDORSED]
The modules on Lavelle's website are extremely helpful, especially when you just want to go over the concepts that you went over in class. Also, the step up classes are helpful and office hours are too. I recommend just going through a lot of the chem problems from the textbook (the odd ones, since ...
- Sat Nov 09, 2019 4:48 pm
- Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
- Topic: Boiling Points
- Replies: 6
- Views: 903
Re: Boiling Points
When you draw the lewis structure for both AsF3 and AsF5, the former has a lone pair of electrons over As. This results in polarity, and there are dipole-dipole moments in the molecule. However, in AsF5, there are no lone pairs on As, meaning that the whole molecule is nonpolar and has no dipole-dip...
- Sat Nov 09, 2019 4:45 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: Intermolecular forces
- Replies: 3
- Views: 170
Re: Intermolecular forces
Hydrogen bonds are the strongest IMFs. They are significantly stronger than London Dispersion Forces because those are only temporary and are not necessarily "permanent." They tend to move around more than hydrogen bonds, which are usually always polarized.
- Sat Nov 09, 2019 4:44 pm
- Forum: SI Units, Unit Conversions
- Topic: Memorizing Conversions
- Replies: 25
- Views: 1403
Re: Memorizing Conversions
It's really nice to know the conversions at the top of your head so you're not looking around the reference sheet for them. However, I believe Lavelle is quite generous and provides most of the formulas and conversions for the exams.
- Sat Nov 02, 2019 10:13 pm
- Forum: Ionic & Covalent Bonds
- Topic: Lewis Structure for Ionic Bonds
- Replies: 4
- Views: 162
Re: Lewis Structure for Ionic Bonds
Charged molecules are completely bracketed with the total charge written outside in the top right corner outside the brackets.
- Sat Nov 02, 2019 10:08 pm
- Forum: Lewis Structures
- Topic: Expanded Octet
- Replies: 3
- Views: 146
Re: Expanded Octet
Elements in or after the third period have expanded octets. The central elements usually end up with the expanded octets (the extra pairs of electrons).
- Sat Nov 02, 2019 10:06 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3916538
Re: Post All Chemistry Jokes Here
All the chemistry jokes argon!
- Sat Nov 02, 2019 10:04 pm
- Forum: Resonance Structures
- Topic: Drawing Resonance Structures
- Replies: 3
- Views: 299
Re: Drawing Resonance Structures
When a molecule has resonance, you usually have to draw all the possible structures.
- Sat Nov 02, 2019 10:02 pm
- Forum: Lewis Structures
- Topic: drawing lewis structures
- Replies: 5
- Views: 222
Re: drawing lewis structures
Br has an expanded octet in this case. Any element in or after period 3 can have an expanded octet.
- Sat Nov 02, 2019 10:00 pm
- Forum: Ionic & Covalent Bonds
- Topic: ionic vs. covalent
- Replies: 7
- Views: 392
Re: ionic vs. covalent
Covalent bonds share electrons across the elements in the molecule. In ionic bonds, the cation "gives" its electron(s) to the anion.
- Sun Oct 27, 2019 5:09 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: determining the number of orbitals
- Replies: 7
- Views: 332
Re: determining the number of orbitals
l=0; s
l=1; p
l=2; d
l=3; f
l=1; p
l=2; d
l=3; f
- Sun Oct 27, 2019 5:08 pm
- Forum: Student Social/Study Group
- Topic: Miderm Review
- Replies: 10
- Views: 670
Re: Miderm Review
Sapling Learning is a good resource to use other than the midterm review sessions. Doing all the recommended practice problems on the outlines is also really helpful.
- Sun Oct 27, 2019 5:07 pm
- Forum: Student Social/Study Group
- Topic: Study Tips
- Replies: 58
- Views: 4764
Re: Study Tips
Studying chemistry is really just practice. I find it best to do practice problems. Lavelle's Step Up Program is also really helpful if you're struggling with the material in general.
- Sun Oct 27, 2019 5:06 pm
- Forum: Ionic & Covalent Bonds
- Topic: Valence Electrons
- Replies: 16
- Views: 794
Re: Valence Electrons
Valence electrons are the number of electrons in the valence (last) shell of the atom. For example, Cl has 7 valence electrons.
- Sun Oct 27, 2019 5:05 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Exceptions to Electron Configuration
- Replies: 7
- Views: 370
Re: Exceptions to Electron Configuration
Cu and Cr are the only exceptions.
- Sat Oct 19, 2019 10:26 pm
- Forum: Properties of Electrons
- Topic: mass of electron, proton, neutron
- Replies: 7
- Views: 405
Re: mass of electron, proton, neutron
I am pretty sure that these are provided on the 'reference sheet' that Lavelle gives us. It will probably be similar to the one on the first test we took Week 3.
- Sat Oct 19, 2019 10:20 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Inner e- and Outer e-
- Replies: 14
- Views: 531
Re: Inner e- and Outer e-
In multi-electron atoms, there is a shielding effect that causes the outer electrons to be 'shielded' from the nucleus by the inner electrons. Because of this, there is a lesser attraction between the outer electrons and the nucleus, and this results in a larger atomic radius.
- Sat Oct 19, 2019 10:18 pm
- Forum: General Science Questions
- Topic: Tests
- Replies: 9
- Views: 450
Re: Tests
It's very helpful to know the basic conversions, especially the metric system (because they're all multiples of ten). However, I believe that on the tests, Lavelle provides some of the conversions as a reference sheet.
- Sat Oct 19, 2019 10:16 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Which Element to Use in Electron Configurations
- Replies: 5
- Views: 258
Re: Which Element to Use in Electron Configurations
When shortening the electron configuration to make it easier to sort through, people use the noble gas and write out the last line of the electron configuration. However, you can also just write out the whole thing.
- Sat Oct 19, 2019 10:13 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Unit for Avogadro's Number
- Replies: 10
- Views: 2229
Re: Unit for Avogadro's Number
The answer depends on each problem. Avogadro's number represents the number of (mcls, atoms, ions) per mol of the given element or compound.
- Sat Oct 12, 2019 4:35 pm
- Forum: *Black Body Radiation
- Topic: Black Body Radiation
- Replies: 12
- Views: 755
Re: Black Body Radiation
Black body radiation is not necessary to the course. It's more of a physics experiment.
- Sat Oct 12, 2019 4:34 pm
- Forum: Properties of Light
- Topic: Light Intensity
- Replies: 6
- Views: 214
Re: Light Intensity
Yes, this is correct. The light intensity is directly related to the number of photons.
- Sat Oct 12, 2019 4:27 pm
- Forum: Properties of Light
- Topic: Quantum Levels
- Replies: 9
- Views: 424
Re: Quantum Levels
There is no maximum to the number of energy levels. But in the diagram that is drawn in class, the energy levels get closer and closer together.
- Sat Oct 12, 2019 4:18 pm
- Forum: Properties of Electrons
- Topic: Electron After Excited State
- Replies: 7
- Views: 439
Re: Electron After Excited State
An electron is excited and rises to a higher energy level. However, electrons can release energy in the form of a photon. This will cause the electron to eventually fall back to its original state.
- Sat Oct 12, 2019 4:12 pm
- Forum: Properties of Light
- Topic: Frequency vs. Wavelength
- Replies: 15
- Views: 734
Re: Frequency vs. Wavelength
Frequency and wavelength are inversely related. So if frequency increases, then wavelength decreases. Frequency is in Hz (s^-1), and wavelength is usually in nm. However, if you're finding wavelength to put it into another equation, make sure the units cancel out.
- Tue Oct 01, 2019 10:55 pm
- Forum: Balancing Chemical Reactions
- Topic: Tips on what number to multiply the entire equation if needed
- Replies: 8
- Views: 1695
Re: Tips on what number to multiply the entire equation if needed
The best way to ensure that you will end up with whole numbers on all of the stoichiometric coefficients is to multiply all the coefficients by the common denominator of the fractions. For example, if you had two fractions as stoichiometric coefficients with the denominators 2 and 3, you should mult...