Search found 98 matches

by SavannahScriven_1F
Sat Feb 27, 2021 10:11 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cell
Replies: 1
Views: 13

Re: Concentration Cell

Both of the electrodes are Ag(s) and the electrons are driven to the cathode because the concentration is higher on that side. When the anode (also Ag) is oxidized, Ag+ goes into the solution and raises its concentration.
by SavannahScriven_1F
Sat Feb 27, 2021 10:05 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Textbook Problem 6O.1
Replies: 1
Views: 9

Re: Textbook Problem 6O.1

I think Dr. Lavelle removed this question from the syllabus!
by SavannahScriven_1F
Sat Feb 27, 2021 9:57 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Hydrogen Electrode
Replies: 3
Views: 14

Re: Standard Hydrogen Electrode

The S.H.E has an Eº value of 0 just because electrochemists decided to define it that way. Then, they can use it as reference to find the electrode potential of other electrodes. I think making it 0 just made it easy as a reference value.
by SavannahScriven_1F
Fri Feb 26, 2021 7:29 pm
Forum: Van't Hoff Equation
Topic: How deltaG affects product/reactant formation
Replies: 6
Views: 25

Re: How deltaG affects product/reactant formation

When K is > 1, the equilibrium lies to the right (i.e. at equilibrium, there is a higher concentration of products than reactants). Delta G would be negative because the forward reaction is favored (product form is more stable than reactant form, so rxn is spontaneous).
by SavannahScriven_1F
Fri Feb 26, 2021 7:23 pm
Forum: Phase Changes & Related Calculations
Topic: Voltage difference
Replies: 4
Views: 11

Re: Voltage difference

Emax is the difference in voltage across the electrodes. E is a maximum because when there is a difference in voltage (switch open and no current is flowing), the potential energy is very high.
by SavannahScriven_1F
Sun Feb 21, 2021 11:44 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Textbook 4H.9
Replies: 4
Views: 15

Re: Textbook 4H.9

Also, as clarification because the question isn't worded very well, A has the highest change in entropy because it has the greatest number of particles. Container A, B, and C all have 1 mole of atoms, but in B and C they are bounded together so there are half as many particles.
by SavannahScriven_1F
Sun Feb 21, 2021 11:38 am
Forum: Balancing Redox Reactions
Topic: salt bridge
Replies: 19
Views: 53

Re: salt bridge

the salt bridge allows ions in the solution to flow to the other side balance out the charge caused by electrons leaving 1 solution and going to the other.
by SavannahScriven_1F
Sun Feb 21, 2021 11:36 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Max Potential
Replies: 4
Views: 23

Re: Max Potential

I have a hard time with this too and have an explanation for max potential in my mind that may help (it's not super scientific so hopefully this isn't wrong). When the switch is open (and current is 0) there aren't any actual electrons flowing but they are built up and have the potential to flow if ...
by SavannahScriven_1F
Sat Feb 13, 2021 10:26 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: sapling #15
Replies: 3
Views: 22

Re: sapling #15

First, flip the second equation and multiply it by 2 so that when the 2 equations are added, you are left with the 3rd one. Flip the signs and multiply the ΔH∘ and ΔS∘ by 2 to get -960 and 312. Combine the two equations' ΔH∘ and ΔS∘ values to get -1669.3kJ and 671J. Use ΔG∘= ΔH∘-T ΔS∘ Make sure to c...
by SavannahScriven_1F
Sat Feb 13, 2021 11:40 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Example 4.F.4
Replies: 2
Views: 8

Re: Example 4.F.4

In example 4.F.4 page 302, it shows they used the calculation \Delta S=C v ln(T2/T1) with C v =nC v,m So C v should be equal to (3/2)R, or 12.5. However, the textbook shows 20.79, which is actually equal to (5/2)R, or C p . Is this a mistake? Should Cv be used, or is the calculation correct in usin...
by SavannahScriven_1F
Sat Feb 13, 2021 11:36 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Example 4.F.4
Replies: 2
Views: 8

Example 4.F.4

In example 4.F.4 page 302, it shows they used the calculation \Delta S=C v ln(T2/T1) with C v =nC v,m So C v should be equal to (3/2)R, or 12.5. However, the textbook shows 20.79, which is actually equal to (5/2)R, or C p . Is this a mistake? Should Cv be used, or is the calculation correct in using...
by SavannahScriven_1F
Thu Feb 11, 2021 7:57 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 4F.11
Replies: 3
Views: 9

Re: 4F.11

I think 4F.11 has an error! The correct worked out solution is on Dr. Lavelle's external website under the tab, Solution Manual Errors, Chemical Principles, 7thEdition.
by SavannahScriven_1F
Thu Feb 11, 2021 7:54 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 4F.7 using Cp and Cv
Replies: 1
Views: 11

Re: 4F.7 using Cp and Cv

Hey! On the constants and formulas sheet there are the equations : ideal gas, Cp=5/2*R and Cv=3/2 R. The information that the gas is ideal means you can use these values for C. There is more info on how Cp=5/2*R and Cv=3/2 R in the textbook too.
by SavannahScriven_1F
Thu Feb 11, 2021 7:50 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem Community Points
Replies: 6
Views: 38

Re: Chem Community Points

your grade is lower because lavelle updated it in the middle of week 5, before all your posts were in for that week. The next time he updates the scores from chemistry community will reflect your actual number of posts up to that point.
by SavannahScriven_1F
Thu Feb 11, 2021 7:47 pm
Forum: Calculating Work of Expansion
Topic: Textbook 4.7
Replies: 2
Views: 16

Re: Textbook 4.7

I was confused at first on this problem too because I thought 9 moles of gas were produced (both water vapor and C02), so I got a positive delta n (9-7.5). I found out though that the water produced is in a liquid state so delta n is negative (6-7.5) and cancels out the other -.
by SavannahScriven_1F
Thu Feb 11, 2021 9:54 am
Forum: Calculating Work of Expansion
Topic: Textbook 4.7 a
Replies: 2
Views: 20

Re: Textbook 4.7 a

Rachel Jiang 3H wrote:You assume that the water produced is a liquid because water is a liquid at room temperature 25 °C, which is the temperature given in the question. Therefore, your delta n should be -1.5mol. Hope this helps!


Thank you! that makes sense.
by SavannahScriven_1F
Thu Feb 11, 2021 7:40 am
Forum: Calculating Work of Expansion
Topic: Textbook 4.7 a
Replies: 2
Views: 20

Textbook 4.7 a

The question is: Calculate the work that must be done against the atmosphere for the expansion of the gaseous products in the combustion of 1.00 mol C6H6 (l ) at 25 °C and 1.00 bar. I got the same answer as the textbook (3.72kJ), but my answer had a negative sign in front of it. This happened becaus...
by SavannahScriven_1F
Thu Feb 04, 2021 1:32 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: How to know the sign for work
Replies: 26
Views: 97

Re: How to know the sign for work

To help me with the sign for work, I think of work as a flow of energy (because energy is calculated based off work). If energy is flowing into the system, the sign is positive. If energy is flowing out of the system (the system is using energy), the sign is negative. For this class, we are only foc...
by SavannahScriven_1F
Thu Feb 04, 2021 1:24 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Temperature vs Enthalpy
Replies: 6
Views: 27

Re: Temperature vs Enthalpy

Temperature is a measurement of particle motion (higher temp = faster/more particle motion). When you measure a the temperature you are looking to see if heat is gained or lost. Enthalpy is the heat gained or lost at constant pressure. So when pressure isn’t constant heat doesn’t equal delta H.
by SavannahScriven_1F
Tue Feb 02, 2021 9:18 pm
Forum: Student Social/Study Group
Topic: Best study methods
Replies: 3
Views: 20

Re: Best study methods

For me, the most helpful practice problems are the ones from the textbook and the ones from LA workshops. The LAs have usually taken the class so they try to structure their practice problems for the tests.
by SavannahScriven_1F
Tue Feb 02, 2021 9:13 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimeters
Replies: 15
Views: 82

Re: Calorimeters

It's helpful to know which type of calorimeter you're using because then you can determine if the change in temperature correlates to the change in enthalpy.
by SavannahScriven_1F
Tue Feb 02, 2021 9:06 pm
Forum: Student Social/Study Group
Topic: Spring 2021
Replies: 104
Views: 437

Re: Spring 2021

Hello! I'm currently taking Chem 14BL right now, and I just want to advise that this class, while not the most difficult material, is a lot of work. So if you think you are already going to have a busy schedule next quarter, you might want to consider whether you can handle this extra workload (wee...
by SavannahScriven_1F
Tue Feb 02, 2021 11:19 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 6E.1 Textbook Question
Replies: 3
Views: 21

Re: 6E.1 Textbook Question

H2SO4 is pretty much the only strong diprotic acid. First you get the concentration of H3O+ from the concentration of H2SO4 itself because it completely dissociates into H3O+ and HSO4-. Now, you have to take into account the contribution of H3O+ from HSO4-. You would make an ICE table like any other...
by SavannahScriven_1F
Tue Feb 02, 2021 11:08 am
Forum: Calculating Work of Expansion
Topic: Constant volume and work
Replies: 3
Views: 29

Re: Constant volume and work

It's also helpful to note that Lavelle mentioned in one of his lectures that for this class (and most gen chem classes) we will ONLY be focuses on volume changes when calculating work.
by SavannahScriven_1F
Tue Feb 02, 2021 11:01 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: closed system
Replies: 43
Views: 275

Re: closed system

I'm a little confused on this too. I think that only certain closed systems prevent volume changes (e.g a sealed beaker). Systems that are closed with a piston do allow for volume changes due to expansion (of gases).
by SavannahScriven_1F
Wed Jan 27, 2021 10:43 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: deltaH specifics
Replies: 2
Views: 17

Re: deltaH specifics

Samiha Molla 3G wrote:Yes, I think that's correct! Without the subscript it'd just be the overall reaction's enthalpy under standard conditions.

Thank you!
by SavannahScriven_1F
Tue Jan 26, 2021 5:46 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: deltaH specifics
Replies: 2
Views: 17

deltaH specifics

When is written without a subscript, does it imply rxn?
by SavannahScriven_1F
Sun Jan 24, 2021 4:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: equilibrium constants and solubility
Replies: 3
Views: 36

Re: equilibrium constants and solubility

A chemical equation with a high K value would indicate higher solubility because it favors the formation of ions (dissociation). So you can picture a chemical equation sort of like those for acids and bases - where water is a sort of reactant, and the product is an ionized form of the compound. If K...
by SavannahScriven_1F
Sun Jan 24, 2021 4:30 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook Question 5I.15
Replies: 2
Views: 24

Re: Textbook Question 5I.15

I believe it would still proceed toward the products (even though you were given an initial concentration of a product) because there is still 0mol of H2S. This makes the reaction favor the forward direction because in order to achieve equilibrium concentration, H2S must be greater than 0. If it wer...
by SavannahScriven_1F
Sat Jan 23, 2021 2:13 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: sapling 2 week 2
Replies: 7
Views: 67

Re: sapling 2 week 2

Could it be that a negative sign was forgotten somewhere? In the part of the quadratic equation "-4ac", the c value should be negative which makes it +4ac. Since this is added to b2 under the square root, there shouldn't be an error.
by SavannahScriven_1F
Sat Jan 23, 2021 2:04 pm
Forum: General Science Questions
Topic: Second Deprotonations
Replies: 6
Views: 45

Re: Second Deprotonations

Specifically, the second deprotonation (with Ka2) does not affect the pH and can be ignored when Ka2 is less than Ka1*10-3. Usually though Ka2 is much smaller than Ka1 so it's pretty obvious. Hope this helps!
by SavannahScriven_1F
Sat Jan 23, 2021 1:59 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Polyprotic Acids
Replies: 8
Views: 55

Re: Polyprotic Acids

The textbook does give a cutoff: Ka2 must be less than about Ka1*10-3 for Ka2 to not affect the pH.
by SavannahScriven_1F
Fri Jan 15, 2021 5:08 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: When x is negligible in Equilibrium constant
Replies: 34
Views: 159

Re: When x is negligible in Equilibrium constant

For this class, because we are considering small K values to be those that are x 10^-3, we can safely use the x approximation when K is x 10^-4.
by SavannahScriven_1F
Fri Jan 15, 2021 5:04 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 5J.11 Part b
Replies: 2
Views: 30

Re: 5J.11 Part b

adding onto the previous response, you know that going from X2 to 2X requires energy because X2 is the more stable species. Halogens often exist as diatomic molecules (X2) because they are very reactive and more stable as a pair. Breaking this bond reduces stability, so lots of energy is required to...
by SavannahScriven_1F
Fri Jan 15, 2021 4:54 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook Problem 5.35
Replies: 2
Views: 27

Re: Textbook Problem 5.35

I think it is because the y-axis of the textbook graph is written in units of kPa. The conversion factor from kPa to barr is approx 100.
by SavannahScriven_1F
Fri Jan 15, 2021 4:51 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: lecture 5 question
Replies: 13
Views: 84

Re: lecture 5 question

A conjugate base is formed when an acid protonates a solution. The compound loses its H, so it now has the ability to accept an H. This is the definition of a bronsted base. The word "conjugate" is there because the base formed from a different compound (the original acid).
by SavannahScriven_1F
Fri Jan 15, 2021 4:43 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling Week 1 #9
Replies: 3
Views: 34

Re: Sapling Week 1 #9

for my ice table I put 0.2 for N2 and O2 and 0.7 for NO. Because Q>K, the change for NO is negative. So that row I put +x for N2 and O2 and -2x for NO. E would then be 0.2+x for N2 and O2 and 0.7-2x for NO. Then plug these E values into the K expression. Hope this helps!
by SavannahScriven_1F
Thu Jan 07, 2021 2:35 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Reactant in Excess
Replies: 9
Views: 80

Re: Reactant in Excess

I have a similar question: Let's say you have a reaction at equilibrium aA +bB \rightleftharpoons cC. If a ton of reactant B is added, how would it be able to reach equilibrium if there is not enough A present for B to react with? Do the B molecules just eventually "find" and react with th...
by SavannahScriven_1F
Thu Jan 07, 2021 2:21 pm
Forum: Ideal Gases
Topic: Kc vs Kp
Replies: 109
Views: 996

Re: Kc vs Kp

If given a chemical equation and some of the reactants and products are in a solution (designated by aq), then you must use Kc. This makes sense as you are dealing with solutions and in a lab setting, concentration is important to know. (you wouldn't randomly measure/convert the reagents to P). If g...
by SavannahScriven_1F
Thu Jan 07, 2021 2:05 pm
Forum: Ideal Gases
Topic: Ideal Gas Law Question
Replies: 11
Views: 78

Re: Ideal Gas Law Question

T isn't a constant in the way R is. R is the exact same value every single time PV=nRT is used - no matter what. T, on the other hand, can be different for each reaction. It may be 421K for one or 90K for another. However, when using PV=nRT, we are assuming the Temperature is constant in that it is ...
by SavannahScriven_1F
Thu Jan 07, 2021 1:57 pm
Forum: Ideal Gases
Topic: Ideal vs real gases
Replies: 12
Views: 74

Re: Ideal vs real gases

When we consider a real gas to be ideal, we assume it does not condense into a liquid when the temperature is reduced. In other words, we ignore the attractive forces between the gas molecules (intermolecular forces).
by SavannahScriven_1F
Thu Jan 07, 2021 1:53 pm
Forum: Student Social/Study Group
Topic: Learning Sessions
Replies: 24
Views: 148

Re: Learning Sessions

Like everyone else has said, whatever fits your schedule! I tried to go to as many workshops as I could because I found additional practice problems was what helped me the most. Even though I could have gone to more than 2 per week, 2 felt like a good number. I ended up always going to workshops fro...
by SavannahScriven_1F
Sun Dec 13, 2020 10:26 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angle and Terminal Atoms
Replies: 2
Views: 28

Bond Angle and Terminal Atoms

If there is a molecule with a trigonal planar shape, but one of its terminal atoms is larger than the other two, this would affect the bond angles. Would we still say it's 120 or would we say it's <120 (or greater than, depending on which bond angle is specified)? Would a multiple choice question ev...
by SavannahScriven_1F
Sat Dec 12, 2020 7:29 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: chelating ligands [ENDORSED]
Replies: 31
Views: 7382

Re: chelating ligands [ENDORSED]

Renny_kim_2G wrote:Does this mean polydentate ligands and chelating ligands are the same thing?


not always. A ligand can be polydentate but bind to two different transition metals. The result wouldn't be a ring, so the compound wouldn't be a chelate. A ligand that does this would be called a bridging ligand instead.
by SavannahScriven_1F
Fri Dec 11, 2020 1:06 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: chelating ligands [ENDORSED]
Replies: 31
Views: 7382

Re: chelating ligands [ENDORSED]

Hi! This is just a clarification statement I wanted to type out to be sure I'm understanding resonance/chelating ligands properly. In today's review session with C 2 O 4 2- , it doesn't matter when we draw the 2 Os that share lone pairs opposite one another (a structure that, on paper, looks as if t...
by SavannahScriven_1F
Wed Dec 09, 2020 12:36 pm
Forum: Administrative Questions and Class Announcements
Topic: Lecture Videos Not Playing [ENDORSED]
Replies: 16
Views: 158

Re: Lecture Videos Not Playing [ENDORSED]

Same happening to me. I've tried both videos (1 and 2), restarting my computer, and it works for a few minutes then just stops again.
by SavannahScriven_1F
Tue Dec 08, 2020 7:15 pm
Forum: Identifying Acidic & Basic Salts
Topic: NH4Cl Salt- Spectator Ions
Replies: 3
Views: 33

Re: NH4Cl Salt- Spectator Ions

When Nh4Cl is mixed with water, it dissociates into its ions because NH4Cl is a salt. So in water, the salt becomes the NH4+ ion and the Cl- ion. Now N really wants to donate its proton to have a formal charge of 0, so it will "donate" it's H to an H2O molecule to form H3O. Cl- doesn't rea...
by SavannahScriven_1F
Sun Dec 06, 2020 1:46 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Ligand Types
Replies: 3
Views: 25

Re: Ligand Types

If a ligand only has 1 lone pair, then it clearly can only be monodentate. However, some ligands have multiple lone pairs but are still monodentate. Drawing out the lewis structure helps you determine if a ligand can bind multiple times to the same TM cation. For example, Cl- is surrounded by 4 lone...
by SavannahScriven_1F
Sun Dec 06, 2020 1:37 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular shape and polarity
Replies: 3
Views: 21

Re: Molecular shape and polarity

This may not exactly answer your question, but I think of it like this: lone pairs on the central atom affect the positions of the bound atoms, which determine the molecule's shape. The shape then determines if the dipoles have the potential to cancel out. If all the dipoles cancel, then the molecul...
by SavannahScriven_1F
Sat Dec 05, 2020 3:35 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Strong/Weak acids
Replies: 5
Views: 51

Re: Strong/Weak acids

Another helpful note is that I learned in a UA worksop is that if you are trying to determine the stability of anions that are all within the same group, the stability increases down a group because the charge is "diluted" more in larger atoms. I believe this only holds true if you are loo...
by SavannahScriven_1F
Sat Dec 05, 2020 3:27 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Calculating pH with H+ or H3O+
Replies: 3
Views: 54

Re: Calculating pH with H+ or H3O+

I would assume the H+ concentrations and H3O+ concentrations are always equal. I think Lavelle said H+ and H3O+ mean the exact same thing, but some chemists prefer to write H3O+ because it is more descriptive of what is going on in the solution.
by SavannahScriven_1F
Sat Dec 05, 2020 11:17 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Tetrahedral v Square Planar
Replies: 6
Views: 50

Tetrahedral v Square Planar

I know how to find the coordination number, but when it's 4 I'm not sure how to tell if the TM cation has lone pairs (and would then be square planar). Do I need to know how to do this for Chem14A? Or do I just need to be able to determine that the compound could be tetrahedral/square planar? Thank ...
by SavannahScriven_1F
Sun Nov 29, 2020 8:34 pm
Forum: Hybridization
Topic: hybridization model in textbook
Replies: 2
Views: 40

Re: hybridization model in textbook

the x, y, and z, indicate the 3D orientation of each of the 3 p orbitals: one is lying on the x axis, one is lying on the y axis, and one is lying on the z axis. Each hybridization has a combination of these 3 p orbitals (plus an s orbital), but only the signs are different. The different signs are ...
by SavannahScriven_1F
Sun Nov 29, 2020 8:23 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration for Transition Metals
Replies: 3
Views: 43

Re: Electron Configuration for Transition Metals

Adding on to a specific part of the previous response, it helps me to realize that the 4s orbitals fill up first, but once there is an electron in a 3d state, it has lower energy than those in 4s. That's why 3d is written before 4s, even though the periodic table shows that 4s is before 3d. That's a...
by SavannahScriven_1F
Sun Nov 29, 2020 8:14 pm
Forum: Lewis Structures
Topic: Octet Exceptions
Replies: 4
Views: 25

Re: Octet Exceptions

Adding onto the previous responses, most times expanded octets occur in the p block (starting with n=3) because metals don't like to gain electrons.
by SavannahScriven_1F
Tue Nov 24, 2020 12:48 pm
Forum: Sigma & Pi Bonds
Topic: Figuring out Carbon hybridization
Replies: 2
Views: 16

Re: Figuring out Carbon hybridization

Adding on to the previous response, the reason why it's x,y,z specifically is because it's designating the orientation in 3D space -Picture a p orbital as the 2 3D lobes. A px orbital lies along the x axis, a py orbital lies along the y axis, and a pz orbital lies along the z axis.
by SavannahScriven_1F
Thu Nov 19, 2020 3:55 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 3d fills before or after 4s?
Replies: 7
Views: 79

Re: 3d fills before or after 4s?

Adding onto the previous responses, 4s fills up before 3d, but once 3d is occupied, it has a lower energy than 4s. So when electrons enter the 3d state, the electron configuration is written with 3d before 4s.
by SavannahScriven_1F
Thu Nov 19, 2020 3:52 pm
Forum: Dipole Moments
Topic: Focus Problem 3F.1
Replies: 5
Views: 42

Re: Focus Problem 3F.1

If you're having trouble identifying which molecules are polar and nonpolar, I wouldn't worry about it too much because we will learn this in greater detail as we dive more into the molecular shape :) Knowledge of the molecular shape really helps in determining if something is polar or not.
by SavannahScriven_1F
Thu Nov 19, 2020 3:50 pm
Forum: Dipole Moments
Topic: Focus Problem 3F.1
Replies: 5
Views: 42

Re: Focus Problem 3F.1

I would first go through the rules of drawing lewis structures. From there, you have to identify which molecules are polar and which are nonpolar. Polar molecules would have dipole-dipole intermolecular forces. To tell if a molecular is polar, you should look to see if the molecule has different reg...
by SavannahScriven_1F
Thu Nov 19, 2020 3:40 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic v. Covalent Character
Replies: 6
Views: 63

Re: Ionic v. Covalent Character

Adding onto Tam's response, covalent character is in an ionic bond because in the bond, there is a cation and an anion. The cation is positive, so it attracts a little bit of the anion's electrons into the bonding region. This leaves a little bit of a shared region (aka covalent character). When the...
by SavannahScriven_1F
Thu Nov 19, 2020 3:33 pm
Forum: Lewis Structures
Topic: Expanded Valence
Replies: 11
Views: 65

Re: Expanded Valence

Expanded valence shells can begin starting with the p block in row 3. (because once you get to n=3, l can be 0, 1, or 2 and l=2 is a d orbital. The d orbital has the capacity to hold more electrons). After the p block in row 3, I'm pretty sure any element can theoretically have an expanded shell (ex...
by SavannahScriven_1F
Thu Nov 19, 2020 3:23 pm
Forum: Electronegativity
Topic: Electronegativity difference
Replies: 8
Views: 70

Re: Electronegativity difference

For electronegativity, I find it a little bit misleading to look at the periodic table for covalently bonded molecules - as you pointed out, C and F appear to be very close together. In these cases, I just have it memorized that the four most electronegative elements are: N<Cl<O<F. This seems to hel...
by SavannahScriven_1F
Sat Nov 14, 2020 12:39 pm
Forum: Lewis Structures
Topic: Polyatomic Ions
Replies: 2
Views: 15

Re: Polyatomic Ions

Hi! Appendix 3 in the textbook (page A25) has a helpful table of common polyatomic ions. I've been reviewing that to help me memorize them. Hope this info helps :)
by SavannahScriven_1F
Sat Nov 14, 2020 12:33 pm
Forum: Student Social/Study Group
Topic: Constants/Equations Sheet
Replies: 5
Views: 59

Re: Constants/Equations Sheet

Hi! Although this hasn't been stated explicitly, I would assume that for this midterm we would only have access to the periodic table. Periodic trends, exceptions to rules, etc. should be memorized.
by SavannahScriven_1F
Fri Nov 13, 2020 8:38 pm
Forum: Lewis Structures
Topic: Drawing Lewis Structures on Midterm
Replies: 31
Views: 163

Re: Drawing Lewis Structures on Midterm

I also have a question about drawing lewis structures on the midterm. I noticed that sometimes the textbook writes the molecular formula in the order it wants us to draw the lewis structure, even if this order doesn't minimize formal charge. Like ClNO2 would be drawn with Cl attached to N, and then ...
by SavannahScriven_1F
Wed Nov 11, 2020 11:15 pm
Forum: Lewis Structures
Topic: Textbook q 2B #15
Replies: 2
Views: 15

Re: Textbook q 2B #15

Usually the least electronegative atom is placed in the middle (that's why we've seen carbon in the middle so much). So since N is the least electronegative, it's the central atom. Hope this helps!
by SavannahScriven_1F
Wed Nov 11, 2020 11:09 pm
Forum: Lewis Structures
Topic: Sapling Week 5-6 HW Question 13
Replies: 4
Views: 22

Re: Sapling Week 5-6 HW Question 13

It can theoretically form 8 bonds because each H in urea can hydrogen bond to an O in H20 (so 4 hydrogen bonds). then two Hs in 2 different molecules of H20 can hydrogen bond to the O in urea. And an H from each molecule of H2O can theoretically bond with the 2 Ns in Urea. Hope this helps
by SavannahScriven_1F
Wed Nov 04, 2020 5:22 pm
Forum: Student Social/Study Group
Topic: Constants and Equations Page
Replies: 8
Views: 73

Re: Constants and Equations Page

BKoh_3H wrote:The Rydberg constant (R) should be in the formula. On the online version its in a different font and italicized. It appears very lightly when printed, so maybe that's why it didn't appear on your sheet.


ah that makes sense thank you!
by SavannahScriven_1F
Wed Nov 04, 2020 5:20 pm
Forum: Electronegativity
Topic: Electron spin part 2
Replies: 4
Views: 58

Re: Electron spin part 2

I know -1/2 and +1/2 denote if its clockwise or counterclockwise. And that in the presence of a magnetic field a beam of electron will split into 2 directions due to their electron spin. So it has an impact when there's a magnetic field, but that's all I know.
by SavannahScriven_1F
Wed Nov 04, 2020 5:17 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 2A.21 Textbook Question
Replies: 5
Views: 27

Re: 2A.21 Textbook Question

Lavelle did say we just had to remember copper and chromium because in Chem 14A we will only be doing d electron configurations in the 3rd row. But he also said to know the rule that d subshells prefer be half filled (5) and filled (10). I think it'd be best to be able to apply this rule because it ...
by SavannahScriven_1F
Wed Nov 04, 2020 5:12 pm
Forum: Student Social/Study Group
Topic: Constants and Equations Page
Replies: 8
Views: 73

Re: Constants and Equations Page

I also have a question on the Constants and Equations page. I noticed the equation that gives the energy of n in Hydrogen is En=-h/n^2. Is the missing R a typo or is it written like that on purpose? Thanks!
by SavannahScriven_1F
Wed Nov 04, 2020 5:07 pm
Forum: Quantum Numbers and The H-Atom
Topic: How do they know that ml quantum number is half that of the # of elements in its respective block?
Replies: 2
Views: 12

Re: How do they know that ml quantum number is half that of the # of elements in its respective block?

They knew ml had 3 orbitals for the p block because ml gives the orientation of the p shape. The p shape is a 3D figure with 2 lobes (like a 3D infinity sign). This 3D shape can be arranged along the x plane, the y plane, or the z plane. This gives rise to p x , p y , and p z . Each of these is an o...
by SavannahScriven_1F
Wed Nov 04, 2020 5:02 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbital vs Subshell
Replies: 7
Views: 93

Re: Orbital vs Subshell

n is the principle quantum number and is often referred to as the "shell" l is the angular momentum quantum number and references a subshell. The value of l also gives the shape. (l=0 is s, l=1 is p, l=2 is d, l=3 is f) ml gives the orientation of the "shape". remember s is only ...
by SavannahScriven_1F
Wed Oct 28, 2020 9:37 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Delta E and negative symbol
Replies: 3
Views: 40

Re: Delta E and negative symbol

Oh ya and then adding on to my first post, Energy never technically has a negative value. It's just negative relative to our reference point: E=0. This is the "maximum" E - when an electron is completely removed from an atom. So anything less than the reference point has a negative sign.
by SavannahScriven_1F
Wed Oct 28, 2020 9:35 pm
Forum: DeBroglie Equation
Topic: Conversions
Replies: 9
Views: 94

Re: Conversions

I believe they will be given if asked. Most weird conversion factors like that are usually given in the problem, or on our reference sheet. Lavelle seems to prefer to test conceptual knowledge/application rather than be grade based on memorizing certain weird conversion factors. So I wouldn't worry ...
by SavannahScriven_1F
Wed Oct 28, 2020 9:30 pm
Forum: Molarity, Solutions, Dilutions
Topic: Dilution module
Replies: 6
Views: 65

Re: Dilution module

Adding onto Nathan's point, dilution calculations' practical purpose is for use in the lab. Often, people are working with rather small volumes of liquids, so it's more practical to know the required volume in mL. There's no set rule that the answer has to be in mL or L, both are correct - the answe...
by SavannahScriven_1F
Wed Oct 28, 2020 9:18 pm
Forum: General Science Questions
Topic: polyatomic ions
Replies: 6
Views: 99

Re: polyatomic ions

Yes Mikayla is correct! I just wanted to add that my TA mentioned that if a question does have the name of something we haven't learned yet, its formula/any needed info would be given in the problem :)
by SavannahScriven_1F
Wed Oct 28, 2020 9:15 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Delta E and negative symbol
Replies: 3
Views: 40

Re: Delta E and negative symbol

When you use the E=-hr/n^2 equation, you get the energy for that n value (let's say 3. We'll make that the initial n). And then you do it again for the final n (let's say 2). To calculate delta E it would be Efinal - Einital. This represents the energy difference between energy levels. But since the...
by SavannahScriven_1F
Wed Oct 28, 2020 9:09 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Thorium and Silver
Replies: 4
Views: 48

Re: Thorium and Silver

I can answer for Ag. Lavelle mentioned in Monday's lecture that there are two exceptions: when the d level is half full d^5 and when the d level is full d^10. The electron seeks to occupy the lowest energy state so it is stable. So for silver, it is more stable (lower E) when the d level is full tha...
by SavannahScriven_1F
Sat Oct 24, 2020 9:44 pm
Forum: Student Social/Study Group
Topic: Midterm Question
Replies: 9
Views: 71

Re: Midterm Question

Lavelle sent out an email on 10/21 with a reference sheet and periodic table that we are allowed to use during the midterm. If have didn't receive that email, they are also on his class website!
by SavannahScriven_1F
Sat Oct 24, 2020 9:39 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Multi-Electron Atoms
Replies: 3
Views: 35

Re: Multi-Electron Atoms

In multi-electron systems, there is the factor of electron electron interactions, so there's repulsion between them (repulsion is positive electrostatic potential, but I don't know if we have to know this.) In multielectron systems, there can also be nuclear charges greater than 1. A higher nuclear ...
by SavannahScriven_1F
Sat Oct 24, 2020 9:28 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: s and p Orbitals
Replies: 4
Views: 62

Re: s and p Orbitals

Adding on to the previous response, the reason why multi-electron systems behave differently than single-electron systems is because there are more factors at play. Now there are electron-electron interactions, electrons in different shells (resulting in shielding of nuclear charge), and the magnitu...
by SavannahScriven_1F
Sat Oct 24, 2020 8:56 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Textbook Question 1A.13
Replies: 1
Views: 28

Re: Textbook Question 1A.13

Hi! For part a: The Ryberg formula with the energy states for this particular problem would be: v =R{(1/1^2) - (1/2^2)} This simplifies to (3R)/4. From c= \lambda v you get \lambda =c/v=c/(3R/4)=4c/3R Plugging in the values for c and R, you get 1.21 x 10^7 m or 121 nm. For part b: The questi...
by SavannahScriven_1F
Mon Oct 19, 2020 10:39 pm
Forum: Student Social/Study Group
Topic: Workshops
Replies: 3
Views: 35

Re: Workshops

Isabella Chou 1E wrote:Each workshop has problems separate from other workshops because each UA creates their own worksheets, so going to multiple workshops will give you more practice problems to do.


Thank you!
by SavannahScriven_1F
Mon Oct 19, 2020 9:47 pm
Forum: Student Social/Study Group
Topic: Workshops
Replies: 3
Views: 35

Workshops

If I go to multiple workshops in one week, do they all have the same prepared worksheets? Or does each workshop have problems separate from the other workshops of the week? I'm curious because I want to do as many practice problems as I can.
by SavannahScriven_1F
Sat Oct 17, 2020 12:42 pm
Forum: Properties of Electrons
Topic: Spectral Lines
Replies: 7
Views: 90

Re: Spectral Lines

He didn't cover how to find them yet. From my understanding, they are detected when a bunch of different frequencies of light are shined on an element. The lines only show up if they match a certain very specific energy level. So the numbers appear to be empirically derived from experimental observ...
by SavannahScriven_1F
Fri Oct 16, 2020 11:14 pm
Forum: Properties of Light
Topic: Spectral Lines
Replies: 11
Views: 115

Re: Spectral Lines

Professor Lavelle went over the atomic spectra today, and he mentioned something about gases when describing the spectral lines. Can someone explain how "gases" are related to the spectra? He mentioned gases because in the experiments that gave rise to spectra, they used gaseous elements....
by SavannahScriven_1F
Fri Oct 16, 2020 8:06 pm
Forum: Properties of Electrons
Topic: Energy Levels
Replies: 4
Views: 34

Re: Energy Levels

Yes an electron can go straight from n=1 to n=5 assuming there is an "energy match" to do so. When it comes back down, it doesn't have to jump all the way back down to 1. It can then go down to 4, or 3, or jump to 1 or whatever. Spectral lines are found when the electron drops energy level...
by SavannahScriven_1F
Fri Oct 16, 2020 8:00 pm
Forum: Properties of Light
Topic: Spectral Lines
Replies: 11
Views: 115

Re: Spectral Lines

A way that helped me understand spectral lines was by looking at the visible light spectrum. (Like the rainbow part of the EM spectrum - pg 6/7 in textbook). This whole rainbow is from around 400nm-700nm, and it is shown "blending in" to each other to form a continuous rainbow. Spectral li...
by SavannahScriven_1F
Fri Oct 16, 2020 7:52 pm
Forum: Properties of Electrons
Topic: Spectral Lines
Replies: 7
Views: 90

Re: Spectral Lines

He didn't cover how to find them yet. From my understanding, they are detected when a bunch of different frequencies of light are shined on an element. The lines only show up if they match a certain very specific energy level. So the numbers appear to be empirically derived from experimental observa...
by SavannahScriven_1F
Fri Oct 16, 2020 7:45 pm
Forum: Properties of Light
Topic: Balmer and Lyman series
Replies: 7
Views: 58

Re: Balmer and Lyman series

Oops just saw that Hailey added on what I was going to say :)
by SavannahScriven_1F
Fri Oct 16, 2020 7:44 pm
Forum: Properties of Light
Topic: Balmer and Lyman series
Replies: 7
Views: 58

Re: Balmer and Lyman series

Adding on to what Jared said, a non-mathematical way to tell if an electron goes down to n=2 or n=1 is if the question gives you information regarding the light emitted. If the light emitted had color (i.e. visible light) then it would belong to the Balmer series (& goes down to n=2). If the emi...
by SavannahScriven_1F
Thu Oct 08, 2020 3:05 pm
Forum: Empirical & Molecular Formulas
Topic: Sapling Hw Week 1 #10
Replies: 20
Views: 308

Re: Sapling Hw Week 1 #10

Does anyone know what place we should round the final percentage? I'm confident I have the right answer, but every time I plug it in the system says I got it wrong. I had the same issue. I finally got the right answer when I wrote 90%. The solution showed the answer as 9.0 x 10^1% even though their...
by SavannahScriven_1F
Wed Oct 07, 2020 9:43 pm
Forum: Empirical & Molecular Formulas
Topic: Fundamentals Self-test M.4A
Replies: 2
Views: 61

Fundamentals Self-test M.4A

The question deals with combustion analysis. It is, "When 0.528 g of sucrose (a compound of carbon, hydrogen, and oxygen) is burned, 0.306 g of water and 0.815 g of carbon dioxide are formed. Deduce the empirical formula of sucrose." I understand the steps and also went through the textboo...
by SavannahScriven_1F
Wed Oct 07, 2020 9:34 pm
Forum: Limiting Reactant Calculations
Topic: Fundamentals Self-test M.2A
Replies: 2
Views: 39

Fundamentals Self-test M.2A

The question is "(a) Identify the limiting reactant in the reaction 6 Na(l) + Al2O3(s) →2 Al(l) + 3 Na2O(s) when 5.52 g of sodium is heated with 5.10 g of Al2O3. (b) What mass of aluminum can be produced? (c) What mass of excess reactant remains at the end of the reaction?" The answers to ...
by SavannahScriven_1F
Wed Oct 07, 2020 9:18 pm
Forum: Molarity, Solutions, Dilutions
Topic: Molarity written with (aq)
Replies: 4
Views: 59

Molarity written with (aq)

One thing I quickly noticed when reading Fundamental section G.3 is that the molar concentration is reported as 0.123 M HCl (aq). For some reason this looks weird to me. It could be because last time I took chem, we did calculations with molarity before starting the practice of labeling substances w...
by SavannahScriven_1F
Wed Oct 07, 2020 9:05 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Self-test E.5A
Replies: 2
Views: 31

Self-test E.5A

The question is, "Calculate the amount of urea molecules, OC(NH2)2, in 2.3 x 10^5 g urea..." I understand the math and process, I'm just confused on the phrasing of the question. My first thought was to convert mass to moles and then to number of molecules using Avogadro's number. However,...

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