Search found 144 matches

by John Pham 3L
Sun Mar 07, 2021 9:32 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Sapling (5/6) #7
Replies: 2
Views: 16

Re: Sapling (5/6) #7

In this case, you are looking for the numbers of moles consumed in order to find the Enthalpy of Vaporization. You would subtract the final mass from the initial mass in order to get a positive value for grams consumed in the reaction. Either way works though. As long as you know the number of moles...
by John Pham 3L
Wed Mar 03, 2021 9:40 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 6M- Standard Molar Potential
Replies: 2
Views: 13

Re: 6M- Standard Molar Potential

Eo represents the Standard Reduction potential of that half-reaction at Standard Conditions.
In this case, it would be Zn +2 being reduced to become Zn
by John Pham 3L
Wed Mar 03, 2021 9:39 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Textbook question 6L.1
Replies: 1
Views: 7

Re: Textbook question 6L.1

You could look at the relative charges of the ions on each side and their corresponding stoichiometric coefficients. In part A, there are 2 Ce +4 ions on the reactant side and 2 Ce +3 ions on the other side. This must mean that there was 2 e- transferred to Ce +4 in order to become Ce +3. You could ...
by John Pham 3L
Tue Mar 02, 2021 10:47 pm
Forum: Balancing Redox Reactions
Topic: Textbook 6L.3 Solution
Replies: 2
Views: 8

Re: Textbook 6L.3 Solution

I don't think the E° values would be needed for this question. You are only solving for the half-reactions and the balanced overall equation so there's no need to find the potential. It might be that the textbook answer key is demonstrating that the E° cell value would be positive for a Galvanic cel...
by John Pham 3L
Tue Mar 02, 2021 10:56 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Judging reduction strength when an element has multiple charges
Replies: 2
Views: 12

Re: Judging reduction strength when an element has multiple charges

For this question, I would assume that you would use the reactions that fully reduced the given metal elements.

Since they give you the neutral metals and asks for their strength as reducing agents, I would find the half-reduction reactions that produce the neutral metal.
by John Pham 3L
Mon Mar 01, 2021 1:16 pm
Forum: General Rate Laws
Topic: order reactions
Replies: 2
Views: 19

Re: order reactions

Adding on, another way to think of the zeroth-order reactions is that they are independent of the concentration.
No matter how much concentration is present (as long as there is concentration), the rate is set at the given rate constant.
by John Pham 3L
Tue Feb 23, 2021 4:06 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L.3
Replies: 2
Views: 17

Re: 6L.3

I think that most of these Standard Reduction Potentials are given in Appendix 2B.
The problems don't refer to this Appendix but that's where I found most of the potentials
by John Pham 3L
Tue Feb 23, 2021 8:58 am
Forum: Student Social/Study Group
Topic: How to Reduce Nervousness before getting results
Replies: 37
Views: 102

Re: How to Reduce Nervousness before getting results

Like a lot of the other responses, I try to keep myself busy with other things and keep my mind of the exam.
You don't have much control over what you did on the exam so it's best to just wait for your score once it comes out.
by John Pham 3L
Tue Feb 23, 2021 8:54 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Question About Textbook Example 6M.1
Replies: 2
Views: 13

Re: Question About Textbook Example 6M.1

They're using the same equation of E°cell = E°cathode (right) - E°anode (left) but rearranged as E°cathode (right) = E°cell + E°anode (left)
In this equation, you are using the Standard Reduction Potentials so you don't need to reverse the signs since you were already subtracting the E°anode
by John Pham 3L
Mon Feb 22, 2021 11:20 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: When to use single line
Replies: 2
Views: 15

Re: When to use single line

Adding on, you would use a comma to signify that they are in the same phase and in contact with one another.
by John Pham 3L
Mon Feb 22, 2021 8:58 am
Forum: Student Social/Study Group
Topic: Chem 14B Final
Replies: 86
Views: 221

Re: Chem 14B Final

Adding on to what everyone else has said, UA sessions also add in past exam questions from previous years to their worksheets.
The difficulty and content of these worksheets are very similar to that of the exams so it's good to attend as many as possible.
by John Pham 3L
Tue Feb 16, 2021 9:46 pm
Forum: General Science Questions
Topic: Grade Cutoffs?
Replies: 4
Views: 47

Re: Grade Cutoffs?

I think that 50% for a C is just an exception.
For the other grades, you'd calculate them with the same scales as normal.
- I.e. -A is 360/400 points, A is 372/400
by John Pham 3L
Tue Feb 16, 2021 9:44 pm
Forum: Administrative Questions and Class Announcements
Topic: Textbook Problems
Replies: 8
Views: 40

Re: Textbook Problems

There's a solution manual on Sapling.
Log onto Sapling, click on Resources, and then click on Atkins 7e SSM for the solutions manual.
by John Pham 3L
Tue Feb 16, 2021 9:00 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Question about 4H.11 part d
Replies: 3
Views: 40

Re: Question about 4H.11 part d

For this question, you would just use the entropy calculated from molar entropies to determine which side is more ordered.
Like you said, it would be hard to tell which side is more ordered since there is an equal number of moles of solid on each side so you'd have to calculate the entropy change.
by John Pham 3L
Mon Feb 15, 2021 8:49 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: textbook problem 4.5
Replies: 1
Views: 15

Re: textbook problem 4.5

Since it is telling you that the difference in time represents the difference in heat required for the samples, you can assume that every 30 minutes of heating is equivalent to the value of 3135 J. You would multiply 3135 J by 10h/0.5h to find the heat required to heat the ice since the ice required...
by John Pham 3L
Mon Feb 15, 2021 1:46 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 4I.7
Replies: 1
Views: 18

Re: 4I.7

You would use the value 158.7 K for the melting point; this value also represents the freezing point.
If you heat C2H5OH to that point, it would melt.
If you cool C2H5OH to that point, it would freeze.
by John Pham 3L
Wed Feb 10, 2021 2:56 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Textbook 4D.7
Replies: 2
Views: 17

Re: Textbook 4D.7

I think you just have to assume that the temperature is in standard conditions for this expression.
Since they don't explicitly say the temperature, you would assume it is 298 K
by John Pham 3L
Wed Feb 10, 2021 2:52 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Sapling #6
Replies: 2
Views: 18

Re: Sapling #6

We have to solve for both the entropy change from the temperature change and the volume change.
- You would then have to use both equations for temperature and volume change
Since entropy is a state function, we would then add these two entropies together to solve for the overall change in entropy.
by John Pham 3L
Tue Feb 09, 2021 11:34 am
Forum: Administrative Questions and Class Announcements
Topic: Midterm 2
Replies: 6
Views: 44

Re: Midterm 2

I think we're currently on bullet point 11 for the Thermodynamics 2nd and 3rd Law Outline. I would assume that the midterm will cover Outlines 3 and 4 but I'm not sure if there will be a little from Outline 5.
by John Pham 3L
Tue Feb 09, 2021 9:09 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 4F.13
Replies: 1
Views: 18

Re: 4F.13

You multiply by -6.01 kJ/mol to account for the heat released for one mole of H2O when freezing.
You'd then divide by the temperature in Kelvin to get entropy
by John Pham 3L
Mon Feb 08, 2021 9:39 pm
Forum: Student Social/Study Group
Topic: Preparing for Midterm 2
Replies: 14
Views: 51

Re: Preparing for Midterm 2

For Midterm 2, I am going to primarily study the textbook problems and attend as many UA sessions as possible. This worked well for me last midterm so I'm hoping it helps this time too. I feel like this section of Thermochemistry and Thermodynamic is very heavy with calculations so doing as much pra...
by John Pham 3L
Thu Feb 04, 2021 10:57 am
Forum: Administrative Questions and Class Announcements
Topic: Chem Community Grade Error
Replies: 15
Views: 102

Re: Chem Community Grade Error

The Chem Community points also include this week. You would just need to have 25 posts by the end of this week to get the full 25/25
by John Pham 3L
Wed Feb 03, 2021 11:29 am
Forum: Calculating Work of Expansion
Topic: Sapling Week 3&4 HW #14
Replies: 4
Views: 44

Re: Sapling Week 3&4 HW #14

Your work looks correct for this question. It might be something with your units and conversion?
I would check your calculations again and make sure everything is converted to the correct units and in the right places.
by John Pham 3L
Wed Feb 03, 2021 9:19 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Sapling Weeks 3,4,5 Question 19
Replies: 3
Views: 44

Re: Sapling Weeks 3,4,5 Question 19

I usually try to look at what information is given and the specific wording in these types of questions. As the question is asking for the change in internal energy, we'll need to find delta U through work and heat - However, we won't need to find work as it is a constant-volume calorimeter and no w...
by John Pham 3L
Mon Feb 01, 2021 5:01 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Memorizing molar entropies
Replies: 13
Views: 26

Re: Memorizing molar entropies

I would assume that any molar entropies needed would be given to us on exams.
by John Pham 3L
Mon Feb 01, 2021 12:52 pm
Forum: Administrative Questions and Class Announcements
Topic: Can We Review our Exams?
Replies: 69
Views: 254

Re: Can We Review our Exams?

I would assume that, like 14A, you can only review your midterm during a TA's office hour. They aren't allowed to directly tell you the question you got wrong but the content covered in the question.
by John Pham 3L
Wed Jan 27, 2021 8:42 pm
Forum: Phase Changes & Related Calculations
Topic: 4D practice problems
Replies: 2
Views: 24

Re: 4D practice problems

On the Midterm Info doc, Lavelle said that 4D.15, 4D.17, 4D.19, 4D.21, and 4D.23 will be covered on the midterm this Friday.
The other questions from Outline 3 that have material from the exam are 4E.5, 4E.7, 4E.9, 4.29, and 4.31.
by John Pham 3L
Tue Jan 26, 2021 2:36 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Textbook problem 6e 1
Replies: 2
Views: 22

Re: Textbook problem 6e 1

You still need to find the amount of H3O+ formed from HSO4-. H2SO4 is both a Strong Acid and a Polyprotic Acid which means that it will fully dissociate. In this case, it will dissociate into 0.15M HSO4- and 0.15M H3O+. Since it is Polyprotic, however, HSO4- will dissociate again and produce additio...
by John Pham 3L
Tue Jan 26, 2021 1:01 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: increasing base strength sapling
Replies: 2
Views: 26

Re: increasing base strength sapling

Adding on, a lower value of pOH would mean that it is more basic and has a higher OH- concentration.
Since taking the pX of a value is taking the negative log, the larger the value plugged into -log, the smaller the p value
by John Pham 3L
Tue Jan 26, 2021 8:59 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Question 5.39
Replies: 1
Views: 20

Re: Question 5.39

It's an error from table 5G.2 for that reaction.
In the Solution Manual Errors document, it says that the values are supposed to be 6.1*10^3, not 6.1*10^23.
by John Pham 3L
Mon Jan 25, 2021 10:01 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: question about equilibrium reactions vs. equilibrium constants
Replies: 2
Views: 9

Re: question about equilibrium reactions vs. equilibrium constants

The equilibrium constant will stay the same for any changes to concentration. The only thing that can change the value of the equilibrium constant is temperature. The equilibrium reaction is affected by increasing the concentration of reactants or products since the reaction needs to get back to its...
by John Pham 3L
Mon Jan 25, 2021 9:57 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: textbook question 5G #11
Replies: 4
Views: 28

Re: textbook question 5G #11

K and Q have the same expression.
You don't include solids or liquids for both K and Q.
by John Pham 3L
Wed Jan 20, 2021 2:56 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm 1
Replies: 9
Views: 81

Re: Midterm 1

I think we will still need to print out another equation sheet and a periodic table like for 14A. There's a new equation sheet for 14B that is on the class website so I'm assuming that's the one we'll need. Lavelle will probably send out an email either at the end of this week or early next week abo...
by John Pham 3L
Wed Jan 20, 2021 10:51 am
Forum: General Science Questions
Topic: Polyprotic Acids
Replies: 6
Views: 47

Re: Polyprotic Acids

It is safe just to use the Ka1 for solving for the pH of a polyprotic weak acid.
You can assume that any further deprotonation is insignificant and won't affect the pH.
by John Pham 3L
Wed Jan 20, 2021 10:47 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Identifying Strong & Weak Acids/Bases
Replies: 7
Views: 64

Re: Identifying Strong & Weak Acids/Bases

I think that we will just have to memorize which are weak or strong. The best way to memorize them is to memorize the 7 strong acids and the strong bases. - Strong Acids: HCl, HBr, HI, HClO4, HClO3, HNO3, and H2SO4 - Strong Bases: Group 1 and 2 Oxides and Hydroxides If they aren't a strong acid or s...
by John Pham 3L
Tue Jan 19, 2021 9:23 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook Problem 5.35
Replies: 2
Views: 12

Re: Textbook Problem 5.35

Adding on to what Katarina said, make sure that you convert to the correct units of pressure when you are solving for the K expression.
Since you are given the pressure in kPA, you still need to convert to bar (1 bar = 100 kPa) and then plug in
by John Pham 3L
Mon Jan 18, 2021 10:38 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: textbook 5I.11
Replies: 2
Views: 32

Re: textbook 5I.11

You still need to convert from mmol to mol (1 mmol = 10^-3 mol)
Make sure to also calculate the molarity by dividing by 0.500 L before plugging into the Kc equation.
by John Pham 3L
Thu Jan 14, 2021 5:19 pm
Forum: Student Social/Study Group
Topic: Study Tips for Chem 14B
Replies: 11
Views: 77

Re: Study Tips for Chem 14B

I would say going through all of the problems on the outline and reviewing Sapling assignments are the best way to prepare for the class. Most of Lavelle's problems on his exams are structured very similarly to these assigned problems and as long as you can do these problems, you'll be set for the e...
by John Pham 3L
Wed Jan 13, 2021 9:38 am
Forum: Student Social/Study Group
Topic: Advice for study
Replies: 31
Views: 112

Re: Advice for study

For me, I usually go through all the assigned textbook problems and try to go to around 2-3 UA sessions each week.
Usually, the UA's have some past midterm and final on their worksheets so those are good practice for the actual exams.
by John Pham 3L
Tue Jan 12, 2021 9:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: textbook 5.35
Replies: 3
Views: 48

Re: textbook 5.35

I think that you divide by 100 to convert kPa to bar.
You wouldn't need to convert to Pa since Kp usually uses atm or bar
by John Pham 3L
Tue Jan 12, 2021 2:32 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling Homework #5
Replies: 2
Views: 39

Re: Sapling Homework #5

For this question, you need to know the rules for manipulating K - If you reverse a reaction, you take the reciprocal of K - If you multiply a reaction by a given coefficient, you raise K to the power of the coefficient - If you add two reactions together, you multiply the K values together You are ...
by John Pham 3L
Mon Jan 11, 2021 11:18 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling 5.57 b)
Replies: 3
Views: 40

Re: Sapling 5.57 b)

For this question, you could use an ICE table to solve for the change in concentration x Looking at the ICE table, you can see that the change in concentration would be 0.24 mol since there are 0.24 mol SO2 present at equilibrium - This is because there were initially 0 mol of NO2 but became 0.24 mo...
by John Pham 3L
Mon Jan 11, 2021 9:02 am
Forum: Ideal Gases
Topic: Ice method
Replies: 14
Views: 73

Re: Ice method

To add on, the change variable x also takes into account the stoichiometric coefficients in the balanced equation.
- I.e. Cl2 --> 2Cl would have a change of +2x for Cl if you started with Cl2 only
by John Pham 3L
Sat Jan 09, 2021 5:28 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Change inn temperature
Replies: 6
Views: 40

Re: Change inn temperature

It depends on whether the reaction is endothermic or exothermic.
If the reaction is endothermic, adding heat would produce more products and a larger K.
If the reaction is exothermic, adding heat would produce more reactants and a smaller K.
by John Pham 3L
Wed Jan 06, 2021 8:46 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Change in concentration
Replies: 2
Views: 33

Re: Change in concentration

For the change in concentration, you would use the same coefficient as that in the balanced chemical equations. It depends when determining whether the change in concentration will be positive or negative. If you only have reactants and no products, there will be a negative change in concentration f...
by John Pham 3L
Wed Jan 06, 2021 7:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Concentration of a Reactant/Product
Replies: 2
Views: 34

Re: Concentration of a Reactant/Product

In this question, you don't need to have a K value to solve for equilibrium concentrations. You already know the initial amount of reactants and the equilibrium concentration of NH3. With the equilibrium concentration of NH3 and initial concentrations of N2 and H2, you can solve for the change in co...
by John Pham 3L
Wed Jan 06, 2021 10:07 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling Q10 Part2
Replies: 2
Views: 23

Re: Sapling Q10 Part2

Here are the steps I used, 1. Find the K value from the original equilibrium concentrations - K value doesn't change with change in concentration so you can use this K value to determine the equilibrium again 2. Find the new concentrations after accounting for the additional 1.00 mol NO2 is added - ...
by John Pham 3L
Mon Jan 04, 2021 8:23 pm
Forum: Administrative Questions and Class Announcements
Topic: UA Sessions
Replies: 3
Views: 33

Re: UA Sessions

All UA sessions started today
by John Pham 3L
Mon Jan 04, 2021 8:21 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Part 2 Module Review Question 30
Replies: 1
Views: 21

Re: Part 2 Module Review Question 30

I got the same equation for that question. K = [CO]*[H2]/[H2O]
For the values I plugged in, I ended with [0.040]^2/0.010 which was 0.16
by John Pham 3L
Tue Dec 08, 2020 10:55 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bent v Angular
Replies: 3
Views: 12

Re: Bent v Angular

Bent and Angular describe the same VSEPR shape and are interchangeable terms.
I think we would have to know what produces bent structures like 3 e- densities with 1 lone pair or 4 e- densities with 2 lone pairs.
by John Pham 3L
Tue Dec 08, 2020 6:29 pm
Forum: Naming
Topic: Memorization
Replies: 4
Views: 101

Re: Memorization

I would also recommend remembering which ligands are polydentate.
- I.e en is bidentate, edta is hexadentate, etc
by John Pham 3L
Tue Dec 08, 2020 4:44 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: IMFs
Replies: 2
Views: 33

Re: IMFs

There would be H-bonds present in H2SeO4.
Drawing the Lewis structure shows that each of the H is attached to an Oxygen which makes it an H-Bond
by John Pham 3L
Tue Dec 08, 2020 9:10 am
Forum: Bronsted Acids & Bases
Topic: Bronsted vs Lewis
Replies: 8
Views: 59

Re: Bronsted vs Lewis

All Bronsted Acids are also Lewis Acids.
All Bronsted Bases are also Lewis Bases.

The reverse isn't usually true though. Some Lewis Acids don't have a proton to donate and cannot be considered a Bronsted Acid (I.e. Mg +2).
by John Pham 3L
Tue Dec 08, 2020 9:06 am
Forum: Lewis Acids & Bases
Topic: general conceptual question
Replies: 9
Views: 103

Re: general conceptual question

I usually look at whether the acid is a binary acid first. For binary acids (HCl, HBr, etc), you can look at the bond lengths and determine which are the longest. The longer the bond, the easier to break and the more acidic. If it isn't a binary acid, then you can use EN to determine acidity. The bo...
by John Pham 3L
Mon Dec 07, 2020 4:55 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: From pOH- to [H+]
Replies: 3
Views: 29

Re: From pOH- to [H+]

You can use the equation pH + pOH = 14 to solve for pH.
With pH, you can plug into [H+] = to solve for molarity
by John Pham 3L
Sat Dec 05, 2020 9:43 pm
Forum: Naming
Topic: en
Replies: 8
Views: 78

Re: en

en is Ethylene Diamine
by John Pham 3L
Thu Dec 03, 2020 11:29 am
Forum: Bronsted Acids & Bases
Topic: Bronsted Acids Strength
Replies: 3
Views: 29

Re: Bronsted Acids Strength

HBr is a stronger acid since it is more likely to give its proton compared to HCl.
The longer bond length means weaker bond strength of HBr than HCl.
by John Pham 3L
Thu Dec 03, 2020 11:25 am
Forum: Coordinate Covalent Bonds
Topic: sapling number 5
Replies: 1
Views: 19

Re: sapling number 5

Each Br- is monodentate and binds to Cd to form 1 bond.
Each Ethylenediamine is bidentate and forms 2 bonds.

This would make the coordination number equal to 4 for[Cd(en)Br2]
by John Pham 3L
Wed Dec 02, 2020 2:48 pm
Forum: Naming
Topic: Sapling Question 6
Replies: 4
Views: 59

Re: Sapling Question 6

Yes, you would need to account for oxidation numbers outside the brackets too.
You want to make sure that the charge of the coordination compound and outer ion add up to 0.
by John Pham 3L
Tue Dec 01, 2020 10:55 pm
Forum: Naming
Topic: use of bis,tris,etc
Replies: 3
Views: 44

Re: use of bis,tris,etc

You would use it if there was already a Greek prefix anywhere already in the ligand.
For your example, you would use bisethylenediammine to signify two ethylenediammine ligands.
by John Pham 3L
Tue Dec 01, 2020 5:38 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: charge of oxalato
Replies: 4
Views: 61

Re: charge of oxalato

I would assume that you'd need to know the charges of command ligands for coordination compounds like oxalate, en, edta, etc.

There should be a table in the textbook that lists common ligands and whether they are neutral or charged.
by John Pham 3L
Tue Dec 01, 2020 3:09 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Energy level of orbitals
Replies: 5
Views: 73

Re: Energy level of orbitals

Just to add on, s<p<d<f is due to the effects of penetration and shielding (I.e. S has the lowest energy since it has no nodal planes). This follows the building-up/Aufbau's principle as well.
by John Pham 3L
Mon Nov 30, 2020 7:41 pm
Forum: Lewis Structures
Topic: Varying Arrangements of Structure
Replies: 5
Views: 65

Re: Varying Arrangements of Structure

I'm not sure if you meant CH2Cl2 instead, but for CH2Cl2 there's no difference where you draw the H or Cl atoms.
All of the atom arrangements would result in the same tetrahedral VSEPR structure.
by John Pham 3L
Sun Nov 29, 2020 5:52 pm
Forum: Lewis Structures
Topic: Sapling Week 7/8 #12
Replies: 8
Views: 59

Re: Sapling Week 7/8 #12

When given the mass percentages, you can assume that it is a 100 g sample and convert the percentages to grams. In this case, you'd have 37.5 g C, 12.6 g H, and 49.9 g O. You can then do the same steps to find the molecular formula of the compound. - Convert from grams to moles - Divide by the lowes...
by John Pham 3L
Wed Nov 25, 2020 5:51 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Structure
Replies: 3
Views: 59

Re: Structure

Dashed line would represent the atoms going away from you.
Wedged shape line would represent the atoms going towards you.
They are used in the structure to help differentiate the 3D model of the molecule as a Lewis Structure (i.e. Tetrahedral, Trigonal Planar)
by John Pham 3L
Wed Nov 25, 2020 11:21 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Sapling #3
Replies: 2
Views: 17

Re: Sapling #3

We need to take into account the structure predicted by VSEPR in order to identify the bond angles. For my question 3, the structure was tetrahedral since it has 4 outer atoms and no lone pairs. Tetrahedral arrangement would then have a bond angle of 109.5. The same process applies to all other VSEP...
by John Pham 3L
Tue Nov 24, 2020 4:48 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 2E.13 Solution Manual Part A
Replies: 3
Views: 16

Re: 2E.13 Solution Manual Part A

It's an error in the solution manual.
The pdf solution manual has the answer correctly written as AX2E3
by John Pham 3L
Mon Nov 23, 2020 11:18 pm
Forum: Trends in The Periodic Table
Topic: Textbook Question Focus 1.13
Replies: 2
Views: 17

Re: Textbook Question Focus 1.13

Oxygen is one of the exceptions due to the electron repulsion that it experiences in the 2p orbitals. Nitrogen has each of its orbitals in the 2p subshell half-filled. Oxygen, on the other hand, has 4 e- in the 2p subshell and will have a paired e- in one of its orbitals. This additional electron ad...
by John Pham 3L
Mon Nov 23, 2020 11:14 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining Molecular Polarity using VSEPR
Replies: 8
Views: 72

Re: Determining Molecular Polarity using VSEPR

A linear shape describes a nonpolar molecule since the dipoles cancel each other out.

In the case of CO2, it has two polar bonds with the Carbon atom and each Oxygen atom.
But since they are placed opposite to each other, the dipoles cancel out and result in a nonpolar molecule
by John Pham 3L
Wed Nov 18, 2020 9:28 pm
Forum: Dipole Moments
Topic: Dipole vs Polar molecule
Replies: 2
Views: 15

Re: Dipole vs Polar molecule

Dipole means that there are partial charges present in the molecule, which occurs when two atoms have a difference in electronegativity. However, having dipoles does not necessarily mean that a molecule is polar; these dipoles can cancel each other out and result in a non-polar molecule. An example ...
by John Pham 3L
Wed Nov 18, 2020 10:38 am
Forum: Administrative Questions and Class Announcements
Topic: Midterm 2 Grades
Replies: 6
Views: 159

Re: Midterm 2 Grades

My TA said to expect the grades around next week after Lavelle reviews the exams.
I don't think they will be out by end of Friday though.
by John Pham 3L
Tue Nov 17, 2020 1:50 pm
Forum: Lewis Structures
Topic: Txtbook 2B.3(d) Answer
Replies: 1
Views: 13

Re: Txtbook 2B.3(d) Answer

Yeah there should be another lone pair on the F atom.
The pdf solutions manual on Sapling has a fixed version with all the lone pairs added
by John Pham 3L
Tue Nov 17, 2020 1:45 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem 14BL and Chem 14B
Replies: 6
Views: 53

Re: Chem 14BL and Chem 14B

I'm pretty sure that you can take Chem 14B and 14BL separately.
Most people usually take Chem 14BL along with Chem 14C after taking Chem 14B
by John Pham 3L
Mon Nov 16, 2020 8:05 am
Forum: Bond Lengths & Energies
Topic: 2D.13 Part B
Replies: 3
Views: 47

Re: 2D.13 Part B

You should always draw the structure with the lowest formal charge. The lower the formal charges, the more stable the structure and more likely the structure.
by John Pham 3L
Sat Nov 14, 2020 10:24 am
Forum: Lewis Structures
Topic: NH2OH Polar or non polar
Replies: 2
Views: 34

Re: NH2OH Polar or non polar

NH2OH is polar because, like you said, there is a dipole moment between the N-H and the N-O with partial charges. Since they are unequal in strength and arranged asymmetrically, the dipoles will still remain and not cancel out. This results in the molecule being polar. A molecule like NH4+, on the o...
by John Pham 3L
Sat Nov 14, 2020 10:19 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Textbook 1E.13: e- configuration for Silver (Ag)
Replies: 3
Views: 18

Re: Textbook 1E.13: e- configuration for Silver (Ag)

Elements in the d-block have two exceptions. Some of these elements tend to either want to be fully filled or half-filled to become the most stable state. In order to do this, they will take an e- from the higher s-orbital and add it to their orbitals in the p-subshell. If you have np9 or np4, the e...
by John Pham 3L
Wed Nov 11, 2020 9:23 am
Forum: Quantum Numbers and The H-Atom
Topic: 2s to 2p in a hydrogen atom
Replies: 1
Views: 33

Re: 2s to 2p in a hydrogen atom

The energy of the electron wouldn't change.
Hydrogen is an exception where all of its orbitals in a given shell are degenerate and have the same energy.
by John Pham 3L
Tue Nov 10, 2020 5:04 pm
Forum: Lewis Structures
Topic: Drawing the formula unit
Replies: 2
Views: 22

Re: Drawing the formula unit

I would assume that we would have to find the formula for Lithium Nitride.
Looking at the periodic table, you would see Li forming a +1 charge and Nitrogen forming a -3 charge, and form Li3N
by John Pham 3L
Tue Nov 10, 2020 3:40 pm
Forum: Trends in The Periodic Table
Topic: Which directions do cation and anions of elements move?
Replies: 3
Views: 29

Re: Which directions do cation and anions of elements move?

For the anion electron configuration, you would gain electrons and find the electron configuration to the right of the element For the cation electron configuration, you would lose electrons and find the electron configuration to the left of the element In the case of Br -2, - It normally has the co...
by John Pham 3L
Tue Nov 10, 2020 12:06 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm 2 Questions
Replies: 16
Views: 176

Re: Midterm 2 Questions

To add on, I was told that there won't be any partial credit for the next midterm most likely.
Since there are more questions that are shorter and more conceptual, these questions won't involve too many calculations
by John Pham 3L
Tue Nov 10, 2020 12:03 pm
Forum: Electronegativity
Topic: Electronegativity Difference Between 1.5 and 2
Replies: 2
Views: 27

Re: Electronegativity Difference Between 1.5 and 2

If I remember correctly, Lavelle said that we would have to then look at the properties of these molecules in addition to the bonds.
The values of electronegativity are a rough guideline we use to estimate whether it is an ionic or covalent bond.
by John Pham 3L
Sun Nov 08, 2020 6:22 pm
Forum: Ionic & Covalent Bonds
Topic: London dispersion forces
Replies: 12
Views: 57

Re: London dispersion forces

To add on, we can determine the strength in London dispersion forces by looking at the atom's polarizability. Polarizability refers to the ease at which the electron cloud can be distorted. Atoms that are highly polarizable have stronger London dispersion forces than those less polarizable. This mea...
by John Pham 3L
Sat Nov 07, 2020 9:39 pm
Forum: Lewis Structures
Topic: Sapling Weeks 5-6 HW Question 2
Replies: 7
Views: 65

Re: Sapling Weeks 5-6 HW Question 2

How do you know when it's best to use a double bond as opposed to using a single bond and a lone pair? it depends on the molecule but for the most part, you'd use a double bond over a single bond and a lone pair if it reduced the formal charges on the atoms. The structure with the lowest formal cha...
by John Pham 3L
Fri Nov 06, 2020 8:56 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Charges on Individual Atoms
Replies: 3
Views: 31

Re: Charges on Individual Atoms

A formal charge of 0 is more stable than both a formal charge of +1 or -1.
Lewis structures with formal charges of 0 are better representations of the molecule since it is in a stable state
by John Pham 3L
Thu Nov 05, 2020 6:44 pm
Forum: General Science Questions
Topic: Sapling HW question
Replies: 5
Views: 120

Re: Sapling HW question

Those are common polyatomic ions that are recommended to know.
Nitrate would be NO3- and Nitrite would be NO2-
Phosphate would be PO4 -3 and Phosphite would be PO3 -3
by John Pham 3L
Wed Nov 04, 2020 10:44 pm
Forum: Lewis Structures
Topic: Lewis structure for formaldehyde
Replies: 4
Views: 44

Re: Lewis structure for formaldehyde

Hydrogen can only hold 2 electrons in its valence shell and is an exception to the octet rule.
It only has access to the 1s subshell which holds a maximum of 2 electrons.
by John Pham 3L
Wed Nov 04, 2020 5:10 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 2A.21 Textbook Question
Replies: 5
Views: 27

Re: 2A.21 Textbook Question

I would just remember the general exceptions for the d-subshell.
Atoms will never have the electron configuration of nd^4 or nd^9 and would take an e- from the higher s-subshell to become half-filled or fully-filled.
by John Pham 3L
Wed Nov 04, 2020 11:19 am
Forum: Lewis Structures
Topic: Lewis Acid-Base
Replies: 6
Views: 41

Re: Lewis Acid-Base

To add on, Boron normally has 6 valence electrons and would maintain a Formal Charge of 0 in its current structure. Adding another bond would result in the FC becoming +1 and less stable of a structure.
by John Pham 3L
Wed Nov 04, 2020 9:01 am
Forum: Quantum Numbers and The H-Atom
Topic: ml number possibilities
Replies: 4
Views: 51

Re: ml number possibilities

I think that the question would specify the number of electrons in the final subshell. You would then just follow Hund's Rule to fill these orbitals and see which orbitals each electron occupies. Generally, I don't think we'll be asked on specifics to electron location but just knowing the orbitals ...
by John Pham 3L
Tue Nov 03, 2020 10:27 am
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge and Lewis Structures
Replies: 10
Views: 88

Re: Formal Charge and Lewis Structures

For structures that have resonance, you would check the formal charges to see which of the structures has the lowest energy and is most stable. But if there's only a single Lewis structure for a given molecule, there would be no need to check formal charges since that's the only structure that could...
by John Pham 3L
Mon Nov 02, 2020 3:27 pm
Forum: Student Social/Study Group
Topic: Midterm 2
Replies: 31
Views: 327

Re: Midterm 2

During Lavelle's office hours, he said that Midterm 2 will cover the remaining 8 bullet points from Quantum World Outline and most likely all of Chemical Bonds Outline.

There won't be content from Midterm 1 on the second Midterm. The final, however, is going to be cumulative
by John Pham 3L
Sat Oct 31, 2020 7:09 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron configuration 4s and 3d
Replies: 2
Views: 38

Re: Electron configuration 4s and 3d

I think the energy depends on whether or not the 3d orbitals have electrons in them. When there are no electrons occupied in the 3d orbitals, then 4s has lower energy than 3d. When there are electrons in the 3d orbitals, then 4s has higher energy than 3d. After Ca, the 4s shell has higher energy tha...
by John Pham 3L
Thu Oct 29, 2020 3:54 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Determining Element with e- Configuration
Replies: 2
Views: 20

Re: Determining Element with e- Configuration

In the excited state, it means that an electron went to a subshell that is higher than the one it is usually in. For this question, they give you that the excited electron configuration is 1s2 2s2 2p3 3s1 This means that one electron from the 2p subshell was excited to the 3s1 subshell The ground-st...
by John Pham 3L
Thu Oct 29, 2020 3:51 pm
Forum: Properties of Electrons
Topic: Sapling Week 4 #25
Replies: 4
Views: 51

Re: Sapling Week 4 #25

Since it's asking for the energy of the electron, you would just plug in the mass of an electron.
m would be kg
by John Pham 3L
Thu Oct 29, 2020 12:46 pm
Forum: General Science Questions
Topic: Enrolling in Chem 14B and BL simultaneously?
Replies: 14
Views: 207

Re: Enrolling in Chem 14B and BL simultaneously?

It's probably better to take Chem 14BL after you take 14B. I've heard from other students who've already taken these courses that it's better to take 14BL after 14B Chem 14B covers the content in 14BL and you would have a better background in the content in 14BL since you've taken 14B already. I'm p...
by John Pham 3L
Wed Oct 28, 2020 1:34 pm
Forum: Properties of Light
Topic: UA Workshop Question
Replies: 4
Views: 72

Re: UA Workshop Question

You already have the total number of Joule produced which is 2000J.
All you need to do now is find the energy per photon using the wavelength given with the formula .
Then you can divide total Joules produced by energy per photon to find the total number of photons produced.
by John Pham 3L
Wed Oct 28, 2020 10:54 am
Forum: Administrative Questions and Class Announcements
Topic: Chem 14BL
Replies: 5
Views: 102

Re: Chem 14BL

I've heard from people that already taken the class and older posts on Chem Community that it's probably better to take Chem 14BL after you take 14B. This is because 14B covers the content in 14BL and it makes sense to have a background in the content covered before taking 14BL. You could still take...
by John Pham 3L
Wed Oct 28, 2020 10:49 am
Forum: Administrative Questions and Class Announcements
Topic: Participation Points [ENDORSED]
Replies: 62
Views: 1046

Re: Participation Points [ENDORSED]

Can Yilgor 1D wrote:If we post less than five times in a week, can we make up for it by posting more the following week?


I don't think that posts can carry over or be used for the previous week.
I'm pretty sure that you can only get a maximum of 5 points per week
by John Pham 3L
Wed Oct 28, 2020 10:46 am
Forum: Quantum Numbers and The H-Atom
Topic: relationship between ml and l
Replies: 2
Views: 30

Re: relationship between ml and l

As you said, the relationship is determined for ml as 2l + 1 and each value represents an orbital for the subshell. You can determine the subshell if given the electron configuration. Example: Using the electron configuration of C: 1s2 2s2 2p2 - Since there are 2 electrons in the 2p subshell, we can...
by John Pham 3L
Mon Oct 26, 2020 4:57 pm
Forum: Properties of Electrons
Topic: Lecture #8
Replies: 1
Views: 16

Re: Lecture #8

That's correct. All objects have wavelike properties but you can't see or detect the wavelike properties for objects like a baseball.
Wavelike properties are detectable for objects with very small masses and high velocities

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