Search found 101 matches

by Alan Huang 1E
Sat Mar 13, 2021 10:23 pm
Forum: Administrative Questions and Class Announcements
Topic: Saying Thank You to Dr. Lavelle
Replies: 416
Views: 144049

Re: Saying Thank You to Dr. Lavelle

Thank you so much for all the resources and effort you put into the classes to both help your students and make the class more enjoyable! Thank you for everything and have a good spring break Dr. Lavelle!
by Alan Huang 1E
Fri Mar 12, 2021 8:06 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: textbook 7D.5
Replies: 4
Views: 37

Re: textbook 7D.5

There are two typos in this question that were corrected in the solution manual errors pdf on Dr.Lavelle's website. First, 37 degrees C should be 310 K and the -0.59 you mentioned should be positive 0.59. Even with the typo, I was still wondering where the value came from. If someone could provide ...
by Alan Huang 1E
Fri Mar 12, 2021 8:02 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 7.11 Textbook
Replies: 2
Views: 16

Re: 7.11 Textbook

When given the overall rate law of the reaction, we can find the slow step since the slowest step of a reaction is the rate-determining step. Given that the rate law is rate = k[NO]^2[H2], we should find the step in which the reactants consist of the same amounts of the elements found in the rate la...
by Alan Huang 1E
Fri Mar 12, 2021 7:58 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction type
Replies: 2
Views: 17

Re: Reaction type

I think we can use thermodynamic concepts. For example, if you are forming a product from simple elements usually that means you are releasing energy, so it is exothermic (NH3 formation is exothermic from N2 and H2). Endothermic reactions break bonds, thus requiring energy. I hope this helps! I thi...
by Alan Huang 1E
Fri Mar 12, 2021 7:55 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Sapling HW Week 9/10 #17
Replies: 9
Views: 55

Re: Sapling HW Week 9/10 #17

The activation energy can be described in terms of the transition state, sometimes called the activated complex, and the starting materials. Ea(forward) = Etransition − Ereactants Ea(reverse) = Etransition − Eproducts Taking the difference of the two Ea values for the forward and reverse reactions g...
by Alan Huang 1E
Fri Mar 12, 2021 7:52 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediates in overall rate law
Replies: 3
Views: 18

Re: Intermediates in overall rate law

I perhaps think that this could be the case, but to be safe if asked a question about overall rate law, I would do the pre-equilibrium method and solve for the intermediate to be safe.
by Alan Huang 1E
Fri Mar 12, 2021 7:47 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Textbook Problem 7.27 Focus Exercise
Replies: 2
Views: 17

Re: Textbook Problem 7.27 Focus Exercise

First, use the half-life of a first order reaction: t(1/2) = 0.693/k Solving for k nets us: k = 0.693/t(1/2) We are given half life of the drug, 4.5 hours, solving for k: k = 0.693/4.5 k = 0.154 hours^-1 Then use the first order integrated rate law: ln([A]t/[A]0) = -kt Solving for ([A]t/[A]0) nets u...
by Alan Huang 1E
Fri Mar 12, 2021 7:38 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Consumption of Catalyst
Replies: 2
Views: 9

Re: Consumption of Catalyst

The point of a catalyst is to speed up slow reactions, lowering its activation energy, without changing what products are made. If catalysts were consumed, the products would change and the reaction would no longer be the same as you are trying to speed up. A catalyst, however, is used to bring a di...
by Alan Huang 1E
Fri Mar 12, 2021 7:33 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: A (pre-exponential factor)
Replies: 3
Views: 12

Re: A (pre-exponential factor)

In the Arrhenius equation k = Ae^(-Ea/RT) where we will be using it most often, A is the used to describe the rate of molecular collisions that occur in the chemical reaction. Its significance mainly lies in that it is a part of the Arrhenius equation, so remember that.
by Alan Huang 1E
Fri Mar 12, 2021 7:31 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Does temperature affect A?
Replies: 9
Views: 52

Re: Does temperature affect A?

In terms of the actual equation, we see that k = Ae^(-Ea/RT)

Strictly speaking, A is slightly variable with temperature, but it is negligible.
by Alan Huang 1E
Fri Mar 12, 2021 7:24 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 4D.5
Replies: 2
Views: 19

Re: 4D.5

Using ΔU = q + w:

We find that ΔU = ΔH + w

Just plug in values of ΔH = -15 and w = 22 we get

ΔU = -15 + 22
ΔU = +7 kJ
by Alan Huang 1E
Fri Mar 12, 2021 7:21 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram Notation
Replies: 2
Views: 17

Re: Cell Diagram Notation

Molly Posta 1H wrote:From my understanding, the concentration is not included for the shorthand cell diagram. Someone please correct me if that isn't the case, though.


I believe this is the case. However, if given the concentration in the problem, I would put the concentration in the final cell diagram just in case.
by Alan Huang 1E
Fri Mar 12, 2021 7:20 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Concentration Cell
Replies: 2
Views: 12

Re: Concentration Cell

I believe it depends and it will vary because of the nature of concentration cells. Concentration cells are meant to dilute the more concentrated solution and concentrate the more dilute solution, so it doesn't matter which side, and both sides are using the same type of solution.
by Alan Huang 1E
Fri Mar 12, 2021 7:15 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Cell Potentials
Replies: 2
Views: 12

Re: Standard Cell Potentials

Your first comment was correct. You flip the sign of the anode's cell potential when you're trying to calculate standard cell potential. You do not alter the cell potential in other ways though. The only alteration you would make is flipping the anode cell potential since: Ecell = anode - cathode Wh...
by Alan Huang 1E
Fri Mar 12, 2021 7:09 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Sapling week 9&10 #16
Replies: 4
Views: 24

Re: Sapling week 9&10 #16

Equilibrium constant K is equal to k(forward)/k(reverse). In your case, k(forward) is given as 263 and k(reverse) is given as 365. So equilibrium constant K = 263/365.
by Alan Huang 1E
Fri Mar 12, 2021 7:07 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow Step
Replies: 14
Views: 84

Re: Slow Step

The slow step of a reaction is, well, the slowest part of a reaction. As most chemical reactions don't occur in one motion, there are several stages that a reaction goes through. The slow step is the step that takes the longest time in a reaction. It is the rate determining step and can be compared ...
by Alan Huang 1E
Fri Mar 12, 2021 7:04 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 2nd order reaction
Replies: 2
Views: 15

Re: 2nd order reaction

It means that the reaction depends on the concentrations of two reactants or one that is squared. It takes the form rate = k[A][B] or rate = k[A]^2 and the rate is directly proportional.
by Alan Huang 1E
Fri Mar 12, 2021 5:49 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Integrated rate laws
Replies: 4
Views: 19

Re: Integrated rate laws

How do you know which one you are looking to solve for? Will it just specifically say it, or is there also some other indicator? I would guess that in general, if they're asking for a reaction and are giving you specific variables, you would use Integrated Rate Laws. You would write a rate law for ...
by Alan Huang 1E
Fri Mar 12, 2021 5:39 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediates
Replies: 6
Views: 16

Re: Intermediates

Yes, that is correct. Intermediates are always consumed and thus are never written in a rate law apart from individual steps. Even in those individual steps though, however, if an intermediate is present in your rate law, you are expected to use the pre-equilibrium approach to solve for the intermed...
by Alan Huang 1E
Sun Mar 07, 2021 11:41 pm
Forum: Zero Order Reactions
Topic: Sapling Question
Replies: 9
Views: 70

Re: Sapling Question

In this problem, we found the orders of C by comparing reactions in which A and B were held constant while C changed. Comparing experiments 1 and 4 which fulfilled these requirements found that while the concentration of C changed, the initial rate did not. This means that changing the concentration...
by Alan Huang 1E
Sun Mar 07, 2021 11:08 pm
Forum: General Rate Laws
Topic: Sapling #7
Replies: 3
Views: 33

Re: Sapling #7

As others have stated, the steps are to: First, compare the different reactions where the molarities of some reactants are held constant while one changes. Compare how the reactant changes to how the molarity changes, and from there determine the order of each of the reactants. This will get you mos...
by Alan Huang 1E
Sun Mar 07, 2021 10:59 pm
Forum: General Rate Laws
Topic: The value, 0.693
Replies: 4
Views: 23

Re: The value, 0.693

Sara_Lim_2C wrote:It's from the 1st order half life equation, t1/2=0.693/k; The derivation is in Lecture 23 if you're curious :D


This is correct! The 0.693 is also written as ln(2).
by Alan Huang 1E
Sun Mar 07, 2021 10:39 pm
Forum: Balancing Redox Reactions
Topic: How to Determine if a Reaction is in Basic or Acidic Solution?
Replies: 41
Views: 121

Re: How to Determine if a Reaction is in Basic or Acidic Solution?

As others have stated, I think it would be part of the question and given.
by Alan Huang 1E
Sun Mar 07, 2021 10:39 pm
Forum: Balancing Redox Reactions
Topic: Oxidation Numbers
Replies: 13
Views: 90

Re: Oxidation Numbers

As others have stated, there are some general rules to remember that are beneficial. Namely: The oxidation number of a free element is always 0. The atoms in He and N2, for example, have oxidation numbers of 0. The oxidation number of a monatomic ion equals the charge of the ion. For example, the ox...
by Alan Huang 1E
Sun Feb 28, 2021 9:49 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Reaction Potentials
Replies: 3
Views: 17

Re: Standard Reaction Potentials

I've also heard that it's because it's an intensive property. In other words, it doesn't depend on how many times the reaction occurs, therefore multiplication of the elements in the equation doesn't affect the potential.
by Alan Huang 1E
Sun Feb 28, 2021 9:34 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: sapling no. 9
Replies: 1
Views: 13

Re: sapling no. 9

The overall reaction in a Galvanic cell is spontaneous, meaning that Ecell is positive. Therefore, the half-reaction with the higher reduction potential occurs at the cathode.
by Alan Huang 1E
Sun Feb 28, 2021 9:31 pm
Forum: Balancing Redox Reactions
Topic: Balancing Reactions
Replies: 22
Views: 97

Re: Balancing Reactions

As others have said, the order of the elements does not matter as long as they are on the correct side of the equation and the coefficients are correct as well.
by Alan Huang 1E
Sun Feb 28, 2021 9:27 pm
Forum: Balancing Redox Reactions
Topic: Determining Phases
Replies: 28
Views: 100

Re: Determining Phases

As others have said, I mainly just look at the original equation given and use the phases from there. For other places, I've found that H+ and OH- are aqueous while the H2O added in is a liquid.
by Alan Huang 1E
Sun Feb 28, 2021 9:25 pm
Forum: Balancing Redox Reactions
Topic: Sapling Glitch
Replies: 2
Views: 34

Re: Sapling Glitch

Yes, this happens to me as well.
by Alan Huang 1E
Mon Feb 15, 2021 12:38 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: rearranging equation
Replies: 3
Views: 13

Re: rearranging equation

Maybe just moving them one at a time might help. It might take a little longer but as long as you can keep track of each individual piece, it should be helpful.
by Alan Huang 1E
Mon Feb 15, 2021 12:36 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Textbook Problem 4.37
Replies: 1
Views: 7

Re: Textbook Problem 4.37

"Under what conditions, if any, does the sign of each of the following quantities provide a criterion for assessing the spontaneity of a reaction? (a) Δ G ° (b) Δ H ° (c) Δ S ° (d) Δ S tot" The answer manual says that for part d, the reaction is spontaneous when delta S (total)>0. How did...
by Alan Huang 1E
Mon Feb 15, 2021 12:31 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Sampling #19
Replies: 2
Views: 17

Re: Sampling #19

I'm not really sure where to start to solve this problem? Any help would be greatly appreciated! For a gaseous reaction, standard conditions are 298 K and a partial pressure of 1 bar for all species. For the reaction N2(g)+3H2(g)↽−−⇀2NH3(g) the standard change in Gibbs free energy is ΔG∘=−69.0 kJ/m...
by Alan Huang 1E
Mon Feb 15, 2021 12:25 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Meaning of K
Replies: 55
Views: 171

Re: Meaning of K

In most problems I think the K would be for Kelvin. However, if the problems ask for an equilibrium constant than K could be that as well. It depends on context so it could be case-by-case.
by Alan Huang 1E
Sun Feb 14, 2021 9:51 pm
Forum: Calculating Work of Expansion
Topic: Sapling #18
Replies: 8
Views: 125

Re: Sapling #18

The way to solve for ΔU also depends on the molar specific heat of the gas. For q, you use the constant-pressure molar specific heat, which you are given as 4R. However, the equation for ΔU is ΔU = nCvΔT The ΔU equation requires the constant-volume molar specific heat. So how are constant-pressure ...
by Alan Huang 1E
Sat Feb 06, 2021 11:58 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: relation between Cv and Cp
Replies: 4
Views: 34

Re: relation between Cv and Cp

"For an ideal gas at constant pressure, it takes more heat to achieve the same temperature change than it does at constant volume. At constant volume all the heat added goes into raising the temperature. At constant pressure some of the heat goes to doing work." This is the explanation I r...
by Alan Huang 1E
Sat Feb 06, 2021 11:56 pm
Forum: Calculating Work of Expansion
Topic: Sapling #14
Replies: 5
Views: 55

Re: Sapling #14

The equation for reversible expansion would be w = nRTln(V2/V1)

Alternatively you could use w = -2.303nRTlog(V2/V1) but the two equations serve the same purpose.
by Alan Huang 1E
Sat Feb 06, 2021 11:50 pm
Forum: Calculating Work of Expansion
Topic: Sapling #18
Replies: 8
Views: 125

Re: Sapling #18

The way to solve for ΔU also depends on the molar specific heat of the gas. For q, you use the constant-pressure molar specific heat, which you are given as 4R. However, the equation for ΔU is ΔU = nCvΔT The ΔU equation requires the constant-volume molar specific heat. So how are constant-pressure m...
by Alan Huang 1E
Sat Feb 06, 2021 11:41 pm
Forum: Calculating Work of Expansion
Topic: Sapling 15
Replies: 6
Views: 59

Re: Sapling 15

The first step would find the number of moles of N2 are produced: You are given grams of NaN3, so simple stoichiometry gives us number of N2 moles. Next, using the moles of N2, find the volume using the Ideal Gas Law PV = nRT. This would equate to V = nRT/P Plugging in values would give us: V = (mol...
by Alan Huang 1E
Sat Feb 06, 2021 11:36 pm
Forum: Calculating Work of Expansion
Topic: Sapling #15n W3+4
Replies: 10
Views: 57

Re: Sapling #15n W3+4

Yes, you would use the volume you found in the Ideal Gas Law in the work function.

You can use this volume because, in this problem, it is assumed that the volume of the solid reactant was negligible.
by Alan Huang 1E
Mon Jan 25, 2021 12:55 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Determining whether a reaction is Exothermic/Endothermic
Replies: 4
Views: 50

Re: Determining whether a reaction is Exothermic/Endothermic

In general, a strong bond to a weak bond is endothermic, while a weak bond to a strong bond is exothermic.
by Alan Huang 1E
Mon Jan 25, 2021 12:34 am
Forum: Ideal Gases
Topic: pv=nRT
Replies: 16
Views: 80

Re: pv=nRT

Speaking of which, how exactly would PV = nRT be used to convert from molarity to pressure?

Would the equation P/RT = n/V be correct?
by Alan Huang 1E
Sun Jan 24, 2021 11:47 pm
Forum: Phase Changes & Related Calculations
Topic: Textbook 4A.1 systems
Replies: 2
Views: 14

Re: Textbook 4A.1 systems

A bomb calorimeter is an isolated system since the burning of the benzene does not affect the surrounding water and has no contact with it. The gasoline burning would be a closed system since the explosion is contained in the cylinder but heat energy is still able to transfer through the metal wall...
by Alan Huang 1E
Sun Jan 24, 2021 11:26 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Sapling Question 6
Replies: 2
Views: 22

Re: Sapling Question 6

The answer is D because of your reasoning.

The entire equation, because it has CH4 reacting with O2 to form CO2 and H20, is a combustion reaction. Since CH4 is the one reacting with O2, finding enthalpy would be finding the enthalpy of combustion for CH4.
by Alan Huang 1E
Sun Jan 24, 2021 11:04 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Sapling #4
Replies: 3
Views: 49

Re: Sapling #4

You should look at whether the bonds are going from strong to weak or weak to strong.

In endothermic reactions, the reaction proceeds from strong bonds to weak bonds.
In exothermic reactions, the reaction proceeds from compounds with weak bonds to strong bonds.
by Alan Huang 1E
Sun Jan 17, 2021 7:36 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: 5% rule
Replies: 5
Views: 52

Re: 5% rule

In Lavelle's lectures, he mentions that you can only assume x is small enough if K < 10^-3.
by Alan Huang 1E
Sun Jan 17, 2021 7:34 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: % Ionization vs Checking Assumption Equation
Replies: 2
Views: 19

Re: % Ionization vs Checking Assumption Equation

How you calculate % ionization depends on the assumption. If your assumption is under 5%, it means your assumption is valid and you can consider subtracting x as negligent. However, if your assumption is over 5%, it means your assumption is invalid and must use the quadratic formula to calculate % i...
by Alan Huang 1E
Sun Jan 17, 2021 7:14 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: % Ionization and % Protonation
Replies: 11
Views: 83

Re: % Ionization and % Protonation

Alexis Sanft 1E wrote:
Shreya Patel- 2D wrote:What's the difference between protonation and ionization then?

Does anyone know if we are supposed to have already learned this and if there will be questions on this on the exam?


I think protonation and ionization are synonymous?
by Alan Huang 1E
Sun Jan 17, 2021 7:08 pm
Forum: Ideal Gases
Topic: R Value
Replies: 17
Views: 114

Re: R Value

I also agree with the above answers. Last quarter in 14A, Lavelle gave us a sheet with all the formulas we may or may not have needed, so don't sweat it :)
by Alan Huang 1E
Mon Jan 11, 2021 12:55 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Partial Pressure on the Same Side of a Rxn
Replies: 5
Views: 50

Re: Partial Pressure on the Same Side of a Rxn

Yes, changing the concentrations or partial pressures of any reactant/product will affect all other compounds in a reaction. For example, in the equation: N2 + 3H2 <--> 2NH3 An increase in N2 would tip the reaction towards the reactants. As a result, to balance the reaction, there will be a decrease...
by Alan Huang 1E
Mon Jan 11, 2021 12:50 am
Forum: Ideal Gases
Topic: Kp to Kc
Replies: 6
Views: 58

Re: Kp to Kc

You can make these conversions with PV = nRT, and it is likely one of the most simple but effective ways to do so.
by Alan Huang 1E
Mon Jan 11, 2021 12:49 am
Forum: Ideal Gases
Topic: Ice method
Replies: 14
Views: 78

Re: Ice method

Using ICE as a method is a bit more involved than what explanation allows, but a brief overview is what follows. ICE is an acronym standing for Initial, Change, and Equilibrium. When given a chemical equation and their initial concentrations, you can input their initial concentrations into Initial a...
by Alan Huang 1E
Sun Jan 10, 2021 10:48 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Textbook 5J #5 Part D?
Replies: 6
Views: 60

Textbook 5J #5 Part D?

Hi, I understand the rest of the problems other than part D. The equation reads: 2HD (g) + H2 (g) <--> D2 (g) Now according to the problem, there is an increase in pressure. As a result, according to Le Chatelier's Principle, the reaction should proceed to the side with fewer moles of gas. By this d...
by Alan Huang 1E
Sun Jan 10, 2021 4:10 pm
Forum: Ideal Gases
Topic: Sapling Homework
Replies: 22
Views: 228

Re: Sapling Homework

I believe that if you bought the recommended textbook from Chem 14A, the credits will transfer over and you can use your $72 credits to enroll in Chem 14B at no extra cost. That's what I did.
by Alan Huang 1E
Mon Dec 07, 2020 12:07 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Textbook Question 2E.13 (I3-)
Replies: 2
Views: 13

Re: Textbook Question 2E.13 (I3-)

I3- is linear when you look at the lewis structure of I3- The central I atom has two bonded pairs of electrons with the two other I atoms and 3 lone pairs. This formation of 2 bonded pairs + 3 lone pairs is a linear molecular structure with 180 degree bond angles. Theoretically, for the three lone p...
by Alan Huang 1E
Sun Dec 06, 2020 11:46 pm
Forum: Hybridization
Topic: Pi bonds Hybridization
Replies: 2
Views: 24

Re: Pi bonds Hybridization

I'm unsure what you mean. Pi bonds and hybridization overlap.

As an example: Let's assume one pi bond in a molecule. That still only counts as one bond for hybridization. So, it would be s
by Alan Huang 1E
Sun Dec 06, 2020 11:09 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: Vapor pressure
Replies: 3
Views: 61

Re: Vapor pressure

I think what we need to remember is that weak intermolecular forces produce higher vapor pressures and strong forces produce lower vapor pressures.
by Alan Huang 1E
Sun Dec 06, 2020 10:41 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Polarity
Replies: 7
Views: 48

Re: Polarity

Yes.

Polarity of a molecule depends entirely on its shape: there could be polar bonds within the molecule, but if they cancel each other out, then the molecule won't be polar.
by Alan Huang 1E
Sun Dec 06, 2020 10:35 pm
Forum: Significant Figures
Topic: When should I start looking at sig figs?
Replies: 31
Views: 329

Re: When should I start looking at sig figs?

Like others in this thread have said, it's usually best to focus on sig figs once you have your final answer such that your answer is most precise.
by Alan Huang 1E
Sun Dec 06, 2020 10:24 pm
Forum: Identifying Acidic & Basic Salts
Topic: Salt as a Base
Replies: 4
Views: 37

Re: Salt as a Base

I think it depends on whether the salt is acidic or basic as well. If it's acidic then the compound would be as well, and vice versa.
by Alan Huang 1E
Sun Dec 06, 2020 10:19 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Calculating pH or pOH for Strong & Weak Acids & Bases
Replies: 2
Views: 29

Re: Calculating pH or pOH for Strong & Weak Acids & Bases

7 is neutral.

0-7 describes acids with 0-1 describing strong acids.

7-14 is bases with 12-13 describing strong bases.
by Alan Huang 1E
Mon Nov 30, 2020 10:28 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 2.63 in the textbook
Replies: 1
Views: 26

2.63 in the textbook

2.63 asks to find the bond angles marked with lowercase letters in the molecule peroxyacetylnitrate I understand both parts a and c, but fail to understand b. B asks for the bond angle between a carbon and oxygen atom with oxygen as the central atom. The solution manual says the bond angle is 109.5 ...
by Alan Huang 1E
Mon Nov 30, 2020 12:01 am
Forum: Determining Molecular Shape (VSEPR)
Topic: electronic geometry vs molecular geometry
Replies: 9
Views: 83

Re: electronic geometry vs molecular geometry

Electron geometry describes the arrangement of electron groups while molecular geometry describes the arrangement of atoms excluding lone pairs.

In essence, electron geometry includes lone pairs while molecular geometry does not.
by Alan Huang 1E
Sun Nov 29, 2020 11:59 pm
Forum: Hybridization
Topic: PBr5
Replies: 6
Views: 63

Re: PBr5

The PBr5 molecule has a Lewis Structure that has the P as the central atom with 5 single bonds connecting it to each of the 5 Br atoms.

Counting up these bonds nets you 5 total bonds for a sp3d hybridization.
S = first bond
p1 = second bond
p2 = third
p3 = fourth
d = fifth bond

sp3d
by Alan Huang 1E
Sun Nov 29, 2020 11:55 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining Type of Bond from Shape
Replies: 12
Views: 66

Re: Determining Type of Bond from Shape

You probably should draw the Lewis Structure out every time since molecular shape doesn't tell you anything about which bonds they are.
by Alan Huang 1E
Sun Nov 29, 2020 10:47 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Equatorial/ Axial Planes
Replies: 14
Views: 106

Re: Equatorial/ Axial Planes

I think the Sapling explained it very well. It's similar to the Earth with equator and its axes.

Atoms will be on the equatorial plane if they are on the sides of the molecule surrounding it and they will be on the axial planes if they are above or below I suppose.
by Alan Huang 1E
Sun Nov 29, 2020 10:05 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Resonance Structures and Molecular Shape
Replies: 3
Views: 33

Re: Resonance Structures and Molecular Shape

It's more so that resonance structures explain molecular shape of a molecule rather than the other way around. The combination of resonance structures each adds a specific part to the overall resonance hybrid and overall shape of the molecule. For example, carbonate ion CO3 2- would be predicted to ...
by Alan Huang 1E
Sun Nov 29, 2020 9:59 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: AsO43-
Replies: 9
Views: 117

Re: AsO43-

To find polarity of a molecule, you should check only electronegativity. In the case of AsO4 3-, the molecule is nonpolar when you look at the predominant resonance structure. The molecule is tetrahedral and has a dipole moment because of the difference in electronegativities between arsenic and oxy...
by Alan Huang 1E
Sun Nov 22, 2020 8:50 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 2E.11 Part B T-Shaped
Replies: 2
Views: 12

Re: 2E.11 Part B T-Shaped

Yes, I think we are expected to know about it. I also think we may have covered it in lecture as it rings a bell to me at least. Maybe in the November 20 lecture?
by Alan Huang 1E
Sun Nov 22, 2020 8:47 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Axial and Equatorial atoms
Replies: 6
Views: 38

Re: Axial and Equatorial atoms

According to Sapling, thinking about the atoms in a way similar to Earth is very helpful.

Axial atoms would be akin to Earth's axes while equatorial atoms would be similar to Earth's equator.

The difference between the atoms would be in which plane they exist in I assume.
by Alan Huang 1E
Sun Nov 22, 2020 8:44 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: determining molecular structure
Replies: 4
Views: 29

Re: determining molecular structure

I suspect chemists use some sort of spectroscopy to excite molecules? I'm not completely sure though.
by Alan Huang 1E
Sun Nov 22, 2020 8:41 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: sapling #4
Replies: 3
Views: 18

Re: sapling #4

For me at least, I memorize VSEPR shapes based on bonding and lone pairs. At this point in time I'm not sure if you can derive it.

In this case, I memorized that Square Pyramidal shape has 5 bonding pairs and 1 lone pair
by Alan Huang 1E
Sun Nov 22, 2020 8:38 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: linear shape?
Replies: 5
Views: 27

Re: linear shape?

Finding the molecular shape from a chemical formula ultimately stems from finding the product of said chemical reaction and then drawing the Lewis Structure of the molecule. From the Lewis Structure, you can analyze the bonds of the atom. A linear shape will have 2 bonding electron pairs and no lone...
by Alan Huang 1E
Fri Nov 13, 2020 7:09 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Sampling week 5/6 Q5
Replies: 3
Views: 96

Re: Sampling week 5/6 Q5

Your formal charges (FC) for N and O are correct. The only discrepancy is the lack of formal charges for C. With the equation FC = Valence electrons - ((number of paired electrons) + (number of unpaired electrons)), we get FC = 4 valence - (2 paired + 4 unpaired) = 4 - 6 = -2 So the formal charge fo...
by Alan Huang 1E
Fri Nov 13, 2020 7:05 pm
Forum: Formal Charge and Oxidation Numbers
Topic: radicals
Replies: 3
Views: 52

Re: radicals

It may be a mistake. NO2- does not have any unpaired electrons so it would not be a radical.

NO2, however, is a radical.
by Alan Huang 1E
Fri Nov 13, 2020 7:02 pm
Forum: Dipole Moments
Topic: Sapling #19
Replies: 2
Views: 32

Re: Sapling #19

In the picture, one S atom is attracted to an O atom, forming a S-O bond.

Per electronegativities, S-O is a polar bond and has a dipole moment, thus forming a dipole-dipole bond.
by Alan Huang 1E
Fri Nov 13, 2020 7:00 pm
Forum: Dipole Moments
Topic: H-Bonds
Replies: 14
Views: 150

Re: H-Bonds

Hydrogen bonding is a special type of dipole-dipole attraction between molecules and occurs with atoms with lone pairs. Hydrogen molecules can only bond to the F, O, or N elements and several examples include C5H8O2 and HF
by Alan Huang 1E
Fri Nov 13, 2020 6:57 pm
Forum: Dipole Moments
Topic: Sapling W 5/6 #17
Replies: 10
Views: 119

Re: Sapling W 5/6 #17

In general, all molecules will have London forces. The tricky part is figuring out which ones have dipoles. Dipole-dipole forces occur when electronegativities between the elements tend to be between 0.4 and 1.9, and also when such bonds aren't cancelled out. It's often beneficial to compare electro...
by Alan Huang 1E
Sun Nov 01, 2020 3:15 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: [Ar]3d14s2 vs [Ar] Ar4s23d1
Replies: 3
Views: 28

Re: [Ar]3d14s2 vs [Ar] Ar4s23d1

The energy difference between the 4s and 3d orbitals are small to the point where it varies in each instance. To put it simply, the two electrons are in 4s orbital instead of being in 3d orbital because 4s orbital has less energy than the 3d orbital in this instance. In addition, 4s orbital also giv...
by Alan Huang 1E
Sun Nov 01, 2020 3:07 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbital vs. Subshell
Replies: 13
Views: 130

Re: Orbital vs. Subshell

Subshells would be like s, p, d, f.
Orbitals depend on which subshell.
S has 1 orbital
P has 3 orbitals
D has 5 orbitals
F has 7 orbitals
by Alan Huang 1E
Sun Nov 01, 2020 2:29 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: The orbitals
Replies: 8
Views: 90

Re: The orbitals

For the s, p, d, and f orbitals, you should probably know number of orbitals. S has 1, p has 3, d has 5, f has 7.
You should probably also know number of electrons. S has 2, p has 6, d has 10, and f has 14.

2s is the 2nd shell, s orbital. 3s would be 3rd shell, s orbital.
by Alan Huang 1E
Sun Nov 01, 2020 2:24 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbital reference sheet
Replies: 4
Views: 25

Re: Orbital reference sheet

I don't think Dr. Lavelle has stated he would provide a reference sheet, so I would remember the various orbitals and whatnot.
by Alan Huang 1E
Sun Nov 01, 2020 1:49 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Sapling #24
Replies: 16
Views: 80

Re: Sapling #24

Yes, as others have said, the wave needs to look like one continuous function so there must be no breaks and stops in between the different graphs.
by Alan Huang 1E
Sun Oct 25, 2020 1:55 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Sampling 29
Replies: 3
Views: 39

Re: Sampling 29

The method you achieve this is essentially by writing in order of filling, from lowest to highest energy level, with orbital diagram organized from lowest to highest as well. S has a max of 2 electrons, and p has a max of 6 electrons. You fill up the first 2 shells first since Aluminum isn't there. ...
by Alan Huang 1E
Sun Oct 25, 2020 1:42 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Chromium and Copper
Replies: 5
Views: 60

Chromium and Copper

Why don't the electron configurations for chromium and copper not follow the standard configuration rules?
by Alan Huang 1E
Sun Oct 25, 2020 1:24 am
Forum: Quantum Numbers and The H-Atom
Topic: Sapling Question 13
Replies: 4
Views: 52

Re: Sapling Question 13

As others have already stated, this will not be on the first midterm. However, if you still want some guidance: n=3: n represents the principal quantum number or shell. n=3 means that this is the 3rd shell, and there are 18 electrons in the 3rd shell (from 3s, 3p, 3d for a total of 9 orbitals * 2 el...
by Alan Huang 1E
Sun Oct 25, 2020 1:02 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbitals
Replies: 6
Views: 94

Re: Orbitals

Hm, I'm not sure that's correct? Maybe Dr. Lavelle misspoke but when n = 2, l should be only equal to 0 or 1 since l's upper bound is l = n-1. However, I may be incorrect.
by Alan Huang 1E
Fri Oct 23, 2020 7:25 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Sapling #13
Replies: 1
Views: 39

Sapling #13

Magnetic quantum numbers are confusing me. The question asks: How many electrons in an atom could have this set of quantum numbers? n = 6, l = 3, ml = -1 I understand that it's asking for the 6th shell, 3rd orbital so f-orbital, but what does the -1 add? Furthermore, how is it 2 electrons when the f...
by Alan Huang 1E
Sun Oct 18, 2020 10:07 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron config for copper
Replies: 2
Views: 158

Re: Electron config for copper

When you add up all the electrons in 1s2 2s2 2p6 3s2 3d10 4s1 you get (2+2+6+2+10+1) = 29, the atomic number for Cu and the amount of electrons it has.

For potassium, it would just be omitting the 3d10
by Alan Huang 1E
Sun Oct 18, 2020 10:03 pm
Forum: Photoelectric Effect
Topic: Sapling Homework
Replies: 3
Views: 45

Re: Sapling Homework

For number of spectral lines, it is determined in terms of the number of possible transitions an electron can make from the n = 5 energy level. An electron in the n = 5 energy level can transition to the 4, 3, 2, and 1 energy levels, for a total of 4 unique spectral lines. The range of wavelengths i...
by Alan Huang 1E
Sun Oct 18, 2020 9:24 pm
Forum: DeBroglie Equation
Topic: Sapling 2 Question 10
Replies: 2
Views: 43

Re: Sapling 2 Question 10

You divide by Avogadro's number since molar mass is not expressed in molecules.

Your goal is to find grams for molecule

Since molar mass is grams per mole and Avogadro's number is expressed in molecules per mole, you divide molar mass by Avogadro to find grams/molecule
by Alan Huang 1E
Thu Oct 15, 2020 10:36 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Formulas
Replies: 2
Views: 42

Formulas

Hi, I saw that the formula posted here for uncertainty was

ΔpΔx ≥ h/4π

However, the solutions manual uses

ΔpΔx = (1/2)ħ

What's the difference between the two?
by Alan Huang 1E
Thu Oct 15, 2020 10:23 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Problem 1B.25
Replies: 6
Views: 85

Re: Problem 1B.25

This might be kind of a side question, but what exactly does the "minimum uncertainty" mean? Is it supposed to represent a range or like a "margin of error" of some sorts? Yes, uncertainty would mean the range of possible values within which the true value of the measurement lie...
by Alan Huang 1E
Thu Oct 08, 2020 12:35 am
Forum: Molarity, Solutions, Dilutions
Topic: Fundamentals L: #37
Replies: 5
Views: 69

Fundamentals L: #37

If someone can explain to me how to solve for this that would be appreciated!

Question:
37)

(a) How would you prepare 1.00 L of 0.50 M HNO3 (aq) from “concentrated” (16 M) HNO3(aq)?

(b) How many milliliters of 0.20 M NaOH(aq) could be neutralized by 100. mL of the diluted solution?
by Alan Huang 1E
Wed Oct 07, 2020 1:20 am
Forum: SI Units, Unit Conversions
Topic: E.9
Replies: 2
Views: 41

Re: E.9

For water molecules, you are told that Epsom salts contain magnesium sulfate heptahydrate.

Writing this out would give you MgSO4 * 7H2O

As you can see, there are 7 moles of H2O that you would then multiply by moles of MgSO4 to give you number of moles for H2O.
by Alan Huang 1E
Wed Oct 07, 2020 1:15 am
Forum: Significant Figures
Topic: Integers in calculations
Replies: 6
Views: 47

Re: Integers in calculations

Integers are exact numbers, meaning they are known with complete certainty. In the context of significant figures, exact numbers can be considered to have an infinite number of significant figures, so the number of sig figs in any exact number can be ignored. So the answer to 325 * .10101 would have...
by Alan Huang 1E
Wed Oct 07, 2020 1:08 am
Forum: SI Units, Unit Conversions
Topic: Homework Q about finding the sulfide of a metal
Replies: 2
Views: 78

Re: Homework Q about finding the sulfide of a metal

In general, sulfide would be sulfur with another metal, and you can find the sulfide of a metal by comparing charges and putting them together.
by Alan Huang 1E
Wed Oct 07, 2020 1:06 am
Forum: SI Units, Unit Conversions
Topic: E.15
Replies: 3
Views: 52

Re: E.15

In general: Sulfide would be sulfur with a charge of -2. S^-2
by Alan Huang 1E
Wed Oct 07, 2020 1:05 am
Forum: SI Units, Unit Conversions
Topic: 1.Homework 1 Problem: G5
Replies: 2
Views: 82

Re: 1.Homework 1 Problem: G5

You should double molarity in (a) because you are asked to find volume of Na, which has 2 moles.

You should NOT triple molarity in (b) because CO3 is one mole. Don't see it is 1 mole C + 3 moles O, but rather one mole of the entire CO3.
by Alan Huang 1E
Wed Oct 07, 2020 12:57 am
Forum: SI Units, Unit Conversions
Topic: Fundamental F.1
Replies: 2
Views: 81

Re: Fundamental F.1

We don't need to divide by the smallest number because we aren't finding empirical formula, in which we should dividing by smallest mole value. The molecular formula is given to us via diagram.
by Alan Huang 1E
Wed Oct 07, 2020 12:55 am
Forum: SI Units, Unit Conversions
Topic: E.23 Part B
Replies: 3
Views: 68

Re: E.23 Part B

Scientific notation is a way of writing very large or very small numbers. A number is written in scientific notation when a number between 1 and 10 is multiplied by a power of 10. Numbers smaller than 1 would be multiplied by a negative power of 10. If you aren't getting correct numbers, you should ...

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