Search found 109 matches

by Edward Tang 1k
Sat Mar 06, 2021 8:30 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: kinetics vs. thermodynamics
Replies: 22
Views: 206

Re: kinetics vs. thermodynamics

Kinetics is about how the reaction occurs and thermodynamics concerns whether the reaction is possible. A reaction that has a negative delta G but high activation energy is kinetically controlled because it is "thermodynamically possible" but the steps by which is happens take a long time ...
by Edward Tang 1k
Sat Mar 06, 2021 8:21 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: q. 5 sapling
Replies: 6
Views: 26

Re: q. 5 sapling

Since the reaction is second order with respect to B, if [B] is tripled the overall reaction rate would be multiplied by 9. So we just multiply the original rate by 1/2 and 9 to get the new rate.
by Edward Tang 1k
Sat Mar 06, 2021 8:19 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Catalyst
Replies: 9
Views: 111

Re: Catalyst

Thomas Vu 1A wrote:I know intermediates aren't allowed to be in the final rate law, but does the same go for catalysts?


I believe so. Neither the catalysts nor the intermediates would be present in the overall final reaction.
by Edward Tang 1k
Sat Mar 06, 2021 6:31 pm
Forum: Zero Order Reactions
Topic: Sapling Weeks 9/10 #7
Replies: 2
Views: 14

Re: Sapling Weeks 9/10 #7

The first thing we needed to figure out was that the reaction with respect to C is zero order. Therefore we can just ignore C and look for experiments where either only A or only B changed to figure out their respective order.
by Edward Tang 1k
Sat Mar 06, 2021 6:25 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Pseudo rate constant and rate constant
Replies: 2
Views: 21

Re: Pseudo rate constant and rate constant

Yes I believe so. We would just need to plug in m and l obtained from experimentally determined orders.
by Edward Tang 1k
Fri Feb 26, 2021 10:42 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Diamond vs. Graphite
Replies: 21
Views: 68

Re: Diamond vs. Graphite

Yup. You'll probably get diamonds the size of a grain of sand turning into graphite under standard conditions in a few billion years :)
by Edward Tang 1k
Fri Feb 26, 2021 10:36 pm
Forum: Balancing Redox Reactions
Topic: Sapling #18 for Wk 7 and 8
Replies: 3
Views: 39

Re: Sapling #18 for Wk 7 and 8

This one feels to me like balancing normal chemical equations instead of balancing redox reaction. Just set it up as Fe + O2+ H2O --> Fe2O3 3H2O and balance it as a whole instead of half reactions.
by Edward Tang 1k
Fri Feb 26, 2021 10:30 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Oxidation Rules
Replies: 3
Views: 19

Re: Oxidation Rules

I think it has to do with the fact that O is more electronegative than both Cl and K so both Cl and K each loses an electron to O when forming KClO. Halogens aren't too compliant with what we expect their oxidation numbers to be especially when they are put together with more electronegative elements.
by Edward Tang 1k
Fri Feb 26, 2021 10:09 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Sapling Week 7/8 #7 ion movement
Replies: 6
Views: 27

Re: Sapling Week 7/8 #7 ion movement

You are correct. The presence of potassium keeps the solution neutral and thus maximizing the potential without interfering with the redox reaction themselves.
by Edward Tang 1k
Mon Feb 22, 2021 8:06 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electrodes
Replies: 4
Views: 30

Re: Electrodes

Electrode is the conductor through which electrons leave or enter some place. You need a conducting solid as the electrode because you want electrons to travel from anode to the cathode. I'm not sure what would happen exactly if you had no solid electrode and just dip the conducting wire into a solu...
by Edward Tang 1k
Sun Feb 21, 2021 1:53 pm
Forum: Balancing Redox Reactions
Topic: Sapling #2
Replies: 7
Views: 41

Re: Sapling #2

Balancing electrochem half equations is basically balancing the number of electrons transferred. In In⟶In3+ we know ln is oxidized and lost 3 electrons, and in Cd2+⟶Cd we know Cd2+ is reduced and gained 2 electrons. In order to balance the two, you find the smallest common multiple for the number of...
by Edward Tang 1k
Sun Feb 21, 2021 1:44 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Conducting solid
Replies: 2
Views: 10

Re: Conducting solid

Electrons have to travel from the anode to the cathode. If the solid is not conductive, electrons won't be able to travel through it. The situation is the same if there simply isn't an electrode, which is why we use a platinum electrode.
by Edward Tang 1k
Sun Feb 21, 2021 1:42 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell doing work
Replies: 1
Views: 11

Re: Cell doing work

Galvanic cell converts chemical energy to electrical energy spontaneously, so the cell's delta G must be negative for it to operate spontaneously, and delta G is basically the energy available to do work. If a cell doesn't do work spontaneously, it wouldn't be considered a galvanic cell in the first...
by Edward Tang 1k
Sun Feb 21, 2021 1:38 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Platinum inert conductor
Replies: 3
Views: 9

Re: Platinum inert conductor

The platinum serves as a surface for the electrons to be conducted from one end to another. Without a conducting electrode it's difficult for electrons to be transferred from one side to another, because you will be dipping the wire straight into solution instead of connecting to an electrode, as in...
by Edward Tang 1k
Sat Feb 20, 2021 7:28 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Half Reaction Standard Reduction Potential
Replies: 4
Views: 16

Re: Half Reaction Standard Reduction Potential

It's most definitely going to be given to us. I don't think predicting the E nought is possible for now.
by Edward Tang 1k
Sun Feb 14, 2021 2:58 pm
Forum: General Science Questions
Topic: Sapling HW Week 5&6 Question #7
Replies: 4
Views: 47

Re: Sapling HW Week 5&6 Question #7

For calculating the molar enthalpy of vaporization you use q=nC, where n is the mole of element vaporized and C is the enthalpy of vaporization, the value we are looking for. We know what the value of q is, from the fact that a 500W heater is used for 4.02 minutes during the phase change. So q would...
by Edward Tang 1k
Sun Feb 14, 2021 2:38 pm
Forum: Administrative Questions and Class Announcements
Topic: cc update
Replies: 23
Views: 130

Re: cc update

same here mine isn't accurate either. TAs could always just check the number of posts so should be fine even if the grades aren't updated until the end of the quarter.
by Edward Tang 1k
Sun Feb 14, 2021 2:19 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Sapling HW7
Replies: 1
Views: 17

Re: Sapling HW7

I agree sapling is not being very clear here. The way I did it is that the delta S you got is for per mole, so to arrange the three liquids by their entropy you also have to multiply their S of vaporization by their corresponding number of moles. Once you do that and then list the entropy by magnitu...
by Edward Tang 1k
Sun Feb 14, 2021 1:58 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Isothermal reversible
Replies: 1
Views: 13

Re: Isothermal reversible

Reversible expansion occurs slower because its definition is that the change between internal and external pressure is small. Therefore if we wish to have a system expand a certain volume, we need to make a lot of small changes, rather than quick, l large change in pressure. Reversible expansion gen...
by Edward Tang 1k
Sun Feb 14, 2021 1:31 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Sapling 5/6 #7
Replies: 4
Views: 30

Re: Sapling 5/6 #7

For calculating the molar enthalpy of vaporization you use q=nC, where n is the mole of element vaporized and C is the enthalpy of vaporization, the value we are looking for. We know what the value of q is, from the fact that a 525W heater is used for 5.65 minutes during the phase change. So q would...
by Edward Tang 1k
Sun Feb 14, 2021 1:23 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Sapling week 5/6 #3
Replies: 11
Views: 39

Re: Sapling week 5/6 #3

You are right! liquid to gas and solid to liquid have positive values for both enthalpy and entropy because 1) you need energy to break the existing bonds, hence the positive delta H, and 2) the phase change moves to a state with higher entropy because particles in gas has more possible states than ...
by Edward Tang 1k
Sun Feb 07, 2021 5:48 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity of Calorimeter
Replies: 7
Views: 43

Re: Heat Capacity of Calorimeter

Heat capacity of a calorimeter it's the same as any other heat capacity, but without the consideration for mass. Usually we use q=mc deltaT but for calorimeter it's just q=c deltaT. Usually the question will give you the reaction that has taken place in a calorimeter and the temperature the calorime...
by Edward Tang 1k
Sun Feb 07, 2021 5:34 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: delta U
Replies: 6
Views: 19

Re: delta U

delta U of an isolated system is equal to 0 because there is no change in internal energy in a isolated system. In a closed system where no work is being done(constant volume) so delta U is just q, and q under constant volume is nCv delta T. Cv is 3/2R. So in conclusion for a closed system under con...
by Edward Tang 1k
Sun Feb 07, 2021 4:38 pm
Forum: Phase Changes & Related Calculations
Topic: Endo vs. exo & bond strenghts
Replies: 8
Views: 45

Re: Endo vs. exo & bond strenghts

I feel like depending on the magnitude of enthalpy change you can also figure out the strength of a bond. If more heat is required the break the bond, then the bond would be stronger. Or if more heat is released in the formation of a bond, it would also be stronger.
by Edward Tang 1k
Sun Feb 07, 2021 4:35 pm
Forum: Calculating Work of Expansion
Topic: Irreversible reactions?
Replies: 2
Views: 12

Re: Irreversible reactions?

Because in a reversible reaction the pressure between inside and outside are changing by small increments. Constant pressure is part of the definition of an irreversible reaction because the piston pushes against a constant final pressure, and the work being done this way is not enough to reverse th...
by Edward Tang 1k
Sun Feb 07, 2021 4:24 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Cp and Cv
Replies: 7
Views: 47

Re: Cp and Cv

For ideal gas Cp = Cv+R. Under constant pressure work is being done so Cp is larger than Cv.
by Edward Tang 1k
Sun Jan 31, 2021 9:48 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Reversible vs Irreversible
Replies: 5
Views: 66

Re: Reversible vs Irreversible

So a process is said to be reversible if you can use the same amount of work generated by the system to put it back into its initial state. When you are in an irreversible expansion, you need to put in additional work on top of what has been generated by the system to put it back into its initial s...
by Edward Tang 1k
Sat Jan 30, 2021 2:45 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Reversible Process
Replies: 2
Views: 48

Re: Reversible Process

I'm copying my answer from another post about a similar question: So a process is said to be reversible if you can use the same amount of work generated by the system to put the system back into its initial state. When you are in an irreversible expansion, you need to put in additional work on top o...
by Edward Tang 1k
Sat Jan 30, 2021 2:42 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Effect of Kelvin Instead of Celsius
Replies: 12
Views: 50

Re: Effect of Kelvin Instead of Celsius

Well one unit celsius actually measures the same thing as one kelvin. It's just that kelvin is higher in numbers (1 celsius is 274 kelvin, 2 celsius is 275 kelvin.....) So you can virtually just substitute C for K and it wouldn't make a difference because ΔT is the same regardless if you measure in ...
by Edward Tang 1k
Sat Jan 30, 2021 2:35 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Clarification on Heat Required Equation
Replies: 1
Views: 18

Re: Clarification on Heat Required Equation

I'd think it depends on the units for the specific heat (C) that we are given in. If we are given molar specific heat, then we have to find the amount of particles in moles, meaning that if the problem gives us grams of something we have to find the n in moles. If we are given just the specific heat...
by Edward Tang 1k
Sat Jan 30, 2021 2:26 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heating a Gas @ Constant P vs V
Replies: 3
Views: 25

Re: Heating a Gas @ Constant P vs V

The simple answer is no you can't use mCΔT for heating gas at constant volume b/c mCΔT is derived from the work equation(F*Δd or P*A*Δd or P*ΔV), which assumes constant pressure and changing volume. If you wish to derive an equation for constant volume, you will have to incorporate it with the ideal...
by Edward Tang 1k
Sat Jan 30, 2021 2:05 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Reversible vs Irreversible
Replies: 5
Views: 66

Re: Reversible vs Irreversible

So a process is said to be reversible if you can use the same amount of work generated by the system to put it back into its initial state. When you are in an irreversible expansion, you need to put in additional work on top of what has been generated by the system to put it back into its initial st...
by Edward Tang 1k
Sun Jan 24, 2021 3:19 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Overall reaction equation
Replies: 1
Views: 13

Re: Overall reaction equation

Since enthalpy is a state function and you only need to know the sign of the enthalpy before adding them it's easier to just consider the direction of reaction and the sign of the enthalpy. I usually just take note of which reactants and products are needed, and work to cancel out the intermediates....
by Edward Tang 1k
Sun Jan 24, 2021 3:00 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy Value for Reverse Direction
Replies: 3
Views: 10

Re: Enthalpy Value for Reverse Direction

This would just change the sign. Say if H2 -- 2H has an enthalpy of -10kj, 2H -- H2 would have an enthalpy of 10kj.
by Edward Tang 1k
Sun Jan 24, 2021 2:58 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Textbook Q 5I.13
Replies: 4
Views: 14

Re: Textbook Q 5I.13

Chemicals react to achieve chemical, or thermodynamical, stability. For example, two individual Cl atoms are at a higher energy state than one Cl2 atom, meaning that the two Cl would combine to form Cl2 and release the excess energy. As we can see from table 5g.2, under the same temperature, the K f...
by Edward Tang 1k
Sun Jan 24, 2021 2:38 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Sapling #6
Replies: 4
Views: 25

Re: Sapling #6

I think the previous answer addressed your question really well. As a repeat for your second question, the difference between the two is that the enthalpy of formation requires the reactants to be in their standard states: n2 gas, o2 gas, h2 gas, carbon graphite, Br2 liquid, and I2 solid, to name a ...
by Edward Tang 1k
Sun Jan 24, 2021 2:30 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law
Replies: 58
Views: 196

Re: Hess's Law

It basically just says that enthalpy are state functions and therefore are additive
by Edward Tang 1k
Sat Jan 16, 2021 7:12 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Finding Equilibrium Concentrations
Replies: 5
Views: 45

Re: Finding Equilibrium Concentrations

If everything is nonzero then first you probably have to determine is Q greater than or less than K. If Q is greater than K, you've gone over the equilibrium concentration and will need more of the reverse reaction. So your X for reactants would be positive and for products would be negative. If Q i...
by Edward Tang 1k
Sat Jan 16, 2021 7:06 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE box for partial pressures
Replies: 10
Views: 47

Re: ICE box for partial pressures

I believe it would be the same, since there is no difference in the fact that there are initial, change, and final values and an equilibrium expression. You'll still be setting up the same quadratic equation and solving for the change.
by Edward Tang 1k
Sat Jan 16, 2021 7:03 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatelier's Principle with Temperature
Replies: 7
Views: 27

Re: Le Chatelier's Principle with Temperature

Your question about why exothermic has negative enthalpy and endothermic has positive enthalpy should be explained the moment we begin thermochem, which is next week, and I'm afraid I might teach it wrong. But the rough idea is that the release of energy marks an exothermic reaction, where there has...
by Edward Tang 1k
Sat Jan 16, 2021 6:33 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Week 1 Sapling #5
Replies: 2
Views: 53

Re: Week 1 Sapling #5

I'm not sure what you mean by "concept" since the question is basically math but I'll try to explain. By looking at the four chemical expression we are given in the question we can find out that the only way to get the products and reactants we want is by combining three times the first ex...
by Edward Tang 1k
Sat Jan 16, 2021 6:09 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Using the ICE table
Replies: 36
Views: 146

Re: Using the ICE table

Yes. The ice table is just a method for solving anything that has a initial amount, final amount, and change, which would certainly include pressure.
by Edward Tang 1k
Sun Jan 10, 2021 10:28 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook Problem 5.39
Replies: 6
Views: 79

Re: Textbook Problem 5.39

Dr.Lavelle has updated the document solution manual errors. I've copied the part pertaining to this question below:

Table 5G.2 in the textbook has an error.
For the reaction N2O4 ⇌ 2NO2 at 298 K, the Kc value is 6.1 x 10-3
by Edward Tang 1k
Sun Jan 10, 2021 4:25 pm
Forum: Ideal Gases
Topic: inert gas and pressure changes
Replies: 9
Views: 39

Re: inert gas and pressure changes

With pv=nRT we know that the only things that would change the partial pressure of a gas are if its number of moles change or the volume changes, given that temperature is constant. Adding an inert gas does neither of those things, therefore it only changes the total pressure but not the partial pre...
by Edward Tang 1k
Sun Jan 10, 2021 4:19 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Changing Temperature Effect on K
Replies: 5
Views: 21

Re: Changing Temperature Effect on K

I usually think of this in terms of le chatelier's principle, which states that chemical reactions adjust to minimize the any changes. When you increase temperature, the system would try to balance that out by decreasing temperature. If the reaction is endothermic, the product side would be favored ...
by Edward Tang 1k
Sun Jan 10, 2021 4:11 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 2 Solutions to Quadratic Equations
Replies: 5
Views: 46

Re: 2 Solutions to Quadratic Equations

There are two ways to tackle the issue of getting two positive numbers when solving a quadratic. First one is more mathematically complicated and sometimes impossible to do if the numbers aren't too nice. When you set up the question I believe you got something like (X^2)/((0.1-X)^2)=23.2, with X re...
by Edward Tang 1k
Sun Jan 10, 2021 3:56 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Adding Inert Gases
Replies: 3
Views: 15

Re: Adding Inert Gases

Correct. With pv=nRT we know that the only things that would change the partial pressure of a gas are if its number of moles change or the volume changes, given that temperature is constant. Adding an inert gas does neither of those things, therefore it only changes the total pressure but not the pa...
by Edward Tang 1k
Sun Jan 10, 2021 3:40 pm
Forum: Student Social/Study Group
Topic: Chemistry Community
Replies: 29
Views: 141

Re: Chemistry Community

I think it's better to ask your TA. Some TA grades the posts weekly, others just check how many posts you have at the end of the quarter, in which you can make up for things.
by Edward Tang 1k
Tue Dec 15, 2020 8:19 pm
Forum: Conjugate Acids & Bases
Topic: Conjugate Acids and Bases
Replies: 5
Views: 43

Re: Conjugate Acids and Bases

When it's bronsted acid/base, they would differ by one proton. But in lewis/acid base reaction, like F- + BF3 = BF4-, no protons are involved so it's a bit hard to use that as guideline. Usually the conjugate pair would look very similar in chemistry so you just need to figure out which one is the a...
by Edward Tang 1k
Tue Dec 15, 2020 8:11 pm
Forum: Polyprotic Acids & Bases
Topic: Definition of Monoprotic
Replies: 4
Views: 53

Re: Definition of Monoprotic

monoprotic just means the acid has one donatable proton, for example HNO3. Whereas polyprotic would have more than 1 proton like H2SO4.
by Edward Tang 1k
Tue Dec 15, 2020 8:10 pm
Forum: Amphoteric Compounds
Topic: Amphoteric vs Amphiprotic
Replies: 7
Views: 51

Re: Amphoteric vs Amphiprotic

As said above, amphiprotic is about being both protons donors and acceptors and amphoteric is about being both and acid and a base. If we are discussion bronsted acid/base, these two words would p much mean the same thing with amphiprotic describing the nature and amphoteric being a classification. ...
by Edward Tang 1k
Tue Dec 15, 2020 8:05 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Bond Angles
Replies: 8
Views: 116

Re: Bond Angles

What I learned in ap chem in hs is that each lone pair reduces the bond angle by 2.5. So one lone pair in tetrahedral would make the bond go from 109.5 to 107, which is p close to 106.
by Edward Tang 1k
Sat Dec 12, 2020 3:24 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: Textbook 3f 5
Replies: 6
Views: 64

Re: Textbook 3f 5

Hi! I was wondering why size trumps difference in electronegativity. Is a difference in electronegativity less impactful than a difference in size, even if dipole-dipole interactions are stronger than LDF interactions? I don't know if that makes sense; I am a little confused. Thanks! This is becaus...
by Edward Tang 1k
Sat Dec 12, 2020 2:59 pm
Forum: Lewis Acids & Bases
Topic: Textbook Question 6.5
Replies: 2
Views: 19

Re: Textbook Question 6.5

This is an explanation from students from previous years and it made some sense to me. https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=38779 Basically the students said that H2O2 binds to SO3 like two OH- instead of what the textbook seems to suggest (H and OOH). Since H2O2 has a total of 7 pair...
by Edward Tang 1k
Fri Dec 11, 2020 11:17 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: H20
Replies: 6
Views: 71

Re: H20

The two lone pairs are too close for both to bond and be stable. Usually bidentate ligands have electron lone pairs that are far away and point to the same direction.
by Edward Tang 1k
Fri Dec 11, 2020 10:59 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: Textbook 3f 5
Replies: 6
Views: 64

Re: Textbook 3f 5

Hi! I was wondering why size trumps difference in electronegativity. Is a difference in electronegativity less impactful than a difference in size, even if dipole-dipole interactions are stronger than LDF interactions? I don't know if that makes sense; I am a little confused. Thanks! This is becaus...
by Edward Tang 1k
Fri Dec 11, 2020 10:54 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 6B.5
Replies: 1
Views: 15

Re: 6B.5

If you are talking about part C, it's because Ba(OH)2 would carry 2 moles of OH- molecules for each 1 mole itself. So 0.0092M would give you 0.0184 M of OH-.
by Edward Tang 1k
Fri Dec 11, 2020 10:51 pm
Forum: Hybridization
Topic: AsF³ Hybridization
Replies: 6
Views: 94

Re: AsF³ Hybridization

Is this in the textbook? If so it might be a typo b/c AsF3 is sp3 hybridized.
by Edward Tang 1k
Fri Dec 11, 2020 10:42 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bent vs Angular
Replies: 20
Views: 144

Re: Bent vs Angular

NO2- vsepr shape would be bent, and I believe angular just means the same thing.
by Edward Tang 1k
Sun Dec 06, 2020 9:58 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Prefixes
Replies: 9
Views: 79

Re: Prefixes

I'd say there are a few you definitely need to know: di, tri, tetra, penta, hexa, because these are the common number of ligands we'll get in our questions and the extra ones (bis, tris, tetrakis, pentakis, hexakis) are just built on top of that. If you are talking about prefixes as in the nomenclat...
by Edward Tang 1k
Sun Dec 06, 2020 9:50 pm
Forum: Naming
Topic: Steps for Naming Coordination Compounds
Replies: 9
Views: 94

Re: Steps for Naming Coordination Compounds

I'll just walk through my process on your example here 1. Name the cation: in this case it's the complex 2. When naming complexes, ligands go first, so 6 ammonia would give us "hexa(a)mmine." There aren't other ligands in this case but if so they are named alphabetically. 3. After the liga...
by Edward Tang 1k
Sun Dec 06, 2020 9:22 pm
Forum: Bronsted Acids & Bases
Topic: Sulphurous acid
Replies: 1
Views: 13

Re: Sulphurous acid

in my understanding, sulfurous acid would be stronger because S is a stronger electron-pulling atom than C in carbonic acid, so the electron density shifts away from the H and weakens the O-H bonds
by Edward Tang 1k
Sun Dec 06, 2020 9:13 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Textbook 2E15B
Replies: 3
Views: 28

Re: Textbook 2E15B

They are pretty close to 90 and 120 so saying approximately is pretty much equivalent to saying less than
by Edward Tang 1k
Sat Dec 05, 2020 8:20 pm
Forum: Lewis Acids & Bases
Topic: How do you tell if something is a strong base?
Replies: 3
Views: 25

Re: How do you tell if something is a strong base?

Group 1 metal hydroxide is a strong base because the bonds between the hydroxide and metal is weak(as said above, big difference in electronegativity), therefore they dissociate in water and release hydroxides which are strong proton acceptors. Group 1/2 metal oxides work in a similar fashion, excep...
by Edward Tang 1k
Sun Nov 29, 2020 9:17 pm
Forum: Hybridization
Topic: Determining Hybridization
Replies: 3
Views: 52

Re: Determining Hybridization

The other way around, I think. The number of hybridized orbitals determine the number of regions of electron density. Each hybridized orbital would form a sigma bond or a lone pair, resulting in a new region of electron density. But basically, you're right. And I might be wrong here in whether orbit...
by Edward Tang 1k
Sun Nov 29, 2020 9:08 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Polar
Replies: 10
Views: 93

Re: Polar

Lone-pairs play a huge role but they aren't the only factor. In fact, lone pairs play a role only because the VSEPR shape accounts for them when deciding the number of regions of electron density. Being a polar molecule means that there is an overall separation of charge, and such separation are cau...
by Edward Tang 1k
Sun Nov 29, 2020 8:46 pm
Forum: Hybridization
Topic: 2F.15 Question
Replies: 3
Views: 32

Re: 2F.15 Question

As the name suggests, "s character" refers to the percent characteristic of the s orbitals. The stronger the s character of a hybridized orbital, the more similar to an ordinary s orbital it and its electrons behave. So an sp hybridized orbital would have 50% s character, sp3 would have 25...
by Edward Tang 1k
Sun Nov 29, 2020 8:35 pm
Forum: Sigma & Pi Bonds
Topic: Pi vs Delocalized Pi Bonds
Replies: 3
Views: 30

Re: Pi vs Delocalized Pi Bonds

Delocalized pi bonds occur in structures with resonances. Usually pi bonds occurs between 2 unhybridized side-by-side p orbitals. Being delocalized just means the electrons can occupy more than 2 of the plausible pairs of side-by-side p orbitals.
by Edward Tang 1k
Tue Nov 24, 2020 11:59 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Polar Bonds vs. Polar Molecules
Replies: 4
Views: 52

Re: Polar Bonds vs. Polar Molecules

Polarity is created by dipole moments, or a separation of charge as a result of difference in electronegativity in a bond. Having polar bonds doesn't mean the molecule is overall polar, but to be a polar molecule there has to be at least one polar bond. For example, H2, O2, N2, are all nonpolar mole...
by Edward Tang 1k
Sun Nov 22, 2020 3:32 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angle of Molecule
Replies: 7
Views: 42

Re: Bond Angle of Molecule

Well 104.5 is "approximately or slightly less than 109.5" so you're correct in your answer. I believe answers for bond angles are always accepted with in a range of possible angles unless it's for obvious ones like 90, 109.5, 120, or 180.
by Edward Tang 1k
Sun Nov 22, 2020 3:20 pm
Forum: Sigma & Pi Bonds
Topic: Sigma and pi
Replies: 3
Views: 24

Re: Sigma and pi

There are other types of bonds like delta bond which involves two d orbitals overlapping in the formation of a quadruple bond, but I feel like that's beyond the scope of this course so don't worry about it.
by Edward Tang 1k
Sun Nov 22, 2020 1:25 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Tetrahedral vs. Square Planar
Replies: 4
Views: 39

Re: Tetrahedral vs. Square Planar

The thing with vsepr is you can't be looking at the atoms alone. It's the number of electron densities that decide, which means you must include the lone pairs when considering the possible vsepr shapes (although in the end you only look at the bonding regions to determine the actual shape). If the ...
by Edward Tang 1k
Sun Nov 22, 2020 1:15 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Shape Polarity
Replies: 3
Views: 29

Re: Molecular Shape Polarity

While most shapes can be either polar or nonpolar, there are shapes that are always one or the other. Ones that are three dimensional and have one lone pair, for example trigonal pyramidal and square pyramidal, are always polar, because there is no dipole moment to cancel out the axial dipole moment...
by Edward Tang 1k
Sat Nov 21, 2020 7:47 pm
Forum: Hybridization
Topic: Resonance Structures and Sigma & Pi Bonds
Replies: 6
Views: 66

Re: Resonance Structures and Sigma & Pi Bonds

Resonance indicates the presence of delocalized electrons, which are, in fact, the pi bonds. The pi bonds in resonances structures are delocalized and travels between different pairs of two atoms. So to answer your question, yes there are pi and sigma bonds in molecules with resonances.
by Edward Tang 1k
Sat Nov 14, 2020 6:11 pm
Forum: Resonance Structures
Topic: bond length
Replies: 37
Views: 197

Re: bond length

Agree with what is said above^. Maybe sometimes in resonance structures we will be asked to find the actual bond length when there are say two double bonds and one single bond that can be in any place of the three bonds, in that case we just find the average of all the bond lengths. I'm not sure why...
by Edward Tang 1k
Sat Nov 14, 2020 6:04 pm
Forum: Lewis Structures
Topic: Minimizing formal charges
Replies: 3
Views: 33

Re: Minimizing formal charges

So usually the central atom is has the lowest ionization energy, in other words the least electronegative atom (Cl in ClO4 -, N in NO3 -, P in PO4 3-, for example). When minimizing formal charges, you want more atoms to have a formal charge of zero. You can alter the charge by replacing lone pairs w...
by Edward Tang 1k
Sat Nov 14, 2020 1:22 pm
Forum: Resonance Structures
Topic: Finding The Most Plausible Resonance Structure
Replies: 3
Views: 42

Re: Finding The Most Plausible Resonance Structure

I struggled a while with this one too and had to make some educated guesses. For formal charge you are looking for the ones with the lowest number of atoms with non-zero formal charge, so C and D because they only have a minus one on one of their atoms. I put D as wrong first because I didn't think ...
by Edward Tang 1k
Sat Nov 14, 2020 12:54 pm
Forum: Resonance Structures
Topic: Resonance Structures for HCNO
Replies: 2
Views: 29

Re: Resonance Structures for HCNO

Could you tell me where you are seeing this problem? On sapling I think the question about HCNO only asked us to indicate the formal charges on each atom in the resonance structure provided. If you do need to draw the resonance structure for some reason, HCNO's lewis structure would appear linear, a...
by Edward Tang 1k
Fri Nov 13, 2020 7:47 pm
Forum: Ionic & Covalent Bonds
Topic: Orbitals
Replies: 3
Views: 32

Re: Orbitals

schrodinger's equation gives the wave function that describes the states of a quantum mechanical system. It relates to orbitals in that once you square the function, the wave function represent the probability of finding an electron at a giving position. At a peak of the wave function there is a hig...
by Edward Tang 1k
Sat Nov 07, 2020 5:03 pm
Forum: Resonance Structures
Topic: Separate and Identifiable Bonds
Replies: 2
Views: 23

Re: Separate and Identifiable Bonds

You are right. I think of it as resonance structure gives rise to delocalized electrons which makes the molecule more stable by creating more space for the electrons, rather than the other way around (less stability means no resonance) because instability can be due to a lot of things other than res...
by Edward Tang 1k
Sat Nov 07, 2020 4:56 pm
Forum: Octet Exceptions
Topic: Why do Octet Excpetions Happen?
Replies: 4
Views: 66

Re: Why do Octet Excpetions Happen?

There might be other types of exceptions but the two main ones we've seen so far are electron deficiency and expanded octets. Electron deficiency happens with any element that have less than 4 valence electrons, like Li, Be, B. They cannot form an octet because even if they share all their electrons...
by Edward Tang 1k
Sat Nov 07, 2020 4:40 pm
Forum: Lewis Structures
Topic: Lewis Base (NH3)
Replies: 3
Views: 19

Re: Lewis Base (NH3)

In the lewis structure of NH3, you can see that after completing its octet, the nitrogen will have three N-H single bonds and one long pair. That lone pair can then be donated in a lewis acid base reaction to form a coordinate covalent bond. I don't believe all anions are lewis bases, but the haloge...
by Edward Tang 1k
Thu Nov 05, 2020 12:04 am
Forum: Lewis Structures
Topic: Week5/6 Sapling Q4
Replies: 2
Views: 32

Week5/6 Sapling Q4

So one of the resonance structure for CH2NO2 has the two CO single bonds, one CN double bond, and two NH single bonds. Would it be possible to switch the place of carbon and nitrogen and have two NO and two CH bonds instead of CO and NH bonds? If so would that count as another resonance structure? I...
by Edward Tang 1k
Wed Nov 04, 2020 11:45 pm
Forum: Lewis Structures
Topic: Sapling Week 5-6 Q4
Replies: 1
Views: 33

Re: Sapling Week 5-6 Q4

My understanding is that the question is asking which types of bonding does the molecules display. It tells us that the value of the bond length for CN bond (136)and CO bond (128) are between the length of the single bond and double bond. From this we know that the molecule is not displaying overwhe...
by Edward Tang 1k
Sun Nov 01, 2020 8:29 pm
Forum: DeBroglie Equation
Topic: Electron Affinity Sapling
Replies: 6
Views: 97

Re: Electron Affinity Sapling

Actually I dont think you need the wavelength equation. Just do e=(c/wavelength)*plancks to figure out the energy of the photon, convert that to eV by dividing 1.602e-19 and you're good Just making sure, we have to do the conversion because e=(c/wavelength)*plancks gives us an answer in joules, rig...
by Edward Tang 1k
Sat Oct 31, 2020 1:14 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 3d and 4s Orbital
Replies: 3
Views: 36

Re: 3d and 4s Orbital

So due to pretty complex reasons as the number of proton increases that affects the energy of the orbital series, starting at Z>20, at which point 3d would have less energy than 4s. The orbital didn't exactly CHANGE in energy as the electrons are getting filled. The moment that Z is greater than 20 ...
by Edward Tang 1k
Sat Oct 31, 2020 12:57 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Sapling weeks 2-4 #16
Replies: 4
Views: 67

Re: Sapling weeks 2-4 #16

I believe the excited electron in the 3s1 state would fall back to 2p state and fill the 2p5 orbital since the 2p series is more stable, so the ground state would be 1s2 2s2 2p5 so flourine.
by Edward Tang 1k
Sat Oct 31, 2020 12:51 pm
Forum: Properties of Electrons
Topic: Energy needed to remove an electron
Replies: 3
Views: 45

Re: Energy needed to remove an electron

I believe Erad is equal to hf and K is equal to 1/2mv^2, the left part just tells you the name of what you are calculating: Erad for energy of incoming photon(radiation) and K for kinetic energy.
by Edward Tang 1k
Fri Oct 30, 2020 9:11 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: electron configuration of x, y, and z
Replies: 2
Views: 43

Re: electron configuration of x, y, and z

x, y, z represent the axes of the orbitals the electron "occupies" in a 3D space, you can look up images of them it will be a lot clearer.
by Edward Tang 1k
Fri Oct 30, 2020 8:42 pm
Forum: DeBroglie Equation
Topic: Electron Affinity Sapling
Replies: 6
Views: 97

Re: Electron Affinity Sapling

Actually I dont think you need the wavelength equation. Just do e=(c/wavelength)*plancks to figure out the energy of the photon, convert that to eV by dividing 1.602e-19 and you're good
by Edward Tang 1k
Tue Oct 27, 2020 6:22 pm
Forum: Photoelectric Effect
Topic: Kinetic Energy vs De Broglie's wavelength equation
Replies: 2
Views: 56

Re: Kinetic Energy vs De Broglie's wavelength equation

Jordan Tatang 3L wrote:Hi! I think in short the answer to your question is that you can't use E=hv for any object with mass. That equation is for a photon which doesn't have any mass while the de broglie equation is for objects with mass and momentum.


Ok that's what im missing. That answers everything thank you so much.
by Edward Tang 1k
Tue Oct 27, 2020 6:13 pm
Forum: Photoelectric Effect
Topic: Kinetic Energy vs De Broglie's wavelength equation
Replies: 2
Views: 56

Kinetic Energy vs De Broglie's wavelength equation

The velocity of an electron that is emitted from a metallic surface by a photon is 3.6×10^3 km/s (a) What is the wavelength of the ejected electron? (b) No electrons are emitted from the surface of the metal until the frequency of the radiation reaches 2.50×10^16Hz How much energy is required to rem...
by Edward Tang 1k
Sun Oct 25, 2020 10:52 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Problem 1D.25
Replies: 1
Views: 26

Re: Problem 1D.25

4g cannot exist because the highest possible l subshell at this level is f, counting from s, p, d, f. The g shell is only possible at the n=5 level. I think for these problems you'll have to memorize the highest possible subshell for each level. Here's a rough chart but you can search these up with ...
by Edward Tang 1k
Sat Oct 24, 2020 3:49 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Sampling 30
Replies: 3
Views: 36

Re: Sampling 30

Electron configuration can be written as [Closest Noble Gas]blah blah.... For example Na could be written as [Ne]3s1, where [Ne] is used to save time for writing 1s22s22p6. So for [Ne]3s_2 3p_2, just start on the line after Ne and go down the line. 3s series two would be be Na and Mg, 3p1 would be A...
by Edward Tang 1k
Sat Oct 24, 2020 3:34 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Textbook 1D.13
Replies: 1
Views: 48

Re: Textbook 1D.13

a) I believe the number of possible l is the same as n. For n=1 you'd only have l(max)= n-1 = 0. For n=2 l=0 and l=1 so two possibilities. Therefore for n=7 I'd say there are 7 possible l quantum numbers since the l max would be 6 b)for possible ml in a subshell I think you might need to memorize th...
by Edward Tang 1k
Thu Oct 22, 2020 10:40 pm
Forum: *Shrodinger Equation
Topic: Schrodinger Equation
Replies: 3
Views: 57

Re: Schrodinger Equation

I think he said it works because the energy from the equation matches empirical data of the energy of an electron.
by Edward Tang 1k
Wed Oct 21, 2020 10:33 pm
Forum: Properties of Light
Topic: Sapling Weeks 2-4 Question 4
Replies: 3
Views: 57

Re: Sapling Weeks 2-4 Question 4

i believe 5.63e-4 cm should go into 5.63e-6 meters, other than that I don't see anything wrong.
by Edward Tang 1k
Wed Oct 21, 2020 7:24 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Week 2,3,4 Question 13
Replies: 2
Views: 46

Re: Week 2,3,4 Question 13

The equation 2n^2 gives the number of electrons in a complete energy level n. So n of 2 would give you 2*2^2=8 electrons possible, and n of 5 would give you 2*5^2 = 50 electrons For l I'm not sure since I haven't read the textbook about this but I figured since it represents the s, p, d, f, g, h... ...
by Edward Tang 1k
Wed Oct 14, 2020 11:08 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Sapling Week 2 & 3 HW Problem 5
Replies: 7
Views: 104

Re: Sapling Week 2 & 3 HW Problem 5

I understand, the question was worded quite confusingly, but once you know what it's asking it's not that hard. Number of spectral lines would be equal to the number of times the electron emits energy, and the electron would do that for each complete energy level it moves down since energy is quanti...
by Edward Tang 1k
Wed Oct 14, 2020 10:49 pm
Forum: Properties of Light
Topic: Q. 28 on the Photoelectric Effect Module
Replies: 4
Views: 52

Re: Q. 28 on the Photoelectric Effect Module

As said above, for part A used KE=1/2 mv^2. Mass of electron would be approx 9.109 * 10^-31 kg. So (1/2)*(9.109*10^-31)*(6.61*10^5)^2 should give you the answer Part B is asking about the energy required to remove one sodium ion. Since we are given the work function of the metal, which is defined as...

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