Search found 104 matches

by alicechien_4F
Tue Mar 10, 2020 1:01 am
Forum: General Rate Laws
Topic: Book Problem 7A.17
Replies: 3
Views: 40

Re: Book Problem 7A.17

A reactant is zero order if changing the concentration of that reactant has no effect on the rate constant.
by alicechien_4F
Tue Mar 10, 2020 1:00 am
Forum: General Rate Laws
Topic: Catalysts and Rate Laws
Replies: 2
Views: 34

Re: Catalysts and Rate Laws

Based on a previous answer given by Chem_Mod, rate laws can include catalysts if it is an elementary reaction.

Here's the link: viewtopic.php?t=1727
by alicechien_4F
Tue Mar 10, 2020 12:58 am
Forum: General Rate Laws
Topic: 7A.15
Replies: 6
Views: 63

Re: 7b.15

Did you by chance post the wrong question? I can't seem to find the corresponding question for 7B15. But in general, the B is squared because it is a second order reaction, while the A is not because it is first order.
by alicechien_4F
Tue Mar 10, 2020 12:55 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius Equation on Equation Sheet
Replies: 1
Views: 18

Arrhenius Equation on Equation Sheet

Will the Arrhenius equation (both forms) be on the equation sheet? I can't find it on the one posted on Lavelle's website, but I know for Test 2 they also added additional equations that weren't on the posted equation sheet.
by alicechien_4F
Tue Mar 10, 2020 12:53 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysts and Rates
Replies: 10
Views: 131

Catalysts and Rates

How come catalysts don't have an effect on the rate of the overall reaction if it lowers the activation energy?
by alicechien_4F
Mon Mar 02, 2020 10:14 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Inert Electrode
Replies: 1
Views: 41

Re: Inert Electrode

If there is no solid metal in the anode or the cathode, you would add an inert electrode to that side.
by alicechien_4F
Mon Mar 02, 2020 10:13 pm
Forum: Phase Changes & Related Calculations
Topic: Absorb means "+"?
Replies: 4
Views: 141

Re: Absorb means "+"?

I think it is -q because it is the cooling system around the chamber, rather than the chamber itself that is absorbing the heat. This means the chamber is releasing heat.
by alicechien_4F
Mon Mar 02, 2020 10:09 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Drawing Cell Diagram
Replies: 7
Views: 91

Re: Drawing Cell Diagram

I didn't realize that the cell diagram does not represent the order of the molecules in the reaction. But a rule I can follow is that the side being oxidized is the anode, and whatever solid that is on that side should be on the side of the anode, right? And that if there is no solid then the elect...
by alicechien_4F
Mon Mar 02, 2020 10:07 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6M.3
Replies: 3
Views: 85

Re: 6M.3

The anode should be on the left side of the cell diagram, and the cathode should be on the right. The Ecell should be cathode - anode and for galvanic cells it should always be positive.
by alicechien_4F
Mon Mar 02, 2020 10:03 pm
Forum: Administrative Questions and Class Announcements
Topic: Sections for Homework
Replies: 3
Views: 74

Sections for Homework

What sections of the outline can we do for this week's homework? Can we do electrochem since the test is this week, or should it be all kinetics?
by alicechien_4F
Mon Feb 24, 2020 2:34 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams
Replies: 9
Views: 124

Re: Cell Diagrams

The single bar represent the species that has undergone a state change, while the double bar is a salt bridge. The double line is usually also used to separate the anode/oxidation reaction from the cathode/reduction equation. You use the commas when there is no phase change, and you would add a sing...
by alicechien_4F
Mon Feb 24, 2020 2:30 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Eo as an intensive property
Replies: 9
Views: 111

Re: Eo as an intensive property

It is similar to the density of water. Even though you change how many electrons (by changing the coefficient), it won't affect the the E nought value of the each material.
by alicechien_4F
Mon Feb 24, 2020 2:28 pm
Forum: Administrative Questions and Class Announcements
Topic: Test 2 info
Replies: 8
Views: 131

Re: Test 2 info

Test 2 is technically not cumulative, but there are many concepts from the midterm that are also applicable to the material after the midterm. For example, we also talked about Gibbs, entropy, and enthalpy, so it would be good to brush up on those concepts.
by alicechien_4F
Mon Feb 24, 2020 2:24 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L.5B
Replies: 1
Views: 36

Re: 6L.5B

I believe the condition was if you do not have a solid on either the anode or cathode side, you add it in. I'm not sure why they included platinum on the right side, but on the left side it is included because both molecules are aqueous.
by alicechien_4F
Mon Feb 24, 2020 1:05 pm
Forum: Administrative Questions and Class Announcements
Topic: Picking up 14A Finals in Young Hall
Replies: 3
Views: 54

Re: Picking up 14A Finals in Young Hall

I don't think you can anymore, but you can try emailing your TA last quarter to see if it is still possible.
by alicechien_4F
Tue Feb 18, 2020 12:52 pm
Forum: Balancing Redox Reactions
Topic: Balancing and Adding together Half-Rxns
Replies: 6
Views: 75

Re: Balancing and Adding together Half-Rxns

It is similar to why we balance all other atoms in a chemical reaction. It is so that conservation of energy, and in this case, the charge of the electrons, is maintained.
by alicechien_4F
Tue Feb 18, 2020 12:05 am
Forum: Administrative Questions and Class Announcements
Topic: Test 2
Replies: 11
Views: 139

Re: Test 2

Test 2 isn't technically cumulative, but what we are learning right now (Van't Hoff) requires knowledge of midterm material (enthalpy, Gibbs, PV = nRT), so it would be good to review that content since everything builds on each other.
by alicechien_4F
Tue Feb 18, 2020 12:02 am
Forum: Administrative Questions and Class Announcements
Topic: Midterm Nerves
Replies: 7
Views: 104

Re: Midterm Nerves

I think re-reading the question and writing down the equations is a great way to start! What I do is write down all the given information in the problems (ex: pressure, temperature, whether it's isothermal, etc.) because sometimes writing the given info down allows you to put values into the equatio...
by alicechien_4F
Mon Feb 17, 2020 11:58 pm
Forum: Van't Hoff Equation
Topic: K rather than Kc
Replies: 10
Views: 169

Re: K rather than Kc

You have to convert from Kp to Kc because the values are different. I believe Kp and Kc are only the same when the number of moles of gas on the reactant and products sides are equal (correct me if I'm wrong!). Van't Hoff's equation relates Kc to change in temperature.
by alicechien_4F
Mon Feb 17, 2020 11:53 pm
Forum: Administrative Questions and Class Announcements
Topic: 14BL and 14C
Replies: 8
Views: 101

Re: 14BL and 14C

I know a lot of people who have taken 14BL and 14C concurrently! Most people think 14C is a lighter in terms of content than 14D, and 14BL is more tedious work with all the labs, but I think with 14B content fresh, you'll be ok!
by alicechien_4F
Sat Feb 15, 2020 9:40 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G naught
Replies: 2
Views: 47

Re: Delta G naught

One way is to use the Gibbs of formation for each molecule and do products - reactants. Another way to find delta G is to use the equation delta(G) = delta(H) - T*delta(S).
by alicechien_4F
Sat Feb 15, 2020 9:38 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Equilibrium
Replies: 15
Views: 137

Re: Equilibrium

At equilibrium, the forward and reverse reactions occur at the same rate. This means that neither reaction is favored, and so neither reaction is spontaneous.
by alicechien_4F
Thu Feb 13, 2020 3:15 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Why are exothermic reactions generally spontaneous?
Replies: 16
Views: 225

Re: Why are exothermic reactions generally spontaneous?

Is this related to the relationship between ∆G and the direction of a spontaneous reaction? Does a spontaneous reaction have a -∆G and proceed in the forward direction? Yes, a spontaneous reaction will always have a negative Gibbs value and proceed in the forward direction. If the reaction has a po...
by alicechien_4F
Thu Feb 13, 2020 3:12 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: reversible entropy and irreversible entropy
Replies: 1
Views: 40

Re: reversible entropy and irreversible entropy

Since entropy is a state function, the change in entropy for an irreversible process is the same as a reversible process.
by alicechien_4F
Thu Feb 13, 2020 3:11 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: delta G
Replies: 2
Views: 64

Re: delta G

If you know that the equation is at equilibrium, then delta G = 0. Also, if all of the molecules are at their most stable state (ex: O2 as a gas) the Gibbs value is also zero.
by alicechien_4F
Thu Feb 06, 2020 2:12 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Question from Wednesday Lecture
Replies: 3
Views: 69

Question from Wednesday Lecture

In the Wednesday Lecture, there was a side by side comparison of two graphs showing the irreversible and reversible pathway for work. The reversible pathway had constant T along the pathway, V increasing, and P decreasing. The irreversible pathway had T changing along the pathway (decrease and then ...
by alicechien_4F
Wed Feb 05, 2020 5:42 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: reversible v irreversible work
Replies: 3
Views: 48

Re: reversible v irreversible work

Reversible work is also isothermal, while irreversible work is not. Irreversible work just has constant pressure.
by alicechien_4F
Wed Feb 05, 2020 5:39 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy Decreasing, Temperature Increasing
Replies: 6
Views: 57

Entropy Decreasing, Temperature Increasing

For problems like 4F.1 and 4F.3, why does change in entropy decrease when temperature is increased? I understand that the equation delta(S) = q/T so increasing the denominator will increase delta(S), but can someone explain conceptually why entropy decreases when temperature increases? I thought hig...
by alicechien_4F
Wed Feb 05, 2020 5:37 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Isothermal and Isobaric
Replies: 1
Views: 57

Isothermal and Isobaric

Can a reaction be isothermal and isobaric at the same time? If so, which equations would you use for work and enthalpy?
by alicechien_4F
Wed Feb 05, 2020 5:34 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy as three steps
Replies: 2
Views: 51

Entropy as three steps

For 4.17, it asks us "Calculate the standard entropy of vaporization of water at 85 degrees C, given that its standard entropy of vaporization at 100 degrees C is 109.0 J/Kmol and the molar heat capacities at constant pressure of liquid water and water vapor are 75.3 J/Kmol and 33.6 J/Kmol, res...
by alicechien_4F
Wed Feb 05, 2020 5:30 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Difference in Cp and Cm
Replies: 1
Views: 23

Difference in Cp and Cm

Why is Cp greater than Cv for ideal gases? I understand that Cp = Cv + R, but can some explain conceptually why? Thanks!
by alicechien_4F
Wed Jan 29, 2020 12:52 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4C.3 Change in Enthalpy
Replies: 3
Views: 120

4C.3 Change in Enthalpy

For question 4C.3, it asks "Calculate the final temperature and the change in enthalpy when 765 J of energy is transferred as heat to 0.820 mol Kr(g) at 298 K and 1.00 atm (a) at constant pressure; (b) at constant vol- ume. Treat the gas as ideal." I understand how to calculate the final t...
by alicechien_4F
Tue Jan 28, 2020 8:26 pm
Forum: Phase Changes & Related Calculations
Topic: Burns
Replies: 4
Views: 54

Re: Burns

The phase change from solid to liquid releases only 6.01 KJ/mol, but the change to vapor releases 46.7KJ/mol, making steam burns much more severe.
by alicechien_4F
Tue Jan 28, 2020 8:23 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: reaction enthalpy
Replies: 14
Views: 91

Re: reaction enthalpy

When you form a bond, you release energy. On the other hand, when you break bonds, you must add energy. This is because atoms/molecules are more stable when they are bonded together, so to break bonds you must add. When you form bonds, electrons typically go to lower, more stable orbitals, so it rel...
by alicechien_4F
Tue Jan 28, 2020 8:19 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 11
Views: 68

Re: Bond Enthalpies

Leila_4E wrote:Is the table we find this in the textbook or is there a general one online that is the same?


I would go with the table in the textbook for homework problems because sometimes the bond enthalpies differ slightly online. It should be roughly the same.
by alicechien_4F
Tue Jan 28, 2020 8:18 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: q vs. delta H
Replies: 6
Views: 107

Re: q vs. delta H

Leila_4E wrote:And -q means heat out of the system and into the surroundings, right?


-Q means exothermic reaction, so the system loses heat while the surroundings gain heat, making it appear warmer.
by alicechien_4F
Tue Jan 28, 2020 8:16 pm
Forum: Phase Changes & Related Calculations
Topic: Why does steam cause burns?
Replies: 29
Views: 255

Re: Why does steam cause burns?

Chantel_2I wrote:Is there a reason why the horizontal line for vaporizing water is so much longer than the one for melting ice?


It takes longer to vaporize water because there is a larger enthalpy, which means more heat has to be applied at a constant rate.
by alicechien_4F
Mon Jan 20, 2020 6:40 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Coverting Kp to Kc
Replies: 2
Views: 37

Coverting Kp to Kc

Can we use Kc for all of the equilibrium problems that have gases in the reactant/products instead of Kp? I don't remember going over converting Kc to Kp in lecture or discussion in depth, so would we have to do it on the test?
by alicechien_4F
Mon Jan 20, 2020 6:37 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Module
Replies: 4
Views: 54

Re: Module

You're given the amount of reactants and products in moles, so you have to divide by 3.0 L to obtain the molarity. Hope this helps!
by alicechien_4F
Mon Jan 20, 2020 6:34 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Low [H3O+]
Replies: 1
Views: 32

Low [H3O+]

Can someone clarify what Dr. Lavelle said in lecture about how a solution with [H3O+] < 10^7 M is considered neutral? Does this only apply to acid reactions or how does it work if it is a basic solution with a lot amount of H3O+? Thanks!
by alicechien_4F
Mon Jan 20, 2020 6:27 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Writing K Expression
Replies: 6
Views: 52

Re: Writing K Expression

All gas reactants/products are included in the K expression, including water vapor. The only things not included are solids, liquids, or solvents. Hope this helps!
by alicechien_4F
Mon Jan 20, 2020 6:26 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE tables
Replies: 5
Views: 48

Re: ICE tables

If you are dealing with a weak acid or base, you would also use an ICE table because you don't know how much dissociates (versus a strong acid/base that dissociates 100%).
by alicechien_4F
Mon Jan 13, 2020 7:17 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatelier's Principle
Replies: 5
Views: 69

Re: Le Chatelier's Principle

Le Chatelier's Principle applies to temperature, concentration, and pressure, but it doesn't apply to catalysts because catalysts speed up the forward and reverse reactions at the same rate.
by alicechien_4F
Mon Jan 13, 2020 7:12 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Changes in pressure
Replies: 4
Views: 59

Re: Changes in pressure

The way I learned the "easy" way in high school was that the gas wants to go into the area with more space so that it can expand. That is why the reaction will proceed towards the side with less moles, since there is more area for the gas.
by alicechien_4F
Mon Jan 13, 2020 7:08 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Partial Pressure
Replies: 19
Views: 131

Re: Partial Pressure

Angela Wu-2H wrote:Can partial pressure be measured in bars and atm or just bars?


Partial pressure can be measure in both bars and atm. I believe for this class, we will assume 1 bar = 1 atm, but you can also convert if necessary.
by alicechien_4F
Mon Jan 13, 2020 7:06 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Reaction Quotient
Replies: 11
Views: 81

Re: Reaction Quotient

I think it is easy to mix up Q and K because they're calculated the same way! However, Q is used to calculate the ratio between products and reactants at any given time, while K is used to calculate the ratio between products and reactants exactly at equilibrium. Q will always proceed towards K in o...
by alicechien_4F
Mon Jan 13, 2020 7:04 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Thermodynamic Stability
Replies: 6
Views: 64

Re: Thermodynamic Stability

A molecule is more thermodynamically stable if it has a smaller K value. The smaller the K value, the less product there is relative to reactant. That means the reactant (in this case, Cl2 and F2) will dissociate less and remain as reactants.
by alicechien_4F
Tue Jan 07, 2020 2:50 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium and Equilibrium Constant
Replies: 4
Views: 47

Equilibrium and Equilibrium Constant

What is the difference between shifting/changing the equilibrium versus changing the equilibrium constant? Why does shifting the equilibrium sometimes not change the equilibrium constant?
by alicechien_4F
Mon Jan 06, 2020 9:53 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatelier's and Endo/Exothermic
Replies: 5
Views: 72

Le Chatelier's and Endo/Exothermic

What is an easy way to remember which side of the chemical equation heat is on? Also, why do exothermic equations have a negative value?
by alicechien_4F
Mon Jan 06, 2020 9:50 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Water as Liquid and Gas
Replies: 1
Views: 33

Water as Liquid and Gas

Why is water included in equilibrium when it is in a gaseous state but not when it is in a liquid state? Is water ever a solvent when it is in its gaseous state?
by alicechien_4F
Mon Jan 06, 2020 9:49 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Equilibrium and Gases
Replies: 3
Views: 58

Equilibrium and Gases

Why does the equilibrium shift to the side with less moles of gas when pressure is increased?
by alicechien_4F
Mon Jan 06, 2020 9:48 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Constant for Solids/Gases
Replies: 5
Views: 65

Equilibrium Constant for Solids/Gases

For the modules, if we were given an equation like A (g) + B (g) --> C (s), why do we write the equilibrium constant as 1/[A][B] instead of just [A][B]? I thought we were supposed to just take solids and liquids out of the equilibrium constant.
by alicechien_4F
Mon Jan 06, 2020 9:47 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Units in Bars
Replies: 4
Views: 55

Units in Bars

Is the unit "bars" a unit of concentration or do we have to convert it when solving partial pressure problems?
by alicechien_4F
Fri Dec 06, 2019 1:32 pm
Forum: Polyprotic Acids & Bases
Topic: Direction of Reaction of Polyprotic Acids
Replies: 2
Views: 64

Re: Direction of Reaction of Polyprotic Acids

It depends on the pH of the solution that it is in. You have to compare the pKa with the pH to see if the acid will protonate or be deprotonated. Hope this helps!
by alicechien_4F
Fri Dec 06, 2019 1:31 pm
Forum: Lewis Acids & Bases
Topic: Identifying Acids and Bases
Replies: 3
Views: 52

Identifying Acids and Bases

On the final if it asks us to identify acids/bases, do we assume they are using the Lewis definition or the Arrhenius definition?
by alicechien_4F
Thu Dec 05, 2019 2:02 pm
Forum: Amphoteric Compounds
Topic: how to determine amphoteric compounds
Replies: 1
Views: 45

Re: how to determine amphoteric compounds

I think the best way to determine whether a compound is amphoteric is to draw out the lewis structure so that you can identify any lone pairs or any hydrogens that can be given off. Other than that, if you know a compound contains a common base (like an amine group in amino acids) and a common acid ...
by alicechien_4F
Thu Dec 05, 2019 1:59 pm
Forum: Lewis Acids & Bases
Topic: Equilibrium Arrows for Acid/Base
Replies: 1
Views: 33

Equilibrium Arrows for Acid/Base

When do we use a one-way arrow and when do we use an arrow pointing in both directions?
by alicechien_4F
Wed Dec 04, 2019 1:00 pm
Forum: Naming
Topic: Naming for Hydrocarbons
Replies: 2
Views: 49

Naming for Hydrocarbons

Do we need to memorize hydrocarbons for coordinate compounds? For example, do we need to know the formula for "ethylene" in ethylenediamine and how to draw it? If we do, what other common hydrocarbons should we know? Thanks!
by alicechien_4F
Wed Nov 27, 2019 4:16 pm
Forum: Lewis Acids & Bases
Topic: Difference between Bronsted and Lewis Acid?
Replies: 6
Views: 62

Re: Difference between Bronsted and Lewis Acid?

Brosted acid and bases are defined by their ability to accept or donate hydrogen ions. Lewis acid and bases are defined by their ability to accept or donate electron pairs. A Lewis Acid is an electron-pair acceptor. A Brosted acid is a substance that can donate a hydrogen ion.
by alicechien_4F
Tue Nov 26, 2019 1:01 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Ligand
Replies: 10
Views: 117

Re: Ligand

How does this term relate to ligands that are discussion in terms of biology? A ligand in chemistry is an ion/molecule that is attached to a metal through coordinate covalent bonds. Similarly, a ligand in biology is a molecule that binds to a larger molecule. Both involve smaller molecules binding ...
by alicechien_4F
Tue Nov 26, 2019 12:57 pm
Forum: Naming
Topic: adding O
Replies: 3
Views: 47

Re: adding O

I think it is chloride and not chloro because it is not part of the coordination compound and is written outside the brackets.
by alicechien_4F
Tue Nov 26, 2019 12:53 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Ligands
Replies: 3
Views: 40

Re: Ligands

You have to draw out the Lewis structure and see how many lone pair there are. You should use VESPR to think about the shape and see whether the multiple lone pairs can orient themselves to bind to another molecule.
by alicechien_4F
Tue Nov 26, 2019 12:50 pm
Forum: Naming
Topic: Naming for Final
Replies: 3
Views: 61

Re: Naming for Final

I think we will need to be able to name coordination compounds and also how to write their chemical formula, which is what the homework is on. We probably will need to know whether coordinations are polydentate or not as well.
by alicechien_4F
Tue Nov 19, 2019 9:01 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: HW 2F:21a
Replies: 2
Views: 48

Re: HW 2F:21a

Most hydrocarbons are chains, so you would put both carbons as "central" atoms. Because you want symmetry, you would bond two H atoms to each of the carbon atoms. Then, add as many bonds as you need between the two carbons for them to fill an octect.
by alicechien_4F
Tue Nov 19, 2019 8:59 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: See-Saw Shape
Replies: 3
Views: 44

Re: See-Saw Shape

Yes, the angles would be less than 120 and less than 90 because the lone pairs causes a slight electron repulsion.
by alicechien_4F
Tue Nov 19, 2019 8:57 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Is ICl2- Polar or Non-polar?
Replies: 2
Views: 47

Is ICl2- Polar or Non-polar?

Is ICl2- polar or non-polar? I know that it is symmetrical with Cls on both side of the I atom, but do the 3 lone pairs create a dipole moment because it's an odd number? Thanks!
by alicechien_4F
Tue Nov 19, 2019 8:54 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Regions of electron density
Replies: 5
Views: 66

Re: Regions of electron density

I believe we only need to know up to octahedral. Dr. Lavelle made a post with the list of molecular geometries to know for the test. Hope this helps!
by alicechien_4F
Tue Nov 19, 2019 8:53 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Why is CH2Cl2 polar?
Replies: 12
Views: 147

Re: Why is CH2Cl2 polar?

The Cl atom has a much higher electronegativity than H and has more electrons in its valence shell (8 vs. 2) after bonding, so there will be a stronger negative charge on that end of the atom. Hope this helps!
by alicechien_4F
Thu Nov 14, 2019 12:42 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: difference between bent and angular
Replies: 4
Views: 47

Re: difference between bent and angular

The two words are interchangeable and refer to a molecule that has lone pairs that distort the bond angles. Hope this helps!
by alicechien_4F
Wed Nov 13, 2019 4:35 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: Intramolecular forces
Replies: 2
Views: 49

Re: Intramolecular forces

All IMFs are between either nonpolar or polar molecules. Within that, there are hydrogen bonds, dipole-dipole, London Dispersion Forces, and ion-dipole. Ion-dipole is the interaction between ion and partial charges on a polar molecule. Dipole-dipole interaction are interactions between partial charg...
by alicechien_4F
Wed Nov 13, 2019 1:03 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR Bond and Regions
Replies: 2
Views: 46

VSEPR Bond and Regions

Why are double and tripe bonding pairs still considered a single region of electron density and not affect the shape/bond angles? I'm confused because I thought if you had more electrons there would be a greater repulsion, so it would affect the shape and the bond angles. Thank you!
by alicechien_4F
Tue Nov 12, 2019 10:47 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: 3F1
Replies: 1
Views: 56

3F1

For part D of 3F.1, the answer for SO2 includes dipole-dipole forces. I thought there were only LDF forces because it is symmetric. Is there a way to know if there are dipole-dipole interactions without knowing the shape of the molecule?
by alicechien_4F
Tue Nov 12, 2019 2:34 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: Hydrogen Bonding in Biological Systems
Replies: 2
Views: 31

Re: Hydrogen Bonding in Biological Systems

Hydrogen bonding is so common because it stabilizes important biological systems. The atoms involved in hydrogen bonding (H, N, O) are very common in biological structures such as DNA, RNA, and proteins which is why we see it so often.
by alicechien_4F
Tue Nov 05, 2019 2:52 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge/Lewis structures
Replies: 5
Views: 101

Re: Formal Charge/Lewis structures

Electrons repel each other, so delocalizing them over more bonds decreases the electron-electron repulsion in any one bond. Because the electrons can move around, they can satisfy the octet for more atoms and make them more stable.
by alicechien_4F
Tue Nov 05, 2019 2:42 pm
Forum: Trends in The Periodic Table
Topic: electron affinity
Replies: 4
Views: 62

Re: electron affinity

Electron affinity is the amount of energy that is released when an electron is added to an atom. It is also thought of as the likelihood of an atom gaining an electron. Electronegativity is how strongly an atom pulls on its bonding electrons instead of gaining electrons.
by alicechien_4F
Tue Nov 05, 2019 2:36 pm
Forum: Trends in The Periodic Table
Topic: Effective Nuclear Charge and Nuclear Charge
Replies: 6
Views: 81

Re: Effective Nuclear Charge and Nuclear Charge

Effective nuclear charge increases as you go across a period because the amount of protons in the nucleus increases, which the pull on the electrons. Effective nuclear charge decreases down a group because the shielding effect of newly added shells means that electrons on the valence shell are not c...
by alicechien_4F
Tue Nov 05, 2019 2:31 pm
Forum: Properties of Light
Topic: Waves/Particles
Replies: 14
Views: 164

Re: Waves/Particles

So the photons are acting as particles when emitted in the photoelectric effect, but I also wrote in my notes that electrons act as waves. Does it acts as both a wave and a particle or did I misunderstand the lecture? We typically treat electrons as particles, but because all objects have wavelengt...
by alicechien_4F
Mon Nov 04, 2019 4:47 pm
Forum: General Science Questions
Topic: Midterm
Replies: 12
Views: 249

Re: Midterm

Lavelle will provide all the information that we need for specific problems. My TA said that he will provide electronegativity values unless it is very obvious based on the periodic trends. I don't think you have to memorize the specific bond lengths, but understand them conceptually.
by alicechien_4F
Sat Nov 02, 2019 1:34 am
Forum: Resonance Structures
Topic: Resonance for Asymmetrical Compounds
Replies: 1
Views: 32

Resonance for Asymmetrical Compounds

For the lewis structures we've done for practice, we've only done resonance structures for compounds that have one element surrounded by multiple identical atoms of another element (like CO 3 - or O 3 ). Do we also draw resonance structures for compounds that are more complex or not symmetrical (lik...
by alicechien_4F
Fri Nov 01, 2019 11:21 pm
Forum: Trends in The Periodic Table
Topic: Exceptions
Replies: 3
Views: 63

Re: Exceptions

The noble gases do not follow the electron affinity trend because they have a full set of valence electrons. They are also often excluded from electronegativity trends because they do not bond since their shell is full. Hope this helps!
by alicechien_4F
Fri Nov 01, 2019 11:15 pm
Forum: Photoelectric Effect
Topic: Work Function
Replies: 9
Views: 158

Re: Work Function

We have only used the work function in the context of the photoelectric effect, so if you see it you can assume you will be using the Energy/KE equation. Hope this helps!
by alicechien_4F
Fri Nov 01, 2019 11:12 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Configurations in 4d, 5d, etc. orbitals
Replies: 3
Views: 59

Re: Configurations in 4d, 5d, etc. orbitals

Yes, elements in the same group will have the same exception because their electron configurations are similar in the amount of electrons and therefore have similar properties. Hope this helps!
by alicechien_4F
Fri Nov 01, 2019 10:36 pm
Forum: DeBroglie Equation
Topic: Dino Nuggets Problem 8b
Replies: 11
Views: 490

Re: Dino Nuggets Problem 8b

You multiply by Avogadro's number since you're looking for the energy of a single electron, not a mol. That way, the units will also cancel out. Hope this helps!
by alicechien_4F
Fri Nov 01, 2019 10:35 pm
Forum: Trends in The Periodic Table
Topic: Studying techniques
Replies: 3
Views: 54

Re: Studying techniques

The way I remember it is that atomic radius increases from top right to bottom left, and all the other trends increase the opposite way, so from bottom left to top right!
by alicechien_4F
Thu Oct 24, 2019 3:49 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: s, p, d, f orbitals
Replies: 15
Views: 175

Re: s, p, d, f orbitals

so at each energy level, are there s- p- d- f- orbitals? In the n=1 energy level, there is only the s-orbital. In n=2, there is only the s-orbital and p-orbital. In n=3, there is only the s-, p-, d-orbitals. Another way to tell which orbitals are present at an energy level is by using the quantum n...
by alicechien_4F
Thu Oct 24, 2019 1:16 pm
Forum: Trends in The Periodic Table
Topic: Periodic Trend Exceptions
Replies: 7
Views: 78

Re: Periodic Trend Exceptions

Along with Cr and Cu, all of the elements that are in the same group underneath those elements exhibit the same exception for their electron configuration.
by alicechien_4F
Thu Oct 24, 2019 1:03 pm
Forum: Trends in The Periodic Table
Topic: Summary of Periodic Trends
Replies: 7
Views: 142

Re: Summary of Periodic Trends

Since ionization energy is the energy required to remove an electron from a neutral atom, atoms of the left side of the period table would have the lowest ionization energy because alkali metals want to lose electrons to maintain a full valence shell and become a cation. The lower the ionization ene...
by alicechien_4F
Thu Oct 24, 2019 12:57 pm
Forum: Trends in The Periodic Table
Topic: Relationship between Electronegativity and Ionization Energy?
Replies: 6
Views: 112

Relationship between Electronegativity and Ionization Energy?

What is the relationship between electronegativity and ionization energy? I know Dr. Lavelle said that the atom with the lowest ionization energy is the central atom for a lewis structure, but in high school I learned that the central atom was the most electronegative atom. Is the atom with the lowe...
by alicechien_4F
Thu Oct 24, 2019 12:51 pm
Forum: Trends in The Periodic Table
Topic: Ionic Radii
Replies: 10
Views: 150

Re: Ionic Radii

Ionic radii is the radius between two ions that are ionically bonded (ex: NaCl). Atomic radius is the radius between two neutral atoms. Hope this helps!
by alicechien_4F
Fri Oct 18, 2019 6:09 pm
Forum: Einstein Equation
Topic: HW 1B. 7
Replies: 6
Views: 298

Re: HW 1B. 7

So avogadro's number is how you get it in the correct mole qty? In part A, you're solving for the amount of energy emitted by one sodium atom. In part B, you're solving for the amount of energy emitted by 5.00 mg of sodium, so you have to convert 5.00 mg to moles, and then multiply by avogadro's nu...
by alicechien_4F
Fri Oct 18, 2019 5:58 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 4s and 3d electron configurations
Replies: 1
Views: 45

Re: 4s and 3d electron configurations

I think in high school many teachers would teach us to write 4s before 3d because that is the order that the shells were filled (and seemed more logical without any experimental data), rather than by the amount of energy. For Zinc, it would still be [Ar] 3d 10 4s 2 because for elements that have an ...
by alicechien_4F
Wed Oct 16, 2019 1:49 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 1D #21
Replies: 2
Views: 72

Re: 1D #21

The n represents the principle quantum number that determines energy and size. It is also called the shell, and it corresponds with the row number for an atom on the period table as well as the coefficent of the subshell notation. The l represents the angular momentum quantum number, where l = 0 is ...
by alicechien_4F
Wed Oct 16, 2019 1:43 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 1D #11
Replies: 2
Views: 51

Re: 1D #11

The angular momentum quantum number (l) corresponds with the subshells so that l = 0 is the s-orbital, l = 1 is the p-orbital, l = 2 is the d-orbital, and l = 3 is the f-orbital. We know that the s-subshell has 1 orbital, the p-subshell has 3 orbitals, the d-subshell has 5 orbitals, and the f-subshe...
by alicechien_4F
Wed Oct 16, 2019 1:35 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: HW Question 1.D.13
Replies: 3
Views: 72

Re: HW Question 1.D.13

I don't understand what to use given in the problem to get the answer. I thought b was 11 because if n=6 and l=5, then shouldn't ml = -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5? Also can someone explain c and d too? L is the angular momentum quantum #, and although the allowed values go from l = 0, 1, 2,...
by alicechien_4F
Fri Oct 11, 2019 12:03 am
Forum: Einstein Equation
Topic: E=hv
Replies: 43
Views: 4442

Re: E=hv

Just to clarify, if there is excess energy after the electron is ejected, that energy would be converted to kinetic energy (Ek). The v in the equation Ek=1/2(mv^2) refers to the velocity of the electron, correct? Because surely it is not referring to nu, as in E=hv. Correct, the v refers to the vel...
by alicechien_4F
Thu Oct 10, 2019 11:53 pm
Forum: Properties of Light
Topic: HW 1.A #9
Replies: 3
Views: 58

Re: HW 1.A #9

Hi Doris! I think the easiest way to match the wave to the activity is by using Hertz since most EM spectrum charts label the radiation based on hertz. Also, the answer key actually matches 3.3E-19 J (which has a frequency of 5.0E14 Hz) to reading instead of microwave, which makes sense because ligh...
by alicechien_4F
Tue Oct 08, 2019 9:39 pm
Forum: Properties of Light
Topic: Question 1A.3 c
Replies: 5
Views: 126

Re: Question 1A.3 c

Can somebody explain to me why it isn't B? The answer (b) states that the wavelength of the radiation decreases. This not correct because with the equation C = λv, wavelength (λ) and frequency (v) are inversely proportional. If you decrease the frequency, the λ must increase to compensate since C (...
by alicechien_4F
Tue Oct 08, 2019 9:33 pm
Forum: Properties of Light
Topic: Work Function
Replies: 2
Views: 72

Work Function

In Lavelle's lecture, I was confused on what the work function is. Can someone help clarify what it is and how to solve for it?
by alicechien_4F
Tue Oct 08, 2019 9:09 pm
Forum: Properties of Light
Topic: Rays of the EM Spectrum
Replies: 2
Views: 63

Re: Rays of the EM Spectrum

All EM waves have radiation, but only wavelengths that are shorter than visible light are harmful to humans. Although many people believe microwaves can cause cancer, it is unfounded because the wavelength of microwaves is significantly longer than visible light and the energy of individual photons ...
by alicechien_4F
Sun Sep 29, 2019 5:21 pm
Forum: Empirical & Molecular Formulas
Topic: Empirical Formula
Replies: 6
Views: 83

Re: Empirical Formula

Even though the ratios are the same, it's important to differentiate between empirical and molecular formula. Like what the people above said, empirical formula is used to find the ratio of atoms. When you're given mass percentages of a unknown compound, you'd find the empirical formula first before...

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