## Search found 107 matches

Mon Mar 08, 2021 12:47 pm
Forum: First Order Reactions
Topic: sapling week 9/10 #20
Replies: 3
Views: 42

### Re: sapling week 9/10 #20

For this question, I solved for k of the catalyzed and k for the uncatalyzed reaction using the Arrhenius equation and inputting the respective Ea given. (Here, I just assumed A=1 because it did not specify). Then, I divided k(cat) by k(uncat). For the second part, just adjust the temperature in the...
Mon Mar 08, 2021 12:32 pm
Forum: Student Social/Study Group
Topic: Favorite TV shows
Replies: 212
Views: 1591

### Re: Favorite TV shows

If you like a good drama, I am absolutely obsessed with The Crown on Netflix. Or for something a little more casual and offbeat, Fleabag on Amazon Prime!
Mon Mar 08, 2021 12:28 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Mechanisms
Replies: 7
Views: 253

### Re: Mechanisms

A reaction mechanism is basically an outline of all the elementary steps that make up a whole reaction. It lists out all the steps and include the intermediates. The slowest step in the entire reaction mechanism determines the rate of the overall reaction. Hope this helps!
Mon Mar 08, 2021 12:25 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Rate Limiting Steps
Replies: 6
Views: 23

### Re: Rate Limiting Steps

The rate-limiting step is the slowest reaction in the reaction mechanism. Because the rate of the overall reaction depends on this slowest step, it essentially "limits" how fast the reaction can proceed. It is also referred to as the rate-determining step because it determines the rate of ...
Mon Mar 08, 2021 12:21 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Ea
Replies: 2
Views: 19

### Re: Ea

Like the post above, Ea is the activation energy while E is the cell potential.To expand, Ea is used in kinetics and is the amount of energy that needs to be supplied in order for the reaction to proceed. We can calculate it by using the Arrhenius equation that related Ea to k, the rate constant. E,...
Mon Mar 01, 2021 2:32 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Textbook 6L.1
Replies: 2
Views: 14

### Re: Textbook 6L.1

Yes, I believe the oxidation numbers are both -1. In the overall reaction, 2 electrons are transferred which comes from the change in oxidation numbers in the first reaction. Hope this helps!
Mon Mar 01, 2021 2:26 pm
Forum: General Rate Laws
Topic: Temperature effect on kinetics equations
Replies: 6
Views: 25

### Re: Temperature effect on kinetics equations

Temperature can affect k, the rate constant. This concept is similar to what we learned in 14a, where temperature can affect equilibrium constants; however, we have not yet learned how temperature affects the rate constant.
Mon Mar 01, 2021 2:10 pm
Forum: Balancing Redox Reactions
Topic: 6L.1
Replies: 3
Views: 30

### Re: 6L.1

n is basically the number of electrons transferred in the overall reaction, so in general, make sure to balance both half reactions first. So like the post above says, n in this example is 2.
Mon Mar 01, 2021 2:03 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: First - Order/Order
Replies: 10
Views: 39

### Re: First - Order/Order

A first order reaction is a reaction that depends on only one reactant. A second order reaction depends on two, and a third order reaction depends on three. The order of a reaction is essentially the sum of the exponents in its rate expression.
Mon Mar 01, 2021 1:55 pm
Forum: General Rate Laws
Topic: Number of Reactants
Replies: 26
Views: 99

### Re: Number of Reactants

I believe Lavelle mentioned we would rarely be working with anything more complex than 3rd order reactions, so yes, I think we will only have to take into account 3 reactants at most.
Fri Feb 26, 2021 10:39 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Labeling/Drawing Cell Diagrams
Replies: 4
Views: 36

### Re: Labeling/Drawing Cell Diagrams

I believe Dr. Lavelle mentioned we should be able to identify the correct cell diagram given a reaction, and also vice versa, identify a reaction given a cell diagram. Since the final will most likely be multiple choice we probably won't have to draw it out ourselves on the exam, but it would defini...
Fri Feb 26, 2021 10:35 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Writing Cell Diagrams
Replies: 5
Views: 23

### Writing Cell Diagrams

I'm a little confused on how to write cell diagrams. I understand that the double line in the middle is the salt bridge, but how do we differentiate what goes on the outside vs what goes on the inside? What is the general outline, if there is one?
Fri Feb 26, 2021 10:30 am
Forum: Balancing Redox Reactions
Topic: Balancing Under Basic Conditions [ENDORSED]
Replies: 2
Views: 17

### Balancing Under Basic Conditions[ENDORSED]

I've noticed I've been having more trouble when balancing basic solutions than acidic solutions. Does anyone have any hints or tips they use when balancing them? Or if anyone could walk me through their general thought process? I have no problem with acidic conditions but when it comes to basic ones...
Fri Feb 26, 2021 10:22 am
Forum: Balancing Redox Reactions
Topic: Textbook 6K.1 [ENDORSED]
Replies: 2
Views: 51

### Re: Textbook 6K.1[ENDORSED]

The oxidation number of C goes from -2 to -1 because it loses one electron in the process. In C 2 H 5 OH, OH has an overall charge of -1, so the H 5 adds +5, resulting in a +4 charge for H 5 OH. Since the overall charge of the entire molecule is 0, we know C must balance this out. Since there are tw...
Fri Feb 26, 2021 10:11 am
Forum: Balancing Redox Reactions
Topic: Acidic vs. Basic
Replies: 20
Views: 76

### Re: Acidic vs. Basic

I agree with the post above. In basic solutions you want to add OH- and H2O to balance the oxygen and hydrogen. However, in acidic solutions, you should add H+ and H2O to balance it. In my opinion, equations under basic conditions require a little more work to figure out, but just remember to identi...
Wed Feb 17, 2021 12:22 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm 2
Replies: 11
Views: 105

### Re: Midterm 2

Yes, we will need to know the van't Hoff equation and how to derive it. I believe Lavelle added at least one of the forms of the equation to our formula sheet, so it would be very helpful to print out the updated version! Basically, the van't Hoff equation shows the temperature dependence of K It ca...
Wed Feb 17, 2021 12:17 pm
Forum: Phase Changes & Related Calculations
Topic: Melting of Ice in Heat equations
Replies: 2
Views: 40

### Re: Melting of Ice in Heat equations

Hi! Yes, we would need to calculate the enthalpy of fusion first. This value we calculate would then be added to the heat required to raise the temperature to the final desired temperature. And to add on, remember this goes for phase changes from liquid to gas as well. Hope this helps!
Wed Feb 17, 2021 12:13 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: High and Low Pressure vs Entropy
Replies: 3
Views: 37

### Re: High and Low Pressure vs Entropy

Entropy generally increases as pressure decreases (as a result of a volume increase) due to the greater availability of positions (microstates) the particles can take.
Wed Feb 17, 2021 12:02 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Phase Changes and Delta G
Replies: 2
Views: 16

### Re: Phase Changes and Delta G

Delta G is 0 when a system is at equilibrium. During a phase change, neither phase is technically favored and thus there is no change in G taking place.
Wed Feb 17, 2021 11:59 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 4C15
Replies: 3
Views: 22

### Re: 4C15

I was also initially confused by the reasoning for this. I believe it is because more heat (which is on the x-axis) supplied per mole is required to cause the same temperature difference, thus making the slope less steep for higher heat capacities.
Tue Feb 09, 2021 6:47 pm
Forum: Phase Changes & Related Calculations
Topic: internal energy equation
Replies: 5
Views: 25

### Re: internal energy equation

Just to add on, sometimes internal energy can also be referred to as delta E, but the equation is more or less the same, q+w. I was confused when I first saw E used, so maybe that is what you saw online.
Tue Feb 09, 2021 6:35 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: entropy change in surroundings formula
Replies: 2
Views: 31

### Re: entropy change in surroundings formula

Hi! I'm not sure if this answers your question, but maybe this can help. deltaS(universe)= deltaS(sys) + deltaS(surr)=0 when the process is at equilibrium. If the process is spontaneous, deltaS(universe)= deltaS(sys) + deltaS(surr) > 0. And finally, if the process is not spontaneous, deltaS(universe...
Tue Feb 09, 2021 6:28 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: 4C.1
Replies: 3
Views: 24

### Re: 4C.1

Yes, entropy generally increases as molar complexity increases because with complexity, the number of available microstates also increases. Entropy is related to this randomness and disorder which is why gaseous substances, that have higher degeneracy, have higher entropy than solids/liquids). Heat ...
Tue Feb 09, 2021 4:41 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: q equation
Replies: 21
Views: 89

### Re: q equation

q=mCdeltaT is used for calculations involving mass in grams and specific heat. q=nCdeltaT is used for calculations with moles (n) and molar heat capacity. These equations are similar but depend on which units you are working with.
Mon Feb 08, 2021 12:18 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy and Phase Changes
Replies: 5
Views: 29

### Entropy and Phase Changes

I understand that phase changes have entropy changes, but in today's lecture, Lavelle mentioned that this "makes sense because H2O(l) can occupy many more positions than H2O(s)." What exactly did he mean by positions? Could anyone expand on this? Thank you!
Tue Feb 02, 2021 12:09 pm
Forum: Calculating Work of Expansion
Topic: What is V1 and V2
Replies: 12
Views: 54

### Re: What is V1 and V2

V1 and V2 are also used in the work equation where w=nRT*ln(V2/V1). I don't believe Lavelle has explicitly covered this equation, but it was useful for the Sapling week 3-4 homework!
Tue Feb 02, 2021 11:55 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: constant pressure in open beaker
Replies: 8
Views: 57

### Re: constant pressure in open beaker

Because the surrounds of the system (the universe) is so large, any change in pressure could not have a significant effect on the system and therefore, is considered negligible. Lavelle gave a good example of this in lecture. It is similar to adding a bucket of water into the ocean; the volume of th...
Tue Feb 02, 2021 11:51 am
Forum: Calculating Work of Expansion
Topic: Sapling #14 Weeks 3 and 4
Replies: 6
Views: 71

### Re: Sapling #14 Weeks 3 and 4

Yes, you would add the two steps together. Because the first step occurs at constant volume, the work done is just 0. To calculate the second step, we use the work equation using the pressure given and volume change, and finally convert from L*atm to J. Hope this helps!
Tue Feb 02, 2021 11:44 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Week 3/4 Sapling #18
Replies: 2
Views: 44

### Re: Week 3/4 Sapling #18

Yes, the change in internal energy would be equal to q+w. So to find delta U, you would take the q value you found in the first part and subtract (if negative) the work value you calculate.
Tue Feb 02, 2021 8:25 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Closed System Volume Changes
Replies: 4
Views: 38

### Re: Closed System Volume Changes

Yes, a closed system can experience volume changes if a piston compresses or expands it. A closed system is simply defined as a system where energy only (as opposed to matter) can exchange with the surroundings.
Tue Jan 26, 2021 1:09 pm
Forum: General Science Questions
Topic: equilibrium concentrations versus just concentrations
Replies: 2
Views: 31

### Re: equilibrium concentrations versus just concentrations

Adding on, equilibrium concentrations are used to calculate K while concentrations at other points in the reaction (not at equilibrium) can be used to calculate Q. This allows you to make comparisons and predict how the reaction will proceed.
Tue Jan 26, 2021 12:59 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: increasing base strength sapling
Replies: 2
Views: 28

### Re: increasing base strength sapling

I believe these are actually the values of the pKb of each base, not the pOH. The larger the pKb the weaker the base. So, F- with a pKb of 10.55 will be the weakest. Hope this helps!
Tue Jan 26, 2021 12:15 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Textbook 4.29
Replies: 4
Views: 60

### Re: Textbook 4.29

I was also a little confused on this. Because the values are so similar, I realized it wouldn't make too much of a difference in the calculation using one value over another, and I just used the enthalpy of formation value as 0. As for what the actual difference between the two means, I'm not quite ...
Tue Jan 26, 2021 12:07 pm
Forum: Student Social/Study Group
Topic: Textbook Q 5G3
Replies: 2
Views: 28

### Re: Textbook Q 5G3

You would still include [H2O] because it is in gas form. The only components that are excluded are solids and liquids.
Mon Jan 25, 2021 9:27 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Textbook question 4E.9
Replies: 8
Views: 63

### Textbook question 4E.9

I'm pretty lost on how to go about this problem. I understand the resonance structures of benzene, but don't know what it is asking for or what it means by "the lowering in molar energy." If anyone would be able to share how they went about this problem I would really appreciate it, thanks...
Wed Jan 20, 2021 11:57 am
Forum: Phase Changes & Related Calculations
Topic: Steam causing severe burns
Replies: 5
Views: 42

### Re: Steam causing severe burns

I agree with the post above! Since hydrogen bonds are hard to break, they require a lot of energy, and therefore result in a high enthalpy of vaporization that is released when it meets something cooler, such as skin. Liquids without hydrogen bonds would not have such a large enthalpy of vaporizatio...
Wed Jan 20, 2021 11:53 am
Forum: Phase Changes & Related Calculations
Topic: Temperature through Phase Changes
Replies: 4
Views: 64

### Re: Temperature through Phase Changes

Frankie Mele 3J wrote:I was wondering what exactly deltaQ is representing in this graph. I understand it is heat supplied but what does this variable verbally represent? Is it just change in heat energy?

I believe Q is just the symbol used for heat. So yes, deltaQ would mean change in heat.
Wed Jan 20, 2021 10:17 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6E #1
Replies: 2
Views: 30

### Re: 6E #1

Since H 2 SO 4 is a diprotic acid, it has two reactions that give off H 3 O+, the first: H 2 SO 4 + H 2 O --> H 3 O+ + HSO 4 - and the second: HSO 4 - +H 2 O --> H 3 O+ + SO 4 2- . Because H 2 SO 4 is a strong acid, it dissociates completely. However, the second reaction needs an ICE table. Make sur...
Tue Jan 19, 2021 6:54 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Textbook problem 5J.5d
Replies: 5
Views: 49

### Re: Textbook problem 5J.5d

I believe it's a typo. In Lavelle's solution manual errors pdf on his website, the correct equation should have capital letter D in place of the lowercase d. I think it just stands for an unknown halide.
Tue Jan 19, 2021 6:34 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Textbook Problem 6C.13
Replies: 2
Views: 33

### Re: Textbook Problem 6C.13

I was also confused on this. I couldn't find any pattern, but the solutions manual noted that generally, arylamines < ammonia < alkylamines and that methyl < ethyl < etc. I'm not sure if we need to specifically know these patterns, but it gave me a better sense of what question was asking for in the...
Wed Jan 13, 2021 1:59 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: lecture 5 question
Replies: 13
Views: 93

### Re: lecture 5 question

I think it would be important to memorize all the strong acids and bases. That way, when coming across any other acid/base, you will know it has to be weak. A conjugate acid is the product formed when a base reacts with water. A conjugate base is the product formed when an acid reacts with water. Fo...
Wed Jan 13, 2021 12:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Amphoteric vs Amphiprotic
Replies: 5
Views: 44

### Amphoteric vs Amphiprotic

What exactly is the difference between something amphoteric vs something amphiprotic? Amphoteric substances can act as an acid and a base correct? So what distinguishes this from amphiprotic?
Wed Jan 13, 2021 12:06 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Cubic approximation
Replies: 5
Views: 51

### Re: Cubic approximation

Yes, because the K c value is so small, we can approximate that the change taking place is also so small that it is negligible. However, if K c is very large we would not be able to make a similar approximation. In fact, the change would be predicted to be very large and would have a considerable ef...
Mon Jan 11, 2021 11:36 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5I.13
Replies: 2
Views: 22

### Re: 5I.13

I agree with the post above. I used the Kc value because the problem gives you the amount in mmol which you can then convert to concentration.
Mon Jan 11, 2021 11:33 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook 5I.3
Replies: 3
Views: 35

### Re: Textbook 5I.3

The Kc value for this reaction at 500K is actually 160. Carrying out your calculation with this Kc value should get you the right answer. I made this mistake too!
Thu Jan 07, 2021 3:16 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE tables
Replies: 11
Views: 115

### ICE tables

I know Lavelle hasn't gone over ICE tables in lecture yet, but I was wondering how we know when to use them and what the general procedure is. I'm a little rusty on my high school chem, and I vaguely remember using them, but need a quick refresher to help me with the homework.
Thu Jan 07, 2021 3:09 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Including H2O
Replies: 7
Views: 58

### Re: Including H2O

To answer your second question, no liquids are included, so even if liquid H2O was included only on one side, it would not have to be taken into consideration when calculating K.
Thu Jan 07, 2021 3:06 pm
Forum: Ideal Gases
Topic: Reaction Quotient(Q) vs. Equilibrium Constant(K)
Replies: 9
Views: 118

### Re: Reaction Quotient(Q) vs. Equilibrium Constant(K)

For reactions not at equilibrium, the reaction quotient Q tells us whether the forward or reverse reaction will be favored in order to reach equilibrium. For instance, if Q>K, the reverse reaction is favored whereas if Q<K, the forward reaction is favored. And when the reaction is at equilibrium, Q ...
Thu Jan 07, 2021 2:53 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Direction of a non-equilibrium reaction
Replies: 11
Views: 101

### Re: Direction of a non-equilibrium reaction

When Q is less than K, the forward reaction, product formation, is favored because Q is smaller as a result of a larger denominator (reactants). In order to reach equilibrium, more products must be formed. Same goes the other way. When Q is greater than K, the reverse reaction is favored because the...
Thu Jan 07, 2021 9:37 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating Kc
Replies: 4
Views: 56

### Calculating Kc

In Sapling question 2 for week 1, it gives us:

At a certain temperature, 0.680 mol SO3 is placed in a 2.50 L container.
2SO3(g)↽−−⇀2SO2(g)+O2(g)
At equilibrium, 0.120 mol O2 is present.

It asks to calculate Kc. How would you approach this problem?
Wed Dec 09, 2020 4:00 pm
Forum: Bronsted Acids & Bases
Topic: 6C.21 Which acid is stronger?
Replies: 1
Views: 15

### 6C.21 Which acid is stronger?

This question asks to compare the strengths of acetic acid, CH3COOH, and formic acid, CH2O2. The stronger acid is formic acid, but I'm confused as to why. I thought acetic acid would be stronger. If anyone could explain their reasoning on this one, I would really appreciate it.
Wed Dec 09, 2020 3:16 pm
Forum: Amphoteric Compounds
Topic: Identifying Amphoteric Compounds
Replies: 4
Views: 47

### Re: Identifying Amphoteric Compounds

In the textbook, it mentioned that many amphoteric compounds consist of the elements that lie on the diagonal border between the metals and nonmetals. It also gave a nice visual of this section of the periodic table. This helped me a lot, so I think it would be worth looking at too!
Wed Dec 09, 2020 3:07 pm
Forum: Properties & Structures of Inorganic & Organic Bases
Topic: Strong Bases
Replies: 1
Views: 34

### Re: Strong Bases

When Na2O reacts with water, it forms NaOH. Same with CaO, when in an aqueous solution, it forms Ca(OH)2. These are bases because they can accept protons.
Wed Dec 09, 2020 3:01 pm
Forum: Administrative Questions and Class Announcements
Topic: Naming on Final
Replies: 9
Views: 130

### Re: Naming on Final

I think it would be most helpful to memorize them. I saw a post earlier with a link to a quizlet that helps! https://quizlet.com/462765872/ligand-na ... ds/?x=1jqt
Wed Dec 09, 2020 11:54 am
Forum: Identifying Acidic & Basic Salts
Topic: Acidic, basic, or neutral?
Replies: 8
Views: 123

### Acidic, basic, or neutral?

What is the general method of identifying whether a salt is acidic, basic, or neutral? I'm a little confused on this concept, thanks!
Wed Dec 09, 2020 11:43 am
Forum: Bronsted Acids & Bases
Topic: Strong vs weak acid/base
Replies: 2
Views: 20

### Strong vs weak acid/base

Is there a way to tell whether an acid/base is strong or weak? Or would memorization be the best way to learn them?
Wed Dec 02, 2020 11:53 am
Forum: Administrative Questions and Class Announcements
Topic: Midterm 1 and 2 Review
Replies: 8
Views: 127

### Re: Midterm 1 and 2 Review

I'm not completely sure if he is still planning on doing this, but I believe Dr. Lavelle mentioned he would go over commonly missed questions during his final reviews as well.
Wed Dec 02, 2020 11:46 am
Forum: Bronsted Acids & Bases
Topic: HCl vs. HBr
Replies: 6
Views: 68

### Re: HCl vs. HBr

Andrew Wang 1G wrote:So would it be true to say that the weaker the bond, the stronger the acid since it dissociates more easily?

I think so, and that is also why HF is a weak acid since it has a shorter and therefore stronger bond than HCl and HBr.
Wed Dec 02, 2020 11:42 am
Forum: Bronsted Acids & Bases
Topic: Why is HF a weak acid?
Replies: 5
Views: 124

### Re: Why is HF a weak acid?

Because the HF bond is so short, it is very strong and therefore makes it difficult for the bond to be broken. In other words it won't dissociate completely. Stronger acids such as HCl and HBr have weaker bonds and are more likely to dissociate completely.
Wed Dec 02, 2020 11:37 am
Forum: Bronsted Acids & Bases
Topic: Strong Acid vs. Weak Acid
Replies: 7
Views: 79

### Re: Strong Acid vs. Weak Acid

I think it is most important to know that strong acids dissociate completely while weak acids do not dissociate completely. To differentiate, a strong acid will have a lower pH than a weak acid at the same concentration. Other than that, I generally just memorize the most common strong acids and mos...
Wed Dec 02, 2020 11:19 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Sapling Week 9 Q2
Replies: 5
Views: 58

### Sapling Week 9 Q2

In the second part of the question, it asks for the oxidation state of the central atom in [AgCl2]-. How would you calculate this? I'm kind of rusty on my high school chem and would really appreciate it if someone could explain their thought process. Thanks!
Wed Nov 25, 2020 3:03 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Chelate Structures
Replies: 1
Views: 35

### Chelate Structures

In lecture, Lavelle mentioned that longer molecules with multiple lone pairs have the ability to form chelates. In his example, he had ethylenediamine (I think this is the name) forming a ring, bonding to cobalt in two bonding sites. How would this work for tridentates if there must be three bonding...
Wed Nov 25, 2020 2:58 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Chelates
Replies: 2
Views: 24

### Re: Chelates

I think it would also be useful to know that chelates have tight bonds with cations due to the multiple bonding sites. Lavelle mentioned this a couple times in lecture so I made sure to understand that concept as well.
Wed Nov 25, 2020 2:49 pm
Forum: Lewis Structures
Topic: Most Stable Structure
Replies: 23
Views: 203

### Re: Most Stable Structure

The best way to know when the Lewis structure is most stable is by calculating formal charge for each atom using FC= V-(S/2) where V are the valence electrons on that atom, and S is the number of shared electrons. The most stable lewis structure will have formal charges closest to 0. And it is also ...
Wed Nov 25, 2020 2:37 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Number of Ligands?
Replies: 1
Views: 37

### Re: Number of Ligands?

During today's (11/25) lecture, Lavelle specified that we only need to know the oxidation states for s and p block elements. He said that d block elements vary but you can find the oxidation state by looking at the bonds it forms with other charged atoms. So in lecture, his example with [Ni(NH 3 ) 4...
Wed Nov 25, 2020 2:24 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Lecture #24 Ligands and Complexes
Replies: 5
Views: 48

### Re: Lecture #24 Ligands and Complexes

Octahedral wouldn't make sense if the atom is forming four bonds, so I'm pretty sure he meant tetrahedral or square planar.
Wed Nov 18, 2020 9:49 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polarizability vs Polarizing Power in anions/cations & bonding
Replies: 10
Views: 81

### Re: Polarizability vs Polarizing Power in anions/cations & bonding

Large anions are typically highly polarizable, meaning they are likely to have their electrons distorted. So think I - , Br - . This is because their electrons are not as tightly bound to the nucleus, and are pulled away by polarizing cations. Small, highly charged cations like Al 3+ have the large ...
Wed Nov 18, 2020 9:39 pm
Forum: Dipole Moments
Topic: Dipole Dipole Interactions
Replies: 7
Views: 66

### Re: Dipole Dipole Interactions

I think C-Cl would experience dipole-dipole interactions. I believe that dipole-dipole interactions occur when there is a difference between electronegativities in a molecule. However, they do not occur in nonpolar molecules. At least that is the way I think of it. Yeah that's what I'm thinking too...
Wed Nov 18, 2020 7:27 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: outline 2 bullet point
Replies: 1
Views: 20

### outline 2 bullet point

Describe the factors affecting the energy of an electron in a many-electron atom. I'm not quite sure if this is referring to the different energy levels (n) or something maybe completely different. Would someone be able to explain this concept in a little more depth? I wasn't able to think of any ot...
Wed Nov 18, 2020 3:56 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 3d vs 4s orbitals
Replies: 4
Views: 33

### 3d vs 4s orbitals

When writing electron configurations, do we always write the 3d before the 4s? Also, why does the way we fill the orbitals change when we get to the d-block since K and Ca go from 3p to 4s, but something like Sc would be [Ar]3d1 4s2? I'm confused because I'm seeing mixed explanations online, thanks!
Tue Nov 17, 2020 8:46 pm
Forum: Octet Exceptions
Topic: Textbook 2C7 Iodine
Replies: 2
Views: 50

### Re: Textbook 2C7 Iodine

Draw the lewis structures by adding up all the electrons in the ion/molecule. Then divide by 2 to get the number of electron pairs. This will help you see how many pairs are needed to be drawn. Make sure to take formal charge into consideration, "balancing" the molecule so each is closest ...
Tue Nov 17, 2020 7:45 pm
Forum: Lewis Structures
Replies: 2
Views: 28

Are there any tips on knowing when a molecule will be a radical? I'm pretty comfortable with drawing lewis structures, but I haven't had much practice with radicals yet. Not sure if there is anything that would specifically show you it would have to be a radical/biradical. Thanks!
Wed Nov 11, 2020 12:33 pm
Forum: Bond Lengths & Energies
Topic: Bond Strength Clarification
Replies: 5
Views: 80

### Re: Bond Strength Clarification

The bond is stronger between two smaller atoms and weaker between two larger atoms because the bonds get longer as the size of the radius in each atom increases. (Longer bonds result in weaker bonds). The opposite is true for molecules: larger molecules will have stronger intermolecular forces (to p...
Wed Nov 11, 2020 12:23 pm
Forum: Sigma & Pi Bonds
Topic: Sigma and Pi bonds
Replies: 9
Views: 98

### Re: Sigma and Pi bonds

Hi! I don't recall this topic being mentioned in the lectures. Just confirming - we will not need to know this for the midterm next week? Thank you! I don't think Lavelle covered this in lectures yet either, so we won't have to know it. The midterm covers everything from the last eight bullets on o...
Wed Nov 11, 2020 12:17 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Homework Problem #3
Replies: 2
Views: 44

### Re: Homework Problem #3

I agree with the post above, making sure to minimize formal charge and that the formal charges added up match the overall charge of the compound. Also, it is important to note that some elements such as phosphorous can have an expanded octet, meaning they can take on more that 8 valence electrons, t...
Wed Nov 11, 2020 12:06 pm
Forum: Ionic & Covalent Bonds
Topic: Difference between ionic bonding and ion-ion interactions?
Replies: 4
Views: 65

### Re: Difference between ionic bonding and ion-ion interactions?

The basic difference is that ionic bonds occur between atoms that form a salt, like you said, it is intra molecular. Ion-ion interactions are not necessarily bonds, but rather interactions because they occur when charged molecules themselves interact, so inter molecular forces. That is the basic dif...
Mon Nov 09, 2020 10:03 am
Forum: Resonance Structures
Topic: lower energy vs higher energy
Replies: 3
Views: 36

### lower energy vs higher energy

I am a little confused on the concept of the differing energies of resonance structures. If I recall correctly, structures with formal charges of 0 have lower energy than those with charges? Also, how do we know which resonance structures contribute more to the overall structure? I'm stuck on this c...
Fri Nov 06, 2020 12:09 pm
Forum: Octet Exceptions
Topic: Group 13 Elements
Replies: 13
Views: 180

### Re: Group 13 Elements

Are there any cases when a group 13 element forms a complete octet? Or is this too unrealistic to happen in the molecules we are studying? Should we expect group 13 elements to not form a complete octet and instead become Lewis acids? I believe you are right. It is too unreliable for group 13 eleme...
Fri Nov 06, 2020 11:56 am
Forum: Lewis Structures
Topic: Simplifying Formal Charge?
Replies: 3
Views: 28

### Re: Simplifying Formal Charge?

I believe you have to draw your lewis structures in a way that minimizes the formal charges of the atoms. I haven't gotten to the homework questions yet, but if I recall from the lectures, the goal is to get the formal charge to match the charge of the molecule/ion/whatever you are working with.
Fri Nov 06, 2020 11:50 am
Forum: Octet Exceptions
Topic: Octet exceptions
Replies: 4
Views: 36

### Octet exceptions

I know that P, S, and Cl can have more than 8 valence electrons, but I'm still confused as to why this is possible. Also, how will we know when to make these exceptions when drawing Lewis structures? I tried looking back at the lecture, but maybe hearing it in different wording could help me out mor...
Fri Nov 06, 2020 11:32 am
Forum: Ionic & Covalent Bonds
Topic: Covalent Character
Replies: 4
Views: 31

### Re: Covalent Character

All ionic bonds have some covalent character because the there will be some positive charge and some negative charge in the salt. So, the electrons in the negatively charged region (anion) will be attracted to the positive charged cation. What I pulled from the lecture is that all ionic bonds have t...
Mon Nov 02, 2020 12:24 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Textbook question 1E.17
Replies: 2
Views: 45

### Textbook question 1E.17

For each of the following ground-state atoms, predict the type of orbital (1s, 2p, 3d, 4f, etc.) from which an electron will be removed to form the +1 ion: Part b asks to predict the orbital for Mn. I was thinking an electron would be removed from 3d, but the solution says 4s. Can anyone please help...
Wed Oct 28, 2020 3:30 pm
Forum: Properties of Light
Topic: UA Workshop Question
Replies: 4
Views: 74

### Re: UA Workshop Question

Hey! I was super confused on this problem earlier today too. Regarding the 250 nm, you convert that wavelength to m to get 2.5*10^-7 m. With this conversion, we can use the equation E=hc/(lambda) and get the amount of energy per photon. The energy should be 7.95*10^-19 J/photon I believe. Since we'...
Tue Oct 27, 2020 8:25 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectroscopy vs molecular spectroscopy
Replies: 2
Views: 38

### Atomic Spectroscopy vs molecular spectroscopy

On outline 2, one of the bullets says: "With respect to electron transitions that give rise to a UV or visible spectrum: understand the difference between electronic transitions in atomic orbitals (atomic spectroscopy) and electronic transitions in molecular orbitals (molecular spectroscopy).&q...
Tue Oct 27, 2020 8:09 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: E. 23 b
Replies: 3
Views: 54

### Re: E. 23 b

Disregard my answer, I misread the question. The person above me has the correct answer. So sorry!!
Tue Oct 27, 2020 8:07 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: E. 23 b
Replies: 3
Views: 54

### Re: E. 23 b

You only use avogadro's number when converting to/from number of atoms/molecules. Since this question asks you to go from mg to moles, you simple go from mg to g to moles of SO3.
Tue Oct 27, 2020 4:25 pm
Forum: DeBroglie Equation
Topic: Sapling Homework - electron affinity
Replies: 9
Views: 137

### Re: Sapling Homework - electron affinity

hello I am having a lot of trouble with this problem for the energy of an electron. I did: Ke=1/2(m)(v^2) for m i put in the mass of an electron: 9.109x10^-31 I got v from: v= (3.0x10^8 m/s)/(2.1x10^-6 m)= 1.42x10^14s Ke= 1/2(9.109x10^-31 kg )((1.42x10^14 s) ^2) the answer I got was Ke= 9.18x10^-3....
Tue Oct 27, 2020 4:24 pm
Forum: DeBroglie Equation
Topic: Sapling Homework - electron affinity
Replies: 9
Views: 137

### Re: Sapling Homework - electron affinity

To find velocity, you use the de broglie equation lamba=h/p, substituting mv for p. You then solve for v, and input this value into the 1/2mv^2 equation.
Mon Oct 26, 2020 8:54 am
Forum: Limiting Reactant Calculations
Topic: Week 2 Workshop Question
Replies: 2
Views: 77

### Week 2 Workshop Question

Hi, I believe this is a question from a workshop a couple weeks ago. I wasn't able to make it so I couldn't see the solutions. Would anyone be able to walk me through your thought process. I was able to get an answer, but I'm not sure if I did it correctly. Potassium superoxide reacts with water to ...
Sun Oct 25, 2020 9:06 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Equation and Negative Signs
Replies: 11
Views: 116

### Rydberg Equation and Negative Signs

Hi, I had a quick question about how we should be leaving our answers when solving questions using the Rydberg equation/empirical equation. When using the Rydberg equation, we get a positive value, obviously because the answer is in Hz. Then we can convert to E which leaves us with a positive value....
Thu Oct 22, 2020 7:22 pm
Forum: Einstein Equation
Topic: 1B7
Replies: 2
Views: 53

### Re: 1B7

For part b, you need to first calculate the number of sodium atoms in 5.00 mg by doing some dimensional analysis (going from mg to g to mol to atoms). Then use the energy calculated in part a and multiply that by the number of sodium atoms which gives you 44.1J
Thu Oct 22, 2020 11:08 am
Forum: Photoelectric Effect
Topic: Sapling HW 2 Question 4
Replies: 6
Views: 97

### Sapling HW 2 Question 4

Hi, I'm having some trouble with the second part of this question. I found the work function, but how would I go about finding the maximum number of electrons? When a metal was exposed to photons at a frequency of 1.13×1015 s−1, electrons were emitted with a maximum kinetic energy of 3.70×10−19 J. C...
Thu Oct 22, 2020 10:39 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Equation and its Fundamental Equation
Replies: 8
Views: 46

### Re: Rydberg Equation and its Fundamental Equation

I'm sure we would be able to use either equation. My TA said our scratchwork is not going to be graded, so as long as you get the right answer you will get credit. Also, we did a problem on finding n energy levels in our discussion and my TA used the rydberg equation, so I think it's fine to use.
Thu Oct 22, 2020 10:04 am
Forum: Photoelectric Effect
Topic: Work function and incident light
Replies: 3
Views: 54

### Re: Work function and incident light

I believe you did the first part right, and as for part b, I think you would simply use the lamba=h/mv equation. Divide Planck's constant h by massxvolume. To get the mass, you would take the mm of rubidium, 85.468g/mol and divide by avogadro's number. Use the velocity that is given. After plugging ...
Thu Oct 22, 2020 9:25 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: finding n values
Replies: 3
Views: 47

### Re: finding n values

To solve this you would use the v=R(1/n1^2-1/n2^2) equation where v is frequency and R is rydberg's constant. Before solving, you have to figure out the final energy state. You can do this by converting the frequency 6.1684x10^14Hz to wavelength to get 486.35nm. This is in the visible region and the...
Fri Oct 16, 2020 11:07 am
Forum: Properties of Light
Topic: Examples of waves and particles of light
Replies: 2
Views: 37

### Re: Examples of waves and particles of light

I think the most important thing to know is that light is acting like a particle or a "stream of photons" in the photoelectric effect and is acting like a wave in diffraction. As long as we have a strong understanding of the behavior of light in those scenarios, I'm thinking we'll be okay ...
Thu Oct 15, 2020 6:03 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect
Replies: 3
Views: 90

### Re: Photoelectric Effect

For A you need to use Ek = 1/2 mv^2 where m is mass of an electron and v is velocity. Then for B you need to take the work function and divide by avogadro's number since it is asking for energy per sodium atom. Finally for C, I believe you would use E=hv to find the frequency.
Thu Oct 15, 2020 3:16 pm
Forum: Photoelectric Effect
Topic: 1B #7
Replies: 4
Views: 69

### 1B #7

I'm a little confused on finding the energy emitted by 5.00mg of sodium atoms (Part B). I'm okay with parts A and C, but I think I might be overthinking B or messing up somehow. Sodium vapor lamps, used for public lighting, emit yellow light of wavelength 589 nm. How much energy is emitted by (a) an...
Thu Oct 15, 2020 10:26 am
Forum: Properties of Electrons
Topic: Lower energy level
Replies: 3
Views: 36

### Re: Lower energy level

I believe it means each series shares a different lower energy level. For example, the Lyman series shares a lower energy level of n=1, meaning that electron dropped from some higher energy level to n=1. Same with the Balmer series, the electron dropped from a higher energy level down to n=2. These ...
Mon Oct 12, 2020 5:26 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Identifying n1 and n2
Replies: 4
Views: 64

### Re: Identifying n1 and n2

I'm not sure if this answers your question, but it is always going to be final - initial. So I believe in the Rydberg equation you wrote out, n1 would be final and n2 would be the initial.