Search found 104 matches
- Sat Mar 13, 2021 4:29 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Concentration and Reduction
- Replies: 2
- Views: 278
Re: Concentration and Reduction
Hey! You can also think about products vs reactants in a concentration cell in terms of diffusion. Molecules in higher concentration regions move to regions of lower concentration. Thus, the reactants move from a region of high concentration to a region of low concentration as products.
- Sat Mar 13, 2021 3:53 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: E naught in a Concentration Cell
- Replies: 3
- Views: 376
Re: E naught in a Concentration Cell
Hey! well, you can't really use that equation for a concentration cell because you don't know K. You can't use the given concentrations for K, because it's not at equilibrium. The explanation given above is the reason why E nought is 0 for a concentration cell!
- Thu Mar 11, 2021 7:22 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: textbook 4D.9
- Replies: 5
- Views: 656
Re: textbook 4D.9
Yeah, why exactly does the final enthalpy change for a mole of TNT become positive? Shouldn't the combustion of TNT also release energy, so it should be a negative value?
- Thu Mar 11, 2021 1:16 am
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Textbook 6.57
- Replies: 1
- Views: 174
Textbook 6.57
In the solution for textbook question 6.57, the manual says to use the half reaction for the reduction of F2 as the reaction happening at the anode. What in the problem tells us which equation to use in the redox reaction? How exactly are we supposed to know to use the F2 half reaction?
- Tue Mar 09, 2021 11:52 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Question about Textbook 6N.11
- Replies: 1
- Views: 161
Question about Textbook 6N.11
According to the solutions manual, we can add up the E nought values from the individual half reactions to get the E nought value of the redox reaction. I remember E values are technically not state functions, so we can't always just add them up. In what situations can we just add up E nought values...
- Tue Mar 09, 2021 3:00 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Textbook 6N.1 part b
- Replies: 1
- Views: 167
Textbook 6N.1 part b
For part b in question 6N.1, the solutions say that the Nernst equation uses 2 moles of electrons in the redox reaction. However, after going through the problem, only one mole of electron is used in the reaction. Is this a typo in the solutions? Or am I doing something wrong?
- Sat Mar 06, 2021 2:06 pm
- Forum: General Rate Laws
- Topic: Increasing or decreasing the rate constant
- Replies: 3
- Views: 1992
Re: Increasing or decreasing the rate constant
Adding a catalyst should increase the rate constant, but according to the Arrhenius equation, decreasing the activation energy should increase k. Using similar logic, increasing temperature increases k according to the equation. Thus, the rate of the reaction should increase.
- Sat Mar 06, 2021 2:00 pm
- Forum: General Rate Laws
- Topic: Stoichiometry Clarification
- Replies: 2
- Views: 196
Re: Stoichiometry Clarification
Hey! When writing the rate, the reactants are always written with negative coefficients because we assume that the reaction is moving forward as time progresses. Thus, the concentration of reactant decreases over time.
- Sat Mar 06, 2021 1:32 pm
- Forum: Student Social/Study Group
- Topic: What organizations are you guys in?
- Replies: 53
- Views: 3005
Re: What organizations are you guys in?
I'm in a few different orgs! I'm a part of GlobeMed and Project RISHI, which are both global health organizations but have very different takes on how to approach health. I'm also in HOSA and CaHPSA, which are pre-med orgs. How is GlobeMed? It sounds really interesting! I'm definitely considering a...
- Wed Mar 03, 2021 11:18 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Order part II
- Replies: 3
- Views: 250
Re: Order part II
Just to echo everyone else, order can only be determined by using experimental data! Technically, each reactant has a particular order in the reaction. The total order of the reaction is the sum of all the individual orders of the reactants. Hopefully that makes sense!
- Wed Mar 03, 2021 11:13 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Textbook question 6L.9
- Replies: 1
- Views: 169
Re: Textbook question 6L.9
Hey! I could be wrong, but I think we can use the list of redox reactions with their standard reduction potentials as reference to see what the product should be in the half reaction.
- Wed Mar 03, 2021 11:05 pm
- Forum: Student Social/Study Group
- Topic: What organizations are you guys in?
- Replies: 53
- Views: 3005
Re: What organizations are you guys in?
I'm in a few different orgs! I'm a part of GlobeMed and Project RISHI, which are both global health organizations but have very different takes on how to approach health. I'm also in HOSA and CaHPSA, which are pre-med orgs.
- Thu Feb 25, 2021 5:19 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: When to use the right Nernst Equation
- Replies: 3
- Views: 298
Re: When to use the right Nernst Equation
To add on, you can actually just simplify the second equation to 0.05916V in the numerator. This takes into account all of the constants that are multiplied out at a temperature of 25* celsius. But yes, the first two can be used interchangeably and the last one is used for reactions at equilibrium!
- Thu Feb 25, 2021 5:13 pm
- Forum: Balancing Redox Reactions
- Topic: Week 7/8 Sapling #4
- Replies: 3
- Views: 253
Re: Week 7/8 Sapling #4
Hey! You would still need to include the HCl because the Cl- ions it provides is a necessary part of the products. You are right that it doesn't directly participate in the redox reaction, but because it's included in the unbalanced reaction, I'm pretty sure we still use it. Hope that helps!
- Thu Feb 25, 2021 4:40 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: When to use Different Nernst Equations
- Replies: 11
- Views: 833
When to use Different Nernst Equations
I understand the difference between the two Nernst equations: E = E* - RT/nF(lnQ) and E = E* - 0.05916V/n(log 1), but are there specific situations of when to use a specific one? Or can they be used interchangeably? I appreciate any help!
- Wed Feb 24, 2021 3:56 pm
- Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
- Topic: Concentrations
- Replies: 8
- Views: 643
Re: Concentrations
I understand the equation E = E* - (RT/Fn)lnQ when it comes to the relation between concentration and voltage; however, I am a bit confused as to what the term E* specifically means. How does it differ from the E at the left-hand side of the equation? If someone could clear that up for me that'd be...
- Wed Feb 24, 2021 1:59 pm
- Forum: Balancing Redox Reactions
- Topic: Sapling Number 10
- Replies: 6
- Views: 300
Re: Sapling Number 10
Hey! So there is a general trend, although I know there are many exceptions. Because an oxidizing agent ultimately wants to gain electrons, you can use electronegativity as a trend to approximate which oxidizing agent will be the strongest. But of course, if you have access to the reduction potentia...
- Sun Feb 21, 2021 1:26 pm
- Forum: Calculating Work of Expansion
- Topic: Negative Work
- Replies: 30
- Views: 1174
Re: Negative Work
Hey! So like others said, when a system does work on its surroundings, the work will be negative. This is why in our expansion example problems in class, they were all negative work. Expansion means the system is pushing the piston outwards, and thus doing work on its surroundings. Compression would...
- Sun Feb 21, 2021 1:24 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Degeneracy
- Replies: 11
- Views: 827
Re: Degeneracy
When I think about degeneracy, or at least calculating w, I always think about it as the number of possible states the molecule can exist in raised to the amount that is present. So if there is one mole present, the number of possible states would be raised by avagadro's number: 6.022x10^23 molecules.
- Sun Feb 21, 2021 12:05 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Chem community points
- Replies: 10
- Views: 537
Re: Chem community points
By the end of week 7 we should have 35 posts (85 if you had Dr. Lavelle for chem 14A), since we do 5 posts each week :)
- Thu Feb 18, 2021 5:43 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Average Kinetic Energy
- Replies: 5
- Views: 439
Average Kinetic Energy
I was working through problem 4.19 in the textbook, and the question asked to calculate the kinetic energy of Kr. The solution manual mentions that average kinetic energy = 3/2RT. Where does this equation come from? I see that it's equal to the internal energy of an ideal gas, so do we assume that a...
- Wed Feb 17, 2021 6:02 pm
- Forum: Calculating Work of Expansion
- Topic: Textbook 4D.7
- Replies: 2
- Views: 259
Textbook 4D.7
In the textbook on problem 4D.7, the solution manual uses the temperature 298 K in the ideal gas law equation to solve for work. However, where is this temperature given to us in the problem? The only information given is the chemical reaction and the number of moles reacted. I don't really understa...
- Sun Feb 14, 2021 12:49 pm
- Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
- Topic: Statistical Entropy vs. Thermodynamic Entropy
- Replies: 3
- Views: 280
Re: Statistical Entropy vs. Thermodynamic Entropy
Well for one, we would use one over the other depending on the information we have given to us. If we don't know heat of the reversible reaction or temperature, we can't necessarily use the thermodynamic entropy equation. I don't think Dr. Lavelle has explicitly gone over the differences between ent...
- Sun Feb 14, 2021 12:46 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Sapling week 5/6 #3
- Replies: 2
- Views: 191
Re: Sapling week 5/6 #3
I'm not entirely sure, but I don't think there would be a situation where that happens. For each phase change, entropy increases from solid to liquid and liquid to gas, and the only way for these phase changes to occur is for heat to be inputted into the system. Thus, enthalpy must increase as well....
- Sat Feb 13, 2021 11:20 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Question about Sapling week 5/6 #20
- Replies: 2
- Views: 193
Question about Sapling week 5/6 #20
Hey, I have a quick question about delta g and its relation to spontaneity. So on the graph given on #20, the G curve shows a minimum for the reaction in which the reaction always approaches the minimum, which is also the equilibrium, demonstrating that the reaction is spontaneous. If the curve inst...
- Wed Feb 10, 2021 3:54 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Question about Sapling #6 Week 5/6
- Replies: 6
- Views: 280
Question about Sapling #6 Week 5/6
I thought that we could only use the entropy equation that calculates residual entropy due to changes in volume in isothermal reactions. However, on Sapling Week 5/6, problem #6, we use ∆S = nR lnV2/V1 even though the temperature is changing (not an isothermal reaction). Did I have the wrong assumpt...
- Wed Feb 10, 2021 9:59 am
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Isothermal Reactions
- Replies: 26
- Views: 1171
Isothermal Reactions
When a problem says the reaction is isothermal, do we assume it occurs on a reversible pathway as well?
- Sun Feb 07, 2021 7:08 pm
- Forum: Calculating Work of Expansion
- Topic: Deriving equation for work of a reversible reaction
- Replies: 1
- Views: 133
Deriving equation for work of a reversible reaction
I'm not entirely sure if Dr. Lavelle went over this in lecture and I missed it, but could someone explain exactly how we derived the equation for the work of an isothermal, reversible reaction? I believe it is w = -nRTln(V2/V1)
- Sun Feb 07, 2021 7:00 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Sapling Question 19
- Replies: 3
- Views: 224
Sapling Question 19
I got the right answer, but I don't really understand how to get Cv from Cp. I looked it up, but it's not consistent with the relationship shown on the equation sheet. Can someone help? Here's the problem for reference: "A 0.565 mol sample of CO2(g), initially at 298 K and 1.00 atm, is held at ...
- Sun Feb 07, 2021 6:55 pm
- Forum: Calculating Work of Expansion
- Topic: Converting Units
- Replies: 4
- Views: 145
Re: Converting Units
Hey! So, the only reason we have to convert from L*atm to J is just because the problem asks us to give the work in joules. Unless the problem specifies for an answer in joules, it likely won't be necessary to convert!
- Sun Feb 07, 2021 6:41 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Sapling Q#19
- Replies: 2
- Views: 110
Re: Sapling Q#19
Hey! So on that problem, at least on sapling, the heat constant is not Cv but Ccal, meaning its the heat capacity of the calorimeter. The heat capacity of the calorimeter takes into account the moles reacting I think, because it measures the amount of heat to increase the temperature of the entire s...
- Sun Feb 07, 2021 6:10 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: specific heat for ideal gases
- Replies: 3
- Views: 110
Re: specific heat for ideal gases
Hey! Yeah, the specific heat under constant pressure/constant volume for an ideal gas should be given in the problem. In the case of the sapling question, it is important to know that Cp = Cv * R, in which R is the ideal gas constant = 8.3145 j/mol*k.
- Wed Feb 03, 2021 1:58 pm
- Forum: Calculating Work of Expansion
- Topic: Reversible vs Irreversible
- Replies: 6
- Views: 1233
Re: Reversible vs Irreversible
Hey! As everyone mentioned earlier, reversible pathways are when the internal and external pressures are equal, so change only occurs in very small steps. Thus, these reactions take much longer and do more work. In irreversible pathways, the external pressure and internal pressure are not equal, and...
- Sun Jan 31, 2021 7:40 pm
- Forum: Calculating Work of Expansion
- Topic: Sapling Week 3 and 4 #13
- Replies: 2
- Views: 134
Re: Sapling Week 3 and 4 #13
Yes, you're correct! Moles of gas are the only ones doing work when pressure is changed because ultimately the changing concentration of gases is what is affecting the system. Solids and pure liquids don't affect the system through pressure changes.
- Sun Jan 31, 2021 7:30 pm
- Forum: Phase Changes & Related Calculations
- Topic: Vapor vs gas
- Replies: 121
- Views: 8954
Re: Vapor vs gas
Hi! Yes, both words are interchangeable.
- Sun Jan 31, 2021 7:25 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3004001
Re: Post All Chemistry Jokes Here
What do you get when you cut an avocado into 6.022x10^-23 pieces? A guacamole.
- Sat Jan 30, 2021 2:06 pm
- Forum: Phase Changes & Related Calculations
- Topic: when to assume x is insignificant
- Replies: 86
- Views: 6393
Re: when to assume x is insignificant
When working with acid and base equations, use the Ka or Kb value to determine if x is insignificant. If the equilibrium constant is less than 10^-4, it's probably safe to assume that not much of the initial amount of the acid/base was deprotonated/protonated. However, to be even more careful, there...
- Sat Jan 23, 2021 6:44 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Sapling 2 #5
- Replies: 2
- Views: 165
Re: Sapling 2 #5
Hey! So to find percent protonation, you need both the concentration protonated (BH+) divided by the initial concentration. Essentially, to find the initial concentration of amine, you have to add both the equilibrium concentration (B) and the concentration of protonated amine (BH+). This follows th...
- Sat Jan 23, 2021 6:34 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Periodic Tables on Midterm
- Replies: 23
- Views: 807
Re: Periodic Tables on Midterm
Yeah, there should be a periodic table Dr. Lavelle has on his website that we're allowed to print out and use! We can also use the equation sheet that he has put up.
- Sat Jan 23, 2021 6:30 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Le Chatlier (solids)
- Replies: 2
- Views: 107
Re: Le Chatlier (solids)
Exactly! Since solids are not included in equilibrium (you can't really increase the concentration of a solid), they are excluded from equilibrium calculations. So there would be no change.
- Sat Jan 23, 2021 6:14 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: WORKSHEET PROBLEM
- Replies: 2
- Views: 151
Re: WORKSHEET PROBLEM
Hey, yes I think you have to use the reciprocal of the Ka value! Because the reaction involves sodium and propionate, I think you have to use the Kb value instead.
- Sat Jan 23, 2021 6:10 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Compression vs Decreasing Volume
- Replies: 4
- Views: 252
Re: Compression vs Decreasing Volume
Hey! So from my understanding, compressing the system is the same as decreasing the volume. However, there would be no shift in equilibrium because the moles of gas are equal on both sides of the reaction. Decreasing volume causes the equilibrium to shift in the direction that has fewer moles of gas.
- Sun Jan 17, 2021 4:57 pm
- Forum: Student Social/Study Group
- Topic: Campus Resourcees
- Replies: 5
- Views: 427
Re: Campus Resourcees
I thought it would be appropriate to link this resource guide from the CPO! This includes more than just academic resources :)
https://docs.google.com/document/d/1AUb ... ZLmKo/edit
https://docs.google.com/document/d/1AUb ... ZLmKo/edit
- Sun Jan 17, 2021 4:47 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: shifts left or right
- Replies: 23
- Views: 1028
Re: shifts left or right
The shift just refers to the amount of product formed versus the amount of reactant! A shift to the left means more reactant is formed at equilibrium, while a shift to the right means there will be more product formed at equilibrium instead.
- Sun Jan 17, 2021 4:44 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Reaction shift
- Replies: 5
- Views: 236
Re: Reaction shift
Like those above said, adding substance into the reaction will likely mean it will be subtracted as the reaction proceeds. So after adding in reactant, there should be a negative change as the forward reaction will be favored.
- Sun Jan 17, 2021 4:42 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: percent ionization, percentage protonated
- Replies: 4
- Views: 232
Re: percent ionization, percentage protonated
The way I see it, it's the percent of how much of the acid/base actually dissociated in solution. So the lower the percent ionization is, the weaker the acid/base.
- Sun Jan 17, 2021 4:40 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Sapling Week 1 #9
- Replies: 3
- Views: 236
Re: Sapling Week 1 #9
Hey! So, by adding NO, you know that equilibrium should shift to the left (NOT the constant). By bringing the concentration of NO to .800 moles, you solve the ICE table with the following initial values: [N2] = 0.200, [O2] = 0.200, and [NO] = .800. Once you determine equilibrium concentrations, just...
- Fri Jan 08, 2021 5:15 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Change in Temperature
- Replies: 2
- Views: 112
Re: Change in Temperature
Yeah, increasing temperature always favors the side that has greater enthalpy! This is because the added energy has to be used up in the reaction, so it moves away from the side that releases energy (or lower enthalpy, because lower enthalpy means heat was released).
- Fri Jan 08, 2021 3:37 pm
- Forum: Ideal Gases
- Topic: Ideal Gas Assumptions
- Replies: 4
- Views: 233
Re: Ideal Gas Assumptions
Hey! So I think the main assumptions made in regards to ideal gases is that they have completely elastic collisions, which mean that they don't lose any energy after colliding in a closed space. Additionally, the volume of each molecule of gas is small enough to be ignored in calculations. Finally, ...
- Fri Jan 08, 2021 1:59 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Textbook problem 5J.5
- Replies: 2
- Views: 134
Re: Textbook problem 5J.5
I had a similar question after doing the same problem. I'm pretty confident that there must be an error in the textbook, because there is clearly less moles of gas on the product side than on the reactant side. So increasing pressure should favor products!
- Fri Jan 08, 2021 1:54 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Effect of speed on equilibrium
- Replies: 6
- Views: 298
Re: Effect of speed on equilibrium
Yeah exactly! The definition of equilibrium is that the rate of the reverse reaction is equal to the rate of the forward reaction. Thus, the speed at which each reaction occurs should be the same. When one reaction is faster than the other, the reaction is no longer at equilibrium.
- Wed Jan 06, 2021 7:37 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Equilibrium Constant in Le Chatelier's
- Replies: 3
- Views: 140
Equilibrium Constant in Le Chatelier's
Just to clarify, any stresses that result in a change in accordance with le Chatelier's rule do NOT affect the value of the equilibrium constant other than temperature right? So any change in pressure or concentration still cause the equilibrium constant to remain the same value despite the change i...
- Fri Dec 11, 2020 5:11 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: angular and radial nodes
- Replies: 2
- Views: 695
Re: angular and radial nodes
Just a heads up, radial nodes will NOT be on the final! Just focus on angular nodes--particularly those that exist in the 2p subshell.
- Fri Dec 11, 2020 12:40 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Acid Strength of Oxoacids
- Replies: 2
- Views: 399
Acid Strength of Oxoacids
So I was working on a Sapling problem and it said "As the number of of oxygen atoms in an acid increases, the strength of the bond with the Hydrogen decreases, and thus the strength of the acid increases". So, it said that in terms of increasing strength, HIO < HIO2 < HIO3 < HIO4. However,...
- Thu Dec 10, 2020 11:42 am
- Forum: Conjugate Acids & Bases
- Topic: Conjugate Base of a Strong Acid
- Replies: 1
- Views: 155
Conjugate Base of a Strong Acid
In lecture, Dr. Lavelle mentioned that salts containing the conjugate base of a weak acid are able to deprotonate water in solution. I understand this is because these conjugate bases are stronger. Is it possible also, however, for salts containing conjugate bases of a strong acid to deprotonate wat...
- Wed Dec 09, 2020 5:44 pm
- Forum: Ionic & Covalent Bonds
- Topic: Polarizability in Determining Covalent Character in Ionic Bonds
- Replies: 2
- Views: 248
Polarizability in Determining Covalent Character in Ionic Bonds
Today in the Wednesday review session, Dr. Lavelle mentioned that to find covalent character in ionic bonds, compare the electronegativity difference between both cation and anion. However, in a previous lecture, Dr. Lavelle mentioned that the polarizability of the anion and the polarizing power of ...
- Wed Dec 09, 2020 8:30 am
- Forum: Bronsted Acids & Bases
- Topic: Identifying Strong Acids and Bases
- Replies: 7
- Views: 432
Re: Identifying Strong Acids and Bases
Yes, It's probably easiest to memorize them. However there are a few ways to tell if an acid or base will be strong or not. Strong acids also tend to have a very large bond length (hydroiodic acid is strong because iodine has a large atomic radius, and thus is far away from the hydrogen). Additional...
- Sat Dec 05, 2020 9:34 pm
- Forum: Lewis Acids & Bases
- Topic: Lewis Acid
- Replies: 4
- Views: 334
Re: Lewis Acid
Yes, Lewis Acids accept the electron pair! By accepting the electron pair, they use it to form a coordinate covalent bond between the electron pair donor and the proton. I'm not entirely sure if this is unique to an aqueous environment, but I wouldn't be surprised if it was! Remember Dr. Lavelle's e...
- Sat Dec 05, 2020 9:07 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Which is a stronger acid/base
- Replies: 1
- Views: 184
Re: Which is a stronger acid/base
Hey! So both HCN and NH4+ are both decently weak acids to begin with, with very similar pKa values, both around 9.2. If you really want to determine which one would be stronger, we would probably use the relative acidity. Someone feel free to correct me, but I think that NH4+ would be slightly stron...
- Sat Dec 05, 2020 8:50 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Quick rundown on coordination numbers?
- Replies: 4
- Views: 158
Re: Quick rundown on coordination numbers?
Hey! The coordination number is just the number of bonds between the central transition metal ion and the ligands. Don't worry about any other bonds within the ligand! So from what we've went over in class, the coordination number should be either 4 or 6, as we are only looking at compounds with a t...
- Sat Dec 05, 2020 8:48 pm
- Forum: Hybridization
- Topic: Unhybridized Orbitals in Relation to Hybridized Orbitals
- Replies: 4
- Views: 275
Re: Unhybridized Orbitals in Relation to Hybridized Orbitals
Well it depends. If you remember earlier in the quarter, when we first reviewed unhybridized orbitals, we learned that p orbitals have 3 different orientations-- px, py, and pz. Each p orbital was on a different axis. The reason the unhybridized p orbital was perpendicular rather than in plane was b...
- Fri Dec 04, 2020 9:02 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: HF in Water
- Replies: 3
- Views: 209
HF in Water
On Wednesday's lecture, 12/2/2020, Dr. Lavelle used an example in which HCl in H2O would result in a coordinate covalent bond forming between the Oxygen in water and the Hydrogen in HCl. Would this still occur if the acid was HF, considering there would be a greater amount of dissociation energy req...
- Tue Dec 01, 2020 8:36 pm
- Forum: Student Social/Study Group
- Topic: Final Exam Study Tips
- Replies: 48
- Views: 2355
Re: Final Exam Study Tips
Hey! Dr. Lavelle just put up a lot of the synchronous review hours, so I'll be sure to making use of as many of them as I can. I'd spend a lot of time studying the Quantum World because that section will be most prevalent on the final, considering we spent the most time on it. And of course, make su...
- Thu Nov 26, 2020 5:23 pm
- Forum: Electronegativity
- Topic: What determine bond strength?
- Replies: 5
- Views: 537
Re: What determine bond strength?
Yes, you're completely correct in that size contributes a lot to how strong a bond is. Larger radii means larger distance between nuclei, which creates a bond that is easier to break. Also, bond order is extremely important in determining bond strength. Triple bonds are a lot stronger than double b...
- Thu Nov 26, 2020 5:21 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Shape Names
- Replies: 50
- Views: 2301
Re: Shape Names
Yes, the shape is just called bent. Bent can also result from a molecular geometry of 3 regions of electron density, and one lone pair! The bond angles will be different between these two configurations of the bent shape though.
- Thu Nov 26, 2020 4:54 pm
- Forum: Electronegativity
- Topic: What determine bond strength?
- Replies: 5
- Views: 537
Re: What determine bond strength?
Yes, you're completely correct in that size contributes a lot to how strong a bond is. Larger radii means larger distance between nuclei, which creates a bond that is easier to break. Also, bond order is extremely important in determining bond strength. Triple bonds are a lot stronger than double bo...
- Wed Nov 25, 2020 5:55 pm
- Forum: Hybridization
- Topic: Hybridization and Resonance Structures
- Replies: 1
- Views: 249
Hybridization and Resonance Structures
Do all molecules with resonance structures have unhybridized molecules that contribute to delocalization of electrons? In the benzene example in lecture, each C in benzene had 3 hybridized orbitals, but then it had 1 unhybridized p orbital that contributed to its resonance. What exactly is the model...
- Wed Nov 25, 2020 5:52 pm
- Forum: Sigma & Pi Bonds
- Topic: Delocalized Pi Bonds
- Replies: 4
- Views: 583
Re: Delocalized Pi Bonds
Hey! I had a pretty similar question myself because it seems like a pretty non-descriptive term. But from my understanding, I think a delocalized pi bond shares electrons across the molecule like in the benzene example Dr. Lavelle showed us in lecture. Thus, the electrons present in the orbitals tha...
- Sat Nov 21, 2020 10:07 pm
- Forum: Bond Lengths & Energies
- Topic: Tetrahedral Bond Angle
- Replies: 7
- Views: 447
Re: Tetrahedral Bond Angle
Yes, I think Dylan is correct! It's important to know the order of increasing distortion between regions of electron density. Lone pair-lone pair > lone-pair-bonded pair > bonded pair-bonded pair. So at least know that trigonal pyramidal has a slightly smaller bond angle than tetrahedral due to the ...
- Sat Nov 21, 2020 9:58 pm
- Forum: Sigma & Pi Bonds
- Topic: 2F 19
- Replies: 3
- Views: 243
Re: 2F 19
Hey Anil, if the problem is not assigned on the syllabus, then I doubt we need to know it for this class. I checked the syllabus and 2F.19 was not assigned, and neither of those terms are in the required objectives that we need to know, which are outlined on Dr. Lavelle's website. So I'm guessing th...
- Sat Nov 21, 2020 9:53 pm
- Forum: Student Social/Study Group
- Topic: Study Tips for Final Exam
- Replies: 57
- Views: 2506
Re: Study Tips for Final Exam
Hey! Definitely take advantage of as many workshops and synchronous hours that Dr. Lavelle has created before the final. Like everyone else said, going through homework seems like it'll be super important as well. I suggest reviewing all of the objectives that are on Dr. Lavelle's CHEM 14A website! ...
- Wed Nov 18, 2020 2:46 pm
- Forum: Bond Lengths & Energies
- Topic: Dissociation Energy and Unpaired Electrons
- Replies: 3
- Views: 258
Dissociation Energy and Unpaired Electrons
One of the objectives on the outline for Chemical Bonds is "Explain how covalent bond dissociation energy is related to covalent bond multiplicity, atomic radius, and the presence of unpaired electrons." I understand how covalent bond dissociation energy is related to covalent bond multipl...
- Mon Nov 16, 2020 2:19 pm
- Forum: Lewis Structures
- Topic: Identifying Total Charge
- Replies: 1
- Views: 212
Identifying Total Charge
After doing some problems in the textbook, I noticed that some Lewis Structures with a total charge have only one bracket indicating charge. Why is there only one bracket used instead of two? What does it mean when there is only a bracket on one side? This is seen in the answer solution to 2B.5. Tha...
- Fri Nov 13, 2020 10:58 am
- Forum: Student Social/Study Group
- Topic: Test Anxiety
- Replies: 62
- Views: 2973
Re: Test Anxiety
Also, remember to get tons of sleep beforehand! Being well rested is a huge part of being prepared -- which will definitely reduce test anxiety. I like to always wash my face before my exam, because I feel fresh and ready to take on the exam, and it also wakes me up.
- Thu Nov 12, 2020 8:25 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 Clarification
- Replies: 1
- Views: 217
Hydrogen Bonding Clarification
Hey! So in hydrogen bonding, a hydrogen attached to an electronegative atom creates a hydrogen bond with either an N, O, or F atom in another molecule. Do these atoms (N, O, F) also have to be attached to another atom that is significantly different in electronegativity? So, a hydrogen bond cannot f...
- Thu Nov 12, 2020 3:45 pm
- Forum: Dipole Moments
- Topic: Determining Polarity
- Replies: 3
- Views: 220
Re: Determining Polarity
Hey! So not using molecular geometry, one way polarity can be determined is by comparing electronegativities. If there are two atoms in a molecule with a large difference in electronegativity, it is likely to have ionic characteristics and would thus be polar. For example, in a water molecule, H and...
- Thu Nov 12, 2020 3:42 pm
- Forum: Octet Exceptions
- Topic: How to tell
- Replies: 6
- Views: 486
Re: How to tell
Hey! So just to add on, the first 4 elements on the periodic table are all exceptions to the octet rule. Hydrogen, Helium, Lithium, and Beryllium don't have a p subshell, so they only have 2 orbitals rather than a full 8.
- Mon Nov 09, 2020 5:03 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 vs. Dipole-Dipole Attractions
- Replies: 3
- Views: 131
Hydrogen Bonding vs. Dipole-Dipole Attractions
Today in lecture, Dr. Lavelle used the interaction between two HF molecules as an example of a dipole-dipole interactions, as the slightly negative Fluorine interacts with the slightly positive Hydrogen. Dr. Lavelle mentioned that on average, these interactions release about -2 KJ/mol. However, isn'...
- Wed Nov 04, 2020 11:38 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Are there subshells past f?
- Replies: 28
- Views: 1033
Re: Are there subshells past f?
Also, it's important to note that when it comes to electron configurations, we don't even have to know energy levels past 4p!
- Wed Nov 04, 2020 11:32 pm
- Forum: Trends in The Periodic Table
- Topic: Topic 1F. 6 Problem
- Replies: 2
- Views: 97
Re: Topic 1F. 6 Problem
Hey! I got Ca, Mg, and Al instead actually. 1) So I believe Ca would have the lower ionization energy because its electrons are much more shielded than Mg, even when two electrons are removed. This is because Ca is a whole energy level higher than Mg (n=4 vs n=3). 2) Mg would have the lower ionizati...
- Wed Nov 04, 2020 2:42 pm
- Forum: Ionic & Covalent Bonds
- Topic: Ionic v. Covalent Bonds`
- Replies: 10
- Views: 894
Re: Ionic v. Covalent Bonds`
It's also important to note that because metals give up an electron and nonmetals gain an electron during ionic bonding, they gain charges! But in covalent bonding, while there might be shifts in polarity, the atoms involved are not ionized. Some common differences between ionic bonds and covalent b...
- Mon Nov 02, 2020 8:53 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Subshells Existing Out of the Periodic Table
- Replies: 2
- Views: 188
Subshells Existing Out of the Periodic Table
In textbook number 1D.25, the question asks whether it is possible for the subshell 6f to exist. From my understanding, the periodic table only goes up to 5f as a subshell, yet the solutions say that 6f is a possible subshell. So my question is, can subshells that exist past the known elements in a ...
- Mon Nov 02, 2020 4:01 pm
- Forum: Resonance Structures
- Topic: Delocalization of Electrons
- Replies: 2
- Views: 92
Delocalization of Electrons
So to my understanding, in resonance structures, electrons that form double bonds are delocalized because they exist in multiple locations (equivalent electron density). But does this mean electrons involved in single bonding and lone pairs are not delocalized? Or are they also equally shared among ...
- Thu Oct 29, 2020 10:00 pm
- Forum: Trends in The Periodic Table
- Topic: Ionization Energy v. Work Function
- Replies: 3
- Views: 133
Ionization Energy v. Work Function
After looking through trends in the periodic table in the lecture on 10/28, I came across something I don't quite get. I understand the fundamental difference between the two: ionization energy involves removing the outer-most electron of an atom in a gaseous state, while the work function is the en...
- Tue Oct 27, 2020 9:01 pm
- Forum: Properties of Light
- Topic: Which model of light is atomic spectroscopy?
- Replies: 8
- Views: 506
Re: Which model of light is atomic spectroscopy?
Hey, what the others said is completely correct. Just for the sake of clarification, the model of light can be considered as a wave in other experiments, and is even proven by the c = λ ν equation. The equation works for the wave model because as frequency decreases, wavelength increases at an inver...
- Tue Oct 27, 2020 8:51 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Atomic Spectroscopy vs molecular spectroscopy
- Replies: 2
- Views: 136
Re: Atomic Spectroscopy vs molecular spectroscopy
Hey! So I had a similar question and after some digging around I think the major difference between atomic and molecular spectroscopy is the energy levels. In multi-electron systems, which are used in molecular spectroscopy, each subshell has a different level of energy due to a combination of elect...
- Mon Oct 26, 2020 10:30 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Effective Nuclear Charge
- Replies: 1
- Views: 95
Effective Nuclear Charge
For multi-electron systems, are we required to know how to calculate the effective nuclear charge for the nucleus? During the lecture on 10/23/2020, Dr. Lavelle said that the nuclear charge of Lithium was 3+, and its effective charge was between 1+ and 3+, but I wasn't entirely sure how that range w...
- Mon Oct 26, 2020 8:35 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Atomic Spectroscopy v. Molecular Spectroscopy
- Replies: 3
- Views: 170
Atomic Spectroscopy v. Molecular Spectroscopy
Going through the learning objectives in the Quantum World outline, I found the following objective: "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...
- Thu Oct 22, 2020 11:33 pm
- Forum: Trends in The Periodic Table
- Topic: Sapling Hw 2 #20
- Replies: 3
- Views: 214
Re: Sapling Hw 2 #20
Hey! So ionization just means that the atom has become an ion, or lost/gained electrons and now has a charge. In this case, the ionized form of Oxygen has a charge of -2. This means that oxygen has 2 extra electrons. As a result of the greater number of electrons in its shell, the electrons repulse ...
- Thu Oct 22, 2020 11:28 pm
- Forum: *Shrodinger Equation
- Topic: Schrodinger Equation
- Replies: 3
- Views: 127
Re: Schrodinger Equation
I'm also confused about the Schrodinger Equation... When Dr. Lavelle says that we operate a change on the wave function, is that operation always a hamiltonian? Because at the bottom of the equation sheet there are a few formulas involving the wave function that I just don't understand... If someone...
- Thu Oct 22, 2020 11:22 pm
- Forum: Properties of Electrons
- Topic: Electrons emitting photons
- Replies: 3
- Views: 148
Re: Electrons emitting photons
I think that one electron only emits one photon of a given energy level. From my understanding of the photoelectric experiment, one photon can only eject one other electron, because this energy can only be absorbed by a single electron. I would assume this same principle applies as the electron fall...
- Tue Oct 20, 2020 11:01 pm
- Forum: DeBroglie Equation
- Topic: Sapling Question 29
- Replies: 6
- Views: 806
Re: Sapling Question 29
Hey! So for the electron, we can find its energy using the kinetic energy formula, E_k = 1/2 * m * v^2. Because the electron is a moving object, its energy is kinetic and can be calculated by knowing its mass and velocity. The mass of an electron is given to us as 9.11x10^-31 kg. The velocity can be...
- Tue Oct 20, 2020 10:45 pm
- Forum: Student Social/Study Group
- Topic: How are you studying?
- Replies: 204
- Views: 17496
Re: How are you studying?
Personally, I've been studying mainly through textbook problems, especially because those types of problems will be put on future exams. Additionally, UA workshops are SUPER helpful for additional practice. Even if I can't make it to live sessions, I always try to do the worksheets posted on the sha...
- Thu Oct 15, 2020 11:09 am
- Forum: Einstein Equation
- Topic: m vs nm
- Replies: 66
- Views: 3318
Re: m vs nm
All of these replies are correct, but I just want to add on a note to keep in kind. When dealing with equations like (wavelength)(frequency) = c, make sure that wavelength is in meters, as that's the si unit that is used in this calculation. Other than that, yes, your answer can either be in m or nm...
- Thu Oct 15, 2020 11:06 am
- Forum: Properties of Electrons
- Topic: Energy Gaps
- Replies: 8
- Views: 264
Re: Energy Gaps
Hey! Just to add onto the explanations, the energy gaps get progressively smaller because as the electron is further away from the nucleus, there is less of a magnetic force pulling it towards the positively charged center. Because electrons are negatively charged, it is usually very difficult, and ...
- Wed Oct 14, 2020 2:22 pm
- Forum: Photoelectric Effect
- Topic: What happens to emitted electrons?
- Replies: 1
- Views: 152
Re: What happens to emitted electrons?
From my knowledge, the electrons are simply ejected from the metal's surface and actually collide with a detector or some other tool to measure the velocity, ultimately being used in kinetic energy calculations. Looking at diagrams of the experiment, there's a battery that establishes a negative cha...
- Wed Oct 14, 2020 2:18 pm
- Forum: Photoelectric Effect
- Topic: Kinetic Energy Clarification
- Replies: 3
- Views: 117
Re: Kinetic Energy Clarification
Hi! So technically, the energy to remove the electron IS the work function. The work function is essentially the threshold energy. And if the kinetic energy of the electron is 0 J, then this work function or threshold energy will be equal to the energy of the photon hitting the surface of the metal....
- Tue Oct 13, 2020 4:52 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Post-Assessment #29 for Atom Spectroscopy
- Replies: 3
- Views: 110
Post-Assessment #29 for Atom Spectroscopy
Hi, I'm struggling to go about this problem in the post module assessment. In 1.0 s, a 60 W bulb emits 11 J of energy in the form of infrared radiation (heat) of wavelength 1850 nm. What is the energy per photon of light emitted? How many photons of infrared radiation does the lamp generate in 1.0 s...
- Thu Oct 08, 2020 4:51 pm
- Forum: Limiting Reactant Calculations
- Topic: Week 1 Sapling Q. 10
- Replies: 5
- Views: 411
Re: Week 1 Sapling Q. 10
Hey! So finding the molar masses of the reactants and products requires you to actually know a little about how to read line drawings, which are pretty common in organic chemistry. Basically, its just a way to represent carbons and hydrogens. Every "vertex" between the lines represents one...
- Thu Oct 08, 2020 4:46 pm
- Forum: Limiting Reactant Calculations
- Topic: Textbook Question M.5
- Replies: 7
- Views: 347
Re: Textbook Question M.5
Could someone explain why you do 5-4 in order to get the moles leftover of the excess reactant? Hey! So you subtract 4 moles from the 5 moles of excess because 4 moles is the amount that reacts with the limiting reactant in the reaction. The 4 is calculated using molar ratios as the person above sa...