Search found 106 matches
- Thu Mar 11, 2021 10:06 pm
- Forum: First Order Reactions
- Topic: sapling week 10 #11
- Replies: 5
- Views: 316
Re: sapling week 10 #11
This stumped me at first, too, but it's just a matter of not getting overwhelmed by the lack of the "givens" listed in the question. When in doubt, simply go back to the question and think about your formulas. The question is telling you that the reaction obeys first order kinetics, so tha...
- Thu Mar 11, 2021 9:49 pm
- Forum: First Order Reactions
- Topic: Half Life Unit
- Replies: 38
- Views: 1425
Re: Half Life Unit
Always pay attention to the units you are given. A lot of times the units of the half-life of a substance depends on whatever the units of the rate constant, k, are. However, I'm fairly certain questions will let you know what units the half-life should be in, so it doesn't matter as long as you con...
- Thu Mar 11, 2021 9:47 pm
- Forum: Zero Order Reactions
- Topic: Zero Order
- Replies: 4
- Views: 295
Re: Zero Order
I don't think it's a question of when to use A in the Arrhenius Equation, if I'm understanding your meaning correctly. You always use every part of the equation as it is written out. In terms of how to use it, I'm fairly certain that some problems will list it as a given of the problem, so you won't...
- Thu Mar 11, 2021 9:24 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Sapling Week 9/10 #19
- Replies: 2
- Views: 197
Sapling Week 9/10 #19
I was a little confused about the second part of #19. The question asks what other aspects of a catalyzed reaction are different from the uncatalyzed reaction. I was confused as to why the deltaH of the reaction and overall reaction is unchanged with or without the catalyst. I'm probably overthinkin...
- Thu Mar 11, 2021 8:02 pm
- Forum: General Rate Laws
- Topic: Sapling #13
- Replies: 2
- Views: 226
Sapling #13
How come for the solution of #13 of Week 9/10, [OH-] is in the rate law? I used the Pre-equilibrium Approach and got the correct answer, but I was surprised that you did not have to cancel out [OH-] like you had to for [HClO]. Does [OH-] not count as an intermediate? Does the same go for [H+], then?...
- Sun Mar 07, 2021 8:57 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Rate Laws
- Replies: 7
- Views: 437
Re: Rate Laws
I think it will depend on what the question gives you. Obviously, if you are given enough knowns, you will probably have to calculate the rate law yourself. I'm assuming it will just be given to us otherwise. Hope this helps!
- Sun Mar 07, 2021 8:50 pm
- Forum: Zero Order Reactions
- Topic: Overall order of the reaction
- Replies: 45
- Views: 1734
Re: Overall order of the reaction
The orders of individual reactants that are involved in the slowest step of the reaction summed up would equal the overall order of the reaction. We find the individual orders of each reactant through experimentation, where we manipulate each concentration to see if the initial rate changes, and fro...
- Sun Mar 07, 2021 1:44 am
- Forum: First Order Reactions
- Topic: Stoichiometric Coefficients and Integrated Rate Laws
- Replies: 5
- Views: 346
Re: Stoichiometric Coefficients and Integrated Rate Laws
You simply just plug that stoichiometric coefficient into the equation as a in 1/a. There's nothing fancy you need to do when the stoichiometric coefficient isn't one; the reason Dr. Lavelle always had a = 1 was for simplification purposes because he was deriving the different integrated rate laws. ...
- Sun Mar 07, 2021 1:35 am
- Forum: Second Order Reactions
- Topic: Zero-Order Catalysts
- Replies: 9
- Views: 631
Re: Zero-Order Catalysts
A really simple way to think about is that if the catalyst/enzyme is saturated, it means it cannot cannot further speed up the reaction any further because all of its catalyzing power has been utilized. This means if a reaction that no matter how much reactant is present, the rate of the reaction wi...
- Sun Mar 07, 2021 1:22 am
- Forum: First Order Reactions
- Topic: 1st Order Reactions
- Replies: 29
- Views: 1800
Re: 1st Order Reactions
Dr. Lavelle was simply using a different graph when he was describing the rates of first order reactions. In the first graph, a negative linear result in the graph of ln[A] vs. time would be indicative of a first order reaction. in the second graph, a negative exponential result in the graph of [A] ...
- Sun Mar 07, 2021 1:16 am
- Forum: General Rate Laws
- Topic: Number of Reactants
- Replies: 26
- Views: 1031
Re: Number of Reactants
I think it is possible, but highly unlikely. Think about it this way. A fourth order reaction is defined like any other ordered reaction: a reaction wherein a certain number of reactants are involved in the slowest step of the reaction. For a fourth order reaction to happen, all four molecules would...
- Sun Mar 07, 2021 1:09 am
- Forum: Zero Order Reactions
- Topic: Half life
- Replies: 20
- Views: 941
Re: Half life
You use the equation t1/2 = [A]0/2k, with [A]0 being the initial concentration of the reaction and k being the reaction rate constant. This is derived from the zero order integrated rate law, where [A] = -kt + [A]0. The derivation is as follows: [A] = -kt + [A]0 (1/2)[A]0 = -k(t1/2) + [A]0 (At t1/2,...
- Sun Feb 28, 2021 8:21 pm
- Forum: Balancing Redox Reactions
- Topic: states of matter
- Replies: 58
- Views: 2113
Re: states of matter
There are definitely questions, such as Question #5, where you have to make sure you have correctly stated the state each compound of the redox reaction is in. However, if you are still getting the problem wrong and you know you have the phases correct, then there has to be some other error that's c...
- Sun Feb 28, 2021 8:16 pm
- Forum: Balancing Redox Reactions
- Topic: Determining Phases
- Replies: 28
- Views: 974
Re: Determining Phases
I'm fairly certain you don't have to do anything other than look at the original equation to determine the phases of the compounds. They will tell you what compound is in what phases in that original equation. For the compounds you add when balancing redox reactions, H20 is a liquid (l) and OH-/H+ a...
- Sat Feb 27, 2021 3:28 pm
- Forum: Balancing Redox Reactions
- Topic: Adding H20 and OH-/H+
- Replies: 3
- Views: 220
Adding H20 and OH-/H+
I am confused about exactly what methodology to go about adding OH-/H+ and H20 to balance half reactions. Is there a certain procedure for adding H20 to one side and OH-/H+ to the other? The sapling feedback on the homework is giving me contrary statements as to how to go about these problems.
- Thu Feb 25, 2021 9:16 pm
- Forum: Balancing Redox Reactions
- Topic: Sapling Week 7/8 #1
- Replies: 3
- Views: 218
Sapling Week 7/8 #1
I have a quick question about #1 and calculating oxidation numbers. Can someone explain to me why chlorine is the element being reduced and why it can't be potassium? I'm pretty sure there's an easy answer here that I'm just overthinking. Thanks!
- Thu Feb 25, 2021 12:32 am
- Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
- Topic: Electrolysis Example
- Replies: 2
- Views: 199
Electrolysis Example
During Wednesday's lecture, Dr. Lavelle was explaining an example of electrolysis that involved molten magnesium chloride. When he was talking about the adding up the two half reactions, he said, "That overall redox reaction has a positive E not value; it's not favorable." I was under the ...
- Fri Feb 19, 2021 9:59 pm
- Forum: Balancing Redox Reactions
- Topic: Redox Mnemonic
- Replies: 11
- Views: 968
Re: Redox Mnemonic
This is actually really helpful. I learned this in sophomore year, but I had forgotten about it until you reminded me. I was trying to think of the mnemonic for so long, too. Thanks!
- Fri Feb 19, 2021 9:57 pm
- Forum: Balancing Redox Reactions
- Topic: Change in potential as i -> 0
- Replies: 12
- Views: 571
Re: Change in potential as i -> 0
i in this concept refers to the flow of current in the battery, galvanic cell, etc. It is basically saying the electromotive force, or cell potential, is measured as if there was very little to no actually current flowing in the system. Hope this helps!
- Fri Feb 19, 2021 9:53 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidation Numbers
- Replies: 9
- Views: 619
Re: Oxidation Numbers
I was confused about this too, but I think the first step to figuring out oxidation states is memorizing the common oxidation states, which kind of sucks, but that's how it's done. For example, oxygen commonly has an oxidation state of -2, which could be found in a molecule that Dr. Lavelle mentione...
- Fri Feb 19, 2021 9:41 pm
- Forum: Balancing Redox Reactions
- Topic: Redox Charges
- Replies: 3
- Views: 227
Re: Redox Charges
I'm sure we will be given either a balanced equation or enough information to make a balanced equation ourselves so that we know what ion forms and what charge it has. If we're not given either, though, I'm assuming we either might have to know at least some common forms of the ions themselves, or t...
- Fri Feb 19, 2021 9:37 pm
- Forum: Balancing Redox Reactions
- Topic: First Lecture Galvanic Cell
- Replies: 7
- Views: 421
First Lecture Galvanic Cell
I just had some really quick I wanted to clear up. What type of solution was used in the diagram of the example galvanic cell from the first lecture on electrochemistry? I don't know if I just didn't hear it, but I wanted to know what solution the anode and cathode were placed in, and why it matters...
- Sun Feb 14, 2021 6:15 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: delta U and delta H
- Replies: 8
- Views: 348
Re: delta U and delta H
Delta U and Delta H are not the same thing. Delta U describes the change in internal energy while Delta H describes a change in enthalpy. I think they were related when the system was under constant pressure in a closed system, where: delta U = qp + w delta U = delta H - Pex(delta V) But they did no...
- Sun Feb 14, 2021 5:00 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Is it necessary to memorize Cp,m or Cv,m values? [ENDORSED]
- Replies: 26
- Views: 1172
Re: Is it necessary to memorize Cp,m or Cv,m values? [ENDORSED]
These values are on the 14B equations sheet. I had the same question as I was still using the 14A sheet. So no, it is not necessary most likely, but it never hurts to know them by heart. Hope this helps!
- Sun Feb 14, 2021 4:50 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: temperature
- Replies: 32
- Views: 1212
Re: temperature
I think a lot of the times you have to be wary of if the question gives the temperature in Celcius. Things utilizing the gas constant R, the second law of thermodynamics, etc. all have their units in Kelvin. In this case, you have to convert Celsius to Kelvin and make sure your units match up. Howev...
- Sun Feb 14, 2021 4:43 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Temperature Question
- Replies: 8
- Views: 433
Re: Temperature Question
Here's what helps me remember why this conversion is allowed: to convert between Celsius and Kelvin, you follow the formula K = C + 273. If we are finding the change in temperature, we are subtracting the final temp - the initial temp. Thinking about this a little deeper, it's obvious that this addi...
- Sun Feb 14, 2021 4:19 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Temperature and K
- Replies: 21
- Views: 1046
Re: Temperature and K
If you are talking about degrees Kelvin, then K is simply another unit measure of temperature, specifically the SI unit for temperature. But if you're talking about the equilibrium constant Kc, then a change in temperature is the only change to the system that can affect Kc. Hope this helps!
- Sun Feb 07, 2021 8:15 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Sapling #10 Week 3/4
- Replies: 6
- Views: 217
Sapling #10 Week 3/4
I was a little confused on this problem. Why don't we use the specific heat capacity of ice when we calculate the new temperature of an amount of ice melting in an amount of water. Is it because we are already accounting for the phase change of ice with the delta H of fusion?
- Sun Feb 07, 2021 4:56 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Work
- Replies: 39
- Views: 1387
Re: Work
Work is always dependent and centered around the system. If the system does work on its surroundings, work takes on a negative value because the system uses energy. If the surroundings do work on the system, though, work takes on a positive value because the system gains energy. Hope this helps!
- Sun Feb 07, 2021 4:53 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Closed System
- Replies: 52
- Views: 2584
Re: Closed System
I think you are confusing a closed system with an isolated system. Energy can still be transferred in and out of a closed system; matter is the thing that cannot enter or escape. Hope this helps!
- Sun Feb 07, 2021 4:40 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: enthalpy and heat
- Replies: 10
- Views: 359
Re: enthalpy and heat
I'm pretty sure H is used solely for enthalpy and q is used solely for heat, except for conditions of constant pressure. Delta H = q under constant pressure.
- Sun Feb 07, 2021 4:32 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Calorimeters
- Replies: 10
- Views: 415
Re: Calorimeters
It helps if we think about it simply. We have thermometers, which measure the temperature of the system around it. We have barometers, which measures the air pressure of the system around it. These tools help measure a characteristic of a system and give the measurer data to work with. A calorimeter...
- Sun Feb 07, 2021 4:14 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Can heat capacities be negative?
- Replies: 52
- Views: 13518
Re: Can heat capacities be negative?
Be careful here. There is a danger in confusing the functions of reaction enthalpies and heat capacities. Reaction enthalpies can be negative because the sign of the enthalpy is dependent on the system (negative if the reaction is exothermic, positive if the reaction is endothermic), but heat capaci...
- Sun Feb 07, 2021 3:57 pm
- Forum: Phase Changes & Related Calculations
- Topic: Vapor vs gas
- Replies: 121
- Views: 8912
Re: Vapor vs gas
Both terms are interchangeable. I think it just has to do with the context/topic. Vapor is often times used when talking about phase changes (i.e. vaporization of water), while I feel like gas is used when it's being manipulated in a system. you rarely hear "vapor at a constant pressure". ...
- Sun Jan 31, 2021 7:35 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Isolated System
- Replies: 16
- Views: 656
Re: Isolated System
I'm pretty sure a vacuum can be an example of an isolated system! Be sure not to confuse isolated systems as all being vacuums, though! Hope this helps!
- Fri Jan 29, 2021 12:42 pm
- Forum: Phase Changes & Related Calculations
- Topic: Polyprotic acid solutions
- Replies: 4
- Views: 220
Polyprotic acid solutions
I know polyprotic acid solutions just involve multiple steps because there is still ionization to be had after the first reaction, but is this always because a strong acid produces a weak acid as a product? Or are there other situations where a second ionization is utilized?
- Thu Jan 28, 2021 10:44 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Midterm Content
- Replies: 2
- Views: 131
Re: Midterm Content
I just checked the outline; that is correct! Make sure you study all the points above it too!
- Thu Jan 28, 2021 10:42 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Sapling week 3 #6
- Replies: 12
- Views: 452
Re: Sapling week 3 #6
It's usually effective to think about these endothermic/exothermic questions in terms of systems. For this question, in simple terms, the system is forming bonds between C and H. When bonds are being formed, the system actually loses heat (heat is a product) so the reaction is exothermic. If bonds w...
- Thu Jan 28, 2021 10:26 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 4D.15
- Replies: 4
- Views: 240
4D.15
I was reviewing this problem and I was confused about the setup, which led me to a general question that applies to these enthalpy problems. In this problem, we are given one reaction and separate standard enthalpies for three other compounds. To solve the problem, you need to use these compounds to...
- Sat Jan 23, 2021 12:15 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Ordering from weakest to strongest Acd/base
- Replies: 11
- Views: 523
Re: Ordering from weakest to strongest Acd/base
This is actually really simple! Just remember that the larger the Ka and the smaller the pKa, the stronger the acid. A large Ka means that there is more product than reactant, insinuating a stronger H3O+ concentration. A smaller pKa means that the -log of Ka came from a larger Ka (as the logarithm f...
- Fri Jan 22, 2021 11:57 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: H2O and K
- Replies: 11
- Views: 386
Re: H2O and K
You are correct. The only reason why we don't include H20 normally in our calculations for Kc is because the molar concentrations of a pure liquid (and a pure solid) do not change, and therefore are present in equivalent amounts on both the reactant and the product side, and cancel out. In this case...
- Fri Jan 22, 2021 11:44 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Studying for Midterm #1
- Replies: 63
- Views: 2406
Re: Studying for Midterm #1
Repetition of textbook problems is key. Just keep doing them until you can easily recognize the purpose of the question and the procedures you need to follow to solve it. That's what I'll be doing to study! You can also utilize the modules on Dr. Lavelle's website for more problems. They're organize...
- Fri Jan 22, 2021 11:41 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: How to fill in 2nd row of ICE table?
- Replies: 25
- Views: 740
Re: How to fill in 2nd row of ICE table?
This solely depends on if the reaction favors the forward reaction or reverse reaction. We can do this by calculating Q and comparing it to K, or by the setup of the question. No matter what, (stoichiometric number)x will be subtracted from the reactants and (stoichiometric number)x will be added to...
- Fri Jan 22, 2021 11:17 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Calculating -log
- Replies: 8
- Views: 670
Re: Calculating -log
I think the problem is that you might be using ln instead of log_10 (log base 10) when calculating the pH. Remember, pH runs on a base 10 system (every change by 1 ph is actually a 10x change), so if you are not using log_10 then you won't get the right answer. ln calculates a log base of e, which e...
- Sat Jan 16, 2021 4:31 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: aqueous solutions
- Replies: 9
- Views: 341
Re: aqueous solutions
Only liquids and solids aren't counted in Kc. I'm pretty sure everything else counts. Hope this helps!
- Sat Jan 16, 2021 4:29 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: pKA and pH
- Replies: 8
- Views: 214
Re: pKA and pH
They both do add up to 14, but I think pKa and pKb calculate the negative log of equilibrium constants, while pH and pOH calculate the negative log of the concentrations of H30+ and OH-
- Sat Jan 16, 2021 4:23 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: q vs k
- Replies: 62
- Views: 2368
Re: q vs k
I don't know if this right, but I like to think of Q as any random moment in time during my life, and K as my home. I could be out and about at school, hitting the town on a Saturday night, or watching TV on my couch (pre/post quarantine of course). Q can either be greater than, less than, or equal ...
- Sat Jan 16, 2021 4:15 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: K in endo and exo when temp. decreases
- Replies: 11
- Views: 491
Re: K in endo and exo when temp. decreases
I'm fairly certain you are correct. Endothermic reactions require heat to react, so if the temperature decreases, less products would be made, and therefore K would decrease. I'm not entirely sure about the logic of exothermic reactions, but the decrease in temperature probably increases products be...
- Sat Jan 16, 2021 4:07 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Kw
- Replies: 8
- Views: 527
Re: Kw
Water can act as a weak acid or a weak base, but in terms of pH, it is neutral. The little amounts of H30+ and OH- it does contain is exclusively in equal amounts, so they cancel out. In terms of Ka values, a large Ka value indicates a strong acid, not just any Ka value. Hope this helps!
- Sat Jan 16, 2021 3:49 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Sapling Week 1 #9
- Replies: 7
- Views: 345
Re: Sapling Week 1 #9
For me personally, if I get stuck on one of these problems and I KNOW I'm doing them correctly but I'm burning through attempts, there's always just some clerical error I missed that's [censored] up my answer. If you've checked your work and your ICE box has no errors, then there's probably some lit...
- Sat Jan 16, 2021 2:44 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE Box
- Replies: 28
- Views: 1167
Re: ICE Box
I think usually with strong acids/bases you don't NEED to make an ICE box, but I don't know if the question will necessarily tell you if the acid/base is strong or not. Just for simplicity's sake, I would probably just make one every time!
- Sat Jan 16, 2021 2:08 am
- Forum: Ideal Gases
- Topic: Gas for equilibrium equation
- Replies: 8
- Views: 413
Re: Gas for equilibrium equation
When we are finding the equilibrium constant, we either use concentrations or partial pressures of molecules. Your question regards the format of the quantities involved. Instead of denoting concentration with brackets, [molecule], we denote partial pressure with Pmolecule. We are finding two differ...
- Sat Jan 16, 2021 1:23 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Strong Base Dissociation Example
- Replies: 1
- Views: 154
Strong Base Dissociation Example
In Dr. Lavelle's first lecture on acid and base equilibria, he gave us a worked example: what are the molarities of H30+ and OH- 0.0030 M Ba(OH)2, where Ba(OH)2 <-> Ba+ + 2OH-? He then went on to state that because the base is a strong base, it completely dissociates in water. That much I understood...
- Fri Jan 15, 2021 10:58 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Sapling Week 1 #9
- Replies: 7
- Views: 345
Re: Sapling Week 1 #9
There are multiple things that you have to make sure you set up properly before you start solving this problem: First be aware that both of the reactant concentrations are not 0, and this will affect your ice table values. Make sure your reaction is oriented so NO is the product. Just because it is...
- Fri Jan 15, 2021 8:56 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Sapling Question #4
- Replies: 6
- Views: 264
Sapling Question #4
I am a bit confused about the formation of the ICE box in this situation. The feedback, asking for the total pressure at equilibrium, when Kp = 343 and the initial pressure of PCl5 is 0.0280, shows x being added as the change on the reactant side and x being subtracted as the change on the product s...
- Wed Dec 09, 2020 3:04 pm
- Forum: Polyprotic Acids & Bases
- Topic: Calculating Ka
- Replies: 9
- Views: 943
Re: Calculating Ka
In this example, you would divide the product of the concentrations of the products over the concentration of the solvent: AH <—> A- (aq) + H+ (aq) leads to Ka =( [A-][H+] )/[AH] Concentrations, if they aren't given, would be calculated through our molarity formula M = n/V, where n=moles and v= volu...
- Wed Dec 09, 2020 2:57 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: pH to pOH
- Replies: 8
- Views: 530
Re: pH to pOH
Also make sure given any of the four components (pH, pOH, OH - levels, H + levels) that you can get the other three, as seen in the Sapling homework for this week. What do you mean by OH- and H+ levels? I haven't started the homework yet, but I'm assuming this means the concentration of H30+ and OH...
- Wed Dec 09, 2020 2:48 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: pH>pKA
- Replies: 3
- Views: 196
Re: pH>pKA
pH describes the acidity or basicity of a solution, where a lower number describes a more acidic solution. pKA describes the indicates the strength of the acid, where a lower value represents a stronger acid. If the pH < pKA, the solution is already protonated and the acid can't donate any H+. You c...
- Wed Dec 09, 2020 2:26 pm
- Forum: Amphoteric Compounds
- Topic: Identifying Amphoteric Compounds
- Replies: 4
- Views: 238
Re: Identifying Amphoteric Compounds
A commonly-known amphoteric compound is water, so that might be one chemical formula you could look at and instantly know it was amphoteric. Other than that, though, you would have to see how the compound acted in a chemical equation and see if it could both donate and receive a proton in a reaction.
- Wed Dec 09, 2020 2:22 pm
- Forum: Conjugate Acids & Bases
- Topic: Neutral salts
- Replies: 2
- Views: 197
Neutral salts
How can we determine if a salt will be neutral? I may have just missed this in the lecture, but it seems like the only salt mentioned was NaCl that doesn't affect the pH of the solution. Are there any other significant neutral salts we should know about?
- Sun Dec 06, 2020 9:50 pm
- Forum: Bronsted Acids & Bases
- Topic: Acids as proton donors
- Replies: 4
- Views: 251
Re: Acids as proton donors
They aren't the same concept, if that is what you are asking. It really depends on what perspective you are utilizing when you are looking at an acid. Acids act as proton donors and electron pair acceptors. These two characteristics are both applicable to acids, but one focuses on protons and one fo...
- Sun Dec 06, 2020 9:43 pm
- Forum: Bronsted Acids & Bases
- Topic: Identification
- Replies: 3
- Views: 162
Re: Identification
How would you identify acids and bases? For example, what would be the explanation for why HNO3 would be an acid? At least in the example you gave, you would know that HNO3 would be an acid from multiple characteristics about the molecule. From a Bronsted point-of-view, the molecule has to be a Bro...
- Sun Dec 06, 2020 9:28 pm
- Forum: Bronsted Acids & Bases
- Topic: soft salts
- Replies: 6
- Views: 264
Re: soft salts
I believe Dr. Lavelle's use of the term "soft salts" was referring to salts that turn water alkaline. He made a point that salts weren't actually "soft", but they produce that soapy, soft feeling when we touch water that is alkaline.
- Fri Dec 04, 2020 5:31 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Vinegar on a cut
- Replies: 4
- Views: 193
Re: Vinegar on a cut
Well anything slightly acidic will cause pain in any cuts or scrapes that are exposed to it, but actual concerning tissue damage is probably not going to happen. It probably will damage the tissue in fingers to some miniscule degree (plus, it's gonna sting), so I'd just wash your hands. However, if ...
- Fri Dec 04, 2020 4:49 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Calculations involving strong acids
- Replies: 3
- Views: 200
Calculations involving strong acids
In Dr. Lavelle's Wednesday lecture, he started talking about approximating calculations involving strong acids by assuming the acid had 100% ionized. His explanations continued by describing a 0.1 M solution of HCl actually being a 0.1 M solution of H3O+ and 0.1 M solution of Cl-. How can the 0.1 M ...
- Mon Nov 23, 2020 5:22 pm
- Forum: Sigma & Pi Bonds
- Topic: Orbital Hybridization
- Replies: 7
- Views: 383
Re: Orbital Hybridization
Everybody already had great answers, but another way of looking at it is that hybridization is supposed to match the VSEPR model of whatever molecule you are working with. Each hybrid orbital is supposed represent an area of electron density in a molecule, so if you know the Lewis structure, then cr...
- Mon Nov 23, 2020 5:15 pm
- Forum: Sigma & Pi Bonds
- Topic: trans- & cis- Molecules
- Replies: 6
- Views: 224
Re: trans- & cis- Molecules
I believe that both cis-dichloroethene and trans-dichloroethene are fixed and cannot rotate because of the double bond between the two carbons. I think only single bonds are "loose" and can rotate because it is the only bond that doesn't have pi bonds. Yeah I have to agree with Jessie her...
- Mon Nov 23, 2020 5:06 pm
- Forum: Sigma & Pi Bonds
- Topic: Pi Bond Name
- Replies: 5
- Views: 240
Re: Pi Bond Name
"Sigma" and "pi" are the Greek letters for "s" and "p", so I'm assuming it pertains to the s- and p-orbitals that are involved in these bonds (though sigma bonds can occur between two p-orbitals and pi bonds can occur between d-orbitals, so I'm not certain).
- Mon Nov 23, 2020 4:58 pm
- Forum: Sigma & Pi Bonds
- Topic: Double bond- second one is pi
- Replies: 2
- Views: 160
Re: Double bond- second one is pi
I think the most useful way to think about this is thinking about how orbitals p, d, and f have multiple planes of electron density. Because we aren't working with monster-like compounds yet, we'll focus on the p-orbital. The p-orbital has has three subshells: Px, Py, and Pz. They operate on three d...
- Mon Nov 23, 2020 4:42 pm
- Forum: Sigma & Pi Bonds
- Topic: Resonance and pi bonds
- Replies: 3
- Views: 289
Resonance and pi bonds
Because the actual bonds in a molecule with resonance would have a bond length somewhere in between, for example, a single bond and double bond, does this effect formations of pi bonds? I am a little unclear as to how even if a molecule has resonance (like benzene in today's lecture) it would still ...
- Mon Nov 23, 2020 1:03 am
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Ionic Bond and Covalent Character
- Replies: 4
- Views: 290
Re: Ionic Bond and Covalent Character
Generally, I think that the farther away two elements on the periodic table are from each other, the more their ionic character increases. This is because elements of higher differences in electronegativity form ionic bonds. Electronegativity increases across a period and up a group, so distance fro...
- Mon Nov 23, 2020 12:55 am
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Determining Non-Polarity
- Replies: 5
- Views: 262
Re: Determining Non-Polarity
I think the dipole moments have to cancel for the a molecule to be considered nonpolar. Electrons are shared equally or unequally based the relative electronegativities of the atoms involved. If there is an inequality in charge, but another inequality of the same magnitude that cancels the other out...
- Wed Nov 18, 2020 2:21 am
- Forum: Ionic & Covalent Bonds
- Topic: Electronegativity and Ionic/Covalent Character
- Replies: 3
- Views: 230
Electronegativity and Ionic/Covalent Character
I was reviewing and I remembered from one of the lectured about how Dr. Lavelle talked about how if the difference in electronegativity was greater than 2 between two atoms it was considered to have an ionic bond and if the difference in electronegativity was less than 1.5 between two atoms it was c...
- Mon Nov 16, 2020 12:21 pm
- Forum: Bond Lengths & Energies
- Topic: Molecular Shape with double and triple bonds
- Replies: 2
- Views: 170
Molecular Shape with double and triple bonds
I have a question regarding molecular shape. Today, Dr. Lavelle went over an example detailing the shape of a carbonate ion, stating that it was trigonal planar due to its three regions of electron density. The carbonate ion he showed had one double bond and two single bonds connecting the three oxy...
- Sun Nov 15, 2020 10:57 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: Sapling # 20
- Replies: 6
- Views: 651
Re: Sapling # 20
Sofia Lombardo 3F wrote:London dispersion forces are present in all interactions and since the molecule is polar it would also have dipole-dipole interactions as well.
How is the molecule determined to be polar? Is it through constructing the Lewis structure or is there a less complicated way to figure it out?
- Mon Nov 09, 2020 10:01 pm
- Forum: Electronegativity
- Topic: Delta negative and delta positive?
- Replies: 8
- Views: 4517
Re: Delta negative and delta positive?
The atom that is the more electronegative will have the delta negative charge. Remember, electronegativity measures how well an atom can attract electron pairs for bonding, so the atom that is greater in electronegativity will pull the electron pair closer relative to the other atom. Having the elec...
- Mon Nov 09, 2020 9:28 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Sapling oxidation
- Replies: 2
- Views: 139
Re: Sapling oxidation
There are a few rules and exceptions that I would suggest looking up for this one. What I do though is set up an equation. If the overall charge is 0 then I make it equal to 0 or whatever the overall charge is. Then I take the elements in the molecule and add them up based on the charges that I thi...
- Mon Nov 09, 2020 9:00 pm
- Forum: Dipole Moments
- Topic: q for charge
- Replies: 5
- Views: 255
Re: q for charge
I don't believe we will actually have to calculate the value. q is simply the modulus (absolute value) of the charge value.
- Mon Nov 09, 2020 6:20 pm
- Forum: Coordinate Covalent Bonds
- Topic: Coordinate vs polar covalent
- Replies: 10
- Views: 2408
Re: Coordinate vs polar covalent
A coordinate covalent bond happens between a lewis acid and a lewis base, where one lone pair of electron is shared between the two. A polar covalent bond happens when one pair of electrons is unequally shared between two atoms. Hope this helps!
- Mon Nov 09, 2020 5:42 pm
- Forum: Electronegativity
- Topic: Electronegativity vs. Electron Affinity
- Replies: 8
- Views: 454
Re: Electronegativity vs. Electron Affinity
There is a distinct difference in meaning, but they share the exact same trends on the periodic table. Electronegativity describes an atom's ability to attract electrons, while electron affinity describes how much energy is released when one electron binds to a specific element. Both values increase...
- Wed Nov 04, 2020 1:46 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Formal Charge and Stability
- Replies: 7
- Views: 172
Re: Formal Charge and Stability
Because formal charge = 0 has the most stability parts of a molecule will have, generally you want to have the smallest amount of positive or negative charge. Hope this helps!
- Wed Nov 04, 2020 1:34 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: l numbers bigger than 3
- Replies: 5
- Views: 316
Re: l numbers bigger than 3
I'm pretty sure they're all theoretical; as in they don't technically exist (like there isn't a v-orbital that appears at n=5), but if you were able to have a n=7, then the l would theoretically be values [0,6]. Correct me if I'm wrong, though! I am curious what would happen if a n= 5 was possible....
- Wed Nov 04, 2020 1:33 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: l numbers bigger than 3
- Replies: 5
- Views: 316
Re: l numbers bigger than 3
I'm pretty sure they're all theoretical; as in they don't technically exist (like there isn't a v-orbital that appears at n=5), but if you were able to have a n=7, then the l would theoretically be values [0,6]. Correct me if I'm wrong, though!
- Wed Nov 04, 2020 12:29 pm
- Forum: Octet Exceptions
- Topic: Radicals
- Replies: 5
- Views: 131
Re: Radicals
Hey! I think some examples of radicals that we ingest are in fatty foods, or foods with lots of hydrocarbon chains. When we eat them, they are oxidized which can cause them to form free radicals leading to some un-fun results. Lecture today is gonna make me try to eat healthier now. :/ Wow! This is...
- Wed Nov 04, 2020 12:19 pm
- Forum: Octet Exceptions
- Topic: Figuring out expanded valence shells
- Replies: 2
- Views: 128
Figuring out expanded valence shells
Just a quick question: the expanded valence shell depend on if there are still is a d-orbital in n= 3 or above? I am a little confused by the requirements for expansion
- Thu Oct 29, 2020 5:21 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Electron Configuration
- Replies: 5
- Views: 121
Re: Electron Configuration
I had the same question, but I'm fairly certain that the full electron configuration will be required unless explicitly told to use shorthand. Hope this helps!
- Thu Oct 29, 2020 5:19 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Emitting a Photon
- Replies: 9
- Views: 244
Re: Emitting a Photon
Conservation of energy entails that when an electron goes from a high energy state to a low energy state, the energy has to go somewhere, and it will be released in the form of photons. So, yes to both parts of the question, as no matter what, you are still going from high to low energy states in bo...
- Thu Oct 29, 2020 4:59 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Px Py Pz
- Replies: 4
- Views: 222
Re: Px Py Pz
In three dimensions, there would be an x-,y-, and z-plane. Px, Py, and Pz simply designate which plane or axis that the orbital is on.
- Thu Oct 29, 2020 4:55 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Spin state
- Replies: 25
- Views: 1206
Re: Spin state
Is upwards and downwards for spin states arbitrary or do electrons actually adhere to some sort of fixed direction?
- Wed Oct 28, 2020 1:08 am
- Forum: Photoelectric Effect
- Topic: Sapling Week 2,3,4 Q 9
- Replies: 4
- Views: 193
Re: Sapling Week 2,3,4 Q 9
Since the problem asks for the maximum wavelength that will reject electrons, KE=0, so the work function is equal to the energy of the photon. Therefore, you can set 4.810 x 10^-19 J equal to hv. Since we want to find wavelength, you can make v=c/lambda, making the equation 4.810 x 10^-19 J=hc/lamb...
- Tue Oct 27, 2020 11:48 pm
- Forum: Photoelectric Effect
- Topic: Sapling Week 2,3,4 Q 9
- Replies: 4
- Views: 193
Re: Sapling Week 2,3,4 Q 9
Since the problem asks for the maximum wavelength that will reject electrons, KE=0, so the work function is equal to the energy of the photon. Therefore, you can set 4.810 x 10^-19 J equal to hv. Since we want to find wavelength, you can make v=c/lambda, making the equation 4.810 x 10^-19 J=hc/lamb...
- Wed Oct 21, 2020 3:32 pm
- Forum: DeBroglie Equation
- Topic: Rearranging De Broglie Equation
- Replies: 17
- Views: 2115
Re: Rearranging De Broglie Equation
De Broglie's equation: (lambda) = h/p, where h= Planck's constant and p= momentum. It can be further simplified to (lambda) = h/(mv), where m= mass and v= velocity, as momentum is (mass)(veloctity). Then, we can do some relatively simple algebra to solve for velocity (v): (lambda) = h/(mv) (v)(lambd...
- Wed Oct 21, 2020 3:07 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Electromagnetic radiation and associated energy levels
- Replies: 4
- Views: 137
Re: Electromagnetic radiation and associated energy levels
For now, I'm fairly certain we only need to know (n=1), which is the Lyman series, and (n=2), which is the Balmer series.
- Wed Oct 21, 2020 3:02 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Energy for non hydrogen atoms
- Replies: 2
- Views: 292
Re: Energy for non hydrogen atoms
The Rydberg equation that we learned only applies to H-atoms. It is because hydrogen has only one electron and is therefore easier to calculate the energy from level to level. I think in the lecture he mentioned that we would need a more sophisticated model for multi-electron systems, which makes se...
- Wed Oct 21, 2020 2:19 pm
- Forum: *Shrodinger Equation
- Topic: Nodal Planes
- Replies: 3
- Views: 86
Nodal Planes
Just a quick question: are nodal planes simply a plane that has no electron density and therefore zero probability that an electron would be found in the plane? I just want to clarify and make sure I'm not missing anything. Thanks!
- Wed Oct 14, 2020 2:42 pm
- Forum: Einstein Equation
- Topic: Wave Model Question
- Replies: 5
- Views: 270
Re: Wave Model Question
This is a pretty solid question. To put it simply, the classical (wave) model depicts light in a continuous fashion (ie the watering can pouring water analogy), while the quantum (particle) model depicts light acting in discrete units. In the photoelectric experiment, we found that increasing the in...
- Wed Oct 14, 2020 2:29 pm
- Forum: *Black Body Radiation
- Topic: Equation
- Replies: 8
- Views: 622
Re: Equation
Black bodies are more covered as a physics topic, as opposed to a chemistry one. Dr. Lavelle also states that we won't need to know much. Likely, all we need to know is what he's told us so far in the lectures.
- Wed Oct 14, 2020 2:17 pm
- Forum: Photoelectric Effect
- Topic: Photoelectric effect
- Replies: 9
- Views: 292
Re: Photoelectric effect
Increasing the intensity of the light equates to increasing the number of photons shining onto the metal surface. However, electrons do not get ejected from the metal unless on photon has energy greater than or equal to remove one electron e-. Increasing the light intensity does not change anything ...
- Wed Oct 14, 2020 2:06 pm
- Forum: Photoelectric Effect
- Topic: Discussion Problem #3a
- Replies: 2
- Views: 83
Discussion Problem #3a
Today's worked example 3a during the discussion sort of confused me. I understood the objective of finding the wavelength using De Broglie, as we were finding the wavelength of particle, but I am confused as to how to find the mass of the electron in the equation. Is there some way we derive it, or ...
- Tue Oct 13, 2020 12:25 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Inclusive Access
- Replies: 1
- Views: 127
Inclusive Access
I am kind of confused as to what Inclusive Access is. I know it has something to do with the course material, but I've heard that it's recommended to opt out of the program. I'm not exactly sure why, though. Can someone explain to me what Inclusive Access is all about, as well as whether or not I sh...