Search found 153 matches
- Sun Mar 14, 2021 6:34 pm
- Forum: Administrative Questions and Class Announcements
- Topic: THANK YOU DR LAVELLE!
- Replies: 47
- Views: 6276
Re: THANK YOU DR LAVELLE!
BOOST!! Thank you so much Dr. Lavelle, TA's and UA's!!! You have all been incredible! Hope to see you all on campus in the future!
- Fri Mar 12, 2021 7:19 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: 6M.3 Textbook Why cant we add the half reactions?
- Replies: 3
- Views: 236
Re: 6M.3 Textbook Why cant we add the half reactions?
There are two methods to finding the cell potential, and the textbook simply uses the other method. Your method is valid, and if you balance the half reactions and flip the sign of the half reaction being used for oxidation, then you should come up with the same result.
- Fri Mar 12, 2021 7:17 am
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Textbook 4I7 Help
- Replies: 1
- Views: 247
Re: Textbook 4I7 Help
In order to melt a substance, the substance would need to have a positive enthalpy, absorbing heat to break the bonds and go from a solid to a liquid. Melting should be positive, and I would think the vaporization would need to be positive as well by the same principle. However, take another look at...
- Tue Mar 09, 2021 7:57 am
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Approximation for Weak Acid/Base
- Replies: 3
- Views: 310
Approximation for Weak Acid/Base
When can we approximate when calculating the pH of a weak acid or base? I've heard people say when Ka = 10^-4 and I've heard 10^-5 and I'm not sure which is true.
- Tue Mar 09, 2021 7:32 am
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Question 6D. 15 part B in the textbook
- Replies: 1
- Views: 280
Re: Question 6D. 15 part B in the textbook
Also would we need to find the Ka or Kb values somewhere else? I don't think its provided in the question.
- Tue Mar 09, 2021 7:30 am
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Question 6D. 15 part B in the textbook
- Replies: 1
- Views: 280
Question 6D. 15 part B in the textbook
6D.15 Calculate the pH of (a) 0.19 M NH4Cl(aq); (b) 0.055 M AlCl3(aq).
I understand how to do part A, but for part B how do we know how the aluminum chloride will react in solution? I know it's a Lewis Acid so I assume the pH will be acidic, but I don't understand how to go past that.
I understand how to do part A, but for part B how do we know how the aluminum chloride will react in solution? I know it's a Lewis Acid so I assume the pH will be acidic, but I don't understand how to go past that.
- Tue Mar 09, 2021 7:28 am
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: How do we tell if it is acidic?
- Replies: 3
- Views: 2064
Re: How do we tell if it is acidic?
Since ClO4- is a conjugate base of a strong acid (very strong) it will be inactive in solution. Since Cr 3+ is not a conjugate of any strong acids or bases, you know it has to be from a weak base because the other component of the salt came from an acid. Therefore the Cr3+ is a conjugate acid of a w...
- Sat Mar 06, 2021 11:08 am
- Forum: Calculating the pH of Salt Solutions
- Topic: Calculating pH of a weak salt
- Replies: 2
- Views: 434
Calculating pH of a weak salt
For salts like ammonium nitrate or potassium acetate, its easy to see whether the salt would be acidic or basic. How would we tell if the salt had both a weak acidic and a weak basic component, like ammonium acetate?
- Fri Mar 05, 2021 1:49 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 5.35 Question
- Replies: 2
- Views: 193
5.35 Question
5.35 The following plot shows how the partial pressures of reactant and products vary with time for the decomposition of compound A into compounds B and C. All three compounds are gases. Use this plot to do the following: (a) Write a balanced chemical equation for the reaction. (b) Calculate the equ...
- Fri Mar 05, 2021 9:39 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 5I. 15 from Outline 1
- Replies: 3
- Views: 695
5I. 15 from Outline 1
5I.15 When solid NH4HS and 0.400 mol NH3(g) were placed in a vessel of volume 2.0 L at 24 °C, the equilibrium NH4HS(s)⇌NH3(g)+H2S(g), for which Kc=1.6×10−4, was reached. What are the equilibrium concentrations of NH3 and H2S? On the solution manual, it says that products are formed from the initial ...
- Thu Mar 04, 2021 2:43 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Converting from Kp to Kc
- Replies: 2
- Views: 357
Converting from Kp to Kc
In the equilibrium unit did we ever use the equation Kp=Kc(RT)^Delta n?
I'm trying to study for the final and I can't remember if we ever used this equation to convert between Kc and Kp or if we just had to convert the units of one species, like from atm to Molarity.
I'm trying to study for the final and I can't remember if we ever used this equation to convert between Kc and Kp or if we just had to convert the units of one species, like from atm to Molarity.
- Wed Mar 03, 2021 11:04 am
- Forum: Student Social/Study Group
- Topic: Song from Electrochem Lectures
- Replies: 1
- Views: 174
Song from Electrochem Lectures
Does anyone know the song from the beginning of the electrochemistry lectures? It was really catchy and I've been looking all over for it.
- Tue Feb 23, 2021 12:50 pm
- Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
- Topic: Phone Batteries Charging
- Replies: 4
- Views: 322
Phone Batteries Charging
I think Dr. Lavelle is going to cover this in his next lecture, but in our phones does the power from our wall plug sockets cause the reaction to proceed in the reverse and therefore recharge our batteries? I'm assuming this is how most rechargeable batteries function and the energy that causes this...
- Tue Feb 23, 2021 12:48 pm
- Forum: General Science Questions
- Topic: No Lavelle Chem 14C?
- Replies: 68
- Views: 4276
Re: No Lavelle Chem 14C?
Giselle_zamora_1L wrote:No, he doesn't, I believe he teaches some upper-division chem classes if you're interested
Yeah Dr. Lavelle teaches 14A/14B, Chem 192, and Chem 375. This was in Dr. Lavelle's last class email if anyone is curious where I got it from.
- Tue Feb 23, 2021 12:45 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Classes for Biochem Majors
- Replies: 6
- Views: 452
Re: Classes for Biochem Majors
I'm a Biochemistry major. Don't worry about that rule where Biochem majors are supposed to take 20A/20B and then move on to the 30A/30B series. That rule is from earlier years and now Biochem majors can take 14A and 14B as pre-requisites for 30A and 30B. This file shows the Biochem degree requiremen...
- Tue Feb 23, 2021 12:41 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Applications of the Nernst equation in Biology
- Replies: 4
- Views: 401
Applications of the Nernst equation in Biology
In lecture, Dr. Lavelle said the Nernst equation is often used in biology and is fundamental to electrophysiology. Can anyone give me any examples as to when the Nernst equation is used in these fields?
- Tue Feb 23, 2021 12:39 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Calculating Disorder based on molecule size
- Replies: 12
- Views: 682
Re: Calculating Disorder based on molecule size
While more complexity is a really good reason for why larger molecules have more entropy, keep in mind it also has to do with the number of electrons. Molecules like diatomic iodine gas have more entropy than diatomic fluorine gas because it has a larger number of electrons even though complexity is...
- Tue Feb 23, 2021 12:34 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: No conducting solids
- Replies: 4
- Views: 248
Re: No conducting solids
It means that the reactant and product are both aqueous in the cathode and anode and lack a solid electrode to conduct the charge. In this case, you would add platinum into the side (or both) that need a strong electrode as platinum is inert and will not interfere with the reaction.
- Sun Feb 21, 2021 9:39 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Clarification of EMF
- Replies: 3
- Views: 235
Clarification of EMF
Could someone please explain to me what EMF is and why it is useful? I was a little confused by this at the end of Wednesday's lecture from 2/17 and if someone could explain it to me that would be great!
- Sun Feb 21, 2021 9:37 am
- Forum: Balancing Redox Reactions
- Topic: Acidic or Basic Conditions
- Replies: 3
- Views: 223
Acidic or Basic Conditions
When balancing redox reactions, how do you modify the equation when the question states the reaction occurs under acidic or basic conditions?
- Sun Feb 21, 2021 9:36 am
- Forum: Balancing Redox Reactions
- Topic: Textbook 6K.3d
- Replies: 2
- Views: 195
Re: Textbook 6K.3d
Hi I'm a little confused by what you need help with. There's a difference between the oxidizing/reducing agent and the substance being oxidized or reduced. If two substances are involved in a redox reaction, one will act as an oxidizing agent and be reduced, while the reducing agent will be oxidized...
- Sun Feb 21, 2021 9:31 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Concept of qsys=-qsurr
- Replies: 7
- Views: 2439
Re: Concept of qsys=-qsurr
To add on, this can mainly be attributed to reversible systems. Since all energy lost as work is replaced by heat flowing into the system, the heat lost by the surroundings is equal to the heat gained by the system. Of course this is a purely ideal process and does not occur in real scenarios.
- Wed Feb 17, 2021 9:00 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: Uses of the third law
- Replies: 2
- Views: 218
Re: Uses of the third law
I think its helpful because it shows how the idea of absolute zero temperature is purely a limit, and all matter has some degree of entropy since we cannot reach zero degrees Kelvin. It provides a reference point and a minimum for all entropy calculations.
- Wed Feb 17, 2021 8:58 pm
- Forum: Student Social/Study Group
- Topic: Thermochem/Thermodynamics Equation sheet
- Replies: 4
- Views: 506
Re: Thermochem/Thermodynamics Equation sheet
Hi you can find the equation sheet on Dr. Lavelle's website! Its called Constants and Equations. Here's the link to the file! https://lavelle.chem.ucla.edu/wp-conten ... ations.pdf
- Sat Feb 13, 2021 10:22 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Adding 1 to Cv or Cp
- Replies: 4
- Views: 290
Adding 1 to Cv or Cp
In what case do you need to add 1 to the Cp or Cv of an ideal gas? I've heard of this being used in some scenarios but I'm not sure where. Would it be for diatomic ideal gases?
- Sat Feb 13, 2021 10:00 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Examples of G, W, and U
- Replies: 3
- Views: 220
Re: Examples of G, W, and U
In cars, combustion of the gasoline in the gas tank releases heat, and the car's mechanisms (piston/cylinder system) convert that energy into work, which is then used for motion. I would assume in this case the internal energy would be near zero, because the large negative heat would be mostly accou...
- Sat Feb 13, 2021 9:56 am
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Water Entropy [ENDORSED]
- Replies: 6
- Views: 514
Re: Water Entropy [ENDORSED]
Water freezing is an exothermic process, so it releases heat into its surroundings. This increases the entropy of the surroundings. It would not violate the second law because the law can be extended to account for the changes in the entropy of the surroundings, not just of the system. The favorabil...
- Fri Feb 12, 2021 12:26 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Diff between delta G and delta G nought
- Replies: 3
- Views: 110
Diff between delta G and delta G nought
What is the difference between delta G and delta G nought?
- Fri Feb 12, 2021 12:11 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: What is meant by enthalpy or entropy dominating?
- Replies: 2
- Views: 77
What is meant by enthalpy or entropy dominating?
In lecture today, Dr. Lavelle found the boiling point of Br 2 liquid with the equation G = H - TS. He stated that if temperature is higher than 333 K, entropy dominates, and if under 333 K enthalpy dominates. What is meant by enthalpy or entropy dominating in this case? Thank you!
- Wed Feb 10, 2021 11:09 am
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Are all reversible expansions isothermal?
- Replies: 6
- Views: 393
Are all reversible expansions isothermal?
We learned isothermal reversible expansion in a recent lecture, and I just wanted to clarify if all reversible expansions isothermal, or if isothermal reversible expansion was just one example of a type of reversible expansion. Thank you!
- Sun Feb 07, 2021 9:04 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Heat Capacity of a Calorimeter
- Replies: 2
- Views: 72
Heat Capacity of a Calorimeter
When calculating the heat capacity of a calorimeter do we use the equation q=mc delta T or the equation q=C delta T ? On homework problems the usage of these two equations has been interchanged often and I'd like some clarification on when each equation should be used. Thank you!
- Sat Feb 06, 2021 12:59 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Can heat capacities be negative?
- Replies: 52
- Views: 13522
Re: Can heat capacities be negative?
No they cannot be negative. Heat capacity is how much energy has to be gained to raise a substance's temperature by a certain amount. This is endothermic and therefore must be positive.
- Sat Feb 06, 2021 12:35 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Entropy = 0
- Replies: 6
- Views: 228
Re: Entropy = 0
Yes I think you are correct! All diatomic molecules that are only composed of one element will have zero positional entropy. They have no variation in the position of their atoms and the degeneracy is zero. When plugged into the equation, positional entropy also becomes zero.
- Sat Feb 06, 2021 11:37 am
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Lecture 12 2/3
- Replies: 3
- Views: 87
Re: Lecture 12 2/3
To add onto that, the natural log is what accounts for the smaller error in entropy with a larger error in degeneracy. Say if the degeneracy was actually 10,000 but the calculated degeneracy was 15,000. This is a large error, but the natural log of 10,000 is 9.21 and the natural log of 15,000 is 9.6...
- Sat Feb 06, 2021 11:33 am
- 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: Residual Entropy for O2
- Replies: 5
- Views: 542
Re: Residual Entropy for O2
Hi! The residual entropy for O2 is zero because there are no other states the oxygen atoms can have. If they swapped places, the molecule would be identical. Therefore, no variation of their placement is possible and positional entropy is zero.
- Wed Feb 03, 2021 3:45 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Do Resonance Structures have more Degeneracy
- Replies: 6
- Views: 307
Do Resonance Structures have more Degeneracy
Hi, I was wondering if since resonance structures can have bonds in multiple different places would they have a high amount of degeneracy? Or since the real structure is a resonance hybrid would the degeneracy be zero?
- Sat Jan 30, 2021 10:54 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Temperature vs Heat
- Replies: 5
- Views: 232
Re: Temperature vs Heat
I think temperature and heat are closely related, but temperature is just a measure of how much heat, and therefore how much energy an object or substance has. Heat is transferable and measurable, while temperature is measurable but not transferable.
- Sat Jan 30, 2021 8:53 am
- Forum: Calculating Work of Expansion
- Topic: Need clarification on Volume/Pressure changes in small increments
- Replies: 3
- Views: 120
Need clarification on Volume/Pressure changes in small increments
Could someone please explain to me why we decrease the volume/pressure in small increments of about 10^-6 bar to reach equilibrium? What does this do and why is it helpful?
- Sat Jan 30, 2021 7:36 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Why do specific heats differ between different states?
- Replies: 3
- Views: 177
Why do specific heats differ between different states?
On the formula sheet, there is a specific heat listed for water as a liquid, vapor, and as ice. Why does the specific heat of water differ in different states?
- Thu Jan 28, 2021 2:33 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Textbook question 4E.9
- Replies: 8
- Views: 465
Re: Textbook question 4E.9
I had the same issue with this problem, thank you! Could someone please explain what Kekule structures are? I wanted to make a post about this but I thought it would be helpful to add it onto this thread.
- Thu Jan 28, 2021 1:20 pm
- Forum: Student Social/Study Group
- Topic: Midterm 1
- Replies: 3
- Views: 183
Re: Midterm 1
Check out the 'Midterm 1 Information" on Dr. Lavelle's website. It says the specific sections of the textbook that the midterm covers and the logistics of the exam.
- Sat Jan 23, 2021 10:10 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Material Accessible during Exams
- Replies: 6
- Views: 257
Material Accessible during Exams
For several questions in the textbook, they ask questions and do not provide the Ka/Kb, and I assume they want us to reference the table. Would we have access to a table of Ka/Kb values for our exams or would they be provided in the question? Would any need to be memorized?
- Thu Jan 21, 2021 9:39 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Textbook 6E #1
- Replies: 2
- Views: 160
Re: Textbook 6E #1
Hi yes you are right, for polyprotic acids we will need to do the process multiple times. Even though the Ka is much smaller for the second and even third protonation, it will still have an effect on the pH. It will most likely be specified in that the problem will give you the Ka1, Ka2, etc., thus ...
- Thu Jan 21, 2021 9:15 pm
- Forum: Phase Changes & Related Calculations
- Topic: How would a phase change diagram look like for the process of sublimation?
- Replies: 3
- Views: 95
How would a phase change diagram look like for the process of sublimation?
In Wednesday's lecture, we looked at a phase change diagram of water, where it transitioned from solid to vapor with flat lines at the phase changes. How would the diagram look for sublimation, such as the vaporization of dry ice? Would it just jump directly from solid to gas? Thank you!
- Wed Jan 20, 2021 6:01 pm
- Forum: Phase Changes & Related Calculations
- Topic: Question about Steam Causing Severe Burns
- Replies: 3
- Views: 235
Re: Question about Steam Causing Severe Burns
Yes you are correct! Since the skin is much colder than the steam, the heat immediately transfers to the skin and hydrogen bonds are actually being formed, not broken (since energy is released and making bonds releases energy because its favorable).
- Wed Jan 20, 2021 11:58 am
- Forum: Phase Changes & Related Calculations
- Topic: Adding Heat but Temp remains constant
- Replies: 11
- Views: 367
Adding Heat but Temp remains constant
So in lecture today, Dr. Lavelle said that the temperature remains constant during a phase change, even though heat is being supplied. If the heat is being used to break the bonds, where is going after that process is complete? I'm confused by how this follows the Law of Conservation of Energy.
- Wed Jan 20, 2021 9:23 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Help on 5.33 in the Textbook
- Replies: 4
- Views: 243
Help on 5.33 in the Textbook
5.33 Dissociation of a diatomic molecule, X2(g)⇌2 X(g) occurs at 500 K. The equilibrium state of the reaction is shown in 1 and the equilibrium state in the same container after a change has occurred is shown in 2. Which of the following changes will produce the composition shown? (a) Increasing the...
- Fri Jan 15, 2021 11:46 am
- Forum: Administrative Questions and Class Announcements
- Topic: Are we covering Buffers?
- Replies: 1
- Views: 92
Are we covering Buffers?
In this class are we going to be covering buffers? It wasn't in today's lecture but it seems like a pretty important topic in acids and bases.
- Fri Jan 15, 2021 11:30 am
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Factoring in the Hydronium Concentration already present in water from today's Lecture
- Replies: 1
- Views: 85
Factoring in the Hydronium Concentration already present in water from today's Lecture
In today's lecture, Dr. Lavelle mentioned how we ignore the hydronium already present in water because of how small it is compared to the amount from the acid. Wouldn't that 10^-7 moles of hydronium not matter anyway because the 10^-7 moles of hydroxide also present in the water takes away 10^-7 mol...
- Thu Jan 14, 2021 2:39 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Gas
- Replies: 16
- Views: 572
Re: Gas
The question should always specify the units, since the gas constant we use is dependent on the units of the problem. Furthermore, it would only matter when choosing the gas constant because bar and atm are essentially equivalent.
- Thu Jan 14, 2021 2:37 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: pKa and pH
- Replies: 10
- Views: 545
Re: pKa and pH
pKa and pH are not the same, because pKa is standardized for each acid while pH is measured at any time and can vary. Check out this website for some more insight. https://www.differencebetween.com/diffe ... nd-vs-pka/
- Wed Jan 13, 2021 2:27 pm
- Forum: Student Social/Study Group
- Topic: Study Habits
- Replies: 96
- Views: 5402
Re: Study Habits
Hi, the best tips I can give you are to develop a study plan, minimize distractions, and try to avoid procrastinating or cramming.
- Wed Jan 13, 2021 2:25 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Homework problem 7
- Replies: 4
- Views: 165
Re: Homework problem 7
I agree with the above answer, but also if a reaction is endothermic you can think of heat as a reactant, so increasing temperature a.k.a adding heat, will act like adding a reactant. The denominator will be larger and Q will be less than K, and the reactant shifts towards the products.
- Wed Jan 13, 2021 1:30 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: [H30+]=[OH-] ???
- Replies: 8
- Views: 317
Re: [H30+]=[OH-] ???
Yes that is correct, you would square root the value. This makes sense because water should have a neutral pH of 7, which would happen as a result of hydroxide and hydronium concentrations being equal.
- Wed Jan 13, 2021 11:45 am
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Textbook question 6B 11
- Replies: 2
- Views: 135
Re: Textbook question 6B 11
I agree with the above answer, but just keep in mind that when you add a metallic oxide to water it makes a base. Adding solid Na2O to water would create sodium hydroxide, which was the cause of the pH lowering.
- Wed Jan 06, 2021 11:59 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Would equilibrium favor resonance?
- Replies: 3
- Views: 164
Would equilibrium favor resonance?
If a reaction has a reactant or a product that is a resonance hybrid, would the reaction favor that side since the resonance hybrid would be more stable?
- Tue Jan 05, 2021 6:43 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: temperature change in reactions
- Replies: 11
- Views: 371
Re: temperature change in reactions
I agree with all of the previous replies, but if you were asking from more of a technical standpoint we will learn about that more in the Chemical Kinetics unit. When temperature is increased, the molecules move faster and have higher energy, therefore leading to the reaction progressing faster in t...
- Tue Jan 05, 2021 6:36 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Pure Substances Concentration
- Replies: 4
- Views: 229
Re: Pure Substances Concentration
Aqueous substances are simply dissolved in water, they do not make up liquid as a pure substance. For example, hydrochloric acid is not often 100% HCl, it is normally a small percentage of the total volume, such as 5% HCl.
- Tue Jan 05, 2021 6:34 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Chemical Equilibrium 1A Question 19
- Replies: 3
- Views: 509
Re: Chemical Equilibrium 1A Question 19
I'm pretty sure the answer is A, but if anyone else thinks otherwise let me know. It should just be the equilibrium concentrations of the products divided by the equilibrium concentrations of the reactants, all raised to the power of the stoichiometric coefficients.
- Mon Jan 04, 2021 2:37 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K vs. Kc
- Replies: 15
- Views: 485
Re: K vs. Kc
In my understanding, K and Kc are almost interchangeable, but K is more general, while Kc is mainly used in the context of comparing concentrations. K can be used to cover both the equilibrium constant of concentrations, Kc, and the equilibrium constant of gas pressures, Kp. Dr. Lavelle with probabl...
- Mon Jan 04, 2021 2:34 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Pure Liquids [ENDORSED]
- Replies: 3
- Views: 141
Re: Pure Liquids [ENDORSED]
For example, if a compound is aqueous in 1L of water, the concentration of the water would be the moles of water divided by its volume. 1 Liter of water is 1000 grams of water, since 1 g is equal to 1 cubic centimeter. 1000 grams of water divided by 18.016 grams per mole, divided by 1 Liter, gives a...
- Fri Dec 11, 2020 2:58 pm
- Forum: Lewis Acids & Bases
- Topic: Aluminum chloride example from Bruincast review today
- Replies: 1
- Views: 110
Aluminum chloride example from Bruincast review today
In the aluminum chloride example from the lecture today, I know it is a Lewis Acid, but what would aluminum chloride be in the Bronsted definition? Does the Bronsted definition not apply to it?
- Thu Dec 10, 2020 6:16 pm
- Forum: Polyprotic Acids & Bases
- Topic: Polyprotic Acids
- Replies: 7
- Views: 406
Re: Polyprotic Acids
Yes, they are acids that are able to donate more than one hydrogen in solution. Some examples are sulfuric acid and phosphoric acid. Keep in mind the Ka decreases greatly after every proton loss due to increased attraction.
- Thu Dec 10, 2020 6:13 pm
- Forum: Naming
- Topic: "ate" and "ic"
- Replies: 4
- Views: 593
Re: "ate" and "ic"
Hi, I'm not sure where to use "ate", but "ic" is used to name an acid with an "ate" compound. For example, the acid of nitrate is nitric acid and the acid of chlorate is chloric acid.
- Thu Dec 10, 2020 1:39 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Uncertainty of Position in an Atom
- Replies: 2
- Views: 210
Uncertainty of Position in an Atom
If the uncertainty in position of an electron confined to an atomic radius is given, would we use the atomic radius as the uncertainty or would we double it and use the diameter?
- Thu Dec 10, 2020 1:37 pm
- Forum: Properties of Light
- Topic: What are the ranges of wavelength for each type of electromagnetic radiation?
- Replies: 5
- Views: 392
What are the ranges of wavelength for each type of electromagnetic radiation?
Could someone please explain the ranges of wavelength for each type of electromagnetic radiation? The ranges are always so ambiguous to me and I have always had trouble identifying the type of light in the problem based on its wavelength.
- Wed Dec 09, 2020 10:10 am
- Forum: *Titrations & Titration Calculations
- Topic: Stoichiometric Point: Mol acid = mol base
- Replies: 2
- Views: 2245
Stoichiometric Point: Mol acid = mol base
In lecture today, 12/9, Dr. Lavelle said at the stoichiometric point mol acid = mol base. Would it be more accurate to say that at the point mol hydronium equals mol hydroxide? Since some acids are polyprotic and some bases can release 2 moles of hydroxide, like Ca(OH)2. For Ca(OH)2, if the moles of...
- Mon Dec 07, 2020 11:00 am
- Forum: Identifying Acidic & Basic Salts
- Topic: Metal Cation Example from Lecture 12/7
- Replies: 2
- Views: 156
Metal Cation Example from Lecture 12/7
In the example from lecture about Fe3+ releasing H+ in solution by pulling away electron density and making the OH bond weaker, where is the OH- ion going after the H+ is removed? Is it bonding to the Fe3+ ion as a ligand?
- Sun Dec 06, 2020 8:01 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Naming Coordination Compounds
- Replies: 7
- Views: 349
Re: Naming Coordination Compounds
Most ligands and atoms on the left and right sides of the periodic table are given as either polyatomic ions, elements, or simple compounds which we probably already have memorized the charges of. The only difficult ones would be in the Ligand chart on Dr. Lavelle's website, such as the charge of Ox...
- Sun Dec 06, 2020 7:39 am
- Forum: Properties & Structures of Inorganic & Organic Bases
- Topic: List of Strong Bases and Weak Bases
- Replies: 6
- Views: 728
Re: List of Strong Bases and Weak Bases
Andre Fabian 1G wrote:
Mg(OH)2 is not a strong base due to its limited solubility; given that this would decrease the amount of OH- ions dissociated in the solution, the molecule is therefore classified as a weak base.
Hope this helps!
Andre
It does, thank you Andre!
- Sat Dec 05, 2020 11:04 am
- Forum: Properties & Structures of Inorganic & Organic Bases
- Topic: List of Strong Bases and Weak Bases
- Replies: 6
- Views: 728
Re: List of Strong Bases and Weak Bases
To add on to what Alice said, HClO3 can also be considered a strong acid, but not in every situation. For the strong bases, it's pretty much a "b" shape on the left side of the period table (LiOH, NaOH, KOH, RbOH, CsOH, CaOH, SrOH, BaOH) Why does Mg(OH)2 not fall into the strong base cate...
- Fri Dec 04, 2020 3:51 pm
- Forum: Bronsted Acids & Bases
- Topic: HClO3 Strength for 14A
- Replies: 3
- Views: 111
HClO3 Strength for 14A
In Chem 14A, is chloric acid, HClO3, a strong acid or would it classify as a weak acid? In high school we were told that it was weak, but the textbook says its strong.
- Fri Dec 04, 2020 12:43 pm
- Forum: Amphoteric Compounds
- Topic: Amphoteric - how to tell if it is an acid or base
- Replies: 4
- Views: 274
Re: Amphoteric - how to tell if it is an acid or base
In addition, it would be entirely dependent on what molecule the amphoteric molecule is interacting with. If it is interacting with an acidic substance, it would be a base, and vice versa for a basic substance.
- Fri Dec 04, 2020 11:08 am
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: HClO vs. HBrO vs. HIO example
- Replies: 3
- Views: 617
HClO vs. HBrO vs. HIO example
In the example comparing the pH of HClO, HBrO, and HIO, why is the halogen the atom that receives the electrons and makes the anion more stable if Oxygen is more electronegative? Wouldn't oxygen have a stronger pull on the electrons than the halogens?
- Wed Dec 02, 2020 6:39 am
- Forum: Administrative Questions and Class Announcements
- Topic: Textbook Issue
- Replies: 5
- Views: 304
Re: Textbook Issue
I sometimes have this problem too with the math not "Typesetting", so I downloaded the Bookshelf app from the Microsoft Store. It's available offline and it loads like 10 times faster, it's really helpful!
- Tue Dec 01, 2020 8:42 pm
- Forum: Naming
- Topic: Textbook problem 9c.3
- Replies: 4
- Views: 273
Re: Textbook problem 9c.3
If the overall compound is neutral, there would need to be 3 potassiums to balance out the charge. Hexacyanide would be -6, chromium (III) would be 3+, so 3 potassiums would give the other +3 to make the net charge 0. If it didn't specify the overall charge, then I'm not sure how to approach the num...
- Tue Dec 01, 2020 8:38 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: charge of oxalato
- Replies: 4
- Views: 949
Re: charge of oxalato
I think Dr. Lavelle said to memorize the charges for each ligand because they will not be provided. You don't need to worry about the structure, that won't be covered in this class.
- Sun Nov 29, 2020 1:17 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Chelate
- Replies: 3
- Views: 202
Re: Chelate
You would also need to look at the overall structure of the molecule, if the ligands form a ring around the central atom and the ring includes the central atom, it would be a chelate, and the ligands that are part of it would be chelating ligands.
- Sun Nov 29, 2020 1:14 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Table 9C1
- Replies: 1
- Views: 111
Re: Table 9C1
Hi, in a UA Session the UA told me we would need to memorize the common ligands and their specific charges. For example, if a question asked about EDTA we would have to have memorized that it has a -4 charge. That would help us with oxidation numbers and determining how many bonds it can form with t...
- Sun Nov 29, 2020 1:12 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Delocalized pi bond
- Replies: 4
- Views: 154
Re: Delocalized pi bond
A delocalized pi bond is basically what you get when the pi bond is part of a resonance structure. It just means that the electrons of the bond are free to move between the two atoms. So, you'd have a delocalized pi bond when you have a molecule with resonance. I agree, in addition if you remember ...
- Thu Nov 26, 2020 10:37 am
- Forum: Administrative Questions and Class Announcements
- Topic: Final exam (fall 2020 quarter)
- Replies: 20
- Views: 864
Re: Final exam (fall 2020 quarter)
Will the final follow the same format as midterms or will everyone take it at the same time?
- Thu Nov 26, 2020 10:35 am
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: S character
- Replies: 1
- Views: 175
Re: S character
viewtopic.php?t=1255 Check out this post on Chemistry Community, I think it's helpful to explain what S-character means. Hope this helps!
- Thu Nov 26, 2020 8:50 am
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: TM and coordination compounds
- Replies: 2
- Views: 314
Re: TM and coordination compounds
I can answer the first question, coordination compounds do not need to have a transition metal. For example, take BF3, a well known lewis acid. Boron is not a transition metal but can make coordinate covalent bonds, such as with F-.
- Thu Nov 26, 2020 8:47 am
- Forum: Lewis Structures
- Topic: HW 2E.13 (a)
- Replies: 2
- Views: 187
Re: HW 2E.13 (a)
The two molecules would have the same overall formal charge, but three single bonds gives each terminal iodine a formal charge of zero and puts the negative formal charge on the central iodine. A double bond would make one of the terminal iodines have a +1 charge, and the central atom would have a -...
- Wed Nov 25, 2020 10:40 am
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Ni (NH3)2 Cl2 example from Lecture
- Replies: 1
- Views: 164
Ni (NH3)2 Cl2 example from Lecture
How does Nickel 2+ have room for 6 bonds? I know expanded octets apply to atoms in and after the 3rd row, but I thought only p-block elements could use the empty d shells, not transition metals. The nickel 2+ electron configuration only has 2 unpaired electrons in the 3d shell and an empty 4s shell,...
- Sun Nov 22, 2020 6:58 am
- Forum: Student Social/Study Group
- Topic: Study Tips for Final Exam
- Replies: 57
- Views: 2502
Re: Study Tips for Final Exam
I'm definitely going to review Dr.Lavelle's recommended textbook problems because they were super helpful for the midterms! I also plan on rereading the textbook and making condensed notes. I might rewatch Dr. Lavelle's lectures and the Organic Chemistry Tutor on youtube for the concepts I'm strugg...
- Sat Nov 21, 2020 7:34 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: lone pair repulsion
- Replies: 4
- Views: 115
Re: lone pair repulsion
Also, bonding pairs are in between the nuclei of two atoms, so their negative charge is more confined to the bond region. The lone pair is only affected by one nucleus and can move around freely to repel other lone pairs and bonding pairs.
- Fri Nov 20, 2020 11:41 am
- Forum: Hybridization
- Topic: what are terminal atoms?
- Replies: 3
- Views: 8338
Re: what are terminal atoms?
I read from the textbook that terminal atoms are not regarded as hybridized. (i.e. the Cl molecules in PCl 5 ) What are the definition of terminal atoms? Thank you! Yeah, the central atom's valence shell has been hybridized in order to accommodate the electrons needed for a stable structure. The te...
- Thu Nov 19, 2020 3:49 pm
- Forum: Bond Lengths & Energies
- Topic: Boiling/Melting Point
- Replies: 29
- Views: 1145
Re: Boiling/Melting Point
We would look at intermolecular forces because those are the forces that are overcome to initiate a phase change. For example, when H2O (liquid) is evaporated into H2O(gas) the Hydrogen bonds in the liquid have been overcome to separate the molecules. The O-H bonds in each H2O molecule have not been...
- Thu Nov 19, 2020 3:41 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: n, l, mi
- Replies: 8
- Views: 519
Re: n, l, mi
I think this post should be under the forum regarding quantum numbers, not under VSEPR Theory. Just warning you, because I think I remember Dr. Lavelle saying students don't earn points for posts in the wrong section and the post may be deleted.
- Thu Nov 19, 2020 3:38 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: sapling q 5
- Replies: 4
- Views: 241
Re: sapling q 5
From my understanding, axial atoms are located at the poles, at the top and bottom of a structure. Equatorial atoms would be located on the plane horizontal to the central atom. For example, in the structure of SF4, the lone pair would be on the equatorial plane to minimize the number of 90 degree b...
- Thu Nov 19, 2020 3:32 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Shape Names
- Replies: 50
- Views: 2291
Re: Shape Names
Yes, and keep in mind that the shape is also called bent when referencing a molecule with two bonds and one lone pair. For example, Sulfur dioxide would have a trigonal planar electron pair geometry and a bent molecular geometry.
- Wed Nov 18, 2020 3:43 pm
- Forum: General Science Questions
- Topic: Which would have lower ionization energy?
- Replies: 13
- Views: 703
Re: Which would have lower ionization energy?
I asked a question similar to this during a UA Session last week, and the UA told me that we wouldn't be tested on "diagonals", like Chlorine and Oxygen because the trends for diagonals are a little ambiguous. Comparisons made during exams would be much more obvious or predictable.
- Wed Nov 18, 2020 3:20 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Arrangement of Electrons = Electron Pair Geometry
- Replies: 2
- Views: 169
Arrangement of Electrons = Electron Pair Geometry
Hi just to clarify, when Dr. Lavelle mentions the arrangement of the electron regions, is he is referencing electron pair geometry? Just wanted to make sure because in high school we learned VSEPR Theory as two separate parts, electron pair geometry and molecular geometry, and molecular geometry has...
- Mon Nov 16, 2020 10:50 am
- Forum: Bond Lengths & Energies
- Topic: F2 Bond Strength
- Replies: 6
- Views: 4273
Re: F2 Bond Strength
Hello! If you are comparing the bond strength of diatomic halogens, we can compare F2 to Cl2. The bond dissociation energy of F2 is less than Cl2 because fluorine has a high electronegativity, resulting in F−F repelling each other and having lesser bond dissociation enthalpy than Cl2 since Cl is le...
- Mon Nov 16, 2020 10:33 am
- Forum: Bond Lengths & Energies
- Topic: F2 Bond Strength
- Replies: 6
- Views: 4273
F2 Bond Strength
Could someone please explain why the bond between two F2 molecule is so weak compared to other bonds? It seems like it would be strong because fluorine is small and would have short bonds.
- Sun Nov 15, 2020 6:50 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Textbook Problem 1.E.25
- Replies: 7
- Views: 494
Re: Textbook Problem 1.E.25
I had the same issue, thank you everyone!
- Sun Nov 15, 2020 6:48 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Textbook 1E.25
- Replies: 1
- Views: 107
Re: Textbook 1E.25
Hi Alison, to give the electron configuration for a group of multiple atoms, use the variable "n" to state the energy level. For example, for part a, the valence configuration of the alkali metals would be ns^1.
- Thu Nov 12, 2020 5:24 pm
- Forum: Trends in The Periodic Table
- Topic: N 3- vs S 2-
- Replies: 4
- Views: 230
N 3- vs S 2-
So if a question asked about comparing atomic radius of Nitrogen 3- to Sulfur 2-, which would be larger? Would the shielding effect of Sulfur have a greater effect than the extra electron on Nitrogen?
- Thu Nov 12, 2020 8:29 am
- Forum: Lewis Structures
- Topic: Radicals
- Replies: 12
- Views: 260
Re: Radicals
It's pretty easy to see when a molecule is a radical. When you make the lewis structure and there's an odd total number of electrons or the charge isn't what it's supposed to be, those are pretty clear indicators.