Search found 60 matches
- Sun Mar 18, 2018 3:46 pm
- Forum: Student Social/Study Group
- Topic: Final
- Replies: 11
- Views: 2098
Re: Final
I'm guessing they gave us cell potential to plug into our function and check our answer.
- Sat Mar 17, 2018 2:47 pm
- Forum: General Rate Laws
- Topic: 15.49
- Replies: 2
- Views: 543
Re: 15.49
For those questions, you don't have to worry about the order. Just write the reactants into the rate law.
- Fri Mar 16, 2018 10:20 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: What are the units of activation energy?
- Replies: 2
- Views: 11002
Re: What are the units of activation energy?
You use J/mol.
Look at the Arrhenius equation, k = A*e^(-Ea/RT). R has units of J*K-1*mol-1 while T has units of K. The K will cancel out so what you have left is J*mol-1. You want to cancel both of these out which can be done with Ea with units of J*mol-1.
Look at the Arrhenius equation, k = A*e^(-Ea/RT). R has units of J*K-1*mol-1 while T has units of K. The K will cancel out so what you have left is J*mol-1. You want to cancel both of these out which can be done with Ea with units of J*mol-1.
- Thu Mar 15, 2018 5:30 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: H2 Cell Potential
- Replies: 1
- Views: 298
H2 Cell Potential
The book says that 2H+ + 2e- ---> H2 has a standard cell potential of "0, by definition." Why is this so?
- Thu Mar 15, 2018 12:58 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: 15.101b
- Replies: 3
- Views: 446
15.101b
How can OH- be a part of the rate law if it is an intermediate?
- Wed Mar 14, 2018 10:17 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: HW#15.87
- Replies: 2
- Views: 432
Re: HW#15.87
How do we know that ii) at high sucrose concentration is first order?
- Mon Mar 05, 2018 12:09 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: k'
- Replies: 4
- Views: 556
k'
Is there any relation between the pseudo-constant k' and the reverse rate constant k' ?
- Sun Mar 04, 2018 7:11 pm
- Forum: First Order Reactions
- Topic: 15.25
- Replies: 4
- Views: 629
Re: 15.25
The above poster is right. It's a shortcut but you can still use the 1st order integrated rate law to solve the problem.
- Sun Mar 04, 2018 7:08 pm
- Forum: General Rate Laws
- Topic: Knowing rate law equations
- Replies: 5
- Views: 671
Re: Knowing rate law equations
It's a good idea to know the derivations so you know where these equations come from which will give you a better understanding of the concepts.
- Sun Mar 04, 2018 7:04 pm
- Forum: First Order Reactions
- Topic: Units in 15.29
- Replies: 2
- Views: 464
Re: Units in 15.29
It might have been because the question gives you minutes. You're right to say that it is usually standard to use seconds. On the test, I'm sure that you'll still get credit if you use either seconds or minutes unless the question wants a specfic unit.
- Mon Feb 19, 2018 10:14 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Inert conductor
- Replies: 2
- Views: 455
Re: Inert conductor
You include it when a half-cell does not have any other solid or liquid that is part of the half-reaction to conduct electricity.
- Mon Feb 19, 2018 10:10 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Working Cells
- Replies: 1
- Views: 338
Re: Working Cells
The delta G is the maximum cell potential (the potential before we connect the electrical current). When we connect the current, the delta G of the cell gets closer and closer to zero over time since the cell is going towards equilibrium. Therefore, since delta G and E are directly related, E will g...
- Mon Feb 19, 2018 7:54 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Word equations
- Replies: 2
- Views: 495
Re: Word equations
I'm sure he'll give us the molecular formulas on the test
- Mon Feb 19, 2018 7:53 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: 14.15
- Replies: 1
- Views: 311
Re: 14.15
I'm pretty sure you only put a comman if they are both aqueous and therefore in the same solution
- Tue Feb 13, 2018 1:45 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Change in temp vs Change in volume equations
- Replies: 2
- Views: 383
Change in temp vs Change in volume equations
For these equations, , why is there a C for one equation and an R for the other
- Mon Feb 12, 2018 5:13 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: 9.43 HW
- Replies: 3
- Views: 684
Re: 9.43 HW
You usually want entropy to be in J/K so you would use molar heat capacity
- Mon Feb 12, 2018 5:08 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: enthalpy vs standard
- Replies: 2
- Views: 345
Re: enthalpy vs standard
Standard enthalpy is the change in enthalpy for one mole under the conditions of 1 atm and 298 K.
- Sun Feb 11, 2018 11:55 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Entropy of Spontaneous Processes
- Replies: 2
- Views: 426
Re: Entropy of Spontaneous Processes
You can think of a process being spontaneous as the same as it being favorable. A process will naturally go in the direction that is favorable. In other words, it goes in the direction that increases entropy of the universe (this is true because of the 2nd law of thermodynamics).
- Sun Feb 11, 2018 11:51 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: Third Law's W
- Replies: 3
- Views: 570
Re: Third Law's W
No, W does not have any units.
- Sun Feb 11, 2018 11:47 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: delta H
- Replies: 4
- Views: 556
Re: delta H
Molecules want to achieve a low energy state so they do this by releasing energy through the formation of bonds
- Sun Feb 11, 2018 10:11 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidation
- Replies: 5
- Views: 877
Re: Oxidation
The oxidation number is the charge of an atom or molecule.
If it loses, for example, three electrons, the oxidation number becomes 3+. If it gains 3 electrons, the oxidation number becomes 3-.
If it loses, for example, three electrons, the oxidation number becomes 3+. If it gains 3 electrons, the oxidation number becomes 3-.
- Sun Feb 11, 2018 10:08 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: delta S total
- Replies: 2
- Views: 449
Re: delta S total
The 2nd law states that the entropy of the universe is always increasing
- Sun Feb 11, 2018 9:57 pm
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Units of S and H
- Replies: 4
- Views: 865
Re: Units of S and H
Because you just found the standard enthaply or molar entropy of 1 mole of some substance from the chemical reaction
- Sun Feb 11, 2018 9:47 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Gas Constant, R
- Replies: 6
- Views: 838
Re: Gas Constant, R
Some problems from the homework required using 8.206 x 10^-2
- Sat Feb 10, 2018 3:44 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Work
- Replies: 6
- Views: 980
Re: Work
No. Free expansion occurs since there is no external pressure acting upon the system.
- Mon Jan 22, 2018 10:49 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: 8.91
- Replies: 1
- Views: 218
Re: 8.91
Wassup Janine You want to find how long it takes for ice to melt. The question says ice takes 10.5 h to reach 5 degrees Celsius and that the water at a liquid state at 0 degrees Celsius takes 0.5 h to reach 5 degrees Celsius. Therefore, the remaining 10.0 h must be from the ice melting. (10.5 - 0.5 ...
- Mon Jan 22, 2018 8:54 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Problem 8.99
- Replies: 6
- Views: 650
Re: Problem 8.99
The limiting reactant determines the amount of energy released by the reaction which will help us determine the final temperature
- Mon Jan 22, 2018 8:52 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 8.99
- Replies: 6
- Views: 731
Re: 8.99
You would use the enthalpies of formation for Zn+, Cl-, Zn (solid), and H+
- Mon Jan 22, 2018 12:32 am
- Forum: Administrative Questions and Class Announcements
- Topic: Reversible and Isothermal Expansions
- Replies: 2
- Views: 442
Re: Reversible and Isothermal Expansions
Nope! This was taken from his website: "Test 1 covers only Chapter 8 material covered in Weeks 1 and 2. Week 3 I will cover equation 4 (page 266) in Chapter 8. Therefore, no questions on isothermal, reversible expansion on Test 1. Concept questions involving work and internal energy will be on ...
- Mon Jan 22, 2018 12:29 am
- Forum: Administrative Questions and Class Announcements
- Topic: Week 3 Test Topic is endorsed
- Replies: 37
- Views: 4933
Re: Week 3 Test Topic is endorsed
Doing ALL the problems (except for the ones he said to skip) he assigns will prepare you enough for the test
- Mon Jan 22, 2018 12:27 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: heat capacity
- Replies: 2
- Views: 385
Re: heat capacity
Molar = J/(mol*K)
Specific = J/(g*K)
Essentially, use molar heat capacity when dealing with moles and specific heat capacity when dealing with grams.
Specific = J/(g*K)
Essentially, use molar heat capacity when dealing with moles and specific heat capacity when dealing with grams.
- Sun Jan 14, 2018 2:21 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Quiz 1 [ENDORSED]
- Replies: 2
- Views: 552
Re: Quiz 1 [ENDORSED]
Depends on how much stuff we cover by Friday
- Sun Jan 14, 2018 12:53 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Question about Question 8.7
- Replies: 3
- Views: 535
Re: Question about Question 8.7
Work is done ON a system when the system's internal energy increases. This makes sense if you think about a system being compressed (which is work being done ON the system). Since it's being compressed, more pressure is created, leading to more internal energy in that system.
- Fri Jan 12, 2018 8:00 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Δ H=q
- Replies: 3
- Views: 432
Re: Δ H=q
You can use Dr. Lavelle's analogy of a person climbing a mountain. The change in altitude is a state function but the actual distance traveled is not a state function because it depends on what path the person takes (the climber could have taken a shortcut or a longer, more scenic route). The change...
Re: Test 4
Rachel Formaker 1C wrote:Diaquadifluoromercury(I)
Wouldn't mercury have a charge of 3+ and not 1+?
Test 4
What's the name for [HgF2(OH2)2]+ ?
- Thu Nov 30, 2017 5:20 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Ch 11 #89
- Replies: 2
- Views: 242
Re: Ch 11 #89
Clarisse Wikstrom 1F wrote:What do you mean by "ratios of the change in equilibrium"?
When you draw the ICE box, in the "Change" row, you would get 10, 5, and 10 for A, B, and C, respectively. The ratios of 10, 5, and 10 are 2:1:2 which tells you the number of moles for A:B:C.
- Thu Nov 30, 2017 1:36 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Ch 11 #89
- Replies: 2
- Views: 242
Ch 11 #89
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 equilibr...
- Thu Nov 30, 2017 1:29 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Ch 11 #87c
- Replies: 1
- Views: 216
Ch 11 #87c
Dissociation of a diatomic molecule, X2(g) -> 2 X(g) occurs at 500 K. Picture 1 shows the equilibrium state of the dissociation and picture 2 shows the equilibrium state in the same container after a change has occurred. Which of the following changes will produce the change shown? (c) Decreasing th...
- Tue Nov 28, 2017 1:07 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Ch 11 #47
- Replies: 1
- Views: 1065
Ch 11 #47
For the reaction pcl5 \rightleftharpoons pcl3 + cl2 , Kc = 1.1 x 10^-2 at 400 K. (a) Given that 1.0 g of PCl5 is placed in a 250.-mL reaction vessel, determine the molar concentrations in the mixture at equilibrium. (b) What percentage of the PCl5 has decomposed at equilibrium at 400. K? I tried usi...
- Tue Nov 21, 2017 12:29 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Homework Question 11.7 [ENDORSED]
- Replies: 4
- Views: 608
Re: Homework Question 11.7 [ENDORSED]
clararehmann1B wrote:Notice that you can see which molecules have decayed within the flask. Start with counting out how many molecules have split apart!
The answer is flask 3 but I counted the the number of molecules that have split apart and there are 12 of these in both flasks 3 and 4. So why is flask 3 the answer?
- Sun Nov 19, 2017 4:19 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Bond Angles
- Replies: 4
- Views: 547
Bond Angles
Do we have to know any other specific bond angles beside 90, 120, 180, and 109.5? For example, should we know that a trigonal pyramidal molecule has bond angles of 107 degrees or just that it is less than 109.5?
- Sat Nov 18, 2017 1:59 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: trigonal planar vs. t-shaped
- Replies: 5
- Views: 3559
Re: trigonal planar vs. t-shaped
Emma Li 3F wrote:How do you tell if a molecule (with 4 atoms) has a trigonal planar shape or is t-shaped?
I was having trouble with this too but this picture really helps
https://goo.gl/images/2yK9vp
- Fri Nov 17, 2017 2:31 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Midterm on myucla
- Replies: 6
- Views: 857
Re: Midterm on myucla
Essly Mendoza 1J wrote:Do you guys know what the average on the midterm was? Thanks!
Lavelle said 83%
- Fri Nov 17, 2017 12:54 am
- Forum: Hybridization
- Topic: Hybridization in Carbon
- Replies: 3
- Views: 385
Re: Hybridization in Carbon
Remember you're only counting the REGIONS of electron density so single, double, and triple bonds are all considered as one region of electron density
- Fri Nov 17, 2017 12:44 am
- Forum: Administrative Questions and Class Announcements
- Topic: Midterm on myucla
- Replies: 6
- Views: 857
Re: Midterm on myucla
Mine is up but I wouldn't worry about it. It should be up eventually
- Thu Nov 09, 2017 12:16 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Maximum electrons
- Replies: 2
- Views: 339
Re: Maximum electrons
You would count the total number of electrons in the s-, p-, d-, and f- subshells which is 32 electrons. Then, since the question is only asking for electrons with ms = +1/2, you would divide 32 in half to get your answer of 16 electrons.
- Thu Nov 09, 2017 12:11 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Relationship between Orbitals and Properties of Electrons
- Replies: 2
- Views: 342
Re: Relationship between Orbitals and Properties of Electrons
I know that elements in s- and d-orbitals can become cations so therefore, their electrons tend to be given away. Meanwhile, in p-orbitals, the elements can become anions so they want to keep their electrons and pull in more electrons from a cation to create a stable valence shell.
- Thu Nov 02, 2017 4:43 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Quantum Numbers
- Replies: 3
- Views: 266
Re: Quantum Numbers
Remember that l = (n-1) so if n=7, then the possible l values are 0,1,2,3,4,5,6
- Wed Nov 01, 2017 3:20 pm
- Forum: Trends in The Periodic Table
- Topic: 2.67
- Replies: 5
- Views: 725
Re: 2.67
Can anyone explain to me why Cl has a higher electron affinity than Br? In general, electron affinity decreases as you go down a group because there are more shells between the nucleus and the valence electrons. As a result, the nuclear charge has less of an effect in pulling the valence electrons ...
- Tue Oct 31, 2017 11:33 am
- Forum: Trends in The Periodic Table
- Topic: Chapter 2, Question 85
- Replies: 1
- Views: 264
Chapter 2, Question 85
Question: In the heavier transition-metal elements, especially the lanthanoids and actinoids, there are numerous exceptions to the regular order of orbital occupation predicted by the buildingup principle. Suggest why more exceptions would be noted for these elements. Answer from Solutions Manual: ...
- Tue Oct 31, 2017 11:11 am
- Forum: Trends in The Periodic Table
- Topic: Electron affinity of Carbon vs Nitrogen
- Replies: 1
- Views: 333
Electron affinity of Carbon vs Nitrogen
Why does carbon have a higher electron affinity than nitrogen when the general trend is that electron affinity increases to the right?
- Sat Oct 21, 2017 1:46 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Radial Nodes [ENDORSED]
- Replies: 1
- Views: 304
Radial Nodes [ENDORSED]
What is a radial node and how would you determine the number of radial nodes for orbitals?
- Thu Oct 19, 2017 11:50 am
- Forum: Properties of Light
- Topic: EM spectrum
- Replies: 6
- Views: 782
Re: EM spectrum
You should know that visible light is about 400-700 nm.
It also may be useful to know the order of the EM spectrum and that the Balmer series consists of visible light and Lyman consists of UV.
It also may be useful to know the order of the EM spectrum and that the Balmer series consists of visible light and Lyman consists of UV.
- Sun Oct 15, 2017 6:42 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Atomic Spectra Post Module #37
- Replies: 1
- Views: 249
Atomic Spectra Post Module #37
Write the equation that allows one to calculate the electronic energy levels for the hydrogen atom. Do the calculated energies compare favorably with empirical observation (spectroscopic results)?
What does the second part mean?
What does the second part mean?
- Sat Oct 14, 2017 11:07 am
- Forum: Photoelectric Effect
- Topic: Constants that need to be memorized
- Replies: 6
- Views: 758
Re: Constants that need to be memorized
On Lavelle's website, you'll find a link that says "Constants and Equations." I feel like the ones in there will be given on the test.
- Sat Oct 14, 2017 11:03 am
- Forum: Photoelectric Effect
- Topic: Photon vs. Energy [ENDORSED]
- Replies: 6
- Views: 776
Re: Photon vs. Energy [ENDORSED]
They're not really interchangeable terms.
I like to think of photons as "packets" of light. Photons carry an energy that determines how fast they move. This is important because the photon's speed (aka their frequency) can help us find that photon's wavelength and energy.
I like to think of photons as "packets" of light. Photons carry an energy that determines how fast they move. This is important because the photon's speed (aka their frequency) can help us find that photon's wavelength and energy.
- Sat Oct 14, 2017 10:54 am
- Forum: Properties of Electrons
- Topic: Energy Level Change
- Replies: 5
- Views: 750
Re: Energy Level Change
It is possible for the electron to continue to move to higher levels. More often than not, the electron will drop back down to the ground state because it is most stable there. However, if an electron jumps to the first state, it can jump to the second state if the electron absorbs another photon ju...
- Thu Oct 05, 2017 8:43 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: E7 [ENDORSED]
- Replies: 9
- Views: 1300
Re: E7 [ENDORSED]
I don't round my sig figs until the very end to prevent my answer from going too far off from the correct answer.
- Thu Oct 05, 2017 4:29 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: E9 [ENDORSED]
- Replies: 5
- Views: 4794
Re: E9 [ENDORSED]
You multiply it by 11 O atoms because that is how many O atoms are in magnesium sulfate heptahydrate (MgSO4 * 7H20)
Multiplying it by 11 will give you moles of O which you then multiply by Avagadro's constant (6.022 * 10^23) to get the number of O atoms.
Hope this helped!
Multiplying it by 11 will give you moles of O which you then multiply by Avagadro's constant (6.022 * 10^23) to get the number of O atoms.
Hope this helped!