Search found 60 matches
- Mon Mar 11, 2019 10:53 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Calculating k
- Replies: 3
- Views: 579
Re: Calculating k
Since you know concentrations, unique rate (from table), m and n (from prior calculations), you only have one unknown variable (k). Therefore, by plugging in all these values, you'll be able to get k.
- Mon Mar 11, 2019 10:51 pm
- Forum: Second Order Reactions
- Topic: half-life for second order
- Replies: 3
- Views: 367
Re: half-life for second order
You can derive the half life equation for a second order rate law equation by saying that 1/[0.5A]initial = -kt + [A]initial
- Mon Mar 11, 2019 10:49 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Unique rate?
- Replies: 7
- Views: 618
Re: Unique rate?
Unique rate takes into account the stoichiometric coefficients of each product/reactant. This means that the unique rate of any product or any reactant will be the same.
- Mon Mar 04, 2019 4:34 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Collision Theory
- Replies: 1
- Views: 230
Re: Collision Theory
I think what you're referencing if the idea that we talked about in class today that states that higher order reactions are less likely to occur because they involve more specific types of collisions (ie. four molecules colliding at the same time). I think if you know the general idea of why higher ...
- Mon Mar 04, 2019 4:32 pm
- Forum: General Rate Laws
- Topic: Derivatives
- Replies: 5
- Views: 549
Re: Derivatives
So far, the only calculus-type material that we've covered is that integrating the rate law gives you an equation in terms of time rather than concentration. That and the simple fact that the derivative of 1/x is lnx. If you know these things along with the idea that a derivative is the instantaneou...
- Mon Mar 04, 2019 4:29 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Reaction order
- Replies: 4
- Views: 399
Re: Reaction order
To find n and m, use the "division method" we discussed in class. What this means is you use the equation rate = k[R]^n and plug in two of the experimental values so you have two equations with all the constants filled in except m and n. Then you divide them so that either m or n cancels, ...
- Mon Feb 25, 2019 2:41 pm
- Forum: Van't Hoff Equation
- Topic: Derivation
- Replies: 3
- Views: 642
Re: Derivation
At one of the review sessions for the midterm, one of the UAs said that derivations are fair game on the midterm. I assume this means they might be present on a test too.
- Mon Feb 25, 2019 2:38 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: F in Nernst Equation
- Replies: 2
- Views: 231
Re: F in Nernst Equation
The term nF is used to describe the quantity "charge". Since Faraday is the number of coulombs per mole of electrons, you need to n to cancel moles in the equation. This yields a coulomb value.
- Mon Feb 25, 2019 2:36 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Adding Pt(s) to cell diagram
- Replies: 3
- Views: 339
Re: Adding Pt(s) to cell diagram
You use Pt(s) in a diagram to allow electron current to flow. Without platinum or some other solid conductor, electrons would not be able to flow from the anode to cathode and there would be no voltage.
- Tue Feb 19, 2019 12:08 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Concentration and free energy
- Replies: 2
- Views: 415
Re: Concentration and free energy
Yes, since delta G = delta G standard + RTlnQ, and Q is concentration of products over reactants, Gibbs free energy does depend on concentration.
- Tue Feb 19, 2019 12:06 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs free energy
- Replies: 7
- Views: 749
Re: Gibbs free energy
Gibbs free energy is not measured directly (like enthalpy is by a calorimeter). Rather, it is a calculated value that we get when we know enthalpy, entropy, and temperature.
- Tue Feb 19, 2019 12:02 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: entropy and enthalpy
- Replies: 5
- Views: 585
Re: entropy and enthalpy
Since G = H - TS, entropy and enthalpy are correlated since they must subtract to equal Gibbs' free energy.
- Mon Feb 11, 2019 7:32 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: 1 molecule
- Replies: 2
- Views: 245
Re: 1 molecule
Degeneracy is calculated by finding (number of equivalent energy states)^(number of particles)
- Mon Feb 11, 2019 7:30 pm
- Forum: Calculating Work of Expansion
- Topic: Question on the units of work
- Replies: 3
- Views: 339
Re: Question on the units of work
I was in a review session the other day and the UA who was leading it said that we should match our answer's units with the units given in the problem. Therefore, if energy is given in kJ, we should give our answer in kJ, not L. atm or any other unit.
- Mon Feb 11, 2019 7:27 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: enthalpy
- Replies: 2
- Views: 354
Re: enthalpy
Enthalpy is the amount of heat energy in a system. It is equivalent to q when pressure is constant. So when a problem gives you the enthalpy instead of the q value, chances are that pressure is constant.
- Mon Feb 04, 2019 3:41 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Isothermal reversible expansion
- Replies: 2
- Views: 282
Re: Isothermal reversible expansion
At the end of class today, Dr. Lavelle said that the system's temperature is constant despite work being done because heat from the surroundings is being added. I didn't understand how the system could be isothermal then if there is heat exchange between the system and its surroundings.
- Mon Feb 04, 2019 3:30 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Degeneracy
- Replies: 2
- Views: 207
Re: Degeneracy
Degeneracy and entropy are directly related concepts by the Boltzmann equation S=kBlnW. As degeneracy (W) increase, so will entropy. Degeneracy is just a more solid and concrete value, because it is the number of possible states that some particle can be in. Entropy is just a manipulation of this nu...
- Mon Feb 04, 2019 3:26 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: residual entropy
- Replies: 3
- Views: 329
Re: residual entropy
Residual entropy has to do with the placement of certain atoms within a molecule. For example, a molecule like CH3Cl would have residual entropy because there are four different places (degeneracy) where you can put the Cl in the tetrahedral shape. A molecule like O2 on the other hand only has one c...
- Mon Jan 28, 2019 4:15 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Neutralization reactions
- Replies: 6
- Views: 804
Re: Neutralization reactions
Catabolic reactions, or reactions that break bonds, release energy and are therefore exothermic. (Think about ATP - when the phosphate group is broken off, energy is released). Because of this, I'm pretty sure neutralization is exothermic because of the acid and base bonds it breaks, not because of ...
- Mon Jan 28, 2019 4:03 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Delta H
- Replies: 4
- Views: 459
Re: Delta H
Temperature and heat are different things in chemistry. Temperature is measured in Kelvin or degrees Celsius, but heat is an energetic concept measured in joules.
- Mon Jan 28, 2019 4:01 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Extensive vs Intensive properties
- Replies: 4
- Views: 383
Re: Extensive vs Intensive properties
Are state properties like enthalpy intensive or extensive properties? Or are they neither?
- Mon Jan 21, 2019 8:44 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: le chatliers
- Replies: 3
- Views: 310
Re: le chatliers
Solids and liquids do not have concentrations because their atoms are already as condensed as possible.
- Mon Jan 21, 2019 8:41 pm
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: percent ionization
- Replies: 2
- Views: 482
Re: percent ionization
Percent protonated is used to describe weak bases and percent deprotonated is used to describe weak acids. Percent ionization is for both
- Mon Jan 21, 2019 8:37 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: how to determine if something is an acid or base
- Replies: 4
- Views: 354
Re: how to determine if something is an acid or base
A good way to tell if something is an acid or base (if you're not familiar with the molecule already) is to draw a Lewis structure. Then, you can see if there is a free hydrogen that can be donated, or a free lone pair that can take up a hydrogen.
- Mon Jan 14, 2019 3:53 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: 7th Edition 5J.13
- Replies: 1
- Views: 184
Re: 7th Edition 5J.13
LeChatelier's principle states that all reactions will adjust to change in a way that stabilizes the equilibrium. When temperature is changed, K also changes (unlike in problems with pressure changes). Since the K is lower as the temperature rises, this means that the hotter reaction favors the reac...
- Mon Jan 14, 2019 3:47 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Quadratic Formula in Equilibrium
- Replies: 4
- Views: 269
Re: Quadratic Formula in Equilibrium
A better rule for when we can assume x is insignificant is when x is less than 5% of the initial value. (I found this rule in the worksheet that we got in discussion)
- Mon Jan 14, 2019 3:43 pm
- Forum: Ideal Gases
- Topic: Using Kc or Kp
- Replies: 13
- Views: 930
Re: Using Kc or Kp
Since Kc uses concentrations which are approximations, I know that we do not include mol/L units in our calculations. For Kp and partial pressures, do we leave out the units as well?
- Mon Jan 07, 2019 6:11 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 6th edition hw problem 11.31
- Replies: 2
- Views: 154
Re: 6th edition hw problem 11.31
Like we said in class, the more stable side of the equation (R or P) will be the side that has a greater concentration at equilibrium. Therefore, if the equilibrium constant ([P]/[R]) is a large number, that means that there is a high concentration of product and the product is more stable. If K is ...
- Mon Jan 07, 2019 6:06 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Equilibrium vs Initial
- Replies: 2
- Views: 87
Re: Equilibrium vs Initial
Since K is the equilibrium constant, you should use the concentrations present when the reaction reaches equilibrium.
- Mon Jan 07, 2019 6:05 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Solids and Liquids
- Replies: 4
- Views: 379
Re: Solids and Liquids
To clear up what was said above, there is no way to determine the concentration of a solid, however, liquids are not included in the Kc for a different reason. Dr. Lavelle said that the amount of liquids, or solvents, on both sides of the reaction are almost the same. Thus, the concentrations cancel...
- Mon Dec 03, 2018 4:16 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Tetrahedral vs. square-planar
- Replies: 6
- Views: 1757
Re: Tetrahedral vs. square-planar
When we are talking about the electron configuration and not the actual shape, tetrahedral shape is under the tetrahedral class of electron configuration, meaning it has 4 areas of electron density. Square planar is under the octahedral class of electron configuration, meaning it has 6 areas of elec...
- Mon Dec 03, 2018 4:12 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: pOH
- Replies: 5
- Views: 883
Re: pOH
Just know that pOH is the -log[OH-] and a low pOH means that the solution is more basic. While we're on this topic, does anyone know why a low pKA means that it is a stronger acid?
- Mon Dec 03, 2018 4:10 pm
- Forum: Naming
- Topic: Latin Names
- Replies: 5
- Views: 766
Re: Latin Names
I think what you're looking for is the "Naming Coordination Compounds" link midway down on Professor Lavelle's ucla website.
- Mon Dec 03, 2018 4:06 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Problem 12.19 6th ed
- Replies: 3
- Views: 961
Re: Problem 12.19 6th ed
The problem becomes a simple dimensional analysis problem when you remember that pH is just -log[H3O+] in mols of H3O+/Liter. Make sure to remember that since it's a log function, the greater the H3O+ concentration, the LOWER the pH will be.
- Mon Nov 26, 2018 11:19 am
- Forum: Hybridization
- Topic: sigma vs. pi bonds
- Replies: 4
- Views: 378
Re: sigma vs. pi bonds
Interesting addition that we went over in my discussion section: sigma bonds are stronger than pi bonds. Even though pi bonds have two areas where the electron densities overlap, sigma bonds have a larger area of overlap, which makes the bond stronger.
- Mon Nov 26, 2018 11:13 am
- Forum: Hybridization
- Topic: Sigma vs Pi Bonds
- Replies: 2
- Views: 128
Re: Sigma vs Pi Bonds
They relate to resonance structures because sigma bonds are typically single bonds and double bonds are typically formed from one sigma and one pi bod. Depending on which area of electron density you place the pi bond, there will be different resonance structures.
- Mon Nov 19, 2018 4:45 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Sigma and Pi Bonds
- Replies: 3
- Views: 114
Re: Sigma and Pi Bonds
Another trick I use is the fact that "sigma" sounds like "single". Therefore, I can remember that single bonds are usually sigma bonds.
- Mon Nov 19, 2018 4:41 pm
- Forum: Hybridization
- Topic: What hybridization tells us
- Replies: 2
- Views: 243
Re: What hybridization tells us
Since you can only infer the number of areas of electron density from hybridization, you cannot be sure about bond angle. To know the bond angle, you need to know the types of atoms involved and the amount of bound atoms/free electrons.
- Mon Nov 19, 2018 4:38 pm
- Forum: Hybridization
- Topic: 4.33 Homework Problem
- Replies: 2
- Views: 210
Re: 4.33 Homework Problem
In case you needed the answers for the problem, they are a) sp b)sp2 c)sp3 d)sp3
- Mon Nov 12, 2018 5:22 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Polarizing Power
- Replies: 5
- Views: 487
Re: Polarizing Power
Polarizability is the term we use to refer to a low electron affinity/electronegativity element's ability to have its electrons pulled away from it. The higher the polarizability, the more likely it is to form a bond with covalent character.
- Mon Nov 12, 2018 5:18 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: London Forces v Dipole-Induced Dipole
- Replies: 2
- Views: 263
Re: London Forces v Dipole-Induced Dipole
Dipole-induced dipole is probably a little stronger because it includes a dipole in the bond. A London or Van der Waals bond does not have a dipole. It has two induced dipoles which are extremely weak.
- Mon Nov 12, 2018 1:40 pm
- Forum: Electronegativity
- Topic: Ionic Character
- Replies: 2
- Views: 127
Re: Ionic Character
For this problem, you should only be comparing the O to the S since C is present in both molecules. We know that the S has a larger atomic radius because it is lower in the group. Elements with bigger radii have a lower electron affinity and therefore a lower electronegativity. Because of this fact,...
- Mon Nov 05, 2018 2:23 pm
- Forum: Lewis Structures
- Topic: Lewis Structures for Ionic Bonds
- Replies: 5
- Views: 493
Re: Lewis Structures for Ionic Bonds
I was just wondering why we put the 8 electrons around the anion, but we don't for the cation. Don't they both have filled valence shells?
- Mon Nov 05, 2018 2:21 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Alternative version of formula
- Replies: 7
- Views: 946
Re: Alternative version of formula
Dr. Lavelle uses FC=valence electrons - (free electrons + bound electrons/2) because it helps us to understand that each line, or bond, in the Lewis structure represents 2 electrons. You can also use FC=valence electrons - (dots+lines) though because counting each line is the same thing as multiplyi...
- Mon Nov 05, 2018 2:16 pm
- Forum: Ionic & Covalent Bonds
- Topic: Definition of a Covalent Bond
- Replies: 4
- Views: 457
Re: Definition of a Covalent Bond
Covalent bonds are defined as any type of bond between atoms where electrons are shared. Therefore, almost all bonds have covalent character because certain elements will attract electrons from other elements depending on their electron affinities. For example, an atom with a high electron affinity,...
- Mon Oct 29, 2018 3:34 pm
- Forum: Lewis Structures
- Topic: Expanded octet
- Replies: 3
- Views: 272
Re: Expanded octet
As Dr. Lavelle said in class, the octet rule is better described as the "octet guideline". But for the most part, the elements found in many organic compunds (like carbon, nitrogen, and oxygen) are most stable with a complete octet (8 valence electrons).
- Mon Oct 29, 2018 3:27 pm
- Forum: Resonance Structures
- Topic: Delocalized
- Replies: 2
- Views: 343
Re: Delocalized
As Brian stated, delocalized electrons are spread out between atoms in equal proportions. Another way of saying this is that each atom has an equal electron density around it. It is important not to confuse "delocalized" with "electron movement". This is because electrons often b...
- Mon Oct 29, 2018 3:21 pm
- Forum: Lewis Structures
- Topic: central atom
- Replies: 7
- Views: 541
Re: central atom
An atom with a high electron affinity (low ionization energy) will usually be the central atom in a molecule. This is because it can easily form bonds with other atoms without using a lot of energy. Central atoms typically have the most bonds, so it makes sense that an atom that likes to form bonds ...
- Mon Oct 22, 2018 4:05 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Electron Configuration
- Replies: 5
- Views: 447
Re: Electron Configuration
The solutions manual does not include the Aufbau diagram for any of the answers, just the written form. And the use of noble gases in the shorthand is accepted by most chemists, so I'd assume that this is ok as well.
- Mon Oct 22, 2018 4:00 pm
- Forum: Octet Exceptions
- Topic: Specific formula
- Replies: 3
- Views: 382
Re: Specific formula
I know that we covered this a little bit a the end of class today, but how do we know that there are other exceptions in the lower periods of the d-block? I know we don't need to know this for class, but I just want to see if it connects to other concepts. Thanks!
- Mon Oct 22, 2018 3:57 pm
- Forum: Student Social/Study Group
- Topic: 1.37
- Replies: 2
- Views: 230
Re: 1.37
For all the 6th Edition people out here, our question was to calculate the difference as a percentage of the neutron wavelength. This calculation can be done as follows: (wavelength of proton/wavelength of neutron) x 100%.
- Mon Oct 15, 2018 3:50 pm
- Forum: DeBroglie Equation
- Topic: HW 1.41
- Replies: 6
- Views: 306
Re: HW 1.41
Hi,
I think you may be confusing velocity with frequency. In the equation c=lambda*v, the v is referring to the frequency, not the velocity of the neutron. The De Broglie equation is needed because only this equation includes v for velocity. Hope this helps
I think you may be confusing velocity with frequency. In the equation c=lambda*v, the v is referring to the frequency, not the velocity of the neutron. The De Broglie equation is needed because only this equation includes v for velocity. Hope this helps
- Mon Oct 15, 2018 3:46 pm
- Forum: Properties of Light
- Topic: Light Intensity
- Replies: 4
- Views: 502
Re: Light Intensity
The kinetic energy that the posts above have described are referring to the physical velocity that the electron has left over after it is ejected from the metal sheet. If there was only just enough photon energy to eject the electron, there would be no energy left over to move the electron.
- Mon Oct 15, 2018 3:33 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Heisenberg Indeterminacy Equation Limits
- Replies: 1
- Views: 121
Re: Heisenberg Indeterminacy Equation Limits
Hi, Not sure if this is 100% correct, but I believe that the lower bound for indeterminacy in velocity should be 0. My reasoning is that if delta v is 0, then that means delta p also has to be 0 based on v=p/m. Since all of this is based on photons and the De Broglie equation, momentum can never be ...
- Mon Oct 08, 2018 6:31 pm
- Forum: Photoelectric Effect
- Topic: Rydberg constant
- Replies: 3
- Views: 194
Re: Rydberg constant
Hey guys, My TA told us that we would have all the formulas and constants we need provided for us on the front page of each test (including Avagadro's number!). However, I find it helpful to memorize certain equations so I can be more familiar with how to use them and so I don't have to keep flippin...
- Mon Oct 08, 2018 6:29 pm
- Forum: Empirical & Molecular Formulas
- Topic: Mass Percent Composition
- Replies: 7
- Views: 1087
Re: Mass Percent Composition
Mass percent composition problems will always add up to 100% if all the elements in the molecule are listed in the problem. I'm guessing that the reason you aren't getting 100% is round-off error.
- Mon Oct 08, 2018 6:26 pm
- Forum: Photoelectric Effect
- Topic: work function
- Replies: 4
- Views: 452
Re: work function
The term "work" is a physics term. Work refers to the amount of kinetic energy it takes to complete a task. For example, it might take 1 joule of work to lift an apple one meter off the ground. In this context though, I'm pretty sure the work equation is the "phi" symbol that Pro...
- Mon Oct 01, 2018 4:21 pm
- Forum: Balancing Chemical Reactions
- Topic: States of Matter
- Replies: 11
- Views: 2094
Re: States of Matter
I've heard of other states of matter like plasma and Bose-Einstein condensates. Will we be covering how to handle those in this class? Is there any difference in balancing chemical equations with plasmas, etc. in them? Are there even any chemical reactions that involve plasmas?
- Mon Oct 01, 2018 4:15 pm
- Forum: Limiting Reactant Calculations
- Topic: Percent yield
- Replies: 10
- Views: 939
Re: Percent yield
One way I use to remember the formula for percent yield is that I know percent yield will always be under 100%. Therefore, the smaller value (actual yield) will always be divided by the larger value (theoretical yield). By using this, we will always know that the equation for percent yield = actual/...
- Mon Oct 01, 2018 4:09 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Accuracy vs Precision
- Replies: 23
- Views: 2591
Re: Accuracy vs Precision
Another interesting definition of accuracy - Accuracy can be defined as when the average experimental value is close to the true value. For example, if the three following measurements were taken of a 30 mL sample of water: 20 mL, 35 mL, and 35 mL, the average value of this measurement is 30 mL. By ...