Search found 51 matches
- Tue Mar 16, 2021 12:04 am
- Forum: Student Social/Study Group
- Topic: Winter GEs?
- Replies: 33
- Views: 2592
Re: Winter GEs?
Does anyone know of any good GEs that I could possibly take during spring quarter that'll get a requirement out of the way for a chem major. I am taking DESMA 9, it sounds really interesting and fills the visual and performance arts GE. It's also only one, two-hour lecture a week so I think it'll b...
- Wed Mar 10, 2021 6:39 pm
- Forum: Zero Order Reactions
- Topic: zero order
- Replies: 47
- Views: 1801
Re: zero order
The concentration of a reactant that is zero order has no effect on the rate of its reaction. The concentration of this species can triple or halve but the rate of the reaction will stay constant. It is therefore not included in the rate law of that reaction.
- Wed Mar 10, 2021 6:36 pm
- Forum: General Rate Laws
- Topic: Intermediate
- Replies: 59
- Views: 3569
Re: Intermediate
An intermediate is a species found only in multi-step reactions and is fundamental to a reaction's mechanism. It is formed by the reactants of one step and is consumed as a reactant in a following step. They are not included in the overall rate law of the reaction.
- Wed Mar 10, 2021 6:33 pm
- Forum: General Rate Laws
- Topic: Factors Affecting k
- Replies: 83
- Views: 4583
Re: Factors Affecting k
In today's lecture, Lavelle said that k can change with temperature, activation energy, and the frequency factor. The rate constant determines the speed of the reaction, which increases with increasing temperature, decreases with increasing activation energy, and increases with increasing frequency ...
- Wed Mar 10, 2021 6:24 pm
- Forum: *Enzyme Kinetics
- Topic: catalyst
- Replies: 23
- Views: 2589
Re: catalyst
Catalysts speed up a reaction (increase k) by lowering the activation energy. An enzyme is a biological catalyst because it speeds up a chemical reaction without changing the reaction or its components.
- Sun Mar 07, 2021 2:16 am
- Forum: Student Social/Study Group
- Topic: What do you miss / What are you looking forward to?
- Replies: 92
- Views: 8209
Re: What do you miss / What are you looking forward to?
I'm looking forward to the libraries opening, it's been too long since I've been to one and they're my favorite places to study.
- Sun Mar 07, 2021 2:08 am
- Forum: Balancing Redox Reactions
- Topic: Half-Reactions
- Replies: 11
- Views: 557
Re: Half-Reactions
They will most likely be given to us but if not, they can be quickly derived from the rate law equations, which should be given.
- Sun Mar 07, 2021 2:04 am
- Forum: Zero Order Reactions
- Topic: graph for 1st, 2nd, and zero order reactions
- Replies: 8
- Views: 5058
Re: graph for 1st, 2nd, and zero order reactions
A zero order reaction will have a linear plot (straight line) when you plot [A] versus time. First order will have a linear graph when you plot ln[A] versus time. Second order will have a linear graph when you plot 1/[A] versus time (this will have a positive slope unlike the rest). [A] is the conce...
- Sun Mar 07, 2021 1:54 am
- Forum: Zero Order Reactions
- Topic: Half life
- Replies: 20
- Views: 956
Re: Half life
The half life for a zero order reaction is calculated by dividing the initial concentration of the reactant by 2 times the rate constant.
t1/2=[A]0/2k
t1/2=[A]0/2k
- Sun Mar 07, 2021 1:51 am
- Forum: General Rate Laws
- Topic: Number of Reactants
- Replies: 26
- Views: 1042
Re: Number of Reactants
It is possible to have more than three reactants but we will not need to know that for this class. Lavelle said that reactions with just three reactants are extremely rare so we will just be focusing on zero, first, and second order reactions.
- Fri Mar 05, 2021 5:42 pm
- Forum: First Order Reactions
- Topic: 0.693 ?
- Replies: 39
- Views: 8035
Re: 0.693 ?
ln1/2[A]0 = -kt1/2 +ln[A]0
ln(0.5) = -kt1/2
t1/2 = 0.693/k
ln(0.5) = -0.693
ln(0.5) = -kt1/2
t1/2 = 0.693/k
ln(0.5) = -0.693
- Sun Feb 28, 2021 1:42 pm
- Forum: Balancing Redox Reactions
- Topic: Charge vs Oxidation Number
- Replies: 7
- Views: 446
Re: Charge vs Oxidation Number
I think charge is for ions and oxidation numbers are for covalent compounds.
- Sun Feb 28, 2021 1:33 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Meaning of K
- Replies: 55
- Views: 3711
Re: Meaning of K
The problem will tell you what is meant by K and its value will make it obvious too. Usually it is either the equilibrium constant or temperature in kelvins.
- Sun Feb 28, 2021 1:30 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: What is Potential?
- Replies: 14
- Views: 571
Re: What is Potential?
Standard reduction potential is the likelihood that something will be reduced (gain electrons).
- Sun Feb 28, 2021 1:26 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Moles of Electrons
- Replies: 9
- Views: 522
Re: Moles of Electrons
There are 6.022*10^23 electrons in one mole of electrons.
- Sun Feb 28, 2021 1:24 pm
- Forum: Student Social/Study Group
- Topic: Points needed to pass?
- Replies: 76
- Views: 6720
Re: Points needed to pass?
Does he offer extra credit?
- Sat Feb 20, 2021 12:07 am
- Forum: Student Social/Study Group
- Topic: Classes for next quarter?
- Replies: 165
- Views: 13252
Re: Classes for next quarter?
I'm taking Chem14C and Chem14BL next quarter. I'm not too sure what my last class will be because everything else I want/need to take is completely full. I might take my second writing two class in order to fulfill the year of English that med school requires. Not ideal at all. I've realized that ba...
- Sat Feb 13, 2021 2:33 pm
- Forum: Calculating Work of Expansion
- Topic: Sign of work
- Replies: 25
- Views: 861
Re: Sign of work
Work done by the system is negative (decreases internal energy) and work done on the system is positive (increases internal energy).
- Sat Feb 13, 2021 2:31 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Can We Review our Exams?
- Replies: 69
- Views: 2947
Re: Can We Review our Exams?
Go to you TA's office hours and they will put you in a breakout room and then screen share your results. I would join early though because they often run out of time.
- Sat Feb 13, 2021 2:30 pm
- Forum: General Science Questions
- Topic: Tips
- Replies: 53
- Views: 2244
Re: Tips
For the thermochem/thermodynamics stuff I would recommend writing down all of the equations we have been using and make sure you understand all of the variables. A lot of the questions are just variations on using the same equations but solving for different variables in the equation. If you write ...
- Sat Feb 13, 2021 2:27 pm
- Forum: Student Social/Study Group
- Topic: Thoughts on Upcoming Midterm 2
- Replies: 41
- Views: 1588
Re: Thoughts on Upcoming Midterm 2
I am nervous as well, but I think once we all study the material a lot more, we'll finally be able to see the whole picture of this unit and understand it a lot better. Good luck!
- Sat Feb 13, 2021 2:26 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Difference between ΔS° and ΔS
- Replies: 9
- Views: 2691
Re: Difference between ΔS° and ΔS
The naught symbol (°) is used to represent a thermodynamic quantity in its standard state, such as change in enthalpy (ΔH°), change in entropy (ΔS°), or change in Gibbs free energy (ΔG°).
- Sat Feb 13, 2021 2:19 pm
- Forum: Administrative Questions and Class Announcements
- Topic: tips if you're struggling!
- Replies: 77
- Views: 4399
Re: tips if you're struggling!
Thank you, these are really good tips. I also read and takes notes on the textbook in addition to the lecture. I find that getting multiple explanations of a concept helps me understand it better. A lot of this material is review from AP Chemistry, so I also review my old AP Chem practice books to h...
- Sat Feb 13, 2021 2:14 pm
- Forum: Van't Hoff Equation
- Topic: usage
- Replies: 9
- Views: 538
Re: usage
The equation lnK=−ΔHo/RT + −ΔSo/R can be used to find the temperature dependency of K. How K increases or decreases with temperature is linked to whether the reaction enthalpy is positive or negative. This is because the modified version of the equation ln(K2/K1)=−ΔHo/R(1/T2−1/T1) can be used to fin...
- Sat Feb 13, 2021 2:02 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: Microstates
- Replies: 16
- Views: 1036
Re: Microstates
Degeneracy is the number of possible microstates of a system raised to the number of particles in that system.
- Sat Feb 13, 2021 1:56 pm
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Gas Entropy
- Replies: 14
- Views: 791
Re: Gas Entropy
There is a decrease in the disorder of the gas when it turns into a liquid. The entropy of the gas (system) decreases, but the entropy of the surroundings increases.
- Wed Feb 03, 2021 8:27 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Tips for Concentrating during a test
- Replies: 31
- Views: 1162
Re: Tips for Concentrating during a test
Exercise! I find that going for a walk/quick workout (or even just doing a few jumping jacks) an hour or so before a test helps me get into "testing mode". It gives you an adrenaline boost and pumps blood to your brain. Especially because we are indoors for so long, getting a breath of fre...
- Wed Feb 03, 2021 8:20 pm
- Forum: Student Social/Study Group
- Topic: Best study methods
- Replies: 9
- Views: 448
Re: Best study methods
While doing textbook problems is definitely helpful, I don't think it is enough to do well on the exams. I find that taking notes during lecture and reading and taking notes on the textbook really helps me understand the material, instead of just memorizing how to solve the problems.
- Wed Feb 03, 2021 8:17 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Letter Grade Cutoffs
- Replies: 4
- Views: 156
Re: Letter Grade Cutoffs
I assume that unless the grading scale is explicitly stated otherwise, it follows the standard scale of the majority of courses at UCLA: "A range from 90-100%, B range from 80-89.9%, C range from 70-79.9%, D range from 60-69.9%, and F given to 59.9% or lower. Within each letter grade range, a m...
- Wed Feb 03, 2021 7:53 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: closed system
- Replies: 43
- Views: 1485
Re: closed system
What's the difference between a closed system and an isolated system? Can an isolated system not absorb heat or lose heat to its surroundings? An isolated system is insulated, which means it can't exchange matter or heat with the surroundings. A closed system is not insulated so the only constant i...
- Wed Feb 03, 2021 7:44 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Midterm
- Replies: 9
- Views: 470
Re: Midterm
Grades are out now!
- Sat Jan 30, 2021 5:31 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: steam causing burns
- Replies: 40
- Views: 1217
Re: steam causing burns
Steam causes a more severe burn than a liquid (even if they are at the same temperature) because it releases both the energy of cooling down to body temp and the energy of a phase change (from vapor to liquid) onto the skin.
- Sat Jan 30, 2021 5:26 pm
- Forum: Phase Changes & Related Calculations
- Topic: when to assume x is insignificant
- Replies: 86
- Views: 6416
Re: when to assume x is insignificant
K is considered small when it is less than 10^-3, but Dr. Lavelle said that K should be less than 10^-4 to use successive approximation. Always check that the percent ionization is less than 5% to know that x is insignificant because there are many exceptions to the rule.
- Sat Jan 30, 2021 5:20 pm
- Forum: Student Social/Study Group
- Topic: Spring 2021
- Replies: 106
- Views: 12133
Re: Spring 2021
I plan to take 14BL next quarter. I am taking LS23L right now, which has a similar format to 14BL. I would recommend taking a lab only if your other courses are not too much work as they require a lot of time. I would especially wait to take 14BL if you are taking a writing two class in the spring b...
- Sat Jan 30, 2021 5:10 pm
- Forum: Phase Changes & Related Calculations
- Topic: Endothermic v. Exothermic
- Replies: 139
- Views: 10540
Re: Endothermic v. Exothermic
Lorena_Morales_1K wrote:Why is bond formation exothermic again?
Bonded atoms/molecules are more stable. Unbound atoms require energy to keep them apart which is released when they form a bond, making bond formation exothermic.
- Sat Jan 30, 2021 5:01 pm
- Forum: Phase Changes & Related Calculations
- Topic: Endothermic v. Exothermic
- Replies: 139
- Views: 10540
Re: Endothermic v. Exothermic
The definition of delta H is the change in enthalpy of a system. The definition of exothermic is that heat is released during a reaction and the enthalpy of the system decreases (which can only ever be represented by a negative delta H). The opposite is true of endothermic. So, you are right and the...
- Sat Jan 30, 2021 4:55 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Chem 14C Spring Quarter
- Replies: 11
- Views: 597
Re: Chem 14C Spring Quarter
I doubt that more classes will open up, the same thing happened this past quarter where only a fraction of the number of spots LS7B had was available for LS7C. It was just first-come, first-serve. I talked to my counselor about this and she said its because these classes are made to "weed out&q...
- Sun Jan 24, 2021 12:21 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Averages of other molecules
- Replies: 3
- Views: 92
Re: Averages of other molecules
Think of the difference between the C-H bonds in CH4 versus CH3Br. Bromine is much larger and more electronegative than hydrogen so it will pull the central carbon closer to itself, weakening the other bonds in the molecule. Therefore, the C-H bonds in methane will have a slightly different bond ent...
- Sun Jan 24, 2021 12:15 am
- Forum: Phase Changes & Related Calculations
- Topic: No Heat Change
- Replies: 15
- Views: 527
Re: No Heat Change
The temperature will only stay the same when heat is being applied during a phase change. Energy would be used to change the bonding between the molecules. Energy is added to break bonds and energy is subtracted to bond molecules to one another. These energy exchanges are not changes in kinetic ener...
- Sun Jan 24, 2021 12:06 am
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Kelvin or Celsius?
- Replies: 86
- Views: 5241
Re: Kelvin or Celsius?
You would use Kelvin. If you are ever unsure about what units to use, look at the units of the equation's constant to see what needs to be canceled out. For the Ideal Gas Law, the gas constant R= 8.314 J/mol·K, so the temperature needs to be in Kelvins too.
- Sun Jan 24, 2021 12:00 am
- Forum: Phase Changes & Related Calculations
- Topic: Constant Temperature
- Replies: 20
- Views: 692
Re: Constant Temperature
Yes. During a change in phase, energy is used to change the bonding between the molecules. For example, when water is melting, added energy is used to break the bonds between the water molecules and when water is freezing, energy is subtracted as the molecules bond to one another. These energy excha...
- Sat Jan 23, 2021 8:24 pm
- Forum: *Calculations Using ΔG° = -RT ln K
- Topic: Vocabulary
- Replies: 13
- Views: 4602
Re: Vocabulary
Endergonic and exergonic refer to changes in free energy (delta G). Endothermic and exothermic refer to changes in internal energy of molecules, measured as heat given off or taken up (delta H).
- Sat Jan 16, 2021 10:36 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: ka vs kb
- Replies: 20
- Views: 477
Re: ka vs kb
Will we ever use the reverse of Ka (1/Ka), or just always use Kb when we are going in the opposite direction of an acid/base equation?
- Sat Jan 16, 2021 10:27 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Midterm 1
- Replies: 24
- Views: 872
Re: Midterm 1
Can someone who had Lavelle last quarter for 14A explain what his midterms are like?
- Sat Jan 16, 2021 10:20 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE Box
- Replies: 5
- Views: 259
Re: ICE Box
This Youtube video gives a lot of examples of how ICE boxes are used:
"Ice Table - Equilibrium Constant Expression, Initial Concentration, Kp, Kc, Chemistry Examples"
"Ice Table - Equilibrium Constant Expression, Initial Concentration, Kp, Kc, Chemistry Examples"
- Sat Jan 16, 2021 10:15 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: When x is negligible in Equilibrium constant
- Replies: 34
- Views: 1393
Re: When x is negligible in Equilibrium constant
Even in K is less than 10^-4 and we are able to approximate, will we get the correct answer if we use the quadratic formula instead?
- Fri Jan 15, 2021 12:07 am
- Forum: Administrative Questions and Class Announcements
- Topic: midterms
- Replies: 7
- Views: 266
Re: midterms
Can someone who had Lavelle for 14B explain what Respondus is and how we use it for the midterms?
- Sun Jan 10, 2021 5:17 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: sapling week 1 #9
- Replies: 15
- Views: 678
Re: sapling week 1 #9
You can use either K or 1/K for this question and get the same answer. If you use K, make sure you set it equal to [NO]^2/[N2][O2]. And if you use 1/K, make sure you set it equal to [N2][O2]/[NO]^2.
- Sun Jan 10, 2021 1:56 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Definition of an Inert Gas
- Replies: 15
- Views: 926
Re: Definition of an Inert Gas
In Dr. Lavelle's lecture on Le Chatelier's Principle, he talks about how adding an inert gas to a container does not effect the reaction since there is no change in the concentration of reactants, products, and volume. What is the exact definition of an inert gas and why does adding one to a contai...
- Sun Jan 10, 2021 1:26 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Calculating concentration using the quadratic formula
- Replies: 6
- Views: 500
Re: Calculating concentration using the quadratic formula
A good example of this concept is question 3 of the Week 1 Sapling Assignment. I'm not sure if everyone has the same questions with the same values on sapling, but for the question I was given, you solve for x using the quadratic equation and get two positive values. However, one is bigger than the ...
- Sun Jan 10, 2021 1:15 am
- Forum: Administrative Questions and Class Announcements
- Topic: Accessing the E-textbook [ENDORSED]
- Replies: 125
- Views: 30661
Re: Accessing the E-textbook [ENDORSED]
Sapling is required! In the past, I believe it wasn't, but now it is. You buy the bundle that Lavelle has up on the site, it's around $70ish dollars I believe for multiterm access. It gives you access to the ebook and other resources. Sapling is also where you do the homework which I believe is wor...