Search found 58 matches

by Bryan Chen 1H
Wed Mar 11, 2020 10:45 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Strong/weak acids & bases
Replies: 14
Views: 208

Re: Strong/weak acids & bases

yea memorize them
by Bryan Chen 1H
Wed Mar 11, 2020 10:42 pm
Forum: Administrative Questions and Class Announcements
Topic: Format?
Replies: 11
Views: 265

Re: Format?

probably similar to the midterm
by Bryan Chen 1H
Wed Mar 11, 2020 10:41 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Meaning of q=-w
Replies: 14
Views: 268

Re: Meaning of q=-w

isothermal reversible expansion
by Bryan Chen 1H
Wed Mar 11, 2020 10:41 pm
Forum: General Science Questions
Topic: Test 2 Grades [ENDORSED]
Replies: 23
Views: 538

Re: Test 2 Grades [ENDORSED]

mine is available on myucla gradebook right now
by Bryan Chen 1H
Wed Mar 11, 2020 10:40 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: spontaneity
Replies: 34
Views: 636

Re: spontaneity

gibbs free energy!!!!
by Bryan Chen 1H
Wed Mar 11, 2020 10:39 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Microscopic Reversibility
Replies: 3
Views: 22

Re: Microscopic Reversibility

the same pathway both ways
by Bryan Chen 1H
Wed Mar 11, 2020 10:37 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Kinetics v Therodynamics
Replies: 8
Views: 80

Re: Kinetics v Therodynamics

i think one is more related to spontaneity and the other is more related to rate
by Bryan Chen 1H
Wed Mar 11, 2020 10:36 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Relationship Between Ecell and K
Replies: 9
Views: 105

Re: Relationship Between Ecell and K

I remember my TA writing Ecell>0 than K>0 and vice versa, and you can prove this from the equations
by Bryan Chen 1H
Wed Mar 11, 2020 10:35 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: K vs k1/k'1
Replies: 6
Views: 475

Re: K vs k1/k'1

both should work
by Bryan Chen 1H
Wed Mar 11, 2020 10:34 pm
Forum: Second Order Reactions
Topic: Finding out order
Replies: 12
Views: 137

Re: Finding out order

yes, if you look at the rate constant and its units
by Bryan Chen 1H
Wed Mar 11, 2020 10:33 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Mechanisms
Replies: 4
Views: 149

Re: Mechanisms

According to Khan Academy, "The reaction mechanism describes the sequence of elementary reactions that must occur to go from reactants to products."
by Bryan Chen 1H
Wed Mar 11, 2020 10:32 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Fast Step/Slow Step
Replies: 7
Views: 66

Re: Fast Step/Slow Step

^ no matter how "fast" the fast one is the slowest one is always the determinant because each other reaction depends on it to also occur
by Bryan Chen 1H
Wed Mar 11, 2020 10:30 pm
Forum: Administrative Questions and Class Announcements
Topic: "Open Book" Final?
Replies: 30
Views: 762

Re: "Open Book" Final?

im assuming open book means like textbook notes lecture notes etc
by Bryan Chen 1H
Wed Mar 11, 2020 10:28 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: HCl and NaOH producing dT
Replies: 4
Views: 131

Re: HCl and NaOH producing dT

since mols are the same for each, I looked at volume of soln. where the delta temp change is greatest in the smallest volume. I thought of the soln volume like an absorbant, so the more water there is, the less a rxn will be able to shift its temp as compared to a little volume of water
by Bryan Chen 1H
Wed Mar 11, 2020 10:27 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: endo/exo and temp
Replies: 12
Views: 437

Re: endo/exo and temp

in these problems i tend to think of heat as a reactant (endothermic) or product (exothermic). Then depending on an increase or decrease in temp, I use le chatelier's principle treating heat as a R or P
by Bryan Chen 1H
Wed Mar 11, 2020 10:25 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Kelvin or Celsius?
Replies: 47
Views: 966

Re: Kelvin or Celsius?

it depends on the unit of the gas constant. if its .08206 Latm/Kmol then use Kelvin, but another gas constant COULD have its units in celcius for whatever reason and then you should use celcius (but it probably will never ever come up in real life or a problem)
by Bryan Chen 1H
Wed Mar 11, 2020 10:24 pm
Forum: General Rate Laws
Topic: intermediates
Replies: 12
Views: 69

Re: intermediates

yes, since they are made in one step and used up in the next they are not included in the overall final one
by Bryan Chen 1H
Thu Feb 27, 2020 11:11 pm
Forum: Balancing Redox Reactions
Topic: Direction of Reaction
Replies: 3
Views: 52

Re: Direction of Reaction

positive E naught is equal to negative delta G meaning spontaneous
by Bryan Chen 1H
Thu Feb 27, 2020 11:07 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 5G.13
Replies: 8
Views: 192

Re: 5G.13

you should use delta G = -RTlnK + RTlnQ.
by Bryan Chen 1H
Thu Feb 27, 2020 11:01 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: When to apply Pt into cell diagrams
Replies: 9
Views: 90

Re: When to apply Pt into cell diagrams

my TA during discussion says it's always safe to put Pt(s) as the electrode when there is no other metal to act as it
by Bryan Chen 1H
Thu Feb 27, 2020 10:59 pm
Forum: Administrative Questions and Class Announcements
Topic: Test 2 Topics
Replies: 5
Views: 97

Re: Test 2 Topics

i think all of electrochem and 2nd page thermodynamics so if its on the electrochem learning outcomes then yes
by Bryan Chen 1H
Wed Feb 19, 2020 11:06 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: converting T to kelvin
Replies: 21
Views: 320

Re: converting T to kelvin

i would always use the equation sheet and look at the units, especially for constants. for example, .08206 = R, R has units in L, atm, K, and mol. So, on a test you should make sure when plugging into PV=nRT, for example, to match up those units to the R constant.
by Bryan Chen 1H
Wed Feb 19, 2020 11:04 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Adding Inert Gas
Replies: 20
Views: 292

Re: Adding Inert Gas

It increases pressure, but it has no effect on the reaction because volume stays the same and therefore the concentrations of species also do
by Bryan Chen 1H
Wed Feb 19, 2020 11:00 pm
Forum: Balancing Redox Reactions
Topic: Reduction vs. oxidation
Replies: 29
Views: 266

Re: Reduction vs. oxidation

oil rig
oxidation is loss
reduction is gain
by Bryan Chen 1H
Wed Feb 19, 2020 10:58 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Midterm Q6B
Replies: 5
Views: 123

Re: Midterm Q6B

From the equation ∆G= ∆H-T∆S. ∆G= ∆H when the second term is close to 0. Therefore, you should find an equation with very little entropy change, which is often when the reactants and products are in the same state with the same amount of moles (best when all solid).
by Bryan Chen 1H
Wed Feb 19, 2020 10:57 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: midterm Q4
Replies: 4
Views: 95

Re: midterm Q4

i think because the pH of the stomach is so acidic and there are already so many H+ floating around that the high pKa of the compound (and the natural dissociation of it) is too weak to "compete" with the already established acidity
by Bryan Chen 1H
Wed Feb 12, 2020 5:04 pm
Forum: Ideal Gases
Topic: STP
Replies: 7
Views: 153

Re: STP

i think 298 is 25+273 and 25 is considered "room temperature" not "standard"
by Bryan Chen 1H
Wed Feb 12, 2020 5:03 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy of the System for irreversible expansions
Replies: 7
Views: 173

Re: Entropy of the System for irreversible expansions

i believe they are the same, or at least you assume its always reversible
by Bryan Chen 1H
Wed Feb 12, 2020 5:01 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: pizza rolls question 2D
Replies: 2
Views: 96

Re: pizza rolls question 2D

ignore the solid since it is not apart of the K expression, and multiply the other two together to find Q.
by Bryan Chen 1H
Wed Feb 12, 2020 5:00 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isothermal Reversible
Replies: 6
Views: 74

Re: Isothermal Reversible

maybe there are exceptions but i think for this class and the midterms isothermal is always reversible
by Bryan Chen 1H
Wed Feb 12, 2020 3:09 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Irreversible Expansion
Replies: 7
Views: 97

Re: Irreversible Expansion

irreversible expansion refers to a gas expanding against a constant external pressure. use the equation w= -Pex(deltaV)
by Bryan Chen 1H
Tue Feb 11, 2020 7:07 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: pKa and pKb
Replies: 4
Views: 68

Re: pKa and pKb

it just happens to be this way because of the math. its similar to how a higher pH is less H+ concentration, just like how higher pKa is weaker acid
by Bryan Chen 1H
Tue Feb 11, 2020 7:03 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: ∆G, ∆H, ∆S
Replies: 6
Views: 116

Re: ∆G, ∆H, ∆S

basically, deltaG depends on deltaH and deltaS to be a spontaneous(-) or nonspontaneous(+) rxn. Since it is a new topic i dont think we need to know much more than that
by Bryan Chen 1H
Tue Feb 11, 2020 7:01 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: State of matter affect entropy
Replies: 3
Views: 37

Re: State of matter affect entropy

typically, liquids occupy more space or are more disorderly than solids, and same for gas and liquids
by Bryan Chen 1H
Tue Feb 11, 2020 7:00 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Midterm Material
Replies: 10
Views: 132

Re: Midterm Material

probably only the first page of outline 4
by Bryan Chen 1H
Tue Feb 11, 2020 6:57 pm
Forum: Calculating Work of Expansion
Topic: Midterm equation sheet
Replies: 16
Views: 197

Re: Midterm equation sheet

yes im pretty sure
by Bryan Chen 1H
Sun Feb 02, 2020 10:23 pm
Forum: Phase Changes & Related Calculations
Topic: Pressure in an Open Beaker
Replies: 10
Views: 84

Re: Pressure in an Open Beaker

if u imagine an open beaker, the constant pressure will be the force of air pressure acting down on it from the environment
by Bryan Chen 1H
Sun Feb 02, 2020 10:22 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy of Rxn
Replies: 9
Views: 78

Re: Enthalpy of Rxn

i personally dont think about multiplying or dividing, i look at the units of each (kJ, and kJ/mole), and i try to format it so the units cancel. i think its called dimensional analysis or something
by Bryan Chen 1H
Sun Feb 02, 2020 10:21 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Test 1
Replies: 3
Views: 60

Re: Test 1

i got mine back in discussion!
by Bryan Chen 1H
Sun Feb 02, 2020 10:21 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Steam burns
Replies: 8
Views: 71

Re: Steam burns

steam has more energy than boiling water at the same temp
by Bryan Chen 1H
Fri Jan 24, 2020 6:26 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Ka and Kb
Replies: 10
Views: 121

Re: Ka and Kb

No, strong acids and bases also have Ka and Kb i think, it is just very large (and they also dissociate completely) so there's no real need to use it in problems
by Bryan Chen 1H
Fri Jan 24, 2020 6:24 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating Kp
Replies: 6
Views: 65

Re: Calculating Kp

I'm pretty sure you can use partial pressures as well as concentration because partial pressures is based on the similar idea as concentration
by Bryan Chen 1H
Fri Jan 24, 2020 6:23 am
Forum: Ideal Gases
Topic: R Constant
Replies: 26
Views: 320

Re: R Constant

on the equations sheet look at the units for R and make sure they match up with those given in the problem, or those that you may convert to/use
by Bryan Chen 1H
Fri Jan 24, 2020 6:22 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Percent Ionization
Replies: 11
Views: 127

Re: Percent Ionization

Yea I always check to see if K is small but if its around like 10 to -3 or -4, you can do the approximation but make sure to check if x is less than 5% of the initial concentration
by Bryan Chen 1H
Fri Jan 24, 2020 6:20 am
Forum: Phase Changes & Related Calculations
Topic: Steam vs. Boiling Water
Replies: 10
Views: 127

Re: Steam vs. Boiling Water

there requires a large heat of vaporization (delta H) change to convert water molecules from the liquid to gas phase, so steam has much more "energy" in it
by Bryan Chen 1H
Fri Jan 24, 2020 6:18 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: k<10^-3
Replies: 9
Views: 105

Re: k<10^-3

there's no set number that makes something definitely "weak" or "strong" i'd say but compared to strong acids like HCl, an acid that only dissociates 1 proton per 1000 other molecules is much weaker relatively speaking.
by Bryan Chen 1H
Sat Jan 18, 2020 4:56 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Acids and Bases Ice Box
Replies: 5
Views: 55

Re: Acids and Bases Ice Box

i suggest writing out the chemical reaction taking place and looking at the reactants side. If its like a base dissociating, then use kb, for example.
by Bryan Chen 1H
Sat Jan 18, 2020 4:54 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Exponents and the K constant
Replies: 4
Views: 76

Re: Exponents and the K constant

i dont think you need to know how its derived but prof. jukka keranen teaches you how K is derived in his ls30A lecture if youre interested.
by Bryan Chen 1H
Sat Jan 18, 2020 4:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Percent Ionization
Replies: 11
Views: 127

Re: Percent Ionization

yea, and then afterwards do the x value over initial concentration just to double check it is under 5%
by Bryan Chen 1H
Sat Jan 18, 2020 4:38 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc sig figs
Replies: 4
Views: 39

Re: Kc sig figs

i think it would be 2 unless otherwise specified but im not too sure
by Bryan Chen 1H
Sun Jan 12, 2020 11:41 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating K
Replies: 9
Views: 68

Re: Calculating K

water is a pure liquid and a solvent. while it "takes part" in the reaction, the change is so small its negligible
by Bryan Chen 1H
Sun Jan 12, 2020 11:40 pm
Forum: Ideal Gases
Topic: Vapor Pressure
Replies: 4
Views: 38

Re: Vapor Pressure

the pressure the gas above a liquid exerts down on it
by Bryan Chen 1H
Sun Jan 12, 2020 11:39 pm
Forum: Ideal Gases
Topic: Molar Concentration
Replies: 4
Views: 46

Re: Molar Concentration

Usually if there are no products yet and only reactants, the reactants will decrease and the products will increase by a multiple of X depending on the co-efficients.
by Bryan Chen 1H
Sun Jan 12, 2020 11:36 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Q and K
Replies: 6
Views: 76

Re: Q and K

K = equilibrium constant, K is the same for a given reaction at a given temperature. Q = reaction quotient, it is the ratio of P/R at any given moment during a reaction.
by Bryan Chen 1H
Sun Jan 12, 2020 11:33 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K's
Replies: 3
Views: 39

Re: K's

Kc is when you use concentrations of reactants/products to calculate K and Kp is when you use the partial pressures of the gases

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