Search found 33 matches

by Celine Cheng 1H
Wed Mar 13, 2019 11:37 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.67 (6th ed.)
Replies: 1
Views: 37

15.67 (6th ed.)

In the solutions manual, we see how they start off by showing that 0.6 Ea,uncat = Ea,cat and substituting it into the ratio comparing the rates of the catalyzed and uncatalyzed reactions. Is this step necessary, or can we just directly plug in the activation energies given?
by Celine Cheng 1H
Wed Mar 13, 2019 11:15 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: K = k/k'
Replies: 3
Views: 66

Re: K = k/k'

Emmaraf 1K wrote:This statement is true for all equilibrium reactions.


What would your k' be then? Is it the reverse reaction?
by Celine Cheng 1H
Wed Mar 13, 2019 10:49 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Units for K
Replies: 4
Views: 83

Re: Units for K

Rate is usually expressed in M/s (though I've seen it expressed with different time units) Since you have rate = k [reactant] [reactant] ... Every [reactant] must have a concentration with unit M If you have 1 reactant, you have rate = k [reactant] so the units are M/s = k (M), so k's units are 1/s ...
by Celine Cheng 1H
Wed Mar 13, 2019 7:35 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysts vs Intermediates
Replies: 4
Views: 57

Re: Catalysts vs Intermediates

An intermediate is formed and consumed during the multi-step process, whereas a catalyst is there from the beginning. There is no formation of the catalyst.
by Celine Cheng 1H
Wed Mar 13, 2019 7:22 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: T, Ea, and A's effect on K
Replies: 1
Views: 35

Re: T, Ea, and A's effect on K

Regarding your 2nd question about Ea and temperature dependence, when looking at lnk = -Ea/(RT) + lnA, we compared -Ea/R to m (slope) and T to x (y = mx + c). So the larger the Ea, the larger the slope and the greater the effect T has on k. (k changes more drastically w larger slope)
by Celine Cheng 1H
Wed Mar 13, 2019 6:20 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 7th Ed. 7E.3
Replies: 1
Views: 31

Re: 7th Ed. 7E.3

Since you're dividing by e^(-Ea/RT), you can rewrite it so that it is multiplied by e^(Ea/RT), so you get e^(-0.6Ea/RT) * e^(Ea/RT), which you can combine to create e^((-0.6+1)Ea/RT)
by Celine Cheng 1H
Wed Mar 13, 2019 6:15 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: transition state
Replies: 1
Views: 27

Re: transition state

It is when a reactant is bound to the catalyst (so in transition from reactant to product). On a free energy graph of a reaction, it is the highest point at the energy barrier.
by Celine Cheng 1H
Sat Mar 09, 2019 3:10 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow Step
Replies: 5
Views: 85

Re: Slow Step

What would happen if you have 2 slow steps? Is the slower step still the determining rate? Is having more than 2 slow steps possible?
by Celine Cheng 1H
Wed Mar 06, 2019 10:18 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 6th edition 14.43
Replies: 1
Views: 38

6th edition 14.43

Why is Q allowed to have both concentration and partial pressure? Is it because of Q's lack of a unit?
by Celine Cheng 1H
Wed Mar 06, 2019 8:37 pm
Forum: First Order Reactions
Topic: Pseudo-First-Order Reaction
Replies: 5
Views: 99

Re: Pseudo-First-Order Reaction

Is this what we see when we use experimental data and change the concentrations of the reactants in separate trials?
by Celine Cheng 1H
Wed Mar 06, 2019 7:53 pm
Forum: Second Order Reactions
Topic: Pseudo-first-order reaction
Replies: 4
Views: 82

Re: Pseudo-first-order reaction

Are pseudo reactions made by having significantly high concentrations of other reactants so that they are essentially constant? Hence why they're pseudo?
by Celine Cheng 1H
Wed Mar 06, 2019 7:47 pm
Forum: Zero Order Reactions
Topic: General Meaning of "Zero Order" Reactions
Replies: 7
Views: 131

Re: General Meaning of "Zero Order" Reactions

If the reaction rate is dependent on a catalyst, does that mean the substrate has to be in high concentration as well?
by Celine Cheng 1H
Sun Mar 03, 2019 12:22 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 14.55 6th edition
Replies: 1
Views: 32

Re: 14.55 6th edition

From my experience, polyatomic ions usually 'stay' together and keep the same charge, kinda like a package. Instead, whatever element they share a bond with gets reduced/oxidized.
by Celine Cheng 1H
Fri Feb 22, 2019 3:57 pm
Forum: Balancing Redox Reactions
Topic: Number of electrons
Replies: 5
Views: 79

Re: Number of electrons

For the oxidation numbers question, you generally want to look at the charge of the element/compound. The sum of the oxidation numbers of the elements in a compound should equate to the compound's overall charge. There are some specific rules for finding oxidation numbers of certain elements, which ...
by Celine Cheng 1H
Fri Feb 22, 2019 3:49 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.73 part d: if delta S is greater than 0, why is the reaction spontaneous
Replies: 2
Views: 55

Re: 9.73 part d: if delta S is greater than 0, why is the reaction spontaneous

When looking at delta G = delta H - T delta S, since T is positive, if delta S is positive as well, as long as (T delta S) is greater than delta H, delta G would be negative and it's spontaneous. Also, things generally want to have greater entropy.
by Celine Cheng 1H
Thu Feb 21, 2019 2:20 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Equations of delta G
Replies: 4
Views: 86

Re: Equations of delta G

Both can give you the same thing, you just need to look at what you're given and determine which formula has it ex. if you're given delta H, T, and delta S, then you'll want to use delta G = delta H - T delta S
by Celine Cheng 1H
Thu Feb 21, 2019 2:00 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Stable vs Unstable
Replies: 2
Views: 41

Re: Stable vs Unstable

One way you could interpret/imagine it is like Gibbs free energy represents the 'energy' of a system. The less energy, the more stable. So, if the change in Gibbs free energy (delta G) is negative, the system is losing energy and therefore becoming more stable (and the surroundings/universe gains th...
by Celine Cheng 1H
Thu Feb 21, 2019 1:55 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 6th ed 9.65 stability
Replies: 1
Views: 38

6th ed 9.65 stability

Since we're trying to see which compound is less stable with respect to their elements as the temperature is raised, we would want to see which one has a negative delta S (because that would result in delta G being positive, formation of compound is unfavorable compared to elements) I had manipulate...
by Celine Cheng 1H
Wed Feb 13, 2019 3:58 pm
Forum: Calculating Work of Expansion
Topic: Reversible Expansion
Replies: 2
Views: 78

Re: Reversible Expansion

When examining the Pex vs V graph for reversible and irreversible, the area under the reversible curve is greater because Pex can change as well, so it is maximized. Any little change is responded to, whereas in irreversible reactions, super small changes don't really have an effect.
by Celine Cheng 1H
Wed Feb 13, 2019 3:54 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: complex molecules
Replies: 8
Views: 395

Re: complex molecules

Can this also apply to subatomic particles? Like bc there are more neutrons/protons/electrions, an atom have have more entropy vs an atom w less?
by Celine Cheng 1H
Wed Feb 13, 2019 3:52 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Residual vs positional entropy
Replies: 2
Views: 65

Re: Residual vs positional entropy

You can use S=kblnW to find positional (residual) entropy, which is separate from thermal motion (translational, rotational, vibrational)
by Celine Cheng 1H
Wed Feb 13, 2019 3:40 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Hotdog #5
Replies: 6
Views: 480

Re: Hotdog #5

I kinda separated the problem into 2 parts-> when the temperature of the container (and both gases) changes and when the volumes of the separate containers change (so volumes of the gases change), so I use isochoral and isothermal formulas. I asked a friend and he said the same thing about how the o...
by Celine Cheng 1H
Mon Feb 11, 2019 11:08 am
Forum: Student Social/Study Group
Topic: Too cute
Replies: 5
Views: 573

Too cute

Surprise acapella for Dr. Lavelle!!
by Celine Cheng 1H
Thu Jan 24, 2019 9:04 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.57 6th Edition
Replies: 2
Views: 61

Re: 11.57 6th Edition

I'm p sure you can also convert everything into molarity and calculate it from there (and it makes it easier when calculating Kc imo)! Also, the amount of CH4 they mentioned is the amount present at equilibrium, so it gives you a hint as to where to place it in the ICE table ;)
by Celine Cheng 1H
Thu Jan 24, 2019 8:57 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Strong vs. Weak Acids
Replies: 3
Views: 69

Re: Strong vs. Weak Acids

Also, there are lists of common strong acids/bases that you can find online!
Here's one that I really like: http://www.chemistry.pomona.edu/chemist ... dbaset.htm
by Celine Cheng 1H
Fri Jan 18, 2019 2:56 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Inert Gas
Replies: 3
Views: 71

Re: Inert Gas

If another gas is added that is actually part of the reaction, then the partial pressure of that gas increases, and you'll have to use le Chatelier's principle to see how the system has changed and whether it will favor the reactants or products to reach equilibrium again. I've personally never come...
by Celine Cheng 1H
Fri Jan 18, 2019 2:47 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Autoprotolysis
Replies: 2
Views: 52

Re: Autoprotolysis

The autoprotolysis constant of water allows us to easily find out the concentration of H3O+ and OH- when we have one or the other. By comparing the concentrations of hydronium and hydroxide ions, we can see if it is an acidic or basic solution. Additionally, Kw connects to Ka, Kb, pKa, pKb, and pH t...
by Celine Cheng 1H
Wed Jan 16, 2019 10:35 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.89 Part B 6th Edition
Replies: 3
Views: 72

Re: 11.89 Part B 6th Edition

When using partial pressure to calculate K, does it always have to be in atm? How would you know to convert from kPa to atm?
by Celine Cheng 1H
Wed Jan 09, 2019 11:51 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc and Qc
Replies: 4
Views: 798

Re: Kc and Qc

Kc is the equilibrium constant and uses the ratio of the concentrations of products over reactants at equilibrium. It can also be expressed as Kp when using partial pressures. Qc and Qp are the ratio of the concentrations or partial pressures of a system at a specific point at which the forward and ...
by Celine Cheng 1H
Wed Jan 09, 2019 10:24 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: "Shifting"
Replies: 15
Views: 290

Re: "Shifting"

I like to imagine a number line, with 0 being equilibrium, negative numbers being reactants, and positive numbers being products. If you added more reactants to the system, you suddenly have more reactants than equilibrium, so you're sitting to the left of 0 (equilibrium). To move back to 0, you nee...
by Celine Cheng 1H
Wed Jan 09, 2019 10:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Help with question 11.79
Replies: 1
Views: 39

Re: Help with question 11.79

Since you have a change in the system (partial pressure of N2 is increased -> concentration of N2 is increased/more N2 is added), it's a hint for you to use an ICE table. Even though Dr. Lavelle showed it to us with concentration, it can also be used with pressure, since mole ratio and partial press...
by Celine Cheng 1H
Tue Jan 08, 2019 8:14 pm
Forum: Student Social/Study Group
Topic: Changing Discussions Sections
Replies: 1
Views: 67

Re: Changing Discussions Sections

Looking to switch from 1H (R 9 - 9:50 am) to 1F (W 10 - 10:50 am), please pm me if anyone's willing! :)
by Celine Cheng 1H
Mon Jan 07, 2019 11:15 pm
Forum: Student Social/Study Group
Topic: lecture notes first day of class
Replies: 2
Views: 93

Re: lecture notes first day of class

Hi Jennifer! We went over Dr. Lavelle's website and a rough outline of what we learned can be found under Learning Outcomes in "Outline 1: Chemical Equilibrium", we stopped at "Determine an equilibrium concentration or partial pressure". I'm not sure if slides are posted anywhere...

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