Search found 36 matches

by Justin Yu 3H
Sat Mar 17, 2018 12:10 am
Forum: *Nucleophilic Substitution
Topic: Transition States
Replies: 3
Views: 738

Re: Transition States

Transition states are where two molecules hit each other with enough force to create a combined complex that can either form the products or separate back into the reactants. This requires a lot of energy because the products might be more thermodynamically stable in the product form, but a lot of e...
by Justin Yu 3H
Fri Mar 16, 2018 11:57 pm
Forum: General Rate Laws
Topic: Coefficients and Exponents
Replies: 2
Views: 309

Re: Coefficients and Exponents

If this for showing a reaction mechanisms that fits the experimental rate law? Or is this to find the rate law of an unknown reaction? If it's the first, you would need to split the reaction into elementary reactions such that the rate law you find fits the experimental rate law. If the reaction is ...
by Justin Yu 3H
Fri Mar 16, 2018 11:53 pm
Forum: Student Social/Study Group
Topic: what to study for the final
Replies: 1
Views: 267

Re: what to study for the final

He talked a little bit about OChem (functional groups and stuff) in class so maybe that?
by Justin Yu 3H
Fri Mar 16, 2018 11:51 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.57
Replies: 2
Views: 206

Re: 8.57

You would use enthalpy of products minus enthalpy of reactants if the enthalpies given are enthalpies of formation; however, the enthalpies provided in the problem are enthalpies of combustion, meaning you would take the enthalpy of reactants minus the enthalpy of the products.
by Justin Yu 3H
Fri Mar 16, 2018 11:48 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: flipping half reactions
Replies: 2
Views: 164

Re: flipping half reactions

In what situations? Your question is a little vague.
by Justin Yu 3H
Fri Mar 16, 2018 11:56 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius eq and integrated rate law
Replies: 1
Views: 116

Re: Arrhenius eq and integrated rate law

There's probably a very complex reason why it is similar to the first order integrated rated law, but I just kinda see it as putting temperature on the reactant side of the chemical equation. As a result, provided everything else is constant, you can model that reaction as a pseudo first order react...
by Justin Yu 3H
Fri Mar 16, 2018 11:51 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation
Replies: 2
Views: 117

Re: Nernst Equation

When have you seen that in problems? I've never seen that before.
by Justin Yu 3H
Fri Mar 16, 2018 11:35 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Final 2008, Q3
Replies: 1
Views: 131

Re: Final 2008, Q3

If everything else is standardized, then I think it is safe to assume concentrations of 1M/bar. For your second question, there wouldn't be enough information to find the value of Q; you can assume that if something like that shows up on the test, more information will be provided.
by Justin Yu 3H
Fri Mar 16, 2018 11:28 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.85
Replies: 1
Views: 107

Re: 15.85

We know the correct orientation, or at least have a general idea of how the molecules will be oriented because we know what parts of each molecule will react with what parts of the other molecule i.e what bonds are being broken and formed, and then orient them accordingly. For example, in part (c), ...
by Justin Yu 3H
Fri Mar 16, 2018 11:22 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.85
Replies: 1
Views: 112

Re: 15.85

For the proposed activated complex, you have to consider the reactant the products in what bonds are broken and formed. The activated complex for (a) would be drawing CH3CHO where the bond between the carbons is partly dissociated. I'm not entirely sure, but I'm pretty confident that (b) would be te...
by Justin Yu 3H
Fri Mar 16, 2018 11:15 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Example 15.7
Replies: 1
Views: 94

Re: Example 15.7

If you're referring to how they got the net rate of decomposition for O3 after substituting in O, they honestly just added everything on that side together. The term k1[O3], when multiplied by the denominator of the other terms, will cancel the middle term out and double the last term, resulting in ...
by Justin Yu 3H
Fri Mar 16, 2018 11:08 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: drawing activated complexes
Replies: 1
Views: 105

Re: drawing activated complexes

Well, I don't think there's a "set" method of drawing them. You just examine the molecules that are reacting, and see which bonds are being broken between what atoms and which bonds are being formed. You then draw a complex combining the molecules, where the bonds that would form if the re...
by Justin Yu 3H
Tue Mar 13, 2018 5:07 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.57
Replies: 2
Views: 154

Re: 8.57

I'm not too sure what oxygens you are referring to. If you just use the enthalpy of combustion to calculate the reaction enthalpy, you get -1300 - 2(-286) - (-1300) = -312 kJ mol ^-1 I looked up some stuff though; the standard enthalpy of combustion is defined as the change in enthalpy when one mole...
by Justin Yu 3H
Tue Mar 13, 2018 4:54 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 14.33
Replies: 2
Views: 260

Re: 14.33

The reaction between the cathode and anode needs to be spontaneous for the cell to work and have a positive voltage, which implies a negative gibbs free energy. Since the formation of Ti3+ has a positive gibbs free energy, you have to reverse it, then plug it into G = -nFE to find the standard poten...
by Justin Yu 3H
Tue Mar 13, 2018 4:37 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: example 15.7
Replies: 1
Views: 106

Re: example 15.7

Firstly, I will assume that the 2 you are referring to is the exponent of [O3]. If you use pre-equilibrium, you first get that K = [O2][O]/[O3] => [O] = K[O3]/[O2] Plugging [O] into the slow step yields (I don't know how to do subscripts so the "k" below is supposed to be a k sub 2) k[O][O...
by Justin Yu 3H
Tue Mar 13, 2018 4:15 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.18
Replies: 1
Views: 108

Re: 8.18

I agree with the logic you used for part (b) of the problem. I also agree that the work done in (a) is 0; however I am not sure how you are certain that the change in energy is positive, as dissolution reactions can be either exothermic or endothermic.
by Justin Yu 3H
Mon Mar 05, 2018 4:56 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: K'
Replies: 7
Views: 291

Re: K'

To find K' in a pseudo reaction, like a second order reaction, you would solve for k without changing the concentration of one of the reactants that is first order. That reactant must be in so much surplus that its concentration would not change through the reaction. Thus, the reaction becomes a fir...
by Justin Yu 3H
Mon Mar 05, 2018 4:42 pm
Forum: General Rate Laws
Topic: 15.3
Replies: 1
Views: 123

Re: 15.3

Yes, you are correct. Because there is no coefficient on O2, its rate of formation is the same as the unique rate of the reaction.
by Justin Yu 3H
Mon Mar 05, 2018 4:38 pm
Forum: Experimental Details
Topic: 15.17A
Replies: 1
Views: 312

Re: 15.17A

That second element, which I assume is [C], has no effect on the initial rate, so it is zero order. You can see this by comparing experiments 1 and 4. After realizing that, you can then disregard all changes in concentration of [C] and only look at the first two columns to find the order of the othe...
by Justin Yu 3H
Mon Mar 05, 2018 4:35 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate Laws of Elementary Reactions
Replies: 4
Views: 137

Re: Rate Laws of Elementary Reactions

You are right in that elementary reactions always follow the format where bimolecular elementary reactions are second order reactions, but you cannot assume that for all reactions.
by Justin Yu 3H
Mon Mar 05, 2018 4:22 pm
Forum: Zero Order Reactions
Topic: Pseudo Zero Order Reactions
Replies: 3
Views: 461

Re: Pseudo Zero Order Reactions

No, it is not possible to have a pseudo zero order reaction. If we consider the pseudo first order reaction for a second order reaction, we essentially hold one of the reactants at such a high concentration that changes are negligible and we can ignore its effects. Theoretically, we could model a fi...
by Justin Yu 3H
Mon Mar 05, 2018 3:54 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Catalyst in a Equilibria
Replies: 2
Views: 114

Re: Catalyst in a Equilibria

Catalysts just speed up the rate at which reactions reach equilibrium. Since we can reach equilibrium from an excess of products or reactants, it makes logical sense that they would thus work both ways.
by Justin Yu 3H
Mon Mar 05, 2018 3:48 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Catalyst
Replies: 6
Views: 605

Re: Catalyst

Furthermore, a catalyst lowers the free energy of activation by lowering the energy required to break bonds (decreases standard enthalpy of activation) and puts the reactants closer together and in their correct orientations (increases standard entropy of activation). How does that increase the sta...
by Justin Yu 3H
Mon Mar 05, 2018 1:52 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Kinetics [ENDORSED]
Replies: 2
Views: 123

Re: Kinetics [ENDORSED]

Yes. Because the reaction with a higher activation energy proceeds at a slower pace than the other, it is the rate determining step and dictates the speed of reaction.
by Justin Yu 3H
Mon Mar 05, 2018 1:48 pm
Forum: General Rate Laws
Topic: Useful Resource
Replies: 1
Views: 86

Re: Useful Resource

Thanks for sharing this!
by Justin Yu 3H
Sun Feb 18, 2018 4:03 pm
Forum: Balancing Redox Reactions
Topic: agents
Replies: 3
Views: 138

Re: agents

The oxidizing agent acts to oxidize something else. In that sense, the "something else" becomes oxidized, while the oxidizing agent accepts the electrons and becomes reduced.
by Justin Yu 3H
Mon Feb 12, 2018 9:40 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Example 9.5
Replies: 3
Views: 152

Re: Example 9.5

Argon is very very similar to the ideal gas. The molar heat capacity at constant volume for argon is the same as 3/2 R, that of a monoatomic ideal gas. So even though they write argon, you can just interpret that as viewing oxygen as an ideal gas.
by Justin Yu 3H
Mon Feb 12, 2018 9:30 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: General Question on these equations
Replies: 1
Views: 78

Re: General Question on these equations

Yes. For all equations like these, you generally assume that all other factors are held constant.
by Justin Yu 3H
Mon Jan 29, 2018 11:03 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: R value in entropy equation [ENDORSED]
Replies: 2
Views: 108

Re: R value in entropy equation [ENDORSED]

The scalar you multiply R by corresponds with the degrees of freedom of the molecule. Each degree of freedom corresponds to R/2, and there are both directional degrees of freedom and rotational degrees of freedom. The heat capacity at constant volume is the same as the sum of the degrees of freedom ...
by Justin Yu 3H
Wed Jan 17, 2018 3:42 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.67 moving from a gas to a liquid
Replies: 1
Views: 84

Re: 8.67 moving from a gas to a liquid

You are completely correct! When calculating the enthalpy of formation of a molecule where the product has a different phase than the reactants, the change in enthalpy due to phase change would be negative, and in moving from a liquid to a gas, it would be vice versa.
by Justin Yu 3H
Sat Dec 09, 2017 7:20 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7582
Views: 1015184

Re: Post All Chemistry Jokes Here

What's the chemical formula of a banana?
BaNa2
by Justin Yu 3H
Sun Dec 03, 2017 3:04 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7582
Views: 1015184

Re: Post All Chemistry Jokes Here

What do you do with a sick chemist?
If you can't helium and you can't curium, then you might as well barium.
by Justin Yu 3H
Wed Nov 15, 2017 11:44 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: trigonal planar vs. t-shaped
Replies: 5
Views: 578

Re: trigonal planar vs. t-shaped

First off, although trigonal planar and t-shaped molecules both consist of 4 atoms, they differ in the amount of electron pairs on the central atom. Trigonal planar molecules have 4 electron pairs, 1 lone and 3 pairs with the other 3 atoms, while t-shaped molecules have 5 electron pairs, 2 lone and ...
by Justin Yu 3H
Wed Nov 08, 2017 3:48 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Resonance Structure
Replies: 4
Views: 191

Re: Resonance Structure

Another important thing to note is that resonance stabilizes molecules. Since the electrons are more delocalized, they occupy a greater volume and the energy of the molecule is lower, making it more stable. Also, like the previous poster mentioned, the resonance structures you draw would be potentia...
by Justin Yu 3H
Sun Oct 29, 2017 9:58 pm
Forum: *Shrodinger Equation
Topic: Problem 2.3
Replies: 1
Views: 184

Problem 2.3

Hello,
I know that problem 2.3 isn't a required problem, but I was working on it and I didn't really understand how they used the chart to answer the questions. Could anyone help me with this?
by Justin Yu 3H
Tue Oct 17, 2017 5:04 pm
Forum: Properties of Light
Topic: Oscillation of Light
Replies: 3
Views: 185

Oscillation of Light

In Section 1.2, it states that "[the light ray's] electric field pushes the electron first in one direction and then pulls it in the opposite direction, over and over again." This denotes the frequency of the radiation. However, in space, where it is almost all empty space, would the wave ...

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