Search found 31 matches

by Jennifer Ho 1K
Sat Mar 17, 2018 2:13 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: trend for temp and activation energy
Replies: 3
Views: 93

Re: trend for temp and activation energy

At higher temperatures, a greater percentage of molecules will have enough energy to overcome the activation energy and proceed with the reaction.
by Jennifer Ho 1K
Sat Mar 17, 2018 2:12 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Proposing a reaction mechanism
Replies: 5
Views: 99

Re: Proposing a reaction mechanism

You shouldn't have to propose a reaction mechanism on the test because this process mainly involves just guessing and checking to see if it matches the experimental rate constant expression, but you should be able to determine the rate law from the reaction mechanism (given a slow step), or choose t...
by Jennifer Ho 1K
Sat Mar 17, 2018 2:09 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Water in Mechanism
Replies: 5
Views: 146

Re: Water in Mechanism

Water is left out of the equilibrium expression because it is a liquid, and liquids have constant concentrations. Generally this means it is included as part of the equilibrium constant because it's constant anyways. The same applies for the rate constant expression.
by Jennifer Ho 1K
Sat Mar 17, 2018 2:07 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate Determining
Replies: 7
Views: 179

Re: Rate Determining

The slow step should be given, and the other steps are assumed to be fast.
by Jennifer Ho 1K
Fri Mar 16, 2018 11:09 pm
Forum: Administrative Questions and Class Announcements
Topic: Final Topics
Replies: 3
Views: 177

Final Topics

Will Lavelle's final be more geared towards topics after the midterm? Or will it be more of an equal mix of topics from before and after it?
by Jennifer Ho 1K
Tue Mar 06, 2018 12:38 am
Forum: Second Order Reactions
Topic: Order reactions
Replies: 6
Views: 393

Re: Order reactions

The order of the reaction depends on the exponents of the rate law, either determined through a given mechanism or through a table of experimental values showing the rate of reaction at different reactant concentrations.
by Jennifer Ho 1K
Tue Mar 06, 2018 12:35 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysts
Replies: 3
Views: 126

Re: Catalysts

Catalysts speed up the reaction rate by putting stress on the bonds to be broken in the reaction, allowing them to be broken more easily, thus lowering the activation energy. They are not consumed in the overall reaction, but they may be consumed in the reaction mechanism, reforming later on in the ...
by Jennifer Ho 1K
Tue Mar 06, 2018 12:31 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Which Step is Slower?
Replies: 8
Views: 148

Re: Which Step is Slower?

Usually the problem will tell you which step in the mechanism is the slow step, but if it asks for which step is slow, you just need to find which step matches the overall rate law.
by Jennifer Ho 1K
Tue Mar 06, 2018 12:28 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: "Slow" Step Only?
Replies: 4
Views: 141

Re: "Slow" Step Only?

Once the reaction reaches the slow step, the slow step is the only part of the reaction that stops the reaction from proceeding, so the slow step determines the overall rate of reaction, as the fast steps proceed fast enough that they are negligible in comparison to the slow step in the rate of reac...
by Jennifer Ho 1K
Tue Mar 06, 2018 12:22 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate Laws of Elementary Reactions
Replies: 4
Views: 92

Re: Rate Laws of Elementary Reactions

Yes, this assumption is only valid in elementary reactions because you can't determine the rate law from an overall reaction, you can only determine it if you have a mechanism (or if the reaction is an elementary reaction, in which case the mechanism is just that one step anyways).
by Jennifer Ho 1K
Sun Feb 25, 2018 7:29 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 786979

Re: Post All Chemistry Jokes Here

What do you call a ring of Fe+2 ions?

A ferrous wheel
by Jennifer Ho 1K
Sun Feb 25, 2018 7:25 pm
Forum: Balancing Redox Reactions
Topic: Identifying Oxi/Red Agents [ENDORSED]
Replies: 6
Views: 244

Re: Identifying Oxi/Red Agents [ENDORSED]

The convention is to say the whole molecule's being oxidized I believe, even if it's actually just the atom being oxidized.
by Jennifer Ho 1K
Sun Feb 25, 2018 7:23 pm
Forum: Balancing Redox Reactions
Topic: Acidic and Basic Solution
Replies: 3
Views: 119

Re: Acidic and Basic Solution

The problem will usually specify, but it's more often in acidic solutions than basic solutions.
by Jennifer Ho 1K
Sun Feb 25, 2018 7:21 pm
Forum: Balancing Redox Reactions
Topic: Balancing number of electrons
Replies: 10
Views: 267

Re: Balancing number of electrons

You can theoretically multiply the equations by any higher multiple as long as the electrons cancel out, but it's standard convention to have the coefficients in the final equation in their lowest whole number forms.
by Jennifer Ho 1K
Sun Feb 25, 2018 7:19 pm
Forum: Balancing Redox Reactions
Topic: Oxidation state
Replies: 5
Views: 151

Re: Oxidation state

Yes, because there is no net charge on the molecule, and the each oxygen/hydrogen atom will have the same oxidation number in each case, giving each atom an oxidation number of zero.
by Jennifer Ho 1K
Sun Feb 25, 2018 7:17 pm
Forum: Balancing Redox Reactions
Topic: Half Reaction Order
Replies: 9
Views: 186

Re: Half Reaction Order

The direction does matter, as it determines what forms what in the reaction and whether it is oxidized or reduced.
by Jennifer Ho 1K
Sun Feb 25, 2018 7:14 pm
Forum: Balancing Redox Reactions
Topic: Does order matter?
Replies: 7
Views: 194

Re: Does order matter?

There's no correct way of ordering the species, as long as the right species are on the right side, it doesn't matter.
by Jennifer Ho 1K
Thu Feb 22, 2018 1:00 am
Forum: Balancing Redox Reactions
Topic: Writing Half-Reactions
Replies: 6
Views: 180

Re: Writing Half-Reactions

Whenever you flip the half reaction you need to flip the sign of the standard potential.
by Jennifer Ho 1K
Thu Feb 22, 2018 12:58 am
Forum: Balancing Redox Reactions
Topic: OH/H20
Replies: 4
Views: 94

Re: OH/H20

Generally it's assumed to be acidic in most problems unless specified it's in basic solution.
by Jennifer Ho 1K
Thu Feb 22, 2018 12:53 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 786979

Re: Post All Chemistry Jokes Here

Mole Problems?
Don't Worry! Just Call 602-1023!
by Jennifer Ho 1K
Thu Feb 08, 2018 9:50 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Oxidation Numbers
Replies: 4
Views: 393

Re: Oxidation Numbers

In most cases you'll see oxygen will have an oxidation state number of -2 (if not 0) and hydrogen will have an oxidation state of +1, so there is a point of reference to solve for the other ions that commonly have varying oxidation states. There are exceptions, but it's unlikely that you'll see them...
by Jennifer Ho 1K
Thu Feb 08, 2018 9:45 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge
Replies: 7
Views: 156

Re: Salt Bridge

There has to be a salt bridge in the cell so that the electrons can flow cyclically, as they would build up in the cathode otherwise.
by Jennifer Ho 1K
Thu Feb 08, 2018 9:37 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Half Reactions
Replies: 6
Views: 161

Re: Half Reactions

All the half reactions are written as reductions for the sake of consistency; they could just as easily be all written as oxidation reactions (and I think some tables have it like that). When writing the half reactions you should write it with one reduction and one oxidation half reaction, and for t...
by Jennifer Ho 1K
Fri Jan 26, 2018 1:01 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 786979

Re: Post All Chemistry Jokes Here

"Do you know what Sin City is?"
"Yeah, that's Las Vegas."
"Well, do you know what Den City is?"
"No."
"Mass over Volume."
by Jennifer Ho 1K
Thu Jan 25, 2018 1:44 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Formation of a Cation from an Atom
Replies: 3
Views: 199

Re: Formation of a Cation from an Atom

The formation of a cation from an atom is endothermic because to form the cation, an electron must be removed from the atom. To do this, one of the valence electrons must be excited to the point where it can break free from the pull of nucleus, requiring an input of energy to reach this excited stat...
by Jennifer Ho 1K
Tue Jan 23, 2018 11:14 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 786979

Re: Post All Chemistry Jokes Here

A neutron walks into a bar.
He asks the bartender, "How much for a beer?"
The bartender smiles and says, "For you, no charge."
by Jennifer Ho 1K
Tue Jan 23, 2018 10:54 pm
Forum: Environment, Fossil Fuels, Alternative Fuels
Topic: Energy Density
Replies: 5
Views: 373

Re: Energy Density

Efficiency of a fuel is related to how much energy is packed into a set amount of the fuel, so fuel that contains more energy per unit volume will be able to perform more work. In the example of the car, given more energy per unit volume, a car will be able to travel further using the additional ene...
by Jennifer Ho 1K
Tue Jan 23, 2018 10:44 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: calculating specific heat
Replies: 5
Views: 168

Re: calculating specific heat

Volume is not necessary in calculating specific heat because the energy absorbed or released only depends on the mass of the material, how much of that material is present. The density of the material should stay constant anyways, so the greater volume you have of it, the more mass you will have, ma...
by Jennifer Ho 1K
Tue Jan 23, 2018 10:36 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Temperature
Replies: 3
Views: 102

Re: Temperature

We use Kelvin because that's the absolute temperature, representing the average kinetic energy of the molecules, which is what's relevant in thermodynamics. Using any other unit wouldn't work because the conversion factor between Kelvin and Celsius is additive, not multiplicative, so using only Kelv...
by Jennifer Ho 1K
Tue Jan 23, 2018 10:31 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Table of bond enthalpies
Replies: 4
Views: 142

Re: Table of bond enthalpies

You need to add the enthalpy of phase changes because changing phase requires/releases energy. For example, going from solid to liquid, the molecules require enough energy to break free from the intermolecular forces binding them together, so this must be accounted for if the reaction involves these...
by Jennifer Ho 1K
Tue Jan 23, 2018 1:27 am
Forum: Administrative Questions and Class Announcements
Topic: Week 3 Test Topic is endorsed
Replies: 37
Views: 1642

Re: Week 3 Test Topic is endorsed

how similar are the homework questions to lavelle's test questions?

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