Search found 31 matches
- Sat Mar 17, 2018 2:13 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: trend for temp and activation energy
- Replies: 3
- Views: 469
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.
- Sat Mar 17, 2018 2:12 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Proposing a reaction mechanism
- Replies: 5
- Views: 666
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...
- Sat Mar 17, 2018 2:09 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Water in Mechanism
- Replies: 5
- Views: 620
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.
- Sat Mar 17, 2018 2:07 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Rate Determining
- Replies: 7
- Views: 876
Re: Rate Determining
The slow step should be given, and the other steps are assumed to be fast.
- Fri Mar 16, 2018 11:09 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Final Topics
- Replies: 3
- Views: 486
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?
- Tue Mar 06, 2018 12:38 am
- Forum: Second Order Reactions
- Topic: Order reactions
- Replies: 6
- Views: 1107
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.
- Tue Mar 06, 2018 12:35 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Catalysts
- Replies: 3
- Views: 588
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 ...
- Tue Mar 06, 2018 12:31 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Which Step is Slower?
- Replies: 8
- Views: 930
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.
- Tue Mar 06, 2018 12:28 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: "Slow" Step Only?
- Replies: 4
- Views: 667
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...
- Tue Mar 06, 2018 12:22 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Rate Laws of Elementary Reactions
- Replies: 4
- Views: 457
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).
- Sun Feb 25, 2018 7:29 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3617736
Re: Post All Chemistry Jokes Here
What do you call a ring of Fe+2 ions?
A ferrous wheel
A ferrous wheel
- Sun Feb 25, 2018 7:25 pm
- Forum: Balancing Redox Reactions
- Topic: Identifying Oxi/Red Agents [ENDORSED]
- Replies: 6
- Views: 1043
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.
- Sun Feb 25, 2018 7:23 pm
- Forum: Balancing Redox Reactions
- Topic: Acidic and Basic Solution
- Replies: 3
- Views: 505
Re: Acidic and Basic Solution
The problem will usually specify, but it's more often in acidic solutions than basic solutions.
- Sun Feb 25, 2018 7:21 pm
- Forum: Balancing Redox Reactions
- Topic: Balancing number of electrons
- Replies: 10
- Views: 1102
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.
- Sun Feb 25, 2018 7:19 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidation state
- Replies: 5
- Views: 704
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.
- Sun Feb 25, 2018 7:17 pm
- Forum: Balancing Redox Reactions
- Topic: Half Reaction Order
- Replies: 9
- Views: 2886
Re: Half Reaction Order
The direction does matter, as it determines what forms what in the reaction and whether it is oxidized or reduced.
- Sun Feb 25, 2018 7:14 pm
- Forum: Balancing Redox Reactions
- Topic: Does order matter?
- Replies: 7
- Views: 942
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.
- Thu Feb 22, 2018 1:00 am
- Forum: Balancing Redox Reactions
- Topic: Writing Half-Reactions
- Replies: 6
- Views: 909
Re: Writing Half-Reactions
Whenever you flip the half reaction you need to flip the sign of the standard potential.
- Thu Feb 22, 2018 12:58 am
- Forum: Balancing Redox Reactions
- Topic: OH/H20
- Replies: 4
- Views: 477
Re: OH/H20
Generally it's assumed to be acidic in most problems unless specified it's in basic solution.
- Thu Feb 22, 2018 12:53 am
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3617736
Re: Post All Chemistry Jokes Here
Mole Problems?
Don't Worry! Just Call 602-1023!
Don't Worry! Just Call 602-1023!
- Thu Feb 08, 2018 9:50 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Oxidation Numbers
- Replies: 4
- Views: 915
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...
- Thu Feb 08, 2018 9:45 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 7
- Views: 874
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.
- Thu Feb 08, 2018 9:37 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Half Reactions
- Replies: 6
- Views: 696
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...
- Fri Jan 26, 2018 1:01 am
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3617736
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."
"Yeah, that's Las Vegas."
"Well, do you know what Den City is?"
"No."
"Mass over Volume."
- Thu Jan 25, 2018 1:44 am
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Formation of a Cation from an Atom
- Replies: 3
- Views: 1242
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...
- Tue Jan 23, 2018 11:14 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3617736
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."
He asks the bartender, "How much for a beer?"
The bartender smiles and says, "For you, no charge."
- Tue Jan 23, 2018 10:54 pm
- Forum: Environment, Fossil Fuels, Alternative Fuels
- Topic: Energy Density
- Replies: 10
- Views: 4874
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...
- 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: 827
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...
- Tue Jan 23, 2018 10:36 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Temperature
- Replies: 3
- Views: 313
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...
- Tue Jan 23, 2018 10:31 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Table of bond enthalpies
- Replies: 4
- Views: 625
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...
- Tue Jan 23, 2018 1:27 am
- Forum: Administrative Questions and Class Announcements
- Topic: Week 3 Test Topic is endorsed
- Replies: 37
- Views: 4891
Re: Week 3 Test Topic is endorsed
how similar are the homework questions to lavelle's test questions?