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Collision Theory
Energy Changes During Collision
Potential Energy Profiles
Reaction Mechanism
Rate Law
100
Define collision theory!
Collision Theory states that reactions occur only when atoms, ions, or molecules collide, but only a very small portion of the collisions result in a chemical reaction.
100
Name 4 things that will affect the rate of a reaction!
Temperature, concentration, nature of the reactants, catalyst.
100
What is the activated complex?
High-energy, unstable, temporary state between reactants and products.
100
What is an elementary process?
A reaction that occurs in one step!
100
What determines the order of a reaction?
The sum of the exponents!
200
What are the 3 conditions of an effective collision?
1) Stable structure must be formed 2) Molecules must have correct orientation 3) Molecules must have sufficient energy
200
A reaction has the following equation: A + B + water → C If we double the amount of B added and decrease the amount of water, what do we expect to happen to the rate of reaction? Why?
Faster due to more "things" colliding, increasing the chance of effective collisions.
200
Define ∆Hrxn!
The change in potential energy from reactants to products.
200
How will an intermediate appear in a reaction mechanism?
It will be produced in one step and will then be used up in another.
200
What are the units of rate?
M/s
300
A collision between what two things will be most likely to result in an effective collision? Why?
Ions because they're small and attractive charges are more likely to hold them together.
300
Explain what would happen to a reaction if we increased the temperature at which it occured? Why?
Reaction would occur faster because molecules have increased KE, move faster, more collisions which would result in effective collisions more often.
300
What is the importance of the activation energy of a reaction in regards to the rate?
Higher activation energy means a slower reaction!
300
Which step in a reaction mechanism determines the rate law for that reaction? What is that step called?
The slow step, which is called the rate-determining step!
300
If the concentration of molecule A is doubled and the rate increases by a factor of 8, what is the exponent on A?
3!
400
Come up with an analogy to describe effective collisions vs. non-effective collisions!
Woot woot!
400
What happens when you add a catalyst to a reaction? Why?
Reaction occurs faster because the catalyst lowers the activation energy.
400
If a reaction is exothermic and the Ea forward is 60 KJ, will the Ea reverse be more or less than 60 KJ?
More!
400
Is there a catalyst present in this reaction? If so, what is it? Step 1: 2 NO (g) + H2 (g)  N2 (g) + H2O2 (g) Step 2: H2O2 (g) + H2 (g)  2 H2O (g)
No catalyst!
400
Calculate the exponent on [NO] with the following info: Example: 2 NO (g) + 2 H2 (g)  N2 (g) + 2 H2O (g) Trial [NO] mol/L [H2] mol/L Rate mol/(Ls) 1 0.001 0.004 0.002 2 0.002 0.004 0.008
2!
500
When does the orientation of molecules become more important?
When colliding molecules become bigger and more complex.
500
Explain the Maxwell-Boltzmann Distribution Curve!
Shows that, at a higher temperature, more molecules will have the activation energy required to result in a reaction.
500
GIVEN: PE reactants = 0 KJ ∆Hrxn = -70 KJ Ea forward = 60 KJ Calculate Ea reverse!
130 KJ.
500
What is the rate law for this reaction? Step 1: 2 NO (g) + H2 (g)  N2 (g) + H2O2 (g) (slow) Step 2: H2O2 (g) + H2 (g)  2 H2O (g) (fast)
Rate = k[NO][H2]
500
Calculate the rate of the following equation using [A] = 0.5 M and [B] = 0.1 M where k = 25.6 Rate = k[A]2[B]
0.64