Kinetics (Difficult to involve rate determining step) Flashcards
What is kinetics
The study of the factors that affect rates of chemical reactions
Collision theory
For a reaction to take place between 2 particles, they must collide with enough energy and correct orientation to break the bonds
Factors that affect rate of reaction
Increase temp
Increase concentration (solution)
Increase pressure (gas)
Increase surface area (solid)
Use a catalyst
Activation energy
The minimum energy required to start a reaction
On an enthalpy diagram, what is the species at the top of the curve called
A transition state OR activated complex
What does the maxwell-boltzmann distribution tell us
No particles have 0 energy
Most particles have intermediate energy - around peak of curve
Few have very high energy, there is no upper limit
Average energy is not the same as most probable
Effect of temperature on Maxwell-Boltzmann distribution
At high temp, peak of the curve is lower and moves to the right. Number of particles with very high energy increases.
Greater area or particles past the activation energy - more successful collisions
Total area under curve remains the same of all temps with same particle number
Catalyst
Substance that affect the rate of chemical reactions without being chemically changed themselves at the end of reaction. Provide alternative pathway
How do catalysts work
Reduces activation energy
Catalyst effect on maxwell-boltzmann distribution
Shift activation energy left
X and Y axis on maxwell
X = energy
Y = Fraction of particles with energy
What do catalysts not effect
Enthalpy change
Position of equilibrium
2 stages of catalytic converter reaction
Adsorption - gases form weak bonds with metal atoms of catalyst
Desorption - Products break away from atoms
Equation for rate of reaction
Change in conc / time
What is the rate expression equation
Rate = k[X][Y]^2
What order of reaction has a graph with no change in rate of reaction?
0 order
What order of reaction has a graph with a sloping straight line through the origin?
1st order
What order of reaction is it if the graph does not have a straight line
2nd order
What effect does temperature have on the k constant?
For every 10K rise in temp, rate of reaction doubles.
Therefore, value of K increases
What is the arrhenius equation?
k = A e^-Ea/RT
K = rate constant
A = Pre exponential factor (number of collisions)
e^-Ea/RT = fraction of collisions with sufficient activation energy
What arrhenius equation do we use when trying to find Ea? + what do we do with the natural logs?
InK = - Ea/RT + InA
or
InK = -Ea/R x 1/T + InA
With the natural logs, solve them before putting them into the calculation
For the arrhenius equation, in a graph with InK against 1/T, what does the gradient equal to?
-Ea/R
What is the rate determining step?
The slowest step of a reaction
