Kinetics Flashcards
Rate Law
Is the relationship between rate and concentration
- Rate is proportional to [A]
Rate Constant
Is the proportionality constant (K) in the Rate Law
- Rate = k [A]
Third Order
When the overall reaction order in the rate law is 3
- rate is 3rd order in a single reactant
- rate is 2nd order in one reactant and 1st in another
- rate is 1st order in each of 3 reactants
Second Order
When the overall reaction order in the rate law is 2
Rate is proportional to the square of the concentration (factor of 4)
- The rate is 2nd order in a single reactant
- the rate is 1st order in each of 2 reactants
First Order
When the overall reaction order in the rate law is 1.
Rate is directly proportional to the concentration of a reactant
- 1st order in a single reactant
Half Life
The amount of time it takes for the concentration of the reactants to fall by half.
Transition State
Is the point of highest energy in an elementary reaction, between reactants and products - top of activation energy, is an unstable state
Heterogeneous Catalyst
A catalyst which is in a different phase to the reactants
e.g. Solid catalyst and gas reactants
Catalyst
A substance which speeds up a reaction without being consumed in the overall process.
The catalyst provides an alternative reaction pathway of lower activation every.
Homogenous Catalyst
Catalyst working in the same phase as the reactants
e.g. A mixture of two solutions
Rate of Reaction
How many times the reaction occurs per second
- change in concentration / Change in time
Average Rate of Reaction
Is the change in concentration over a period of time in the reaction
Instantaneous Rate of Reaction
The rate of Reaction of one specific moment in time
Initial Rate of Reaction
Rate of Reaction when only reactants are present and t=0
Reaction Order
Gives indication to the effect of concentration on the instantaneous rate of Reaction
e.g. zero order Reaction would show the rate is independent of concentration
[R]=[R]o e^(-kt)
First Order reactions
ln [R] = ln [R]o - kt
ln[R] over time will show a straight line with the slope being -k
1/[R] = 1/[R]o + kt
Second Order Reactions
1/[R] against time will show a straight line of +k
t(1/2) = ln2/ k
[R]/[R]o = 1/2 = e(-kt(1/2))
First Order half Life equations
ln[R] = ln[R]o - kt
t(1/2) = 1/[R]ok
Second Order half Life equation
Elementary Reaction
Reaction where reactions meet and collide forming products in one step
Unimolecular elementary reaction
A single molecule reacting by itself
Bimolecular elementary Reaction
Reaction where two molecules meet and react
Termolecular elementary Reaction
Reaction where 3 molecules meet and react
k = Ae (-Ea/RT)
Arrhenius Equation
- gives the relationship for the temperature dependence of the reaction rate Constant
ln k = ln A (-Ea/RT)
Rate Determining Step
The slow step in the mechanism
This will determine the rate law with reactants added - cannot have intermediates in rate Law can switch them using equilibrium Constant
