Chem kinetics p3 L15 Flashcards
How does temp affect reactions?
Increases the rate
How does temp affect k
K is dependent on temp therefore k is given for a certain temp
The collision model
*Kinetic theory of gases indicate that all molecules are in constant motion
*As molecules constantly collide –> E is transferred from 1 molecule to another
Factors that affect the rate at which molecules react:
*Effectiveness
*Orientation
*Collision rate
What is collision rate?
How often the particles collide i.e no. of collisions per second. More collision = increased rate of reaction
*high conc = more collisions
*more temp = more KE = more speed = more collisions
What is collision effectiveness?
must have enough energy to transfer and to make/break bonds
*Increase E of system even if ∆G is -ve
*Must have enough collisions to have E to overcome the threshold (activation E)
* Not all collisions lead to a reaction, only the successful ones with enough energy
For every 10ºC rise in T
The rate doubles
What is collision orientation?
molecules must be oriented correctly for a successful reaction
What is molecularity?
total no. of species involved in a collision
*uni, bi or ter molecular
What is the transition state?
At the top of the Ea, forms an activated complex that is loosely found (partly broken/formed bonds)
How long can transition state last?
Very short time and hence cannot be isolated like an intermediate
*either forms products (effective collision) or goes back to reactants (ineffective)
What is the Arrhenius equation?
k = Ae ^(-Ea/RT)
What is Ae?
Frequency factor i.e f of successful collisions that are favourably oriented
-Ea
Activation energy - likeliness of r x n being successful
increased Ea = decreased k
R
Gas constant at 8.314 J k-1 mol-1
