Kinetics 1 Flashcards
What factors affect reaction rates?
- Concentration
- Temperature
reaction pathway
the minimum energy route to get from reactants to products
reaction coordinate
abstract coordinate to show progress along a reaction route
activation energy
the minimum energy for a reaction to occur - energy barrier
transition state
as molecules cross the energy barrier, they proceed via a transition state
intermediate molecules
a reaction may proceed by a number of steps, via intermediate molecules
When are transition states seen on a diagram?
at the energy maxima
When are intermediates seen on a diagram?
at an energy minima
Reaction rate equation when characterised by rate of disappearance of reactant
rate = - d[reactant]/ dt
Reaction rate equation when characterised by the appearance of a product
rate = d[product]/ dt
Methods for measuring reaction rates
- ‘stopwatch’ method
- continuous flow
- stopped flow
- relaxation methods
- flash photolysis
Overall order of a reaction
the sum of the orders of the substances in the rate equation
Rate equation of a first order reaction
rate = -d[A]/ dt = d[P]/dt = k[A]
What does integrated rate laws do?
- gives us concentrations as a function of time
- allows us to determine the order of reaction
What do half-lives do?
- another way of characterising reaction rates
What to always plot for integrated rate laws?
f[A] vs t, not [P] vs t
What is the half-life of a reactant?
the time taken for its concentration to drop to half its original value
What is the half life for a first-order reaction?
a constant
What is the half life for a second-order reaction?
it increases as reaction proceeds
What does the arrhenius equation tell us?
a small increase in temperature will produce a significant increase in the magnitude of the rate coefficient of the reaction
What does the A stand for in the arrhenius equation for a bimolecular, gas-phase reaction? k = Aexp(−E/RT)
it is related to the probability of molecules meeting in the correct orientation to react
What does the exponential relate to in the arrhenius equation for a bimolecular, gas-phase reaction? k = Aexp(−E/RT)
the probability molecules have enough energy to react
What does the A stand for in the arrhenius equation for a unimolecular, gas-phase reaction? Aexp(−E/RT)
related to the frequency of the vibration
What does the exponential relate to in the arrhenius equation for a unimolecular, gas-phase reaction?
the probability molecules have enough energy to break bond
