12. Kinetics Flashcards
What does the term kinetics describe?
Provides a mathematical analysis of the rate of a process= How fast a process happens
Rate= Amount or concentration of produced formed per unit time
What is a first order reaction?
Reactions where a single component spontaneously reacts:
A–> various possibilities, but usually B or B + C
SINGLE REACTANT which forms one or more products
What is a second order reaction?
Reactions where two reactants come together for the reaction to occur:
A + B –> Various possibilities, but usually C or C+ D
TWO REACTANTS
REMEMBER: Order is NOT predicted by overall equation= Can break down the steps sequentially
What is the rate equation for a first order process?
-d[A]/ dt = k[A]
Rate of reaction is proportional to the concentration of the reactant A
k has units: s^-1
First order: [A] = [A]0 e^(–kt)
What is the half-life of a reaction?
Time taken to for [A] to fall to half its initial value is a constant
What happens to the half-life of a first order reaction?
Nothing, it stays CONSTANT
What is radioactivity?
The emission of high energy particles from atomic nuclei, the kinetics of radioactive decay is similar to the analysis of reaction kinetics for first order chemical reactions
Since it has a similar equation for the rate of radioactive decay to first order reaction kinetics, there is a constant half life for a radioactive isotope too (time taken for half the atomic nuclei originally present to decay)
What is the rate of collision dependent on for a second order reaction?
Dependent on the product of the concentrations of the two reactants
The higher the concentration, the greater the rate of collisions
What is the rate equation for second order reactions?
v = –d [A] / dt = k [A] [B]
k has units: M^-1 s^-1
BUT: its hard to analyse therefore you assume that the concentration of one reactant is effectively constant by buffering or having it in large excess therefore it simplifies to:
v = –d [A] / dt = kB [A]
where kB= k[B]
What is the main difference between what the rate constants of first and second order reactions are dependent on?
First order: Only on the reactant
Second order: Have an upper limit determined by the environment the reaction is taking place in, which determines how frequently collisions between reacting molecules can occur
May be limited by diffusion in solution and in vivo
What is a zero order reaction?
The rate of reaction does NOT depend on the concentration of the reactant(s)
Example: Drug uptake where its rate of uptake might be limited by the transport system= Constant above a certain level
