Chemical kinetics Flashcards
what is kinetics?
‘the study of rates of reactions’
why is kinetics important in pharmaceutical sciences?
allows predictions of rates of degrading of drugs
important in other pharmaceutical processes
how does kinetics help predict rates of degrading of drugs?
can predict the stability of drugs causing accelerating stability of drugs expiry dates given
how are kinetics important in other pharmaceutical processes?
studying drug release rates and rates of processes that occur in the body
what is pharmacokinetics?
‘behaviour of drugs in the body’
how are reaction rates measures?
concentrations of chemicals measured at certain times throughout the reaction
what are the methods used for slow reactions?
samples removed at different times of the reaction and assayed for cocentration
what methods used for fast reactions?
using stopped-flow and spectroscopic methods
what is the rate of reaction?
‘the rate of change of concentration of any species’
what is the rate of formulation of product?
P= d[P]/dt
what is the rate of destruction of reactant (A)?
A=d[A]/dt
relationship between P and A?
one P molecule is formed for every A that reacts
what is the equation linking P to A?
d[P]/dt = -d[A]/dt
why is d[A]/dt negative?
concentration is decreasing over time
what is the equation when one mole of A reacts with two of B?
d[B]/dt = 2d[A]/dt
rate laws?
‘the rate of the forward reaction is defined as minus the rate of change of one of the reactants.’
what is the law of mass action?
‘Reaction rate is found to be proportional to the concentration of the reactant raised to the power of the number of molecules involved in the reaction’
what happens to reactions as temperature increases?
faster because more molecules have energy greater or equal to the activation energy
what do molecules have to do to react together?
collide
have enough energy to overcome the activation energy
what does the boltzmann equation give?
‘the fraction of molecules with energy higher than the Ea’
what is the boltzmann equation?
F= e^ (-Ea/RT)
what is the Arrhenius equation is standard form?
ln k = ln A - E /RT
what is the Keq called?
equilibrium constant
will be large if forward reaction is rapid so [P] will be large
what equation show at equilibrium the two rates of A converting to P and P converting to A are the equal?
kf/kr =[P]/[A] = Keq
what is the rate of zero reaction?
rate of disappearance of compound is constant and independent of its concentration
differential law:
-d[A]/dt = k
what is the equation of zero order?
[A] = -kt+ [A]o
y=mx+c
what does Zero order reaction look like on graph?
slide 3
lecture 12 chemical kinetics part 2
what is the differential law for first order reactions?
-d[A]/dt = k[A]
what is the rate of first order reaction?
‘rate of decay is proportional to the amount of material remaining at that time’
what is the integrated form of the rate law of first order?
[A]t= [A]o e^(-kt)
what does the graph of first order look like?
slide 6
lecture 12 chemical kinetics part 2
what are the units of K in first order reaction?
s^-1
how is first order reaction equation written in the form of y=mx +c
ln [A]t = ln [A]o -kt
relationship between K and concentration in first order reaction?
‘rate constant is independent of concentration’
what is the equation of lifetime?
= 1/k
what is the equation of half-life?
(ln 2)/k
what happens to the half-life in second order reactions?
not constant
what are the two possible types of reactions that are second order?
either two of the same products colliding
-d[A]/dt = k[A]^2
or two different molecules reacting
-d[A]/dt = k[A][B]
when Keq constant?
‘under a set of conditions’
what is the half-life in first order?
constant
what are parallel reactions?
‘when a reactant decays in one of two products’
what is the differential rate equation of parallel equations?
-d[A]/dt = k [A] + k [A]
what is the integrated rate equation of parallel equation?
[A]t = [A]o e ^(-(k + k ) t)
what are the rate laws of consecutive reactions/
-d[A]/dt = k1 [A]
-d[B]/dt = k2 [B] - k1 [A]
d[C]/dt = k2 [B]
what happens in consecutive reations?
A is turned into B which is then turned into C
what are the different profiles of concentration against time for A, B, C and why for consecutive reactions?
slide 4
SOM lecture 12 chemical kinetics part 5
what are the two concepts for consecutive reactions?
steady-state approximation
rate-limiting step
what is the steady-state approximation?
after reaction has run for some time, concentration of B is 0
d[B]/dt=0
what is the rate-limiting step?
when one step is slower than the rest
