C11. Chemical kinetics Flashcards
what is kinetics?
Kinetics is the study of the rates of reaction and can tell us how
quickly components react with each other, how fast components
decay and how this is affected by temperature
what is the rate of reaction?
The rate of reaction is the rate of change of the concentration of
either the products (P) or reactants (A)
rate of formation (products) equation?
d[P] / dt
rate of loss (reactants) equation?
d[A] / dt
Rate directionally proportional?
Rate directionally proportional to [A][B]
k?
rate constant
rate law?
ONE NOTE
Describe zero order reaction? equation?
-The rate of disappearance of a reagent is constant and does not
depend on its concentration.
-rate of loss of reactant A= -d[A] / dt =k
-by integrating the expression, we get [A]= -kt + [A]0
Describe plotting zero-order reactions
▪ Plot concentration (y) vs time (x).
▪ If you get a straight line your reaction is zero-order
▪ Slope = - k (mol dm-3 s
-1)
ONE NOTE
Describe first order reactions? equations?
-The rate of disappearance of a reagent is proportional to the amount
of material remaining
-Rate of loss of reactant A = −d[A] / dt = k[A]
-By integrating the expression, we get: [A]t = [A]0 e to the power of -kt
describe the concentration time graph of a first order reaction
Because a first-order reaction is an
exponential function, if we plot [A] vs. time we get an exponential decay
ONE NOTE
Describe straight line graphs of first order reactions
-If you plot the ln[concentration] (y) vs time (x) and you get a straight-line your reaction is First-order
-ln(x) is dimensionless, it has no units.
-Slope = - k (s-1)
ln[A]t = ln [A]0 - kt
ONE NOTE
what is half life? equation?
The half-life is the time taken for half the concentration of reactant to decompose.
EQUATION ON ONE NOTE
T=
1/ k
how does temp change rate?
As temperature increases,
more molecules have sufficient
energy to overcome the
activation energy barrier
for two molecules to react they must…
1) Collide
2) Have sufficient energy to overcome Ea
F=?
-Collision rate (z) is linearly dependent on temperature. However, the
fraction of molecules (F) having sufficient energy to overcome Ea
is exponentially dependent on temperate
F= e to the power of -Ea/ RT
R = Gas constant (8.314 J K-1 mol-1)
T = Temperature (K)
k=?
k= Ae to the power of -Ea/ RT
by integrating the equation we get:
ln(k) = -Ea/ RT + ln(A) which is the integrated form of the Arrhenius equation
how to find activation energy?
-by using integrated Arrhenius equation plot a straight line of ln(k) (y) vs 1/T(x) we can find the activation energy for a particular chemical process.
-slope = -Ea / R (Jmol-1)
ONE NOTE
how to predict the rate of degradation? equation?
ONE NOTE
What are parallel reactions
Parallel reactions involve
the decay of a compound into
two (or more) products at
different rates.
ONE NOTE
What are consecutive reactions?
Consecutive reactions can
involve a series of
intermediates which then go
on to form products.
what is the rate-determining step
The slowest rate within a
consecutive reaction is the
rate-determining step. The
reaction cannot go faster than
the rate of the slowest step
Describe reactions in equilibrium
d[A]/ dt = d[P]/dt
kfor[A] = krev[P]
ONE NOTE
Keq=
[P] / [A]
Products dominate Keq»_space; 1
Reactants dominate Keq «_space;1
At equilibrium Keq = 1
At equilibrium ΔG =?
0
ONE NOTE
A reaction is spontaneous if…
Keq»_space; 1 (reaction favours the products)
ΔG°=
ΔG° = -RTlnKeq
ONE NOTE
Keq in terms of ΔG =?
e to the power of (-ΔG/ RT)
Describe Van’t Hoff equation
one note
