kinetics Flashcards
the gradient of a concentration vs time curve at point t gives…
the rate of reaction at time t.
rate is always…
positive
the rate law can only be …
determined experimentally.
the differential rate law tells us…
the rate of the reaction at a particular instant
the integrated rate law is an expression that gives us…
the concentration of a species as a function of time. They can be used to establish the order of a reaction and then the rate constant.
integrated rate law for zeroth order reaction
- on equation sheet
[A] = [A]0 -kt
integrated rate law for first order reaction
- on equation sheet
Exponential graph :
[A] = [A]0 e^-kt
and
straight line graph
ln[A]t = ln[A]0 - kt
where k is the gradient.
integrated rate law for second order reaction
- on equation sheet
exponential graph:
[A]t = [A]0 - kt
straight line graph :
1/[A] = 1/[A]0 + kt
what is the definition of half life
the time taken for the concentration of the species to fall to half its initial value
at equilibrium the rate of forwards and backwards reactions are ….
equal
equation for rate at equilibrium
[B]eq / [A]eq = k1/ k-1 = K
for first order reactions the ln[A] against t should be…
a straight line (linear)
what does the 0 mean in [A]0
the initial concentration
what shape is the graph of lnk vs t
linear
what equation does the graph of lnk vs 1/t represent
the Arrhenius equation
what is the Arrhenius equation
- on equation sheet
k = A e (-Ea / RT)
T = absolute temperature (K)
R = gas constant (8.314 J mol-1 K-1)
A = pre-exponential factor, a constant. (measure of the frequency of collisions.)
what is the y-intercept of the lnk vs 1/t graph
lnA (pre-exponensial factor)
what is a homogeneous catalyst
same phase as the reactants and products
what is a heterogeneous catalyst
different phase as the reactants and products
what is a pseudo first order reaction ?
elementary reaction which has more than one reactant, which concentrations both change during the reaction
what is the method used to solve pseudo first order reactions
isolating one reactant at a time by having the other reactant in a large excess.
if B is in large excess how can we rewrite k’
k[B]0
what is k’
the effective rate constant for a fixed concentration of B ([B]0)
what can you use half live for ?
to decide wether or not the reaction is first order and to get a value for the rate constant, k
