lecture 1 - chemical kinetics Flashcards
what is kinetics the study of
study of rates of chemical reactions
what can kinetics give us insight into
insight into the mechanism of reactions
reactions have equations that correspond to them under certain conditions, why is this important
allows us to control how fast reactions take place
what industry is controlling reactions important in
chemical industry
slow: uneconomical
fast: dangerous
to study the rate we must
monitor the conc of at least 1 reactant
measuring conc inside the reaction vessel
in-situ measurement
measuring conc outside the reaction vessel
ex-situ measurement
how do ex-situ measurements occur
stop the whole reaction then measure conc
take sample from vessel and stop reaction in the sample
both stop reaction to measure conc
how can a reaction be stopped
quenching
what is quenching
stopping a chemical reaction
cool, dilute or neurtalise a reactant (all prevent the reaction from continuing)
what must we do after quenching
use analytical techniques to measure the conc of reactants or products
what must be done if a reaction is stopped to make an ex-situ measurement
we must repeat the experiment but stop the reaction at different times
in-situ measurement of conc examples
observation
spectroscopy
chemical sensor
gas pressure
measure conc without disturbing the reaction
how is spectroscopy insitu
u can gather info on the conc based on absorption of light!
this doesnt disturb the reaction
what do we need to measure rate
concentration as a function of time
over time, reactant conc
falls
over time, product conc
rises
rate of reaction at a specific time is given by
the gradient at that point
gradient equation
change y / change x
gradient of a curve can be measured using a
tangent
gradient can also be given by the differential of a math expression of a curve
gradient = d[A] / dt
rate for reactants isss
- gradient
rate must be a positive number
rate for products isss
gradient
what conc must be measured to find rate
conc of any product or reactant in the equation
if the reactants / products have stoichiometries (large numbers in front of them) we must
divide gradient by the stoichiometry
multiply the gradient by 1/stoichiometry
finding the initial rate of reaction
gradient where t=0
what is a rate law
equation of a reaction based on a conc as a function of time
rate = k [a][b]
how can we see what order a reactant is
the power
overall order for a reaction is
powers added together
what is k
rate constant
what does k depend on
temperature
k for kelvin ;)
what does k not depend on
concentrations
how can we determine rate law
keep temp constant or it will affect k!!!
sometimes based on how many molecules are reacting (its molecularity) in single step reactions!!
what is the rate determinding step
slow step of the reaction
makes up the rate law
0th order rate law equation
rate = k
reaction occurs at a constant rate until all reactants are consumed, then stops
but how can we determine rate laws if its not based on molecularity
we must carry out experiments
what is the integrated rate laws
single reactant
shape of curve tells u the order
plot date in diff ways to find the order
EXCELLLLL
initial rates method
slow reactions
measure the initial rate of a reaction at different starting concentrations
isolation method
determines order when there are multiple reactants
units for rate constant
moldm-3 s-2
/ moldm-3 (conc)
