lecture 3 - chemical kinetics Flashcards
what is a half life
the amount of time taken for a reactants concentration to half
what order reaction is half life used for
first order only
half life is constant
half lives are useful in
radiation
first order reaction integrated rate law is
[a] = [a0] exp(-kt)
half life equation
1/2[a0] = [ao] exp(- kt1/2] )
half life equation
t1/2 = ln(2) / k
equation does not depend on conc
half life is constant for the reaction
how is conc affected after each half life
after each half life, the conc is halved
finding rate constant from half life
t1/2 = ln(2) / k
k = ln(2) / t1/2
why are half lives used for radioactive decay
radioactive decay is a first order reaction
to find half life we must make sure time has a unit in
seconds
altought half life has no practical use for 2nd order reactions due to conc not being constant, what is its equation
t1/2 = 1 / k[a0]
why cant integrated rate laws be used for slow reactions
we must gather data for the whole reaction in order to find their rate law equations.
if a reaction takes years, theres no use in using integrated rate laws
what method allows us to find the order of a reaction for slow reactions
initial rates method
what happens in the initial rates method
reaction is repeated with a range of different starting concentrations
the initial rate of each one is then calculated
what happens in isolation methods
increase conc of 1 until excess so it remains constant during reaction.
find order of other reactant
using integrated rate law (excel)
repeat for the other reactant
