Chem kinetics p2 L14 Flashcards
Drawbacks of the initial rate law
*restricted to using info from start of reaction and cant find out at any given point
*Reaction can go very fast
*Stuff from envir can pollute the environment if reaction is not controlled
Integration law
relates conc. to time and another way to find k
- If we know [A]0 and k, we can find [A]t after some time
integration law formula
for 1st order:
rate law = -d[A]/dt = k[A]
To find [A] at any time:
ln[A]t = ln[A]0 - kt
What equation is like y = mx + c
ln [A] = -kt + ln [A]0
When does this equation work?
Only at first order
How to plot the eq?
Plot different values of [A] at different t to get a negative straight line or monitor the one measurement over time
What is a half life?
Time taken for [A]0 to reach half the value
time taken = [A]0/2
Radioactive dating
The amount of C14 in body is kept constant due to exchange of CO2 when organism is alive but decays when organism dies as exchange stops.
Therefore, we can find out how old something is from the C14 content
Reaction mechanisms
A series of Elementary steps used to describe a reaction
What are elementary steps?
We cannot predict rate law from one equation as most reactions take place in a series of steps called elementary steps
Bimolecular elementary step?
Two reactants coming together
unimolecular elementary step?
one reactant decaying
Reaction intermediates
Plays a role in reaction but isn’t a part of the overall rate equation
Sum of elementary steps
must = the overall rate equation
Deducing reaction mechanisms
*Exp measurement –> conduct the exp –> exp rate law
*proposed mechanism –> predicted rate law
*compare the rate laws, if they are similar, we can say that the exp rate law SUPPORTS the proposed mech NOT PROVES
