Continuous Flow Method •Syringes are filled with A and B solution and compressed at constant rate •Flow rate must exceed turbulent Limit •Age of solution is proportional to flow tube distance and flow rate •Only one time point (age) per measurement position •Large volumes required Position of detector can be moved

Stopped Flow Method Syringes are filled with A and B solution and compressed to small amounts (50-200μl) then stopped •Once the flow is stopped, solution ages with time (can be controlled) •Detector sees more than one “age” •Low dead times (1 ms) •Expensive detection system

Relaxation methods

Relaxation Methods

Relaxation Methods

Determining Mechanism from Rate Law If the rate law is , the total composition of the reactants in the rate limiting step is aA+bB+….. If the rate law is , the total composition of the reactants in the rate limiting step is aA+bB+…..-M-nN…….. A rate law, to be properly interpreted according to rule 1, must be written in terms of the predominate species in the reaction medium.

Determining Mechanism from Rate Law The number of positive terms in the rate law is the number of independent, parallel pathways. Negative terms represent the reverse reaction. A summation of n terms in the denominator implies a succession of n steps, all but nth are reversible. Species whose concentrations appear in single-term denominators are produced in the step prior to rate controlling step.

Determining Mechanism from Rate Law Adding up the steps in a mechanism must yield the net chemical reaction; rapid reaction may follow the rate-controlling step. Alternative mechanisms leading to same pattern of activated complexes are not kinetically distinguishable. The order increases with increasing concentration when the reaction proceeds by parallel pathways but decreases when a series of steps occur.