Continuous Flow Method Syringes are filled with A
- Slides: 8
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 a. A+b. B+…. . - M-n. N……. . • 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 singleterm 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.