Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

3 CHEMICAL RELAXATION METHODS 137to use a buffer which has a high AH. When the temperature is raised, the concentrationof hydrogen ions will be changed slightly by virtue of the buffer’s AH, andthis “concentration jump” might be sufficient to displace the main equilibrium.3.3 STATIONARY METHODSWhereas in the “step-function” relaxation methods a single pulse is applied to anequilibrium system and the consequent rapid adjustment of the concentration isdetermined, in the “stationary” methods a steadily oscillating disturbance is appliedand the behaviour of the system can be analyzed at leisure. This behaviour is representedin Fig. 9, in which the forcing function is given by curve (11. If the frequencyof the forcing function is sufficiently low, the system can adjust itself rapidlyand the concentration changes can effectively keep up with their equilibrium values,in which case the cmcentrations are also given by curve 0. If the forcing frequencyis much too large for the system to readjust itself, there will be no observed concentrationchanges (case