Preferred Label : chemical relaxation;
IUPAC definition : If the equilibrium mixture of a chemical reaction is disturbed by a sudden change,
especially of some external parameter (such as temperature, pressure or electrical
field strength), the system will readjust itself to a new position of the chemical
equilibrium or return to the original position, if the perturbation is temporary.
The readjustment is known as chemical relaxation. In many cases, and in particular
when the displacement from equilibrium is slight, the progress of the system towards
equilibrium can be expressed as a first-order law: \[C_{t}- \left(C_{{eq}}\right)_{2}
[\left(C_{{eq}}\right)_{1}- \left(C_{{eq}}\right)_{2}]\ {e} {\frac{-t}{\tau }}\] where
Ceq1 and Ceq2 are the equilibrium concentrations of one of the chemical species involved
in the reaction before and after the change in the external parameter, and Ct is its
concentration at time t. The time parameter τ, named relaxation time, is related to
the rate constants of the chemical reaction involved. Measurements of the relaxation
times by relaxation methods [involving a temperature jump (T-jump), pressure jump,
electric field jump or a periodic disturbance of an external parameter, as in ultrasonic
techniques] are commonly used to follow the kinetics of very fast reactions.;
Origin ID : C01035;
See also
If the equilibrium mixture of a chemical reaction is disturbed by a sudden change,
especially of some external parameter (such as temperature, pressure or electrical
field strength), the system will readjust itself to a new position of the chemical
equilibrium or return to the original position, if the perturbation is temporary.
The readjustment is known as chemical relaxation. In many cases, and in particular
when the displacement from equilibrium is slight, the progress of the system towards
equilibrium can be expressed as a first-order law: \[C_{t}- \left(C_{{eq}}\right)_{2}
[\left(C_{{eq}}\right)_{1}- \left(C_{{eq}}\right)_{2}]\ {e} {\frac{-t}{\tau }}\] where
Ceq1 and Ceq2 are the equilibrium concentrations of one of the chemical species involved
in the reaction before and after the change in the external parameter, and Ct is its
concentration at time t. The time parameter τ, named relaxation time, is related to
the rate constants of the chemical reaction involved. Measurements of the relaxation
times by relaxation methods [involving a temperature jump (T-jump), pressure jump,
electric field jump or a periodic disturbance of an external parameter, as in ultrasonic
techniques] are commonly used to follow the kinetics of very fast reactions.
