An extra point about first order reactions

2 An extra point about first order reactions 

The half-life of a first order reaction remains constant throughout reaction and is independent of concentration. This applies to any fractional lifetime, though the half-life is the one most commonly used. The relaxation time is the other common fractional lifetime. The relaxation time is relevant only to first order reactions, and is afractional lifetime which bears a very simple relation to the rate constant as a direct consequence of the exponential behaviour of first order reactions. 

Fractional life Half-life Quarter-life t /4 Relaxation time r 

Relaxation times become important when studying the approach to equilibrium either directly or as a result of a small perturbation from equilibrium. They also emerge directly from ultrasonic relaxation techniques for studying single and multiple equilibria (Section 2.6). However, they only apply to first order or pseudo- first order processes (Section 3.15). 

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