The term half-life, as applied to a reactant in a chemical reaction means: the time required for half of the maximum amount of product to be formed. the time taken for the concentration of a reactant to decrease by a factor of 1/2. half of the time it ta kes for all of a reactant to be consumed. the value of time which gives a value of 1/2 when substituted into the expression kt.

The term half lime means: the time taken for the concentration of a reactant to decrease by a factor of 1/2.

Explanation:

In kinetics, the term half-life refers to the time that it takes to decrease the concentration of a reactant to half its initial concentration. Half-life depends on the reaction order, on the rate constant and, except for first-order kinetics, on the initial concentration of the reactant.

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.