In the process for the manufacture of chlorine by direct oxidation of hcl with air over a catalyst to form cl2 and h2o (only), the exit product is composed of mole fractions of cl2 (21.4%), h2o (21.4%), and n2 (45.0%) – the remainder is hcl and o2. calculate and /or identify: (a) the limiting reactant? (b) the percentage excess reactant? (c) the degree of completion of the reaction? (d) the extent of reaction?

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.