For the decomposition of dinitrogen pentoxide in carbon tetrachloride solution at 30 °C 2 N2O54 NO2 + O2 the average rate of disappearance of N2O5 over the time period from t = 0 min to t = 116 min is found to be 8.45×10-4 M min-1. The average rate of formation of O2 over the same time period is M min-1

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.