The balanced equation below represents the reaction between magnesium metal and hydrochloric acid to produce aqueous magnesium chloride and hydrogen gas.

mg(s) + 2hcl(aq) ==> mgcl2(aq) + h2(g)

a piece of mg(s) has a volume of 0.0640 cubic centimeters. this piece of mg(s) reacts completely with hcl(aq) to produce h2(g). the h2(g) produced has a volume of 112 milliliters and a pressure of 1.00 atmosphere at 298 k.

65 the volume of the piece of mg(s) is expressed to what number of significant figures?

they are all solids.

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.