#1. a reaction in which one element replaces another in a compound or in which two elements in different compounds trade places is called a reaction.
#2. the is the amount of one material present in a given volume of another material.

The size (radius) of an oxygen molecule is about 2.0 ×10−10m. make a rough estimate of the pressure at which the finite volume of the molecules should cause noticeable deviations from ideal-gas behavior at ordinary temperatures (t= 300k ). assume that deviatons would be noticeable when volume of the gas per molecule equals the volume of the molecule itself.