"in a pure substance all the particles must be identical; therefore pure substances are composed only of elements." do you agree with this statement? why or why not?

The energy equivalent of the rest mass of an electron is

12. a body is a particular amount of matter. it can be a solid, liquid or gas. it can be described as existing in a. size and shape. b. motion and force c. time and space. d. location and movement.

Aparticle of mass m is placed in a one-dimensional box of length l. the box is so small that the particle’s motion is relativistic, so that e p2/2m is not valid. (a) derive an expression for the energy levels of the particle using the relativistic energy–momentum relation and the quantization of momentum that derives from connement. (b) if the particle is an electron in a box of length l 1.00 1012 m, nd its lowest possible kinetic energy. by what percent is the nonrelativistic formula for the energy in error?