there is not a lot of difference in terms of the physics course, but the difference is that a microchips just contains a set of elements which on their own cannot process anything. They need to be used in conjunction with another microchip or microprocessor...
A microprocessor is capable of performing all processing within the single chip. Although it cannot really operate on its own (like in a computer you need other things other than the cpu) it can do all of the actuall processing on its own.