Heat is just another word for transferring kinetic energy. Temperature above absolute zero is just the random, kinetic energy of atoms. Heat is the process by which the kinetic energy of one thing is transferred to another. How the heat (energy) is transferred depends on circumstances. Radiation, convection, conduction are some ways, but in every case kinetic energy is transferred from one thing to another.

Snow is mostly air. it consists of crystals which occupy a much greater volume than their overall dimensions. Light reflects off the large surface area of the ice structures which make up the snow crystals creating the impression of 'white'. Ice however is almost all water. If it has air embedded, then it starts looking white where the air is, but the frozen water just transmits light through and does not reflects as white.

Not exactly 'help a burn heal'. Cold water, immediately applied will stop the burning process in its tracks. Right after a burn occurs, the flesh is still hot and damages the surrounding area, making the burn worse. Cold water stops this and in addition, temporarily relieves the pain. First aid = cold, clean water. not ice cold, not a forceful stream. Never ice, never butter, yes clean,dry bandage, yes get medical help quickly, if anything other than a very small burn not on a sensitive area, that is just a mild reddening of the skin.

The electronic logic elements that they are made of got smaller and smaller. First they were electric relays (about the size of a ping pong ball, then vacuum tubes, then transistors. The transistors consist of materials that conduct electricity under certain conditions. The transistors became smaller and smaller. A single silicon chip can now contain many millions of transistors, each of which has the function of one electric relay. The limit is the (three dimensional) geometry of the transistors on the chip and the (photographic/deposition) process used to make them.