Does the standard enthalpy of formation of h2o differ from h for the reaction
2h2 + o2 ? 2h2o?

Silica, sio2, is formed on silicon as an electrically insulating layer for microelectronic devices. silica is formed when silicon is exposed to o2 gas at an elevated temperature. at 900˚c, it takes 90 minutes for the oxygen to diffuse from the surface to form a 0.06 micron (0.06 x 10-6 m) thick layer of sio2 on

Idon’t understand this page, can someone ?

Compare and contrast physical changes with chemical changes.