Metals combine with oxygen to form metal oxides. For example iron wool burning in oxygen produces iron oxide
The chemical equation.
Iron + Oxygen –> Iron oxide
Aluminium + Oxygen –> Aluminium oxide
Aluminium is reactive enough to chemically combine with oxygen atoms that are already attached to another metal atom.
Aluminium + Iron oxide –> Aluminium oxide + iron
This is known as a thermite reaction . A huge amount of heat is given out and the iron formed is molten. The reaction has been used by NZ rail to weld continuous sections of line together.
North of New Zealand the Pacific tectonic plate is being subducted beneath the Australian plate. There is a lot of volcanic and earthquake activity along the collision zone.
Deep trenches form at the leading edges of subduction zones. If you watch as the pointer moves around the screen on the video and look at the elevaton numbers at the bottom ( they are negative so indicate the depth below sea level) the sea depth reaches 22,000 feet just east of tonga.
Tonga lies on a tiny microplate trapped as a rise between a spreading zone to the west and the subduction zone to the east. Recent volcanic activity appeared 10 kilometers from the southwest coast of Tongatapu, the main Tongan island. There are 36 other underwater volcanos in the vicinity.
Some metals are clearly very reactive. Sodium and lithium react violently with water and calcium dissolves quickly.
Other metals dissolve in acids and the rate at which they dissolve tells you something about how reactive they are. If they give off lots of bubbles rapidly they are reactive. Aluminium is out of order because it has a protective layer of oxide. It appeqars to be unreactive and this fact often crops up in NCEA level 1 exams.
A list of metals from the most reactive to the least reactive is known as the reactivity series.
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