三題簡短既化學題

1. It is a physical change.
Hydrogen and oxygen do not react chemically under room temperature unless you give a spark to overcome the activation energy. It will explose as the reaction is highly exothermic. They react vigorously to form water.

2. Iron sink in water, obviously iron has higer density than water.
You do not need any figure to support the fact.

3. Any metal, eg. iron, aluminum.
Hig thermal conductivity means any material which is a good thermal conductor. You can find a lot of good thermal conductors around you. You should think a few more yourself.

1) Physical change (no change in the molecules, they just mixed up)
2) Density of iron > water, If A flow on water, then density of A < water
3) Sliver, copper, gold, and others metals