What happens to the atoms in substances when a chemical reaction occurs?

Which type of reaction always has an element and a compound as reactants

If two atoms are bonded to a central atom with no lone pairs,how will they be arranged

Alidded glass container is filled with a colored gas. after a period of time, it is observed that the gas is uniformly spread throughout the box and that the movement has slowed considerably. next, a warm iron plate is carefully placed under the box. why is there resumed movement of the gas in the container?