Question

Explain why aluminum metal is used on the exterior of buildings yet a bottle of aluminum powder is labelled flammable.

Answer 1

Ans :

The rate of reaction depends on number of factors , one of them being the surface area of reactants. Higher the surface area of reagents , faster and vigourous is the reaction.

The reaction of aluminium with air (oxygen ) is highly exothermic. But the metal when used in the exterior of buildings has a protective oxide layer of aluminium oxide over it , which prevents the reaction of oxygen with the fresh aluminium metal. So the reaction doesn't occur vigourously as very less amount of aluminium is exposed to oxygen.

Now the aluminium powder is laboratories is pure , plus due to its fine texture , its surface area is greatly increased. So when this powder reacts with oxygen , it can lead to huge amount of release of energy. So it is labelled flammable.