What is the difference between ' empty ' and ' vacant '?

Empty means, there is nothing in a said area. Vacant mean, empty area ready to occupy.

vacant means some place where there is nobody.empty means some place where there is nothing inside

empty is no more space or there's noting on it

while vacant is available

So easy,

   empty is for concreet things

vacant is used for abstruct things 

- Vacant (of a seat, hotel room, house, etc.) empty; not being used - synonym = unoccupied

Examples: vacant properties - The seat next to him was vacant.

- Empty :with no people or things inside

Examples: An empty box / glass - empty hands (= not holding anything) - an empty plate (= with no food on it) - The theater was half empty.

empty is containing air or other gases while vacant is vacuum even with no air 

Vacant means something which is not occupied; Empty implies there is nothing.

vacant is not occupied; empty while empty is devoid of content; containing nothing or nobody; vacant. 

 (ergative) to make empty; to void; to remove the contents of. 

 a container, especially a bottle, whose contents have been used up, leaving it empty .

• Vacant of a seat, hotel room, house, etc

• Empty  with no people or things inside as box / glass

Vacant is room, look or seat

Empty is any glass, bottle or heart