Question

what is the difference between single displacement and double displacement reaction

Answer 1

A single replacement reaction involves an element replacing another element from its compound forming a new compound and a new element. To use an analogy, a compound is like a dancing couple. Suddenly another man comes up and taps the dancing man on the shoulder and asks to dance with the lady. If everyone agrees, the man who danced became replaced with another. 

Example: A + BC --> AC + B 

Zn(s) + CuCl2(aq) --> ZnCl2(aq) + Cu(s) 

A double replacement reaction usually involves mixing of solutions of two ionic compounds. When all the ions are mixed, usually positive ions from the first compound are very attracted to the negative ions from the second compound and form a solid that precipitates leaving the other positive and negative ions still in solution. To use an analogy, the first two compounds are like two dancing couples across a crowded room. Suddenly the man from the first couple, and the lady from the second couple fall in love at first sight, and decide to switch partners. In fact they are so in love that they leave a party together to be alone. 

Example: AB + CD --> AD + CB 

NaCl(aq) + AgNO3(aq) --> AgCl(s) + NaNO3(aq)

I hope you will understand....

Answer 2

Single displacement - one atom or a group of atom of a compound is replaced by another atom or a group of atoms .
Eg. CuSO4+ Fe ------FeSO4+Cu

Double displacement - two reacting compounds exchange their corresponding ions and form two new compounds
Eg. AgNO3+ NaCl -----AgCl + NaNO3