What is the difference between a single replacement reaction and a double replacement reaction?

Answer 1

A single replacement is of the form A + BC ==> AC + B

Here you usually have an element (A) replacing another element (B) that is part of a compound BC. The end result is the free element B, and the new compound AC. It should be noted that a single replacement only occurs if the free element (A in this example) is more reactive than B. Consult an activity series table. For example if A if more reactive than B, then the following reaction will not occur: B + AC ==> BC + A (no rx)

A double replacement is of the form AB + CD ==> AD + CB

Here, you have the two cations (A and C) exchanging places with the anions B and D forming two new compounds.