A Single replacement reaction(also known as compostion reaction) is when one element replaces another element in a compound. There are two different possibilities:

1. One cation replaces another. When it is written in generic symbols, it is:

AX + Y ---> YX + A

Element Y has replaced A (in the compound AX) to form a new compound YX and the free element A. Remember that A and Y are both cations (postively-charged ions) in this example.

Some examples are:

1) Cu + AgNO3 ---> Ag + Cu(NO3)2 2) Fe + Cu(NO3)2 ---> Fe(NO3)2 + Cu 3) Ca + H2O ---> Ca(OH)2 + H2 4) Zn + HCl ---> ZnCl2 + H2

2. One anion replaces another. Written using generic symbols, it is:

A + XY ---> XA + Y

Element A has replaced Y (in the compound XY) to form a new compound XA and the free element Y. Remember that A and Y are both anions (negatively-charged ions) in this example.

Some of the only examples that involve halogens are here, so here are the two examples:

1) Cl2 + NaBr ---> NaCl + Br2 2) Br2 + KI ---> KBr + I2

In single replacement, one reactant is always an element. It does not matter if the element is written first or second on the reactant side. The other reactant will be a compound.

Typically, you will be given the left-hand (reactant side) and asked to provide the products to the reaction. You need to be able to recognize single replacement reactions AND be able to break a formula apart into proper cations and anions as well as write correct formulas

NANNER