Single and Double displacement Rules

Single Displacement

A reaction where one element replaces another element in a compound.

• usually oxidation-reduction (redox) reactions

A(s)+BC(aq)→AC(aq)+B(s) (doesn’t always involve solids)

• A = a more reactive element that replaces B

• B = the displaced element

If A is not more reactive then B, no reaction occurs.

Single Displacement Rules

Write the balanced molecular equation

Break only aqueous ionic compounds into ions

• Do not split:

  • solids (s)

  • liquids (l)

  • gases (g)

Cancel spectator ions

Write the net ionic equation

• This shows the actual electron transfer.

The final net ionic equation should show:

• the element being oxidized

• the ion being reduced

• the actual chemical change

Double Displacement

Occurs when the ions of two aqueous ionic compounds exchange partners

AB(aq)+CD(aq)→AD+CB

• A and C are cations

• B and D and anions

A reaction occurs when one product is:

• a precipitate (s)

• water (l)

• a gas (g)

The net ionic equation shows only the particles that actually change.

Double Displacement Rules

Write the balanced molecular equation

Split aqueous strong electrolytes into ions

Split:

• soluble ionic compounds (aq)

• strong acids (aq)

• strong bases (aq)

Do not split:

• solids (s)

• liquids (l)

• gases (g)

Cancel spectator ions

Write the net ionic equation

The final equation should show only the species responsible for the reaction.

• the net ionic equation usually contains the new solid, water, or gas being formed.