AB + CD → AD + CB

Where:

* A and C are cations (positively charged ions)

* B and D are anions (negatively charged ions)

Explanation:

In a double displacement reaction, the cations and anions of two reactants switch places. This results in the formation of two new compounds.

Conditions for Double Displacement Reactions:

* Formation of a precipitate: One of the new products must be an insoluble solid (precipitate).

* Formation of a gas: One of the new products must be a gas.

* Formation of water: One of the new products must be water (H₂O).

Examples:

* Precipitation reaction:

AgNO₃ (aq) + NaCl (aq) → AgCl (s) + NaNO₃ (aq)

* Gas evolution reaction:

Na₂CO₃ (aq) + 2HCl (aq) → 2NaCl (aq) + H₂O (l) + CO₂ (g)

* Neutralization reaction:

HCl (aq) + NaOH (aq) → NaCl (aq) + H₂O (l)

Note: Not all double displacement reactions will occur. The reaction will only proceed if one of the conditions listed above is met.