How do you recognize a double displacement reaction?

One of the products must be a solid precipitate, an insoluble gas, or water.

A double displacement (double replacement) reaction occurs when two aqueous ionic react to produce a solid precipitate, an insoluble gas, or water. If none of these are produced, then a double displacement did not take place.

The general equation for a double displacement reaction is ##"AX + BY"####rarr####"AY + BX"##, where ##"A"## and ##"B"## are cations, and ##"X"## and ##"Y"## are anions.

Examples of double displacement reactions.

##"BaCl"_2("aq")" + MgSO"_4("aq")"####rarr####"BaSO"_4darr"+ MgCl"_2("aq")"##

##"Na"_2"S(aq)" + "2HCl(aq)"####rarr####"H"_2"S"uarr"+ 2NaCl(aq)"##

##"HCl(aq)" + "NaOH(aq)"####rarr####"NaCl(aq)" + "H"_2"O(l)"##

The down arrow ##darr## indicates the formation of a solid precipitate, and the up arrow ##uarr## indicates the formation of a gas. You can also use the symbols ##("s")## and ##("g")##.