The give reaction between sodium sulfide and copper nitrate to form sodium nitrate and copper sulfide is an example of double displacement reaction. In this reaction, one of the products is a solid and hence this is a precipitation reaction.
Word equation: Sodium sulfide(aq) + Copper nitrate(aq)-->Sodium nitrate(aq)+Copper sulfide(aq)
Chemical equation: [tex]Na_{2}S(aq)+Cu(NO_{3})_{2}(aq)-->CuS(s)+2NaNO_{3}(aq)[/tex]
