Cu^IIS^-II + 8 HN^VO₃ → Cu^IN^VO₃ + H₂S^VIO₄ + 7 N^IVO₂ + 3 H₂O

This is an oxidation-reduction (redox) reaction:

Cu^II + e^- → Cu^I (reduction)

S^-II - 8 e^- → S^VI (oxidation)

7 N^V + 7 e^- → 7 N^IV (reduction)

CuS is an oxidizing agent, CuS is a reducing agent, HNO₃ is an oxidizing agent.