5 Cu + 4 H2SO4 → Cu2S + 3 CuSO4 + 4 H2O
This is an oxidation-reduction (redox) reaction:
3 Cu0 - 6 e- → 3 CuII (oxidation)
2 Cu0 - 2 e- → 2 CuI (oxidation)
SVI + 8 e- → S-II (reduction)
Cu is a reducing agent, Cu is a reducing agent, H2SO4 is an oxidizing agent.