Question

why copper only react with warm h2so4 not with conctrated h2so4?

Answer 1

Copper does not react with dilute sulphuric acid as its reduction potential is higher than that of hydrogen. Copper does not displace hydrogen from non-oxidising acids like HCl or dilute H2SO4.

But, concentrated sulphuric acid is an oxidising agent. So, when copper is heated with conc.H2SO4, a redox reaction occurs and the acid gets reduced to sulphur dioxide.

                          Cu + 2H2SO4 = CuSO4 + SO2 + 2H2O