Question

What is the reaction of copper in $HCl$ ?

Answer 1

Metals have a tendency to react with water and acid. The reactions shown by various metals depend on their reactivity and their position in the reactivity series as compared to the other cation that they are trying to displace.

Complete answer:
Copper is a transition metal belonging to the eleventh group of the d-block. It has an outer electronic configuration of $4{s^1}3{d^{10}}$ . Copper forms a variety of complexes and compounds but in itself it is not very reactive in nature.
The reaction between copper metal and hydrogen chloride can be seen as a displacement reaction in which the copper ions try to displace the hydrogen ions present in the ionic compound $HCl$ .
Whether a reaction takes place or not and the vigour of the reaction is determined by the reactivity of the reactants involved.
Most metals that are more reactive than hydrogen ions tend to react with hydrochloric acid and form the corresponding metal chloride. Metals like sodium and potassium that occupy the top positions of the reactivity series react vigorously with acids and result in the evolution of hydrogen gas.
Copper ions are less reactive than hydrogen ions (copper occupies a position lower than hydrogen in the reactivity series) and are incapable of displacing them. Thus no visible change is observed in a test tube when copper turnings are mixed with concentrated hydrochloric acid. Also hydrogen gas is not evolved indicating the absence of a reaction.
Thus, copper metal does not react with $HCl$ .
$Cu + HCl \to {\text{ no reaction}}$

Note:
The reactivity of two reactants is dependent on the enthalpies of bond formation and bond dissociation. If the bonds of the reactants are stronger and more stable than the bonds formed in the product then the reaction does not take place in the forward direction.