Which of the following reactions is not spontaneous? Cu (s) + 2HCl (aq) → CuCl2 (aq) + H2 (g) Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2(g) 2Ni (s) + H2SO4 (aq) → Ni2SO4 (aq) + H2 (g) 2Al (s) + 6HBr (aq) → 2AlBr3 (aq) + 3H2 (g) Zn (s) + 2HI (aq) → ZnI2(aq) + H2 (g)

Answer : The reaction not spontaneous is:

Explanation :

The given reactions are the examples of single displacement reactions.

Single displacement reactions : It is defined as the reactions in which most reactive metal displaces the least reactive metal from its chemical reaction. The reactivity of metals is given by the series known as reactivity series.

That means the metals that lie above in the series can replace the metals which lie low in the reactivity series.

For the given options:

Option A :

Copper lies low in the series than hydrogen and hence is less reactive. So, it will not displace hydrogen. Thus, this is a non-spontaneous reaction.

Option B :

Magnesium lies above in the series than hydrogen and hence is more reactive. So, it will easily displace hydrogen. Thus, this is a spontaneous reaction.

Option C :

Nickel lies above in the series than hydrogen and hence is more reactive. So, it will easily displace hydrogen. Thus, this is a spontaneous reaction.

Option D :

Aluminum lies above in the series than hydrogen and hence is more reactive. So, it will easily displace hydrogen. Thus, this is a spontaneous reaction.

Option E :

Zinc lies above in the series than hydrogen and hence is more reactive. So, it will easily displace hydrogen. Thus, this is a spontaneous reaction.

Hence, the reaction not spontaneous is: