Question

Which of these redox reactions is spontaneous as written? (a)Ag + Cu2+ → Ag+ + Cu (b)Al + H+ → Al3+ + H2 (c)H2 + Al3+ → H+ + Al (d)Na + K+ → Na+ + K

Answer 1

The answer is Al + H+ → Al3+ + H2
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Answer 2

Answer: The correct answer is Option b.

Step-by-step explanation:

The given reactions are the examples of single displacement reactions.

Single displacement reactions are defined as the reactions in which more reactive metal replaces the less reactive metal from its chemical reaction. The reactivity of metals is given by the series known as reactivity series.

The metals which lie above in the series can replace the metals which lie low in the reactivity series.

`A+BX\rightarrow AX+B`

For the given options:

Option a:
`Ag+Cu^(2+)\rightarrow Ag^++Cu`

Silver lies low in the series than copper and hence is less reactive. Therefore, it will not replace copper. Thus, this is a non-spontaneous reaction.

Option b:
`Al+H^+\rightarrow Al^(3+)+H_2`

Aluminium lies above in the series than hydrogen and hence is more reactive. Therefore, it will easily replace hydrogen. Thus, this is a spontaneous reaction.

Option c:
`H_2+Al^(3+)\rightarrow H^++Al`

Hydrogen lies low in the series than aluminium and hence is less reactive. Therefore, it will not replace aluminium. Thus, this is a non-spontaneous reaction.

Option d:
`Na+K^+\rightarrow Na^++K`

Sodium lies low in the series than potassium and hence is less reactive. Therefore, it will not replace potassium. Thus, this is a non-spontaneous reaction.

Hence, the correct answer is Option b.