Question

The process that is $NOT$ endothermic in nature is :-

• A. $Ar _{( g )}+ e ^{-} \rightarrow Ar _{( g ) }^{-}$
• B. $H _{( g )}+ e ^{-} \rightarrow H _{( g ) }^{-}$
• C. $Na _{( g )} \rightarrow Na _{ g }^{+}+ e ^{-}$
• D. $O _{( g )}^{-}+ e ^{-} \rightarrow O _{ ( g ) }^{2-}$

Answer 1

The Correct Option is B

To determine which process is NOT endothermic, we need to understand what each of the given processes represents and their typical thermodynamic nature.

1. Ar_{(g)} + e^{-} \rightarrow Ar_{(g)}^{-}: This process involves the addition of an electron to an argon gas atom, which is a noble gas. Noble gases generally have full valence shells and do not favor gaining electrons. Thus, this process is endothermic as it requires energy to add an electron to a stable noble gas.
2. H_{(g)} + e^{-} \rightarrow H_{(g)}^{-}: In this process, an electron is added to a hydrogen gas atom. Hydrogen readily accepts an electron to form a hydride ion H^{-}, which often releases energy in the process, making it exothermic rather than endothermic. Hence, this is NOT an endothermic process.
3. Na_{(g)} \rightarrow Na_{g}^{+} + e^{-}: This is the process of ionization of sodium gas to form a positive ion. Ionization is typically endothermic because energy is required to remove an electron from a neutral atom.
4. O_{(g)}^{-} + e^{-} \rightarrow O_{(g)}^{2-}: Adding an extra electron to an already negative ion O^{-} requires additional energy due to electron-electron repulsion, making this process endothermic.

From the analysis, the most likely process that is NOT endothermic is H_{(g)} + e^{-} \rightarrow H_{(g)}^{-}, as it typically releases energy when hydrogen forms a hydride.

Thus, the correct answer is: H_{(g)} + e^{-} \rightarrow H_{(g)}^{-}.