Question

Select the reaction(s), in which energy need to be provided

• A. $S^{-}\left(g\right)\to S^{2-}\left(g\right)$
• B. $N{a}^{+}\left(g\right)+C{l}^{-}\left(g\right)\to NaCl\left(s\right)$
• C. $N\left(g\right)\to N^{-}\left(g\right)$
• D. $A{l}^{2+}\left(g\right)\to A{l}^{3+}\left(g\right)$

Answer 1

Answer: (A), (C), (D)

$A{l}^{2+}\left(g\right)\to A{l}^{3+}\left(g\right)$

(a) Here the incoming electron will face repulsion, since we are adding the electron in an anion, thus we need to provide energy in this case.

(b) $N{a}^{+}\left(g\right)+C{l}^{-}\left(g\right)\to NaCl\left(s\right)$
Here both the ions are geeting stabilized by forming the $NaCl$ solid. Hence energy will be released in this process.

(c) Again nitrogen has a stable electronic configuration ($1s^{2}2s^{2}2p^3$ and electron density in nitrogen is very high. Thus We will need to provide energy to add an electron in the nitrogen atom.

(d) After loosing $2e^{-}$, aluminium will spontaneously lose $3^{rd}$ electron, as after that it will attain stable noble gas configuration. But we need to provide energy to carry out this reaction also as we are removing an electron from an cation.