Surface Chemistry - Result Question 28
####29. When $O _2$ is adsorbed on a metallic surface, electron transfer occurs from the metal to $O _2$. The true statement(s) regarding this adsorption is (are)
(2015 Adv.)
(a) $O _2$ is physisorbed
(b) heat is released
(c) occupancy of $\pi^{*} 2 p$ of $O _2$ is increased
(d) bond length of $O _2$ is increased
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Answer:
Correct Answer: 29. (c)
Solution:
- Since, adsorption involves electron transfer from metal to $O _2$, it is chemical adsorption not physical adsorption, hence $(a)$ is incorrect. Adsorption is spontaneous which involves some bonding between adsorbent and adsorbate, hence exothermic. The last occupied molecular orbital in $O _2$ is $\pi^{} 2 p$. Hence, electron transfer from metal to oxygen will increase occupancy of $\pi^{} 2 p$ molecular orbitals. Also increase in occupancy of $\pi^{*} 2 p$ orbitals will decrease bond order and hence increase bond length of $O _2$.
