The bond energy of an `O -H` bond is 109 K. cal `"mole"^(-1)`. When a mole of water is formed

Options

A. 109 kcal is released
B. 218 kcal is released
C. 109 kcal is absorbed
D. 218 kcal is absorbed

Answer

B

Explanation

Bond energy of O-H bond `=109 kcal // `mol means that whn 1 mole of O-H bonds are formed,109 kcal energy is released ( because dissociation of bond absorbs energy ). Formation of one mole of water is equivalent to formation of2moles of O-H bond ( H-O-H) . Hence,energy released `=2 xx 109=218 kcal`. ( Strictly speaking, we calculate `Delta_(f)H^(@) `for the reaction.
`H_(2)(g)+(1)/(2) O_(2)(g) rarr H_(2)O(l) .i.e., ( H-O-H)`
`Delta_(f)H^(@) =BE(H-H) + (1)/(2) BE(O=O)-2BE(O-H)`