Question

The value of ΔHO—H is 109 kcal mol⁻¹ . Then formation of one mole of water in gaseous state from H (g) and O (g) is accompained by : 

(a) absorption of 218 kcal of energy 

(b) release of 218 kcal of energy 

(c) release of 109 kcal of energy 

(d) unpredictable

Answer 1

Correct option (b) release of 218 kcal of energy

Explanation:

In water 2(O—H) bonds are formed. 

So the value of ΔH for the formation of one mole of water in gaseous state is 

ΔH = −2 × 109 = −218 kcal