What is the total energy change for the following reaction: 2H2 + O2 -> 2H2O?

Given:
H-H bond: 436 kJ/mol
O-O double bond: 499 kJ/mol
H-O bond: 463 kJ/mol

A. -481 kJ/mol
B. + 445 kJ/mol
C. +63 kJ/mol
D. -730.5 kJ/mol

From the options provided the total energy change for the reaction :

 =  ( A ) ; - 481 kJ/mol

The Total energy change ( Δ ) in a reaction is calculated as  difference in energies between the reactants and products i.e.

Reactants Energy

= 2 * ( 436 kJ/mol ) + 1 * ( 499 kJ/mol )

= ( 872 + 499 ) kJ/mol  = 1371 kJ/mol

Product energy

= 4 * ( 463 ) kJ/mol

= 1852 kJ/mol

Hence Total energy ( )

= ( 1371 - 1852 ) kJ/mol

= -481 kJ/mol

Also from the results obtained we can conclude that the reaction is an endothermic reaction

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Explanation:

You calculate the energy required to break all the bonds in the reactants.

Then you subtract the energy needed to break all the bonds in the products.

                       2H₂  +  O₂ ⟶ 2H₂O

Bonds:          2H-H   1O=O     4O-H

D/kJ·mol⁻¹:     436     499        463

it is the most commonly accepted one