Question

Use the bond energies to answer the question.

H–H = 432
H–O = 467
O=O = 495

Two H2 molecules combine with one O2 molecule, forming two water molecules (H2O) bonded as such: H–O–H. Which option shows the difference in total bond energy between the reactants and the products?

1,359

–7

–509

1,868

Answer 1

The reaction is given by

$\\ \sf\longmapsto {H_2\atop 432}+{O_2\atop 495}\longrightarrow {H_2O\atop 467\times 2=934}$

Now

Simplify energies

$\\ \sf\longmapsto {H_2+O_2\atop 432+495=927KJ/mol}={H_2O\atop 934KJ/mol}$

As we know

$\boxed{\sf \Delta H=\Delta H_1-\Delta H_2}$

• Here H_1 is energy of reactants and H_2 is energy of products

Lets find

$\\ \sf\longmapsto \Delta H=927-934$

$\\ \sf\longmapsto \Delta H=-7KJ/mol$

As $\Delta H$ is -ve its an exothermic reaction.

Option B is correct