Question

When bonds are formed, energy is released. in a water molecule, the two hydrogens are both bonded by single bonds to the central oxygen atom. the bond energy associated with an o–h bond is 463 kj/mol. again, using the balanced chemical equation shown above, how much energy is released in forming the o–h bonds?

Answer 1

The energy released in the process is $\boxed{ - {\text{1852 kJ/mol}}}$. The negative sigh depicts that energy is released.

Further explanation:

The chemical reaction that contains equal number of atoms of the different elements in the reactant as well as in the product side is known as balanced chemical reaction. The chemical equation is required to be balanced to follow the Law of the conservation of mass.

Stoichiometry of a reaction is used to determine the amount of species present in the reaction by the relationship between the reactants and products. It can be used to determine the moles of a chemical species when the moles of other chemical species present in the reaction is given.

Consider the general reaction,

 ${\text{A}} + 2{\text{B}} \to 3{\text{C}}$

Here,

A and B are reactants.

C is the product.

One mole of A reacts with two moles of B to produce three moles of C. Stoichiometric ratio between A and B is 1:2, the stoichiometric ratio between A and C is 1:3 and the stoichiometric ratio between B and C is 2:3.

A balanced chemical equation does provide a lot of quantitative data regarding the number of molecules of the reactant combining to form a particular product.

The balanced equation corresponding for the formation of water in which two molecules of hydrogen gas combine with dioxygen to form two moles of water molecules is as follows:

 $2{{\text{H}}_2} + {{\text{O}}_2} \to 2{{\text{H}}_{\text{2}}}{\text{O}}$

In one water molecule, there are two oxygen-hydrogen bonds so there would be formation of four oxygen-hydrogen bond as per the balanced reaction.

The energy liberated upon formation of one oxygen-hydrogen is $- 463{\text{ }}{\text{kJ/mol}}$. So, upon formation of four such bonds the energy liberated is calculated as follows:

 $\begin{aligned}{\text{Energy liberated }} &= {\text{4}} \times \left( { - {\text{463 kJ/mol}}} \right) \\&=- {\text{1852 kJ/mol}}\\\end{aligned}$

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Answer details:  

Grade: High School

Subject: Chemistry

Chapter: Periodic classification of elements

Keywords: Chemical reaction, balanced chemical equation,energy liberated,oxygen-hydrogen bond, dioxygen and -1852 kj.

Answer 2

The balanced chemical equation is:

2H2 + O2 → 2H2O

Based on the reaction stoichiometry:

2 moles of water are formed.

Each water molecule has 2 O-H. Thus, a total of 4 O-H bonds are formed.

Energy released/O-H bond = 463 kJ/mol

For 4 O-H bonds this would be= 4 * 463 = 1852 kJ

Ans: Thus, -1852 kJ (negative sign indicates that energy is released) in the forming of O-H bonds.