Question

If energy required to dissociate 16 g of gaseous
hydrogen into free atoms is 3488 kJ at 25°C then
the bond energy of H - H bond will be
[NCERT Pg. 177]
(1) 384 kJ/mol
(2) 436 kJ/mol
3) 384 J/mol
(4) 436 J/mol​

Answer 1

Answer:

The reaction involved is,

H

2

(g)→2H(g)

ΔH=H-H bond energy

Since, moles =

molecular mass of compound

mass of compound

• So, moles of H

2

=

2

4

=2

Hence, energy required to break 4gm or 2 moles of H

2

into gaseous atoms = 208Kcal=2×H-H bond energy

H-H bond energy = 104Kcal

Hence, answer is option c

Answer 2

Given: Energy required to dissociate 16 g of gaseous hydrogen into free atoms is 3488 kJ at 25°C.

To find: The bond energy of H - H bond.

Solution:

• The reaction of gaseous hydrogen converting into free atoms is given as,

        $H_{2} (g) -> 2H (g)$

• The number of moles of the gaseous hydrogen is calculated by dividing the mass of the compound by the molecular mass of the compound.
• So, the number of moles is,

        $n = \frac{16 g}{2 g}$

            $= 8 moles$

• Now, the energy required to dissociate 8 moles of hydrogen molecule to free atoms must be equal to 8 times the bond energy between the hydrogen atoms.

        $3488 kJ = 8 * E_{bond}$

        $E_{bond} = 436kJ/mol$

Therefore, the bond energy of H - H bond will be 436 kJ mol⁻¹.