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The energy absorbed by each molecule ($A_2$) of a substance is $4.4\times10^{-19}$ J and bond energy per molecule is $4.0\times10^{-19}$ J. The kinetic energy of the molecule per atom will be
A
$4.0\times10^{-20}$ J
B
$2.0\times10^{-20}$ J
C
$2.2\times10^{-19}$ J
D
$4\times10^{-19}$ J
Detailed Solution
Of the energy absorbed by a molecule, a part equal to the bond energy is used to break the A–A bond; the rest appears as kinetic energy of the two atoms.
Kinetic energy per molecule = energy absorbed − bond energy = $4.4\times10^{-19} - 4.0\times10^{-19} = 0.4\times10^{-19}$ J
Each $A_2$ molecule gives two atoms, which share this energy equally.
Kinetic energy per atom = $\frac{0.4\times10^{-19}}{2} = 0.2\times10^{-19}$ J
$= 2.0\times10^{-20}$ J
Kinetic energy per molecule = energy absorbed − bond energy = $4.4\times10^{-19} - 4.0\times10^{-19} = 0.4\times10^{-19}$ J
Each $A_2$ molecule gives two atoms, which share this energy equally.
Kinetic energy per atom = $\frac{0.4\times10^{-19}}{2} = 0.2\times10^{-19}$ J
$= 2.0\times10^{-20}$ J