The energy absorbed by the system before the reaction start has been 752 kJ/mol.
The bond energy has been defined as the energy possessed by the bond that has been converted into the heat energy and utilized in the reaction.
The energy has been conserved in a chemical reaction. Thus, the energy absorbed by the reactant in the reaction has been the difference in the energy of the reactant and product.
The given reaction has been:
[tex]\rm H_2\;+\;CO_2\;\rightarrow\;CH_2O_2[/tex]
The bond energy of the reactant has been:
H-H bond energy = 432 kJ/mol
2 C=O bond energy= 799 kJ/mol
The total energy of the reactant has been 432 kJ/mol + 799 kJ/mol
The total energy of the reactant has been 1231 kJ/mol
The bond energy of the product has been:
C-O bonds = 358 kJ/mol
C=O bonds = 745 kJ/mol
1 C-H bond = 413 kJ/mol
1 O-H bond = 467 kJ/mol
The total energy of the product has been 358 + 745 + 413 + 467 kJ/mol
The total energy of the product has been 1,983 kJ/mol
According to the law of conservation of energy:
[tex]\text{Product energy=Reactant energy + energy absorbed}[/tex]
Substituting the values for energy absorbed:
[tex]\text{1,983 kJ/mol=1231\;kJ/mol+ energy absorbed}\\\rm Energy\;absorbed=1983-1231\;kJ/mol\\Energy\;absorbed=752\;kJ/mol[/tex]
The energy absorbed by the system before the reaction start has been 752 kJ/mol.
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