In chemical reactions, heat is converted into chemical energy (the potential ene

Question

In chemical reactions, heat is converted into chemical energy (the potential energy stored in chemical bonds) or vice versa. Thus, enthalpy change for a reaction can be approximated from:

where "D" represents bond dissociation energies of the reactants and products, respectively. The table below contains the bond dissociation energies for common bonds. The information can be used to calculate the energy needed to break all the bonds in a given molecule.

C-C 350

C=C 611

C-H 410

C-O 350

C-O 732

O-O 180

O=O 498

H-O 4

1- Calculate the bond dissociation energy for the breaking of all the bonds in a mole of methane, CH4.

2- What is the bond dissociation energy for breaking all the bonds in a mole of O2 molecules?

3- Calculate the bond dissociation energy needed to break all the bonds in a mole of carbon dioxide,CO2.

Explanation / Answer

CH4= 4(410)=1640kJ/mol

O2=1(498)=498kJ/mol

H2O=2(460)=920kJ/mol Therefore the enthalpy change for forming a mole of water is

?920 kJbut the correct answer is just 920kJ/mol

CO2=2(732)=1464kJ/mol

All the answers are writen in dimensions of enthelpy.

Hope this helps.

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