bond enthalpy vs heat of formation

[thebillsfan]

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why can the heat of formation of oxygen be zero, yet the bond enthalpy not be zero? why is there a discrepancy? I realize bond enthalpy is bond energy so obviously it cant be zero...but why do we consider the formation of gaseous oxygen to have be zero?

 

[wanderer]

Think about the reaction that is represented by bond disassociation and the reaction represented by formation.

 

[thebillsfan]

I came across this relating to the equation H=U+PV...EK said regarding this equation that since we consider pressure to be the random translational kinetic energy, enthalpy actually counts this KE twice.

Why would random translation KE be counted twice?

 

[wanderer]

I don't understand what you are saying.

Anyhow, bond disassociation for O2 would be represented by O2----->O + O. formation is represented by O2-----> O2