stability versues enthalpy

[rickrun]

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Okay, I'm confused. Some practice questions I've been reading say that a less stable compound will release more heat when reacting with oxygen because it has more potential energy. This makes sense, and an energy diagram seems to confirm that since the reactant will be at a higher energy if it is less stable.

But then I remember that the bond energy (bond dissociation energy) of more stable compounds will be higher, meaning it requires more energy to break apart. Aren't these counterintuitive ideas?

The only explanation I can think of is that the bond dissociation energy is really the activation energy, which WOULD be larger for a more stable compound. Is that right?

ANY input would be great! Thanks 🙂

 

[V5RED]

Okay, I'm confused. Some practice questions I've been reading say that a less stable compound will release more heat when reacting with oxygen because it has more potential energy. This makes sense, and an energy diagram seems to confirm that since the reactant will be at a higher energy if it is less stable.

But then I remember that the bond energy (bond dissociation energy) of more stable compounds will be higher, meaning it requires more energy to break apart. Aren't these counterintuitive ideas?

The only explanation I can think of is that the bond dissociation energy is really the activation energy, which WOULD be larger for a more stable compound. Is that right?

ANY input would be great! Thanks 🙂

There is no contradiction.

Bond energy is how much energy it takes to break a bond or how much energy is released when a bond is formed.

A more stable bond requires more energy to break and releases more energy when formed.

A less stable bond requires less energy to break and releases less energy when formed.

Combustion reactions lead to very stable products from relatively unstable reactants. The more unstable the reactants, the less energy must be spent to drive the reaction and the more net energy is released.

 

[shaboobly]

as you can see the bonding of hydrogen is at the minimum, even though the magnitude is greatest.

 

[rickrun]

Cool that makes perfect sense. I was thinking of both those concepts without looking at the big picture.

Thanks guys