Dissociation Energy

[Chocolatebear89]

I understand that it takes energy to break bonds, and energy is released when more stable bonds are formed.

Does that mean bonding forming is exothermic?
Is the energy to break bonds the same as dissociation energy?

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[Isoprop]

for the mcat, yes and yes. bond energy is sometimes called bond dissociation energy. it's often expressed in J/mol.

 

[PiBond]

I understand that it takes energy to break bonds, and energy is released when more stable bonds are formed.

Does that mean bonding forming is exothermic?
Is the energy to break bonds the same as dissociation energy?

you can use the bond energies to figure out whether a reaction is exothermic or endothermic based on the whether or not you are forming stronger bonds than you are breaking.

if you form stronger bonds than you broke, the reaction is exothermic
if you form weaker bonds than you broke, the reaction is endothermic

it's also worth noting that BDE (bond dissociation energy) is the energy needed to break a bond "homolytically" resulting in the generation of two radical species. it's not pertaining to heterolytic cleavage

 

[rls303]

you can use the bond energies to figure out whether a reaction is exothermic or endothermic based on the whether or not you are forming stronger bonds than you are breaking.

if you form stronger bonds than you broke, the reaction is exothermic
if you form weaker bonds than you broke, the reaction is endothermic

it's also worth noting that BDE (bond dissociation energy) is the energy needed to break a bond "homolytically" resulting in the generation of two radical species. it's not pertaining to heterolytic cleavage

So is the breaking of ATP bond more favorable because the exothermic energy in breaking the bond is greater than the endothermic energy required tobreak it?

 

[PiBond]

So is the breaking of ATP bond more favorable because the exothermic energy in breaking the bond is greater than the endothermic energy required tobreak it?

hydrolysis of ATP is favorable because we're increasing entropy and because the products are more stable than the reactants (there's more resonance structures for the products)

 

[rls303]

hydrolysis of ATP is favorable because we're increasing entropy and because the products are more stable than the reactants (there's more resonance structures for the products)

Ahh, so dG will be negative, indicating favorable reaction! Thanks !

 

[rls303]

hydrolysis of ATP is favorable because we're increasing entropy and because the products are more stable than the reactants (there's more resonance structures for the products)

So just wanted to confirm for hydrolysis of ATP:
dH + since adding energy to break the bond
dS= + (more molecules)
T (I'm assuming a pretty high temperature, but doesn't really matter)

but the dST term overpowers the dH and thus it yields a dG that is negative indicating a very favorable reaction.