Exothermic?

[freesolo]

K i need some clarification with some thermodynamics stuff. You break bonds its exothermic, you make bonds endothermic? p 113 the note has it the other way break bonds endothermic, make bonds exothermic. Than is has a positive change in enthalpy(endothermic) for vaporization sublimation and fusion.

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[VPDcurt]

In order to break bonds, you need to add heat to the system so it is therefore endothermic i believe. Think about boiling water. Anyone else want to clarify/correct me?

 

[BisMuOxo]

In order to break bonds, you need to add heat to the system so it is therefore endothermic i believe. Think about boiling water. Anyone else want to clarify/correct me?

Absolutely correct.

Make a bond--Release of Energy--exothermic
Break a bond--Requires Energy--Endothermic

Think about it this way:

A bond forms because it will lower the energy of a system. This energy has to go somewhere (conservation of energy), and it is often released as heat. When heat is released, a process is exothermic.

 

[grw0o]

That makes sense, but what gets me is when thinking about this with ATP.

ATP ---> ADP is breaking a bond so this is an endothermic reaction and requires the input of energy.

However ATP is intuitively thought to deliver energy and the fuel source for the body. So this doesn't make sense, can someone clarify this a little better?

 

[VPDcurt]

That makes sense, but what gets me is when thinking about this with ATP.

ATP ---> ADP is breaking a bond so this is an endothermic reaction and requires the input of energy.

However ATP is intuitively thought to deliver energy and the fuel source for the body. So this doesn't make sense, can someone clarify this a little better?

This is correct I believe. The hydrolysis of ATP is therefore coupled to other more favorable reactions, making the overall reaction one that yields energy.

 

[ComicBookHero20]

okay well here it is, yes u need energy to break bonds, and energy is released when bonds form

now there is a delta H for all rxns of this type, which equals delta H of ur reactants - delta H of ur products

now why we use ATP is because that delta H for the rxn is really exothermic, that delta H = -7 kcal/mol (7 kcal are released)

so yeah u put in energy to break off that phosphate but the energy released after is sooo great that its used to power the cell

Im gonna use ADP--Pi instead of ATP

ADP--Pi -> ADP + Pi + 7kcal/mol

u need energy to break the bond (so this part is endothermic), but on the products side, its exothermic bc of the energy that is released, and the net reaction is VERY exothermic