Endergonic & exergonic versus endothermic & exothermic

[549]

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Hi,

I have a question about what endergonic & exergonic versus endothermic & exothermic mean. I get that the first two deal with free energy changes and that the last two deal with enthalpy changes, but how do they look on a reaction coordinate? When I see products with less energy than the reactants, I think -∆H (exothermic) and -∆G (exergonic) and vice versa for endothermic and endergonic. I know that only when the T∆S factor is negligible can you say ∆G and ∆H are equal. Is there any way to tell from the reaction coordinate though if you're given no information about entropy?

Thanks.

 

[maverick09]

the only things we can deduce from a reaction coordinate are delta G and the energy of activation (how it changes with the presence of catalyst, etc). the reason that we can't know anything about enthalpy, as you said, is because we don't know anything about the entropy or temperature from the reaction coordinate.

hope this helps

 

[549]

But we can tell whether it is endothermic or exothermic too, by looking at the relative energies of the products vs. the reactants, right?

I guess another way to phrase the question is- Can a reaction be endothermic and exergonic (or exothermic and endergonic) and if so, how would they look on a reaction coordinate?

 

[inaccensa]

But we can tell whether it is endothermic or exothermic too, by looking at the relative energies of the products vs. the reactants, right?

I guess another way to phrase the question is- Can a reaction be endothermic and exergonic (or exothermic and endergonic) and if so, how would they look on a reaction coordinate?

Lets think about this change in enthalpy = Enthaply of the products - Enthalpy of the rectants. In other words energy change. If the products are at a higher energy than the products, u get exothermic reaction, since the product will be more stable. On the reaction coordinate, the energy of reactant will be higher on the graph and the energy of product will be much lower. for endothermic, it will be opposite.

 

[Izak]

Lets think about this change in enthalpy = Enthaply of the products - Enthalpy of the rectants. In other words energy change. If the products are at a higher energy than the products, u get exothermic reaction, since the product will be more stable. On the reaction coordinate, the energy of reactant will be higher on the graph and the energy of product will be much lower. for endothermic, it will be opposite.

Just wanted to make sure. Don't you mean that if the products are at a LOWER energy level, you get an exothermic rxn with heat being released?

 

[shaboobly]

Just wanted to make sure. Don't you mean that if the products are at a LOWER energy level, you get an exothermic rxn with heat being released?

yes