Confusion Surrounding Entropy, Enthalpy, and Gibbs Free Energy

[SKaminski]

So, I've been reading through the chapters on Entropy and Gibbs Free Energy, and I've come to what seems like a paradox:

We're given the following equation (along with some explination):

(delta)S(system) + (delta)S(surroundings) = (delta)Suniverse > or = 0

So, for a reaction to proceed, the entropy change by must equal to or greater than zero. This is accompanied by an explanation that ONLY reactions that have ZERO entropy are truly reversible.

Next, while talking about Gibbs free energy:

(delta)G = (delta)H - T(delta)S

A following explinations states that reactions will only occur (spontaneously) if delta G is negative. Alright. Easy enough.

So, with these two rules in place, how can a graph show me that this a reaction can proceed under these circumstances:

G = H - TS
-....-......- (at low temperatures)

The logic is that a minusing a negative is positive, and at a low enough temperature this doesn't overcome enthalpy. However, since the entropy change is negative, how does the reaction proceed? It seems like it's violating its own rule?

----------------------

Also (and this is somewhat of a seperate question), can anybody provide me with a definition of enthalpy that doesn't rely on 'heat' or 'heat of reaction'? I'm having a really hard time understanding this concept appropriately.

Thank you so much for taking the time to read my post!

---

Members don't see this ad.

 

[Deadlifts]

So, I've been reading through the chapters on Entropy and Gibbs Free Energy, and I've come to what seems like a paradox:

We're given the following equation (along with some explination):

(delta)S(system) + (delta)S(surroundings) = (delta)Suniverse > or = 0

So, for a reaction to proceed, the entropy change by must equal to or greater than zero. This is accompanied by an explanation that ONLY reactions that have ZERO entropy are truly reversible.
So, with these two rules in place, how can a graph show me that this a reaction can proceed under these circumstances:

G = H - TS
-....-......- (at low temperatures)

The logic is that a minusing a negative is positive, and at a low enough temperature this doesn't overcome enthalpy. However, since the entropy change is negative, how does the reaction proceed? It seems like it's violating its own rule?

G = H - TS refers to the entropy internal. It does not violate the overall entropy of the universe. I can have a negative INTERNAL entropy change (dissolving sugar in water increases its entropy, evaporating that water off the sugar decreases its entropy). It depends on how you define the system (sugar molecules themselves vs. the cup vs. the room).

Also (and this is somewhat of a seperate question), can anybody provide me with a definition of enthalpy that doesn't rely on 'heat' or 'heat of reaction'? I'm having a really hard time understanding this concept appropriately.

Thank you so much for taking the time to read my post!

Enthalpy is the total thermodynamic potential of a system.

Have you taken physics with a thermodynamics component? I feel like the physics explanations of TD concepts are better qualitatively while chemistry can give you quantitative reaction approach.

 

[SKaminski]

YOU. ARE. AWESOME.

G = H - TS refers to the entropy internal. It does not violate the overall entropy of the universe. I can have a negative INTERNAL entropy change (dissolving sugar in water increases its entropy, evaporating that water off the sugar decreases its entropy). It depends on how you define the system (sugar molecules themselves vs. the cup vs. the room).

Makes perfect sense. Awesome.

Enthalpy is the total thermodynamic potential of a system.

Have you taken physics with a thermodynamics component? I feel like the physics explanations of TD concepts are better qualitatively while chemistry can give you quantitative reaction approach.

I have, but i graduated in 2011, so it's been a while. I'm reviewing with exam krackers, and supplement with Chad's Video's where needed. I havn't done chad's on physics/chem yet though, so that could explain the gap in my knowledge.

Thanks for the help again!