Gibbs Free Energy: Queries & Answers

[luysion]

Hi, I've recently started studying chemistry and have being going over gibbs free energy.. I understand it is a driving force causing chemical and physical changes but during my course of reading I did have some queries stem to mind.

1) In relation to equilibrium why is it that a reaction occurs such that G is minimum ? I.e. i read that the reason neither the forward nor reverse reaction proceeds to completion during equilibrium is because Gibbs Free Energy is at a minimum. Is this due to no driving force being provided?

2) When gibbs free energy is positive it indicates the forward reaction (e.g. A --> B) is non-spontaneous why does it still occur? I read something about the reaction still proceeds but the pressure of the product does not read 10^5 P i.e. standard pressure?
im really confused on this bit can someone please simplify this

cheers for any help

 

[neeraj93]

Equilibrium can be viewed as compromise between two opposing tendency of the system:
1. to attain minimum energy (enthalpy)
2. of maximum molecular chaos (entropy)
remember this equation,
$$\Delta$$G=$$\Delta$$H-T$$\Delta$$S
where $$\Delta$$H is the enthalpy change, $$\Delta$$S is the entropy change, and T is the temperature
A higher value of T$$\Delta$$S signifies greater spontaneity. So as this parameter increases, $$\Delta$$G becomes smaller and smaller. For Gibbs energy we have, -$$\Delta$$G$$\geq$$0. At equilibrium, the two tendencies mentioned above are equal. So, $$\Delta$$H=T$$\Delta$$S; & $$\Delta$$G=0.
To make a reaction with positive Gibbs energy occur, you just increase the temperature, that will increase the T$$\Delta$$S factor in the equation.