Standard state represents a 1M solution. The chemical potential of a component A (GA) is equal to the chemical potential at the standard state plus RT ln[A]
At [A] = 1M, GA = GA
Consider moving molecule A from one side of a membrane through which A can pass (region 1) to the other (region 2).
The free energy of moving A out of region 1 is given by
The free energy of moving A into region 2 is given by
Overall,
Thus, if the concentration of A in region 2
is lower than in region 1, 
G is negative and the process
is favorable. On the other hand, if the concentration of A in
region 2 is higher than in region 1, G is positive
and the process is unfavorable
G' and 
