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**Unformatted text preview: **e fraction through the
activity coefficient γA:
aA
? A = x A , or a A = ? A x A.
Note that the textbook uses the symbol fA for activity coefficient of A. This causes
confusion with fugacity, which is also denoted by f. Therefore, I have chosen to
denote this quantity by the Greek letter γ (gamma).
Example 5.8, Problems: 5.34, 5.35. 6 5.5. Partial Molar Quantities
Partial Molar quantities are required to deal with open systems, i.e., systems that
permit mass transfer between themselves and surroundings.
Consider an open system with n1 moles of component 1, n2 moles of component 2,
n3 moles of component 3, etc.. We would write the free energy change dG for
such a system as
dG = æ ¹G ö
dP + æ ¹G ö
dT + æ ¹G ö
dn + ...
ç ¹n ÷
è ¹P ø T,n 1 ,n 2,...
è ¹T ø P,n 1 ,n 2,...
è 1 ø P,T,,n 2,... 1
= VdP − SdT + G 1 dn 1 + G 2 dn 2 + ...
In the second equality, the quantities G1, G2, etc.. are called partial molar free
energies. Similarly, we may define partial molar volumes, partial molar...

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