Module 5 : Electrochemistry
Lecture 21 : Review Of Thermodynamics
 
Ex 21.4
Calculate the change in free energy when the pressure is increased from 1 atm to 10 atmospheres at 298 K for
One mole of liquid water.The molar volume of water is 18 cc.and
1 mole of water vapour.
 
Solution

Let Go be the free energy of the standard state at 298 K.

G - Go = 1200 VdP as the – SdT term = 0 for constant T
= 18 (10-1), cc. atm assuming the molar volume to be independent of pressure. If the volume is given as
a function of pressure in a formula such as V = V0 + aP + bP2 where a and b are coefficients which depend on temperature, this form of V can be substituted in the above equation to get G by integrating VdP.
For the vapour phase, assume ideal gas behaviour. For real gases, the actual equation of state is needed.
G vapour =VdP = nRT 1/P dP.
                = nRT ln (P2 /P1)
                = 0.08206 x 298 ln 10 lit atm.
                = 56.31 lit atm .
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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