Question

An ideal solution is made from 6.0 moles benzene and 2.5 moles of toluene calculate delta G mixing at 298 K & 1 bar

Answer 1

Where x₁ is the mole fraction of benzene ,
x₂ is the mole fraction of toluene , 
n is the total number of moles 
R is the universal gas constant e.g., R = 25/3 J/Kmol
T is the temperature .

Now, x₁ = (n₁)/(n₁ + n₂) = 6/(6 + 2.5) = 6/8.5 = 12/17 
x₂ = n₂/(n₁ + n₂) = 2.5/(6 + 2.5) = 5/17 


n = n₁ + n₂ = 6 + 2.5 = 8.5 
R = 25/3 J/Kmol
T = 298K 
∴  = 8.5 × 25/3 × 298 [12/17ln(12/17) + 5/17ln(5/17)]
=12.5 × 298/3 [12ln(12/17) + 5ln(5/17) ] J 
= 12.5 × 298/3 × (-10.2985) = -12.787 kJ