Question

1/2 mole CCl4 @ 25 C was mixed with 1/2 mole CH2Cl2 @ 25C. The final T was 27 C. Calculate delta S mixing, delta S for CCl4 on heating, delta S for CH2Cl2 on heating, and delta S system. Assume 131.8 J/K for Cp for CCl4 and 100.0 J/K for Cp for CH2Cl2.

Answer 1

I assume that is 131.8 and 100.0 J/K*mol.

dS_mix =
-R(n_i*ln x_i where n_i and x_i stand for mols and mol faction of the components.
dS_mix = -8.314[(1*0.5*ln 0.5) + (1*0.5*ln 0.5)] = +5.763 J/K

q CCl4 = mass x Cp x (Tf-Ti)
q = 0.5 mol x 131.8 J/K*mol x 2 = 131.8 J
dS = q/299 = 0.441 J/K.

q CH2Cl2 = 0.5 mol x 100.0 x 2 = 100.0 J
dS = q/299 = 0.334 J/K.

dS_system = 5.763 + 0.441 + 0.334 = 6.538 J/K.