User:ChrisChiasson/Sandbox

Consider an ideal mixture undergoing equilibrium change between solid and liquid phases of its solvent. The total differential of the Gibbs free energy of the mixture in this case is:


 * $$d G = V d P - S d T + \sum_i \mu_i d N_i \,$$.
 * $$G$$ is the Gibbs free energy
 * $$V$$ is the volume
 * $$P$$ is the pressure
 * $$S$$ is the entropy
 * $$i$$ is an integer indicating a chemical species
 * $$\mu_i$$ is the chemical potential of species $$i$$
 * $$N_i$$ is the particle number of species $$i$$

According to the second law, Gibbs free energy is minimized at equilibrium for constant temperature and pressure:


 * $$\mathrm{d}U = \delta Q - \delta W + \sum_i \mu_i d N_i\,$$
 * $$\mathrm{d}U = \delta Q - P d V + \sum_i \mu_i d N_i\,$$

http://www.chem.arizona.edu/~salzmanr/480a/480ants/colprop/colprop.html

http://antoine.frostburg.edu/chem/senese/101/solutions/faq/thermo-explanation-of-freezingpoint-depression.shtml

http://www.martin.chaplin.btinternet.co.uk/collig.html

http://phasediagram.dk/chemical_potentials.htm saying that the gibbs free energy is equal is equivalent to saying that the chemical potential is equal because the freezing process happens at a specified temperature (and associated pressure), the chemical potential is equivalent to the partial derivative of the gibbs free energy with respect to particle number, and the gibbs free energy is an extensive property, meaning:

gibbs_ice/N_ice = mu_ice = gibbs_water/N_water = mu_water

where may i go from here?

i think i am supposed to assume that if there are impurities present, that they also assume the same chemical potential as the water - but i don't know

i haven't seen - or don't remember a very detailed derivation of the freezing point depression, which is actually why i am writing this scratch page; i want to see if i can come up with the relation

lets consider a solution

in an ideal (what i believe debeye calls classical) solution, the effect of the solute on the chemical potential of the solvent is mathematically (though i have seen no derivation) related to the mole fraction (equivalently number fraction -- strangely the English translation of debeye's paper calls this concentration)


 * $$\mu_{solvent} = \mu_{solvent,ideal}({pressure},{temperature}) + k_B T \ln(x_{solution})$$

another good page for freezing point depression