Question

a. Calculate delta S rxn (in J/K) for the disolusion of calcium floride in water

CdF2 (s) = Cd-2 (aq) + 2F- (aq)

substance                  S (J. mol^-1.K^-1)

CdF2 (s)                           77.38

Cd2+ (aq)                        -73.2

F^-   (aq)                            -13.8

............................ J/K

b. Solvated ion ...........................(are/are not) pure substances so they ............................(do/ do not) necessarly have to abide by the particular conditionof the third law of thermodynamics.. Some ions bind water molecules in spheres of hydration or they may bind to the protons of hydroxide ions in water. This means that for some aqueous ions the hydrated ion is ..........................(more/less) ordered than separate ions and water molecules which gives rise to negative S values.

c. Using simple statistical mechanics assumptions going from an ordered solid state to a dilute dissolved state .................... (increases/decreases/ does not affect) the number of accessible microstates for the ions. You might expect delta Srxn to be ..................... (positive/negative). Howeverthe system (solution) does not merely consists of ions (the solute). The S in the table indicates that in this case the ions......................... (bind to/ do not interact with) the water molecule which .....................(increases/decreases/ does not affect)energy. Since the overall entropy change is ........................... (positive/negative) the loss of entropy in the water must be .......................... (greater than/less than) the gain of entropy for the ions.