AP Chemistry -- Entropy Third Law Calculations Worksheet
1. When solid potassium iodide is dissolved in water, a cooling of the mixture occurs because the solution process is endothermic for these substances. Explain, in terms of what happens to the molecules and ions, why this mixing occurs spontaneously?

2. Will the entropy change for each of the following be positive or negative?
    (a) Moisture condenses on the outside of a cold glass. 
    (b) Raindrops form in a cloud. 
    (c) Gasoline vaporizes in the carburetor of an automobile engine. 
    (d) Air is pumped into a tire. 
    (e) Frost forms on the windshield of your car.
    (f) Sugar dissolves in coffee.

3. In animated cartoons, visual effects are often created (for amusement) that show events that ordinarily don't occur in real life because they are accompanied by huge entropy decreases. Can you think of an example of this? Explain why there is an entropy decrease in your example. (Hint: The coyote and roadrunner cartoons are excellent references for this question.)

4.  Predict the algebraic sign of the entropy change for the following reactions?

     (a)  PCl3(g)  + Cl2(g) ----> PCl5(g)

    (b) SO2(g) + CaO(s) -----> CaSO3(s)

    (c) CO2(g) + H2O(l) ----> H2CO3(aq)

    (d)  Ni(s)  + 2 HCl(aq)  ------->  H2(g)   + NiCl2(aq)

5. Calculate the entropy change in J/K for each of the following reactions.

     (a) CaO(s) + 2 HCl(g) ---> CaCl2(s) + H2O(l)

     (b) C2H4(g) + H2(g) ---> C2H6(g)

6.  Calculate So (in J/K) for the following reaction.

    (a) H2O(l) + SO3(g) ---> H2SO4(l)

    (b) 2 KCl(s) + H2SO4(l) ---> K2SO4(s) + 2 HCl(g)

    (c) C2H4 + H2O(g) ---> C2H5OH(l)