1)       Consider each of the following pairs of substances and predict which will have the greatest entropy, explaining your choice.

a)       Dry ice (CO₂(s)) or carbon dioxide gas

b)       Pure alumina, Al₂O₃ , or ruby, Al_2-nCr_nO₃ (that is, some of the Al atoms are replaced with Cr atoms)

c)       C₂H₄(g) or N₂(g)

d)       H₂SO₄(aq) or H₂SO₄(l)

2)       Is the following reaction spontaneous?

Si(s) + 2 Cl₂(g)  "  SiCl₄(g)

DH⁰(SiCl₄) = -662.75 kJ mol^-1

DS⁰(SiCl₄) = 330.86 J K^-1 mol^-1

1)       Heating some metal carbonates leads to their decomposition.  For example:

MgCO₃(s)  "  MgO(s) + CO₂(g)

a)       Calculate DH⁰ and DS⁰ for the reaction.

b)       Is the reaction spontaneous at 298 K?

c)       Is the reaction predicted to be spontaneous at higher temperatures?  If so, what is the lowest temperature it will become spontaneous?

2)       “Heater Meals” are food packages that contain their own heat source.  Just pour water into the heater unit, wait a few minutes, and you have a hot meal.  The heat for the heater unit is developed by the reaction of magnesium with water.  Confirm that this is a spontaneous reaction.

Mg(s) + 2 H₂O(l)  "  Mg(OH)₂(s) + H₂(g)

DG^o_f (Mg(OH)₂) = -833.51 kJ mol^-1

1)       Methanol is now widely used as fuel in race cars.  Consider the following reaction for the production of methanol:

C(graphite) + ½ O₂(g) + 2 H₂(g) "  CH₃OH(l)

Calculate the Kp for the formation of methanol at 25^oC using this reaction.  Would a different temperature be better for this reaction?  Comment on the relationship between the sign of DG and the magnitude of K_p.

2)       Calculate DG^o and K_sp for the dissolution of barium sulfate in water at 25^oC given the following information:

DG^o_f (BaSO₄) = -1353 kJ/mol
DG^o_f (Ba²⁺) = -561 kJ/mol
DG^o_f (SO₄^2-) = -742 kJ/mol

1)       A cave in Mexico was recently discovered to have some interesting chemistry.  Aqueous hydrogen sulfide, H₂S, reacts with oxygen gas in the cave to give aqueous sulfuric acid, which drips from the ceiling in droplets with a pH less than 1. 

a)       Calculate DH^o, DS^o, and DG^o at 25^oC.

b)       Is the reaction product-favored?

c)       Is the reaction entropy- or enthalpy- driven?