Entropy represents the quantity of a system's thermal energy that couldn't be converted into mechanical work.
Concept #1: Entropy represents the amount of disorder, chaos or randomness in our system.
Concept #2: As the distance between molecules increases there will be an increase in entropy.
Concept #3: When comparing the entropy of ionic compounds it is best to examine their lattice energies.
Example #1: Predict the sign of entropy for each of the following processes?
a) I2 at 90oC and 5.0 atm → I2 at 50oC and 10.0 atm
b) NH4Cl(s) → HCl(g) + NH3(g)
c) CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l)
Example #2: When an aqueous solution containing Al3+ at 25°C is mixed with an aqueous solution of hydroxide at 25°C an immediate precipitate of insoluble aluminum hydroxide is formed:
Al3+ (aq) + 3 OH – (aq) → Al(OH)3 (s)
Practice: Which of the following has the greatest entropy, S?