topic 15.2 - Entropy and spontaneity

Question 1

Entropy

Answer 1

The measure of how much disorder is present: how many different arrangements the molecules can have (ie molecules in ice have significantly fewer possible arrangements than steam)

Question 2

Entropy changes

Answer 2

∆S (reaction) = ∆S (products) - ∆S (reactants)

Remember to multiply by the correct number and use the correct molecule (if 5H₂O (g) is in the reaction, use the value for steam and multiply it by 5)

Question 3

Spontaneity

Answer 3

If ∆S (total) (found by combining ∆S (system) and ∆S (surroundings)) > 0 then the reaction is spontaneous

If ∆G is negative then the reaction is spontaneous

Question 4

Spontaneity table

Answer 4

∆H - ∆S - ∆G - Spon? - Temps?

Exo - Dis - Neg - Always - All temps
(-/<0) (+/>0) (-)

Exo - Order - Neg - dependent - Low temps
(-/<0) (-/<0) (-)

Endo - Dis - Neg - dependent - High temps
(+/>0) (+/>0) (-)

Endo - Order - Neg - never - All temps
(+/>0) (-/<0) (-)