energetics

Question 1

Entropy

Answer 1

Entropy is the measure of the disorder of the system. It gives a measure of the extent to which particles and energy are distributed within the system.

Question 2

ΔSsystem =

Answer 2

Sproducts – Sreactants

Question 3

Units of entropy change, ΔS

Answer 3

J K–1 mol–1

Question 4

Factors causing ΔS

Answer 4

Change in temperature, phase, number of particles
Mixing of particles ( Troye produces nice music)

Question 5

Change in temperature

Answer 5

As temperature increases, KE of the system increases, -> more ways of arranging energy quanta in the hotter system -> increase in disorder & thus entropy

Question 6

Change in phase (no chemical change involved)

Answer 6

S -> L -> G
Orderly arrangement destroyed -> more ways to arrange particles -> more disorder -> increased entropy

Change from S/L -> G means larger volume -> more ways to arrange the gas particles -> gaseous state most disordered -> larger increase in entropy

Question 7

Change in the number of particles (priority given to gaseous particles)

Answer 7

Increased number of particles -> more ways of arranging the particles -> increased disorder -> increased entropy
Greater number of moles of product than reactant -> increased entropy

Question 8

Mixing of particles

Answer 8

Mixing -> more ways of arranging the particles (inclusive of dissolution of a solute) -> higher disorder -> increased entropy

SPECIAL
dissolving ionic solid in water
Ions more hydrated to a greater extent (form more ion-dipole interactions -> more heat released) in dilute solution. -> dissolving may be EXOTHERMIC when dilute but ENDOTHERMIC when saturated