Entropy

Introduced to this in AP Chemistry

Entropy of the Surrounding §

S (Entropy of the surrounding) depends on:

1. Heat flow of the rxn
   • Exothermic rxn - flow to the surrounding S = (+)
   • Endothermic rxn - flow to the system S = (-)
2. Temp. of surroundings:
   • Impact of the transfer of a given quantity of heat energy, will be great at lower temps (of the surroundings)
   • small change in entropy at high temps

S (Entropy of the surrounding) = =

At constant pressure, heat flow = H

S = -

Gibbs Free Energy: G §

use to determine if a rxn is thermodynamically favored

S = S + S

S = - + S

-T S = H - T S

G	Reaction
-	thermodynamically favored (spontaneous)
zero	equilibrium
+	not favored (reverse rxn is favored)

G = H - TS

Provides us a thermodynamically favored reaction ALWAYS

Thermodynamic and Kinetic Control (9.4) §

• Common misconception: Thermodynamically favored reactions occur quickly
• Many favored reactions occur incredibly slowly (example: conversion of diamonds to graphite)
• These types of reactions are often slow because they have a high activation energy

Example §

C (diamond) C (graphite)

• G = -3 kJ
• Occurs spontaneously
• Does not require the input of any external energy to occur
• Incredibly slow, as in thousands of years slow
• Kinetically controlled

Coupled Reactions (9.6) §

• Thermodynamically unfavorable reactions do not occur on their own
• To make an unfavored reaction occur is through use of coupled reactions
• Couple reactions - a combination of a non favored reaction and a favored reaction that have a common intermediate

Example §

FeO + 3CO 2Fe + 3CO:

FeO 2Fe + 3/2O

• G = 742.2 kJ

CO + 1/2O CO

• G = -283.5 kJ