Chapter 12 - Thermodynamics
12.1 Spontaneous Processes
Spontaneous Process: process that proceeds without any ongoing intervention, self-sustaining once initiated; does not necessarily mean a fast or exothermic reaction
Non-spontaneous Process: cannot happen on its own
12.2 Entropy and the Second Law of Thermodynamics
First law of Thermodynamics: energy cannot be created or destroyed - cannot do more work than allowed by available energy
Second law of Thermodynamics: not all energy released by a spontaneous reaction is available to do useful work
- energy unavailable to do useful work spreads out and becomes less concentrated over time
Entropy: measure of energy dispersion of a system; always increases during a spontaneous process
Accessible Microstates: probable number of arrangements of particles in a system at a given temperature
Third Law of Thermodynamics: a perfect crystalline solid has zero entropy at a temperature of absolute zero
12.3 Absolute Entropy and Molecular Structure
Standard Molar Entropy (S°): entropy of one mole of a substance in its standard state
- linked to masses and molecular structures (rotational motion and rigidity)
Entropies of States: Ssolid<Sliquid<Sgas
Entropies increase as temperature, volume and number of independent particles increases
12.4 Applications of the Second Law
A spontaneous process produces an increase in entropy of the universe
ΔSuniv > 0; spontaneous process
ΔSuniv < 0; nonspontaneous process
ΔS = q/T
Reversible Process: happens slowly, can be reversed by changing reaction conditions to restore original state of system with no net flow of energy in/out of system
12.5 Calculating Entropy Changes
Entropy is a state function: ΔSsys = ΔSfinal - ΔSinitial
Each S° value for product/reactant is multiplied by number of moles derived from balanced equation
12.6 Free Energy
Endothermic reactions have thermal energy flowing from surroundings into the system, lowering surrounding temperature and decreasing its entropy
Exothermic reactions have thermal energy flowing into surroundings from system, increasing its entropy
Free Energy: measure of maximum work a thermodynamic system can perform, energy that is freed during process
- ΔE = q + w
- ΔH = ΔG + TΔS
Gibbs free energy: maximum amount of energy available to do useful work in processes happening at a constant temperature and pressure or once temperatures and pressures of reaction mixtures have returned to their initial values, represented by ΔG; is a state function
ΔGsys = -TΔSuniverse = ΔH - TΔS
ΔG < 0, then ΔS > 0, reaction is spontaneous
ΔG > 0, then ΔS < 0, reaction is not spontaneous
ΔG = 0, then ΔS = 0, reaction has reached equilibrium
A decrease in free energy and a spontaneous process at constant temperature and pressure occur when there is an increase in entropy or the process is exothermic
Standard Free Energy of Formation (ΔG°f): change in free energy associated with formation of one mole of it in its standard state from its elements in their standard states
12.7 Temperature and Spontaneity
12.8 Coupled Reactions
- living systems use energy from spontaneous reactions to run non spontaneous reactions
Glycolysis: series of reactions converting glucose to pyruvate; major anaerobic pathway of glucose metabolism
Phosphorylation reaction: reaction resulting in the addition of a phosphate molecule to an organic molecule