AP CHAPTER 18 OUTLINE
THERMODYNAMICS
I. Introduction
     A.
thermodynamics -- the study of energy changes and the flow of energy from one substance to another
     B. The First Law of thermodynamics revisited
          1. E(sys) = KE(sys)  +  PE(sys)
               a. DeltaE = E(final) - E(initial)  or  DeltaE = E(products) - E(reactants)
               b. DeltaE = positive (energy flows in)
               c. DeltaE = negative (energy flows out)
          2.
DeltaE = q + w
               a. q = heat of reaction
                    1. q = positive, heat is abosorbed
                    2. q = negative, heat is released
               b. w = work
                    1. w = positive, work is done on system
                    2. w = negative, work is done by the system

    C. work in Chemical Systems
          1. Pressure-volume work (PV work)
          2. w = - PDeltaV and DeltaE = q - PDeltaV

         3. at constant volume, DeltaE = q(v)
     D. Enthalpy and Enthalpy Change
          1.
Enthalpy -- energy at constant pressure
          2. H = E + PV  and DeltaH = DeltaE + PDeltaV
               a. DeltaH = q(p)
     E. Converting between DeltaE and DeltaH for a Chemical Reaction
          1.
These two values only differ significantly when gases form or are consumed in a reaction
               a. DeltaH = DeltaE + Deltan(gas)RT
II. Enthalpy Changes and Spontaneity
     A.
Spontaneous Change -- a change that occurs by itself without continuous outside assistance
          1. Once a spontaneous event begins, it tends to continue until complete
     B. Spontaneity and Potential Energy Changes
          1. energy lowering favors spontaneity (PE)

         2. Exothermic reactions tend to proceed spontaneously
          3.
DeltaH = negative, reaction tends to proceed spontaneously
III. Entropy and Spontaneous Change
     A.
Universal phenomenon -- something that brings about randomness is more likely to happen than something that brings about order
          1. takes place because of the laws of chance
          2. system passes from a state of low probability to a state of high probability
     B. Entropy Changes and Spontaneity
          1.
Entropy (S) -- degree of randomness of a system (state function)
               a. larger S value, greater randomness
          2. DeltaS = S(final) - S(initial)  or  DeltaS = S(prod) - S(react)
               a. DeltaS = positive, increase in randomness
               b. DeltaS = negative, decrease in randomness
          3.
An increae in entropy is a factor that favors spontaneity
     C. Predicting the Sign of DeltaS
          1. Volume --> for gases, entropy increases with increasing volume
          2. Temperature --> higher temperature, larger entropy
          3. Physical State --> S(solid) < S(liquid) << S(gas)
     D. Entropy Changes in Chemical Reactions
          1.
If the # of gaseous products > # of gaseous reactants, then the entropy change is positive
     E. Molecular Complexity
          1.
When a reaction occurs with a decrease in the degree of molecular complexity and an increase in the number of particles, there tends to be an increase in entropy
IV. The Second Law of Thermodynamics and the Gibbs Free Energy
     A. Three factors that influence spontaneity --> enthalpy change, entropy change, temperature

    B. The Second Law of Thermodynamics
          1.
whenever a spontaneous event takes place in our universe, the total entropy of the universe increases (delta S > 0)
          2. to be spontaneous,  DeltaH(sys) - TDeltaS(sys) <0
          3.
Gibbs Free Energy (G) -- maximum energy in a change that is available to do work
               a. G = H -TS and DeltaG = DeltaH - TDeltaS   (state function)
               b. Delta G = G(final) - G(initial)
          4.
At constant T and P, a change can be spontaneous only if it is accompanied by a decrease in the free energy of the system
     C. When Delta H = neg. & Delta S = pos., Delta G will always be neg. (spontaneous)
     D. When Delta H = pos. & Delta S = neg., Delta G will alwyas be pos. (nonspontaneous)
     E. When Delta H & Delta S are both pos., the change will be spontaneous at high temp. and not at low temp.
     F. WhDelta H & Delta S are both neg., the change will be spontaneous at low temp. and not at high temp. (pg. 810, figure 18.9)
V. The Third Law of Thermodynamics
     A.
At absolute zero the entropy of a perfectly ordered pure crystal is zero
     B.
Standard Entropy {S(o)} -- the entropy of one mole of a substance at 298 K and 1 atm of pressure
          1.
DeltaS(o) = (sum of S(o)prod.) - (sum of S(o)react.)
          1.
Standard entropy of formation {DeltaS(o)f} -- if the product is one mole a substance from its elements
VI. Standard Free Energy Changes
     A.
Standard Free Energy Change {DeltaG(o)} -- free energy at 298 K and 1 atm of pressure
     B.
Standard free energies of formation {DeltaG(o)f}
VII. Free Energy and Maximum Work
     A.
Maximum conversions of chemical energy to work occurs in reversible reactions
          1.
Reversible -- driving force is opposed by another force that is slightly weaker
          2.
The maximum amount of energy that can be theoretically used for work is equal to DeltaG
VIII. Free Energy and Equilibrium
     A.
Equilibrium only occurs when DeltaG = 0 {G(react.) = G(prod.)}
     B. Work and Dynamic Equilibrium

         1. When a system is at equilibrium, no work can be done
          2.
for work to be done, Delta G must start with a large neg. value
    C. Equilibrium in phase changes
          1. Equilibrium can only occur between two states at one temperature at atmospheric pressure
     D. Free Energy Diagram for a Phase Change
          1. Depicts how the free energy changes as we proceed from reactants to products
          2. Ex. - water and ice
               a.
below 0 degree C, free energy decreases until only ice exist
               b.
above 0 degree C, melting is spontaneous and will occur until only water exist
               c.
at 0 degree C, equilibrium exit between any ratio of ice and water
          3. Reation Ex. - equilibrium is reached at the point of lowest free energy
               a.
Delta G(o) = pos., then equilibrium lies closer to the reactants
               b.
Delta G(o) = neg., then equilibrium lies closer to the products (spontaneous)
     E. Predicting the Outcome of a Chemical Reaction
          1.
The size and sign of DeltaG(o) serve as indicators of whether an observable spontaneous reaction will occur
     F. Equilibrium and Temperature
          1. Delta G(o)298 = {G(o)prod.298} - {G(o)react.298}
          2. DeltaG(o)t = {G(o)prod.t} - {G(o)react.t}
               a. DeltaH and DeltaS increase equally when temperature increases
               b.
DeltaG(o)t == DeltaH(o)298 - TDeltaS(o)298
IX. Calculating equilibrium Constants from Thermodynamic Data
     A. DeltaG = DeltaG(o) + RTlnQ  (Q is the natural logarith of the reaction quotient)
          1. Gases, Q uses partial pressures

         2. solutions, Q uses molar concentrations
     B. Thermodynamic Equilibrium Constants
          1. at equilibrium, DeltaG = 0, Q = K (equilibrium constant)
               a. DeltaG(o) = - RTlnK
          2. K = K(p) for reactions with gases or K = K(c) for reactions in solution
     C. Thermodynamic equilibrium Constants at Temperatures other than 25 degree C
          1. DeltaG(o)t can be used to calculate K at tempertures other than 25 degree C by using the above equation
X. Bond energies and Heats of Reactions
     A.
Bond energy -- amount of energy needed to break a chemical bond to give electrically neutral fragments
     B. Measurement of Bond Energies
          1.
Atomization energy {DeltaH(atom)} -- amount of energy needed to rupture the chemical bonds in one mole of gaseous molecules to give gaseous atoms
               a. Problems work like Hess's Law Problems


Outline based upon:
     Brady, J. E., Holum, J. R., Russell, J. W. (2000)
. Chemistry: The Study of Matter and Its Changes. (3rd ed.). New York: John Wiley & Sons, Inc. pp. 793-833.
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