1. Notes #
Reaction spontaneity

2. Spontaneous or Nonspontaneous That is the Question ?
Suppose Δ H is negative Δ Hf products < Δ Hf reactants
It’s EXOTHERMIC
When Δ Hr is negative reaction tends to be
SPONTANEOUS
Spontaneous means that it will occur without any outside influence
How about Δ H positive?

3. Entropy (S) is the measure of the degree of disorder in a system.
A spontaneous process is one that occurs in a system left to itself. No external action is needed to make it happen.

4. Entropy Increase in disorder; Decrease in disorder; ∆S > 0

5. Predicting changes in entropy pgs. 514-515
Entropy changes associated with changes in state H2O(l) → H2O(g)
Dissolving of a gas in a solvent always results in decrease in entropy
CO2(g) →CO2(aq)
Entropy usually increases when the # of moles increases from reactants to products
Increase in temp. always increases entropy.

6. GIBBS FREE ENERGY
Gibbs free energy indicates whether a reaction will occur or not.

7. Exergonic reactions (spontaneous)
Endergonic reactions (nonspontaneous)

8. Practice
Determine if each of the following would be spontaneous or not
∆H= 15.6kJ T=415K ∆S=45 J/K
spontaneous
2. ∆H= 35.6kJ T=415K ∆S=45 J/K
nonspontaneous

9. Endothermic reactions occur spontaneously when T Δ S is large.
The thermodynamic definition of a system in equilibrium is; when Δ H and Δ S have the same sign, and there is some temperature at which Δ H and T Δ S are numerically equal.

10. A spontaneous reaction proceeds toward equilibrium.
Chemical potential energy, G, is least at equilibrium.
Enthalpy, entropy, and free energy depend on temperature. ( We will only work at K and kPa-standard states)

11. GIBBS FREE ENERGY CALCULATIONS
Δ H values are relative; free elements are considered to have
change in enthalpy is found by;

12. entropy changes and Gibbs free energy is computes as follows;

13. 1. Organize the data you will use from the appropriate table.
2. Multiply each Δ Gf0 by the number of moles from the balanced equation. (Always make sure the chemical equation is balanced). Substitute these values into the equation used to determine Δ Gf0 .

14. The Gibbs free energy decreases in a spontaneous reaction because the system is changing to a more stable state.

15. To find Multiply each by the number of moles from the balanced equation Substitute these values into the equation.