Notes #11 16.5

1. Notes #11 16.5 • Reaction spontaneity

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

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 ∆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 ΔS is large. • The thermodynamic definition of a system in equilibrium is; when ΔH and ΔS have the same sign, and there is some temperature at which ΔH and T ΔS 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 298.15 K and 100.00 kPa-standard states)

11. GIBBS FREE ENERGY CALCULATIONS • ΔH 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 ΔGf0 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 ΔGf0 .

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

15. To find 1. Multiply each by the number of moles from the balanced equation.2. Substitute these values into the equation.