Enthalpy, Entropy and Gibbs Law of Free Energy

1. Enthalpy, Entropy and Gibbs Law of Free Energy Chapter 22 and 23

2. Energy reactions Review the Energy Diagram Endothermic have a high startup energy Exothermic have a low start up energy

3. Energy Curve • Activation energy: energy required to get the reaction to move forward • Energy released or absorbed is noted at the end of the curve

4. Factors that effect the Reaction Rate • Temperature: Endothermic vs Exothermic reactions • Concentration: Increase the reactants will increase the products • Surface Area: Smaller particles have large surface area • Catalysts and inhibitors

5. Enthalpy Delta H = Hproducts - Hreactants Delta H represents the transfer of heat

6. Spontaneous Reactions • If the reaction moves forward as written without an intervention then the reaction is said to be spontaneous. • Remember Delta H (enthalpy) • Negative signs represent exothermic • Always spontaneous • Positive sign represents endothermic • Sometimes spontaneous

7. Examples H2O (s) --> H2O (l) delta H = +6kJ 2Na(s) + Cl2 --> 2NaCl (s) delta H = -822kJ The above reactions are all spontaneous. But most endothermic rxn are Nonspontaneous.

8. Delta H • Most enthalpy reactions that are endothermic rxn are not spontaneous. This is because the reaction has a high energy barrier. • Only because of a large difference between entropy and enthalpy can the reaction happen.

9. Entropy • Entropy is the measurement of disorder of particles in a reaction. Equation: Delta S = SProduct - Sreactant *not easy to measure, but we can compare based on the states of matter

10. Comparing Entropy • Sproduct > Sreactants delta S is positive • Sproduct< Sreactants delta S is negative • Solids have a very low entropy • Liquids have a slightly higher entropy • Gases have a very high entropy

11. Example reactions • CO2 (s) --> CO2 (g) S > 0 • H2O (g) --> H2O (s) S<0 • 2NH3(g) --> N2(g) + 2 H2 (g) S>0

12. Law of Thermodynamics • States: in any spontaneous process, the overal entropy of the universe always increases. Suniverse = Sreaction + Ssurroundings

13. Sreaction - calculated using the states of matter • Ssurround - calculated based on enthalpy • If the reaction is endothermic it is taking energy away from the surrounding making it negative • If the reaction is exothermic it is placing energy into the system and making it positive.

15. Gibbs Free Energy • Delta G = Delta H - T deltaS Compares entropy, enthalpy and temperature * If delta G is negative the reaction is spontaneous * If delta G is positive the reaction is nonspontaneous * If delta G is 0 the reaction is at equilibrium

17. Delta G and Equilibrium