 State Function (°)  Property with a specific value only influenced by a system’s present condition  Only dependent on the initial and final states, NOT on the path taken to reach the condition  Initial state Final state ** State functions go back to initial values in opposite process and system returns to initial state** Ex. Enthalpy (H), Entropy (S), Free Energy (G)

 Spontaneous vs. Nonspontaneous 1)Spontaneous Process  Occurs WITHOUT help outside of the system, natural  Many are exothermic—favors energy release to create an energy reduction after a chemical reaction  Ex. Rusting iron with O 2 and H 2 O, cold coffee in a mug  Some are endothermic  Ex. Evaporation of water/boiling,dissolving in water

 Spontaneous vs. Nonspontaneous 2) Nonspontaneous Process  REQUIRES help outside system to perform chemical reaction, gets aid from environment  Ex. Water cannot freeze at standard conditions (25°C, 1atm), cannot boil at 25°C **Chemical processes that are spontaneous have a nonspontaneous process in reverse **

 Entropy (S)  Measure of a system’s disorder  The degree of randomness associated with particles (molecules, etc.)  Disorder is more favorable than order  Δ S = S (products) - S (reactants)  Δ S is (+) with increased disorder  Δ S is (-) with decreased disorder  State function  Only dependent on initial and final states of a reaction  Ex. Evaporation, dissolving, dirty house

 When does a system become MORE disordered from a chemical reaction? ( Δ S > 0) 1)Melting 2)Vaporization 3)More particles present in the products than the reactants  4C 3 H 5 N 3 O 9 (l)  6N 2 (g) + 12CO 2 (g) + 10H 2 O (g) + O 2 (g) 4)Solution formation with liquids and solids 5)Addition of heat, increasing temperature

 Thermodynamic Laws 1 st Law of Thermodynamics  Energy cannot be created or destroyed 2 nd Law of Thermodynamics  The entropy of the universe is always increasing.  Naturally favors a disordered state

 3 rd Law of Thermodynamics The entropy ( Δ S) of a perfect crystal is 0 at a temperature of absolute zero (0°K).  No particle motion at all in crystal structure  All motion stops

 How do we determine if a chemical reaction is spontaneous? 1)Change in entropy ( Δ S) 2)Gibbs Free Energy ( Δ G)

 Gibbs Free Energy (G)  Balances the relationship between enthalpy ( Δ H) and entropy ( Δ S)  State function  Enthalpy of system minus the product of temperature times entropy of system  G = H – TS  Maximum amount of energy available to do work, “free”

 Change in Gibbs Free Energy ( Δ G)  Δ G = Δ H – T Δ S  Relates enthalpy and entropy to determine which has more importance in determining whether a reaction is spontaneous  Combines energy transfer as heat ( Δ H) and energy released to contribute to disorder ( Δ S)

  G is the change in Gibbs free energy.  G can be calculated as  G o =  H o  T  S o The term  H represents enthalpy or heat energy which is available to do work. The term  S represents entropy or random motion which is not available to do work. Gibbs Free Energy

 Example 2: Find Δ G for a chemical reaction given Δ H = -218 kJ and Δ S = -765 J/K at 32°C.

 Change in Gibbs Free Energy ( Δ G)  Δ G = Δ H – T Δ S  Δ G < 0, spontaneous reaction, reaction occurs as written  Energy available to do work  Δ G > 0, nonspontaneous reaction, reaction will NOT occur as written  Energy deficiency, no leftover energy and not enough energy for reaction ** All reactions want to move toward low or minimal Δ G

  A spontaneous reaction is NOT necessarily fast!!!!  Reaction rate involves kinetics ! !

  Entropy( Δ S) > 0, POSITIVE  Reaction creates more disorder  Free Energy ( Δ G) < 0, NEGATIVE What makes a reaction spontaneous?

  Read pp  p. 550 #2-4, 5 Homework