Thermodynamics_1

Thermodynamics_1 - Chapter 19 Chemical Thermodynamics...

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Chapter 19 Chemical Thermodynamics 1 Thermodynamics Entropy and Spontaneity
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Kinetics vs. Thermodynamics Rates of chemical reactions are controlled by activation energy – lower Ea, faster rate. Collision frequency; collisions, rate Equilibrium is reached when rate forward = rate reverse, also depends on energy (temp). Thermodynamics explores connection between energy and the EXTENT of a reaction but tells you nothing about reaction rates. 2 Thermodynamics Entropy and Spontaneity
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State functions are written as uppercase letters (E, H, P, V, T, S…) Changes in state functions are path-independent : reactants products ∆E 1 2 A state function: is a quantity that does not depend on the process by which the system was prepared STATE FUNCTIONS 3 Thermodynamics Entropy and Spontaneity Example: Your altitude (height above sea level) does not depend on the route you took to class this morning.
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THERMOCHEMISTRY 1 st Law of Thermodynamics: E universe = 0 E universe = E system + E surroundings E system = E surroundings 4 Thermodynamics Entropy and Spontaneity
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H = heat transferred at const. P If (+): endo - thermic If ( ): exo- thermic Classify as endo- or exo- thermic : Ice melting Water boiling Wood burning 5 Thermodynamics Entropy and Spontaneity Enthalpy (H) H is a state function – changes are path-independent H = E + PV (sums and products of state functions are also state functions)
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∆H o f : ∆H for making 1 mole of a compound from its component elements in their standard states Standard state is the most stable form (pure solid, pure liquid, or gas at P = 1 atm and 298K) For solutes in solution, standard state is usually 1 M . Appendix C provides values of ∆H o f H o rxn = Σ ∆H o f (products) Σ ∆H o f (reactants) 6 Thermodynamics Entropy and Spontaneity Standard Enthalpy of Formation
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Spontaneous Processes Spontaneous processes: One that is capable of proceeding in the forward direction to a substantial extent under a given set of conditions . Note: Spontaneity has nothing to do with the rate at which a reaction will occur. Processes that are spontaneous in one direction are nonspontaneous in the reverse direction. 7 Thermodynamics Entropy and Spontaneity
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Spontaneous Processes Saying a reaction is spontaneous is not the same as saying it will occur if the reactants are mixed. It means the reaction can occur but may be slow . In the case of a slow spontaneous reaction it is worthwhile to
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Thermodynamics_1 - Chapter 19 Chemical Thermodynamics...

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