Free Energy and Thermodynamics Notes.docx - Free Energy and...

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Free Energy and Thermodynamics Thermodynamics is concept that predicts whether a process will occur under the given conditions, process that will occur naturally are called spontaneous , process that do not occur spontaneously are nonspontaneous and require energy input to proceed. We must note that spontaneity does not determine the speed of a reaction, a reaction being spontaneous DOES NOT necessarily mean that a reaction occurs quickly. Understanding spontaneity can also help you determine the probability of any reaction being reversible by remembering one rule; any spontaneous process is irreversible because there is a net release of energy when it proceeds in that direction, it will proceed only in one direction, so if a process is spontaneous in one direction it must be nonspontaneous in the opposite direction. An example of this is rust forming on a nail, the process of rusting is spontaneous therefore the reverse of the process would be nonspontaneous, this is why once an object is rusted it does not un-rust over time. Factors Affecting Whether a Reaction is Spontaneous: There are two factors that determine spontaneity these are: enthalpy change, and entropy change of the system: Enthalpy change, H, is the difference between the sum of the internal energy and PV work energy of the reactants and that of the products, it is only the heat component. o Enthalpy is measured in kJ/mol o Exothermic: Bonds formed are stronger than the bonds broken. Energy is released; H < 0. A higher energy state to a lower energy state. o Endothermic: Bonds in the products are weaker than the bonds in the reactants. Energy is absorbed; H > 0. Lower energy state to a higher energy state. o The spontaneity is favorable for exothermic reactions and unfavorable for endothermic reactions. Entropy change, S, is the change in randomness or disorder of a system going from reactants to products. Entropy itself is a thermodynamic function that increases the number of energetically equivalent ways of arranging the components increases o Entropy is measured in J/K or J/mol K o S = k ln W k is the Boltzmann constant which is equal to 1.38 × 10 23 J / K W is the number of energetically equivalent ways a system can exist.

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