Chapter 18 Lecture.pptx - Chapter 18 Free Energy and...

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Chapter 18 Free Energy and Thermodynamics
Outline Thermodynamics and Spontaneity Entropy and Enthalpy 2 nd and 3 rd Laws of Thermodynamics Standard conditions revisited Gibbs free energy
Thermodynamics and Spontaneity Thermodynamics predicts whether a process will occur under the given conditions. Processes that will occur are called spontaneous . Nonspontaneous processes require energy input to go. Spontaneity ≠ fast or slow That is the subject of kinetics
Reversibility of Process Any spontaneous process is irreversible because there is a net release of energy when it proceeds in that direction. It will proceed in only one direction. If a process is spontaneous in one direction, it must be nonspontaneous in the opposite direction.
Factors Affecting whether a Reaction Is Spontaneous Two factors that determine spontaneity: enthalpy change and entropy change of the system. The enthalpy change, Δ 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. The entropy change, Δ S , is the change in randomness or disorder of a system going from reactants to products.
Enthalpy Change: Δ H Enthalpy change, Δ H , is measured in kJ/mol. Exothermic Bonds formed are stronger than the bonds broken. Energy released; Δ H < 0. A higher energy state to a lower energy state Endothermic Bonds in the products are weaker than the bonds in the reactants. Energy absorbed; Δ H > 0. Lower energy state to a higher energy state The spontaneity is favorable for exothermic reactions and unfavorable for endothermic reactions (we’ll see why).
Changes in Entropy, Δ S Δ S = S final S initial Entropy change is favorable when the result is a more random or disordered system. Δ S > 0 Changes that increase the entropy are as follows: Reactions whose products are in a more random state Solid more ordered than liquid; liquid more ordered than gas
Δ S : Change in Entropy and Chemical Reactions For a process in which the final condition is more random than the initial condition, Δ S sys > 0 Entropy change is favorable for being spontaneous.

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