Predicting Spontaneity

Using data from Appendix 2, calculate AS° (in J/K mol) for the following reaction  

3 The diagrams show a spontaneous chemical reaction. What can we deduce about ASsu for this process  

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In Chapter 1 we described the fundamental thermodynamic properties internal energy U and entropy S. They are the subjects of the First and Second Laws of Thermodynamics. These laws not only provide the mathematical relationships we need to calculate changes in U, S, H,A, and G, but also allow us to predict spontaneity and the point of equilibrium in a chemical process. The mathematical relationships provided by the laws are numerous, and we want to move ahead now to develop these equations.1... 

Spontaneous processes result in the dispersal of matter and energy, hi many cases, however, the spontaneous direction of a process may not be obvious. Can we use energy changes to predict spontaneity To answer that question, consider two everyday events, the melting of ice at room temperature and the formation of ice in a freezer. 

There is no single criterion for the system alone that applies to all processes. However, if we restrict the conditions to constant temperature and pressure, there is a state function whose change for the system predicts spontaneity. This new state function is the free energy (G), which was introduced by the American J. Willard Gibbs and is defined by Equation G = H - T S As usual, H is enthalpy, T is absolute temperature, and S is entropy. 

How does free energy allow us to predict spontaneity while ignoring the surroundings To answer this question, we examine the change in free energy of a system, A Gsys = A Hsys -A(T If we hope to use A G ys to... 

The semiclassical treatment just given has the defect of not predicting spontaneous emission. According to (3.13), if there is no outside perturbation, that is, if // (0 = 0, then dcm/dt = 0 for all m if the atom is in the nth stationary state at / = 0, it will persist in that state forever. However, experimentally we find that unperturbed atoms in excited states spontaneously radiate energy and drop to lower states. Quantum field theory does predict spontaneous emission. Since quantum field theory is beyond us, we shall use an argument given by Einstein in 1917 to find the spontaneous-emission probability. 

By itself, ASmix is incapable of predicting spontaneity and randomness this is demonstrated in crystallization and helix formation that anomalously result in a high degree of order (-AS), but are nevertheless spontaneous processes more significantly driven by a loss of latent heat ( — AH). 

Now we have two functions that can be used to predict spontaneity the entropy of the universe, which applies to all processes and free energy, which can be used for processes carried out at constant temperature and pressure. Since so many chemical reactions occur under the latter conditions, the free The superscript degree symbol (°) in- energy function is more useful to chemists. 

M.D. Gourlay, J. Kendrick, F.J.J. Leusen, Rationalization of racemate resolution predicting spontaneous resolution through crystal structure prediction, Cryst. Growth Des. 7 (2007) 56-63. 

What determines whether a process under consideration will be spontaneous Where does a spontaneous process end How are energy, volume, and matter partitioned between the system and surroundings at equilibrium What is the nature of the final equilibrium state These questions cannot be answered by the first law. Their answers require the second law and properties of the entropy, and a few developments are necessary before we can address these questions. We define entropy by molecular motions in Section 13.2 and by macroscopic process variables in Section 13.3. Finally, we present the methods for calculating entropy changes and for predicting spontaneity in Section 13.5. 

Stated as an abstraction and generalization of engineering observations on the efficiency of heat engines. We start the discussion by presenting a nonmathematical qualitative summary of the arguments on efficiency. Then we define entropy and state the second law. Section 13.5 applies the definition to calculate entropy changes and to predict spontaneity of processes. 

Predicts spontaneous dissociation of O when going from S=0 (d ) to S=1 (d% ) transition. 

ORMAS Same active space as CASSCF, divided into 6 groups. Also predicts spontaneous dissociation when going from S=0 to S=l. 

Consider the equation AG = AG° + RT ln(g). What is the value of AG for a reaction at equilibrium What does Q equal at equilibrium At equilibrium, the previous equation reduces to AG° = -RT ln(A. When AG° > 0, what does it indicate about K When AG° < 0, what does it indicate about K When AG° = 0, what does it indicate about K AG predicts spontaneity for a reaction, whereas AG° predicts the equilibrium position. Explain what this statement means. Under what conditions can you use AG° to determine the spontaneity of a reaction ... 

The Nernst equation allows determination of the cell potential for a galvanic cell at nonstandard conditions. Write out the Nernst equation. What are nonstandard conditions What do %, n, and Q stand for in the Nernst equation What does the Nernst equation reduce to when a redox reaction is at equilibrium What are the signs of AG° and when < 1 When > 1 When = 1 Explain the following statement % determines spontaneity, while determines the equilibrium position. Under what conditions can you use to predict spontaneity ... 

In using AG° in predicting spontaneity of a reaction, students did not appreciate that this function applies to a reaction where all reactants and products are in their standard states and temperature is held constant. 

This chart will help identify four possible scenarios for the values of AH, AS and AG to predict spontaneity of the reaction. 

AG predicts spontaneity for a reaction at constant T and P, whereas AG° predicts the equilibrium position. Explain what this statement means. Under what conditions can you use AG° to determine the spontaneity of a reaction ... 

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