Chapter 20:
Spontaneous Change: Entropy and Free Energy

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Chapter Objectives


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  1. State the first law of thermodynamics and the sign conventions used for heat, q , and work , w.

  2. Calculate the value of one of the following from known values of the other two: [Delta]E, q, and w.

  3. Explain the purpose served by the thermodynamic property of enthalpy (H), describe how [Delta]H is related to [Delta]E, and calculate one from the other for reactions involving gases.

  4. Explain the meaning of the term "spontaneous change" as it applies to chemical reactions.

  5. Explain why entropy is important and how entropy is related to the disorder of the system.

  6. Predict whether entropy increases or decreases for certain processes.

  7. Explain why entropy alone is not used to predict a spontaneous change and why free energy is needed.

  8. Qualitatively predict whether reactions are spontaneous or nonspontaneous based on their [Delta]H and [Delta]S values.

  9. Determine [Delta]Go from tabulated data, both tables of [Delta]Gof and those of [Delta]Hof and So.

  10. Use [Delta]Go =[Delta]Ho - T[Delta]So, the Gibbs-Helmholtz equation, to determine [Delta]Go at various temperatures.

  11. Know that [Delta]Gtr = 0 at equilibrium. For phase changes, use [Delta]Str =[Delta]Htr/Ttr = the molar entropy of transition.

  12. Write thermodynamic equilibrium constant expressions Keq for reactions and relate these to Kp and Kc.

  13. Compute values of Keq from tabulated data and [Delta]Go = -RT ln Keq.

  14. Explain how absolute entropies of substances can be determined with the third law of thermodynamics.

  15. Relate the equilibrium constant to the standard molar enthalpy of reaction, [Delta]Ho and to Kelvin temperature, both graphically and algebraically.


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