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Chapter-10-Handouts

Chapter-10-Handouts - Chapter 10 Spontaneity Entropy Free...

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1 Chapter 10 Spontaneity, Entropy, & Free Energy o Entropy o Isothermal Processes o ΔS of Physical Reactions o 2 nd Law of Thermo o Free Energy o Hess’s Law/ 3 rd Law of Thermo o Equilibrium 1 Big Idea: The change in free energy of a reaction indicates whether a reaction is spontaneous. In any spontaneous process there is always an increase in the entropy of the universe. Chapter 10: Spontaneity, Entropy, and Free Energy Entropy Entropy (S): Entropy is a measure of how energy and matter can be distributed in a chemical system. 2 # of molecules of left side # of ways of arranging (microstates) 4 3 2 1 0 Chapter 10: Spontaneity, Entropy, and Free Energy Entropy In General: Entropy increases from solid to liquid to gas corresponding to an increase in positional probability. Entropy increases when you dissolve a solid in liquid corresponding to an increase in positional probability. The larger the volume the larger the positional probability and the greater the entropy (n constant). The larger the pressure the smaller the positional probability and the lower the entropy (n constant). The larger the molecule the larger the number of relative positions of the atoms resulting in a greater positional probability and a greater entropy. The higher the temperature the greater the range of energies, therefore the larger the entropy. 3 Chapter 10: Spontaneity, Entropy, and Free Energy Student Question Entropy The normal boiling point of the element rubidium is 688°C. The following equilibrium is important in rubidium vapor at that temperature: 2Rb(g) Rb 2 (g) + heat. Predict the signs of ΔH ° and ΔS ° for this reaction assume the reaction occurs at constant pressure. a) ΔH ° is negative ΔS ° is positive b) ΔH ° is negative ΔS ° is negative c) ΔH ° is positive ΔS ° is positive d) ΔH ° is positive ΔS ° is negative 4 Chapter 10: Spontaneity, Entropy, and Free Energy Student Question Entropy Predict which of the following reactions has a negative entropy change. I. CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(l) II. NH 3 (g) + HCl(g) NH 4 Cl(s) III. 2KClO 4 (s) 2KClO 3 (s) + O 2 (g) a) II and III b) III c) II d) I e) I and II 5 Chapter 10: Spontaneity, Entropy, and Free Energy Entropy Phase Change: The condition (for a given pressure, and temperature) at which two different phases are in dynamic equilibrium.
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