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Entropy

Learn about entropy, spontaneous reactions, and free energy in chemical systems. Discover how disorder and entropy affect reaction outcomes, and why some reactions require energy input. Understand the relationship between entropy, enthalpy, and free energy in determining reaction spontaneity.

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Entropy

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  1. Entropy Chapter 16-5

  2. 18.4 Entropy and Free Energy • Inside a pile of oily rags or a stack of hay that has not been thoroughly dried, decomposition causes heat to build up. When heat cannot escape, the temperature can become high enough to cause a fire. You will learn about the conditions that will produce a spontaneous chemical reaction.

  3. 18.4 Free Energy and SpontaneousReactions • A spontaneous reactionis a physical or chemical change that occurs with no outside intervention.

  4. 18.4 Free Energy and SpontaneousReactions • A nonspontaneous reaction is a reaction that does not favor the formation of products at the specified conditions. Photosynthesis is a nonspontaneous reaction that requires an input of energy.

  5. 18.4 Free Energy and SpontaneousReactions • Spontaneous reactions produce substantial amounts of products at equilibrium and release free energy. • Free energy is energy that is available to do work.

  6. 18.4 Entropy • Entropy is a measure of the disorder of a system. • Physical and chemical systems attain the lowest possible energy. • The law of disorder states that the natural tendency is for systems to move in the direction of maximum disorder or randomness. An increase in entropy favors the spontaneous chemical reaction; a decrease favors the nonspontaneous reaction. The law of disorder states that spontaneous processes always proceed in such a way that entropy of the universe increases. This is the second law of thermodynamics.

  7. 18.4 Entropy • For a given substance, the entropy of the gas is greater than the entropy of the liquid or the solid. Similarly, the entropy of the liquid is greater than that of the solid.

  8. 18.4 Entropy • Entropy increases when a substance is divided into parts.

  9. 18.4 Entropy • Entropy tends to increase in chemical reactions in which the total number of product molecules is greater than the total number of reactant molecules.

  10. 18.4 Entropy • Entropy tends to increase when temperature increases. As the temperature increases, the molecules move faster and faster, which increases the disorder.

  11. 18.4 Enthalpy, Entropy, and Free Energy • The size and direction of enthalpy changes and entropy changes together determine whether a reaction is spontaneous; that is, whether it favors products and releases free energy.

  12. 18.4 Enthalpy, Entropy, and Free Energy

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