1. Chemistry 18.4

2. Entropy and Free Energy
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. Free Energy and Spontaneous Reactions
18.4
Free Energy and Spontaneous Reactions
Free Energy and Spontaneous Reactions
What are two characteristics of spontaneous reactions?

4. Free Energy and Spontaneous Reactions
18.4
Free Energy and Spontaneous Reactions
A spontaneous reaction occurs naturally and favors the formation of products at the specified conditions.
Cadmium sulfide forms spontaneously when solutions of sodium sulfide and cadmium nitrate are mixed. Inferring Is free energy released in this reaction?

5. Free Energy and Spontaneous Reactions
18.4
Free Energy and Spontaneous Reactions
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.
Many non-spontaneous reactions are required for a plant to grow. Nonspontaneous reactions can occur when they are coupled with spontaneous reactions. Inferring What is another requirement for this photosynthesis reaction?

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

7. Entropy What part does entropy play in chemical reactions? 18.4

8. Entropy is a measure of the disorder of a system.
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.

9. 18.4
Entropy
An increase in entropy favors the spontaneous chemical reaction; a decrease favors the nonspontaneous reaction.

10. 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.
Entropy is a measure of the disorder of a system. a) 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.Thus entropy increases in reactions in which solid reactants form liquid or gaseous products. Entropy also increases when liquid reactants form gaseous products. b) Entropy increases when a substance is divided into parts. For instance, entropy increases when a crystalline ionic compound, such as sodium chloride, dissolves in water. This is because the solute particles— sodium ions and chloride ions—are more separated in solution than they are in the crystal form. c) Entropy tends to increase in chemical reactions in which the total number of product molecules is greater than the total number of reactant molecules. d) Entropy tends to increase when temperature increases. As the temperature increases, the molecules move faster and faster, which increases the disorder.

11. Entropy increases when a substance is divided into parts.
18.4
Entropy
Entropy increases when a substance is divided into parts.
Entropy is a measure of the disorder of a system. a) 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. Thus entropy increases in reactions in which solid reactants form liquid or gaseous products. Entropy also increases when liquid reactants form gaseous products. b) Entropy increases when a substance is divided into parts. For instance, entropy increases when a crystalline ionic compound, such as sodium chloride, dissolves in water. This is because the solute particles— sodium ions and chloride ions—are more separated in solution than they are in the crystal form. c) Entropy tends to increase in chemical reactions in which the total number of product molecules is greater than the total number of reactant molecules. d) Entropy tends to increase when temperature increases. As the temperature increases, the molecules move faster and faster, which increases the disorder.

12. 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.
Entropy is a measure of the disorder of a system. a) 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. Thus entropy increases in reactions in which solid reactants form liquid or gaseous products. Entropy also increases when liquid reactants form gaseous products. b) Entropy increases when a substance is divided into parts. For instance, entropy increases when a crystalline ionic compound, such as sodium chloride, dissolves in water. This is because the solute particles— sodium ions and chloride ions—are more separated in solution than they are in the crystal form. c) Entropy tends to increase in chemical reactions in which the total number of product molecules is greater than the total number of reactant molecules. d) Entropy tends to increase when temperature increases. As the temperature increases, the molecules move faster and faster, which increases the disorder.

13. 18.4
Entropy
Entropy tends to increase when temperature increases. As the temperature increases, the molecules move faster and faster, which increases the disorder.
Entropy is a measure of the disorder of a system. a) 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. Thus entropy increases in reactions in which solid reactants form liquid or gaseous products. Entropy also increases when liquid reactants form gaseous products. b) Entropy increases when a substance is divided into parts. For instance, entropy increases when a crystalline ionic compound, such as sodium chloride, dissolves in water. This is because the solute particles— sodium ions and chloride ions—are more separated in solution than they are in the crystal form. c) Entropy tends to increase in chemical reactions in which the total number of product molecules is greater than the total number of reactant molecules. d) Entropy tends to increase when temperature increases. As the temperature increases, the molecules move faster and faster, which increases the disorder.

14. Enthalpy, Entropy, and Free Energy
18.4
Enthalpy, Entropy, and Free Energy
Enthalpy, Entropy, and Free Energy
What two factors determine the spontaneity of a reaction?

15. Enthalpy, Entropy, and Free Energy
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.

16. Enthalpy, Entropy, and Free Energy
18.4
Enthalpy, Entropy, and Free Energy

17. Enthalpy, Entropy, and Free Energy
Simulation 25
Simulate how enthalpy and entropy changes combine to determine the spontaneity of a reaction.

18. 18.4
Gibbs Free-Energy
Gibbs Free-Energy
Is the Gibbs free-energy change positive or negative in a spontaneous process?

19. 18.4
Gibbs Free-Energy
The Gibbs free-energy change is the maximum amount of energy that can be coupled to another process to do useful work.
The numerical value of ΔG is negative in spontaneous processes because the system loses free energy.

20. 18.4
Gibbs Free-Energy
The combination of the enthalpy change and the change in entropy for a reaction determines whether or not the reaction is spontaneous.

21. 18.4
Gibbs Free-Energy
The combination of the enthalpy change and the change in entropy for a reaction determines whether or not the reaction is spontaneous.

22. 18.4 Section Quiz.
18.4

23. 18.4 Section Quiz.
1. Free energy from a reaction is the amount of energy that is
absorbed by an entropy decrease.
equal to the enthalpy change.
wasted as heat.
available to do work.

24. 18.4 Section Quiz.
2. Free energy is always available from reactions that are
endothermic.
nonspontaneous.
at equilibrium.
spontaneous.

25. 18.4 Section Quiz.
3. Choose the correct words for the spaces: Spontaneous reactions produce ________ and substantial amounts of _________ at equilibrium.
free energy, products
no free energy, reactants
free energy, reactants
no free energy, products

26. 18.4 Section Quiz.
4. Which of the following involves a decrease in entropy?
Natural gas burns.
A liquid freezes.
Dry ice sublimes.
Water evaporates.

27. 18.4 Section Quiz.
5. A reaction is spontaneous if
enthalpy decreases and entropy increases.
enthalpy increases and entropy increases.
enthalpy decreases and entropy decreases.
enthalpy increases and entropy decreases.

28. 18.4 Section Quiz.
6. Choose the correct words for the spaces: Gibbs free-energy change is the _________ amount of energy that can be ___________ another process to do useful work.
maximum, coupled to
maximum, duplicated by
spontaneous, coupled to
minimum, duplicated by

29. END OF SHOW