CHAPTER 18 LEARNING OBJECTIVES
To satisfy the minimum requirements for this course, you should master the following
learning objectives.
Understand and be able to use the terms spontaneous reaction, and nonspontaneous
reaction.
Review and understand the first law of thermodynamics. (Chapter 6, pg 233: Energy is
neither created or destroyed…)
Describe how entropy is related to randomness/disorder or dispersal of energy, and
• be able to relate the number of microstates for a chemical system to the entropy
of the system. (pg 804-5, ARIS 1,2)
• predict whether the sign of ΔS is positive, negative, or near zero for a chemical
or physical change.( pg 806, ARIS 3, example 18.1,3)
• describe how and why the entropy of a substance changes with temperature or
when a phase change occurs. (pg 805- 806)
• be able to describe the role of entropy in the solution process. (pg 805-806)
• calculate ∆S° for any reaction from tabulated absolute entropy values, S°. (pg
809, ARIS 4,6,7, example 18.2)
Know the second law of thermodynamics and explain the role that entropy plays in
determining whether a process will be spontaneous. (pg. 808-812, ARIS 5: Entropy of the
Universe is increasing…)
Know the third law of thermodynamics and explain why it’s needed to calculate
absolute entropies. (pg. 812-813: Entropy of a perfect crystal is zero at…)
Discuss how the second law leads to the definition of Gibbs free energy. (pg 814-815)
Know the definitions of standard state for elements, solids, liquids, gases and solutes in
solution. (pg 807, 253)
Calculate the standard free-energy change, ∆G°, at 25 oC from standard free energies of
formation. (pg 810 example 18.4)
Explain the relationship between the sign of the free-energy change, ∆G, and
whether a process is spontaneous in the forward direction. (pg 817-818, Table 18.3)
Predict how ∆G will change with temperature, given the signs for ∆H and ∆S. (pg. 818,
ARIS 8)
Use the equation ∆G = ∆H – T∆S to calculate the free energy change for a reaction and to
determine the temperature at which a nonspontaneous reaction becomes spontaneous.
(pg. 818-819, ARIS 9,10,11,12,13)
Understand the relationship between ∆G° and K (pg 821-823)
and be able to
• calculate ∆G° from K and perform the reverse operation. (Example 18.6,7, ARIS
14,15,16,17,18)
• explain how ∆G differs from ∆G° and discuss how ∆G changes during the
course of a reaction.(pg. 822)
• calculate the free-energy ∆G for given reaction concentrations. (example 18.8)
Understand the meaning of the Key Words on page 828.