Chemistry Outcomes Review: Chapter 8

Entropy and Molecular Organization

In this chapter, we introduced the thermodynamic function, entropy, which is responsible for the direction of all spontaneous changes. We found that net entropy is a measure of the number of distinguishable arrangements of atoms, molecules, and energy quanta in a system and its surroundings and that net entropy always increases in spontaneous changes. The net entropy is the sum of positional and thermal entropies of the system and surroundings. The examples we used to understand and analyze the role of net entropy were phase changes in pure compounds and in solutions, osmosis, oxidation of glucose, solubility of ionic and molecular solutes, and the formation of micelles, phospholipid bilayers, and cell membranes.

We also introduced another thermodynamic function, the Gibbs free energy, which is directly related to net entropy changes, but is more convenient to calculate from system changes alone. Net entropy change and free energy can be used interchangeably to understand and analyze actual or hypothetical changes.

Check your understanding of the ideas in the chapter by reviewing these expected outcomes of your study.

You should be able to:

  • Relate the relative probability of two outcomes to the number of ways each outcome can be achieved [Sections 8.2, 8.3, and 8.4].
  • Calculate the number of distinguishable arrangements of a small number of identical particles (molecules) among a limited number of distinguishable locations [Section 8.3].
  • Relate mixing to osmosis and be able to explain both in terms of increasing number of distinguishable molecular arrangements [Sections 8.1 and 8.4].
  • Describe the conditions required for osmosis, predict the direction of osmosis, and calculate the osmotic pressure for aqueous systems [Sections 8.1, 8.4, and 8.13].
  • Calculate the number of distinguishable arrangements of a small number of identical energy quanta among a limited number of distinguishable atoms [Section 8.5].
  • Predict the direction and final outcome of energy transfer between two systems containing a countable number of energy quanta distributed among a countable number of distinguishable atoms [Section 8.5].
  • Relate the results for countable systems, both matter and energy distributions, to real systems [Sections 8.4 and 8.5].
  • Use the definition of entropy in terms of distinguishable arrangements to predict the relative entropies of different systems, for example, phases of matter or reactants and products of a reaction [Sections 8.7, 8.10, 8.12, 8.13, and 8.14].
  • Distinguish between positional and thermal entropy changes for a process and combine them to determine net entropy change for the process [Sections 8.6, 8.7, 8.9, 8.10, 8.12, and 8.13].
  • Use positional entropy changes and the relative thermal entropy changes for the same energy change at different temperatures to analyze and predict the direction of phase changes in pure compounds and solutions [Sections 8.7 and 8.10].
  • State the criterion for equilibrium in chemical systems and relate the state of equilibrium to the positional and thermal entropy changes occurring [Sections 8.7 and 8.8].
  • Explain the relationship of Gibbs free energy change to net entropy change for a process and use the sign and/or magnitude of either one to predict whether the process is possible, not possible, or in equilibrium [Sections 8.8 and 8.12].
  • Calculate the free energy change for a process in a system using values for the enthalpy and entropy changes for the process [Section 8.8]
  • Use standard enthalpies and standard free energies of formation, and standard entropies (from tabulated values) to calculate the standard enthalpy, free energy, and entropy changes for a reaction [Section 8.12].
  • Predict the direction of the positional entropy change(s) that must occur to produce the observed effects of heating or cooling a system, such as a rubber band [Section 8.9].
  • Calculate freezing point lowering, boiling point elevation, and osmotic pressure for solutions [Sections 8.10 and 8.11].
  • Use experimental values for colligative properties to determine the concentration of solutes in the solution and/or the molar mass of the solute [Sections 8.10 and 8.11].
  • Explain in words, equations, diagrams, and/or molecular-level sketches the origin and direction of positional and thermal entropy changes for dissolving ionic and molecular solutes in water and predict the observable outcomes [Sections 8.11 and 8.13].
  • Explain in words, equations, diagrams, and/or molecular-level sketches the origin and direction of positional and thermal entropy changes for formation of micelles and phospholipid bilayer membranes by ambiphilic molecules [Section 8.14].
  • Use words and/or molecular level sketches to describe the structure and properties of micelles, bilayer membranes, and liposomes [Section 8.14].
  • Connect the formation of organized collections of molecules to increases in positional and/or thermal entropy in the system and surroundings that drive the organization [Sections 8.7, 8.14, 8.14, and 8.15