The Foundations of Chemistry

OUTLINE

Heat Changes and Thermochemistry

15-1 The First Law of

Thermodynamics

15-2 Some Thermodynamic Terms

15-3 Enthalpy Changes

15-4 Calorimetry

15-5 Thermochemical Equations

15-6 Standard States and Standard

Enthalpy Changes

15-7 Standard Molar Enthalpies of

Formation, 
Hf^0

15-8 Hess’s Law

15-9 Bond Energies

15-10 Changes in Internal Energy,


E

15-11 Relationship of 
Hand 
E

Spontaneity of Physical and

Chemical Changes

15-12 The Two Aspects of

Spontaneity

15-13 The Second Law of

Thermodynamics

15-14 Entropy, S

15-15 Free Energy Change, 
G,and

Spontaneity

15-16 The Temperature Dependence

of Spontaneity

OBJECTIVES

After you have finished studying this chapter, you should be able to

• Understand the terminology of thermodynamics, and the meaning of the signs of changes


• Use the concept of state functions


• Carry out calculations of calorimetry to determine changes in energy and enthalpy


• Use Hess’s Law to find the enthalpy change,
  H, for a reaction by combining

thermochemical equations with known 
H values

• Use Hess’s Law to find the enthalpy change,
  H, for a reaction by using tabulated
  values of standard molar enthalpies of formation


• Use Hess’s Law to find the enthalpy of formation given
  H for a reaction and the
  known enthalpies of formation of the other substances in the reaction


• Use the First Law of Thermodynamics to relate heat, work, and energy changes


• Relate the work done on or by a system to changes in its volume


• Use bond energies to estimate heats of reaction for gas phase reactions; use
  H values

for gas phase reactions to find bond energies

• Understand what is meant by a product-favored process; by a reactant-favored process


• Understand the relationship of entropy to the order or disorder of a system


• Understand how the spontaneity of a process is related to entropy changes—the Second

Law of Thermodynamics

• Use tabulated values of absolute entropies to calculate the entropy change,
  S


• Calculate changes in Gibbs free energy,
  G, (a) from values of
  H and
  S and (b)

from tabulated values of standard molar free energies of formation; know when to use

each type of calculation

• Use
  G to predict whether a process is product-favored at constant T and P


• Understand how changes in temperature can affect the spontaneity of a process


• Predict the temperature range of spontaneity of a chemical or physical process

The launch of the space shuttle

requires about 2
 1010 kilojoules

of energy. About one sixth of this

comes from the combustion of

hydrogen, H 2 , in oxygen, O 2. The

rest comes from the explosive

decomposition of ammonium

perchlorate, NH 4 ClO 4 , in

solid-fuel rockets.