Lecture #19: March 18-19

Review sections 5.2 – 5.7 in the textbook, especially topics including: The 1st Law of Thermodynamics, Enthalpy, and how q and ΔH are related.

In Chapter 5, the term enthalpy was introduced and in this chapter we will use enthalpy and introduce a new concept, entropy, to tell a more complete story of Thermodynamics.

First, we will look into combustion reactions (which are exothermic) and see that as we progress from reactants to products there is a lowering in the potential energy stored in the chemical bonds, and the potential energy is converted to thermal energy (release of heat).

19.1 Thermodynamics

The first law of Thermodynamics provides the means for accounting for energy, but it gives no hint as to why a particular process occurs in a given direction. A process is considered to be spontaneous if it occurs without outside intervention, and the driving force for a spontaneous process is an increase in entropy. We can define entropy as the measure of randomness or disorder and entropy can be expressed mathematically using macro/microstates and we can also compare the entropy of various systems.

19.1 Spontaneous Process and Entropy

Show PHET tutorial of an ideal gas.

19.3 Macro and Micro States

19.3 Comparing Entropy of Various Systems

Mastering Chemistry Tutorial Question:
•Qualitative Predictions About Entropy

Mastering Chemistry Tutorial Question:
•The Boltzmann Equation

The second law of Thermodynamics states that in any spontaneous process there is always an increase in entropy of the universe.

19.3 2nd Law of Thermodynamics

The third law of Thermodynamics states that the entropy of a pure crystal at zero degress kelvin is zero. The change in entropy of a reaction can be calculated from the standard entropy of each substance.

19.3 3rd Law of Thermodynamics

Mastering Chemistry Tutorial Question:
•Entropy and the Second Law of Thermodynamics