Pr. CHIKHAOUI Abdallah Science & Technologies
The first year of: Science and Technology
Module: Thermodynamics (Chemistry 02)
Chapter 05: The second Principe of thermodynamics
1. Entropy (S):
Entropy is a thermodynamic state function that measures the degree of disorder or
randomness in a system. It plays a central role in determining the spontaneity of physical and
chemical processes:
➢ S: absolute entropy
➢ ΔS: change in entropy
➢ Unit: J/K.mol
2. Standard Entropy Change of a Reaction:
S = S ( product ) − S ( reac tan ts )
3. Dependence of Entropy on Temperature and Pressure:
Entropy is an extensive property that depends on temperature (T) and pressure (P). In most
practical cases, temperature has the dominant effect.
3.1. Entropy of a Solid:
For a solid undergoing a temperature change:
Note: This relation is valid as long as the substance remains in the solid phase. If a
phase change occurs, additional entropy contributions must be included.
This represents the entropy change when a substance melts from solid to liquid:
1
The first year of: Science and Technology
Module: Thermodynamics (Chemistry 02)
Chapter 05: The second Principe of thermodynamics
1. Entropy (S):
Entropy is a thermodynamic state function that measures the degree of disorder or
randomness in a system. It plays a central role in determining the spontaneity of physical and
chemical processes:
➢ S: absolute entropy
➢ ΔS: change in entropy
➢ Unit: J/K.mol
2. Standard Entropy Change of a Reaction:
S = S ( product ) − S ( reac tan ts )
3. Dependence of Entropy on Temperature and Pressure:
Entropy is an extensive property that depends on temperature (T) and pressure (P). In most
practical cases, temperature has the dominant effect.
3.1. Entropy of a Solid:
For a solid undergoing a temperature change:
Note: This relation is valid as long as the substance remains in the solid phase. If a
phase change occurs, additional entropy contributions must be included.
This represents the entropy change when a substance melts from solid to liquid:
1
