9.14 Summary of laws of thermodynamics
361
δG = δH − T δS .
(9.99)
For an isobaric change of a materially closed system, δH = δQ. If the system is
adiabatically closed, δQ = 0, so δG = −T δS. Since the entropy must not decrease,
the Gibbs free energy must not increase. Spontaneous reactions in a closed system
at fixed T and p must proceed in the direction that makes δG smaller.
From the 2nd Law, near equilibrium, dG| T ,p ≥ 0. This means the Gibbs free
energy has reached a minimum, and any small change in the particle numbers will
cause G to increase.
9.14 Summary of the Classical Laws of Thermodynamics
Thermodynamics relies on the observation that most systems near but not at
equilibrium, when left isolated, will tend toward equilibrium. In the process, local
excesses in pressure may be relieved by changes in volume, and local excesses in
temperature causes a redistribution of particles among the available energy states. 42
Macrosystems (systems with a large number of interacting particles), when near or
at thermal equilibrium, satisfy:
• The “zeroth” law of thermodynamics is taken as the observation that if system A
has the same temperature as B and B has the same temperature as C, then A will
have the same temperature as C.
• The first law of thermodynamics, taken as the energy conservation statement, is
often written as
dE = δQ − δW .
(9.100)
The left side is the change in the internal energy of a system. On the right is
the heat into the system minus the work done by the system. For systems with
a mixture of chemical components, the work term can be generalized to include
the energy transferred by the binding, unbinding, or recombining components.
• The second law may be stated as: There exists a property of a thermodynamic
system, called its entropy, S, found by integrating the heat input to the system
divided by its temperature through a reversible process from a standard state
with a standard value of the entropy. For a CLOSED system, the entropy never
decreases. In general,
42 The changes of a system to relieve stresses within is often called ‘Le Châtelier’s’ principle.
Physically, the principle comes from the action of natural forces and of the tendency toward greater
disorder predicted by probability theory.
361
δG = δH − T δS .
(9.99)
For an isobaric change of a materially closed system, δH = δQ. If the system is
adiabatically closed, δQ = 0, so δG = −T δS. Since the entropy must not decrease,
the Gibbs free energy must not increase. Spontaneous reactions in a closed system
at fixed T and p must proceed in the direction that makes δG smaller.
From the 2nd Law, near equilibrium, dG| T ,p ≥ 0. This means the Gibbs free
energy has reached a minimum, and any small change in the particle numbers will
cause G to increase.
9.14 Summary of the Classical Laws of Thermodynamics
Thermodynamics relies on the observation that most systems near but not at
equilibrium, when left isolated, will tend toward equilibrium. In the process, local
excesses in pressure may be relieved by changes in volume, and local excesses in
temperature causes a redistribution of particles among the available energy states. 42
Macrosystems (systems with a large number of interacting particles), when near or
at thermal equilibrium, satisfy:
• The “zeroth” law of thermodynamics is taken as the observation that if system A
has the same temperature as B and B has the same temperature as C, then A will
have the same temperature as C.
• The first law of thermodynamics, taken as the energy conservation statement, is
often written as
dE = δQ − δW .
(9.100)
The left side is the change in the internal energy of a system. On the right is
the heat into the system minus the work done by the system. For systems with
a mixture of chemical components, the work term can be generalized to include
the energy transferred by the binding, unbinding, or recombining components.
• The second law may be stated as: There exists a property of a thermodynamic
system, called its entropy, S, found by integrating the heat input to the system
divided by its temperature through a reversible process from a standard state
with a standard value of the entropy. For a CLOSED system, the entropy never
decreases. In general,
42 The changes of a system to relieve stresses within is often called ‘Le Châtelier’s’ principle.
Physically, the principle comes from the action of natural forces and of the tendency toward greater
disorder predicted by probability theory.