Thermodynamics
Thermodynamics is a macroscopic science, and at its most fundamental
level, is the study of two physical quantities, energy and entropy. Energy may
be regarded as the capacity to do work, whilst entropy may be regarded as a
measure of the disorder of a system.
Thermodynamics considers the relationship between the system-the reaction, process or
organism under study and the surroundings-the
rest of universe.
System:
Open system: matter and energy may be interchanged between the
system and surroundings.
Closed system: energy may be exchanged between the surroundings and
system, but the amount of matter in the system remains constant.
Isolated system: neither matter nor energy may be exchanged with the
surroundings.
Isothermal process: a process which is held at constant temperature is
referred to as isothermal process.
Heat: heat is the transfer of energy as disorderly motion as the result of
temperature difference between the system and the its surroundings.
Work: work is the transfer of
energy as orderly motion. In mechanical terms, the work is equal to the product
of the force and the distance moved against it. Work in chemistry systems generally
manifests itself in only a limited number of forms. Those most commonly
encountered are pressure-volume(PV)work and electrical work.
Internal energy: A fundamental parameter in
thermodynamics is the internal energy
denoted as U. Internal energy is the
sum total of all kinetic and potential energy within the system. U is a state function, in all practical
systems, the value of U itself can not be measured, thermodynamics therefore
only deal with changes in U, denoted ΔU. The sign of ΔU is important, when a
system loses energy to the surroundings, ΔU has a negative value. When the internal
energy of a system is increased by gain of energy, ΔU has a positive value.
Extensive properties and intensive
properties:
An extensive property is one
in which the value of the property changes according to the amount of material
which is present. For example: volume; mass; internal energy. The value of an
intensive property is independent of the amount of material present. For example:
temperature; pressure; density of a substance.
state function: The value of a particular property for
a system depends on the state of the system, it is referred to as a state
function.(pressure, volume, internal energy and entropy)
path function: The value of a property depends upon
the path by which a system in one state is changed into another state, it is
referred to as a path function.(work and heat)
The distinction is very important because it is
necessary in performing calculations.
The first law: The first law of thermodynamics states that “The total energy of an
isolated thermodynamic system is constant”. The law is often referred to as the conservation of energy。In other words,
energy maybe lost from a system in only two ways, either as work or as heat, U
cannot change in any other way. Thus, for a finite change:
ΔU=Q-W or dU=δQ-δW
heat: Q is the heat. The Q is positive if the
heat is gained by system, and the Q is negative if the heat is lost from the
system.
Work:
W is the work. The W is positive if the work is done by system in
expanding, and the W is negative when the system is compressed.
When a reaction
releases a gas at a constant external pressure Pex,
the work done is given by:
W= Pex ΔV or δW= Pex
dV
First of all, I would like
to introduce myself, My name is Li Naijun ,graduated from Northern East
University, with bachelor degree in 1982, and a master degree in 1988. and then
in 1994-1995,I studied in Edinbergh University U.K， researched the nano-magnetic material. I lectured the physical chemistry
for 22 years. My telephone number is 83971432. After Pm 6 o’clock, I will be at
home.