# thermo

**THERMODYNAMICS**

Investigations of energy conversion processes
in macroscopic systems as well as properties of matter that takes part in these
processes. **Thermodynamics** is broadly
interpreted to include all aspects of energy transformations, including power
generation, refrigeration, and relationships among the properties of matter.

Depending on the method – **two general kinds of the thermodynamics** may be distinguished:

-phenomenological (technical) thermodynamics, which uses the concepts related to measurements made by any macroscopic or mesoscopic scale.

-statistical (molecular) thermodynamics, which penetrates deeper into the construction of the substance, considering it as a collection of atoms and molecules, where a huge amount of molecules force to describe their behavior methods of mathematical statistics.

System is defined as a quantity of matter or a space chosen for a study

The space outside the system is called the surroundings.

The real or imaginary surface that separates the system from its surroundings is called the boundary: fixed and movable.

There are **two
types of the system**:

•Closed system consists of a fixed amount of substance, and no substance can cross its boundary.

•Open system: substance and energy can cross the system boundary.

An **intensive
quantity** is a physical quantity whose value does not depend on the amount
of the substance for which it is measured.

·Examples: temperature, density, velocity, viscosity, pressure and elasticity.

An **extensive quantity **is a physical
quantity whose value is proportional to the amount of substance as well as size
of the system it describes. Such a property can be expressed as the sum of the
quantities for the separate subsystems that compose the entire system.

·Examples: mass, energy, volume, enthalpy and entropy.

**Pressure** is defined as a normal force
exerted by a fluid per unit area. Pressure is defined for fluids (gas or a
liquid). Since pressure is defined as force per unit area, it has the unit of newton
per square meter (N/m2), which is called Pascal (Pa). The pressure unit Pascal
is too small for pressures encountered in practice, so there is used 1 kPa 10^{3}
Pa and 1 MPa 10^{6} Pa.

**Density** is defined as mass per volume unit.

**Specific volume** is defined as volume per mass unit.

**TEMPERATURE** is a measure of the average energy
of kinetic energy of particles in matter. When particles of matter, whether in
solids, liquids, gases, move faster or have greater mass, they carry more
kinetic energy, and the material appears warmer than a material with slower or
less massive particles.

**Function of state**

Consider a system not undergoing any change. At this point, all the properties can be measured or calculated throughout the entire system, which gives us a set of properties that completely describes the condition of the system. At a given state, all the properties of a system have fixed values.

**State function** is a property of a system that
depends only on the current state of the system, not on the way in which the
system acquired that state. They describe quantitatively an equilibrium state
of thermodynamic systems. Examples: energy, density, enthalpy, temperature,
entropy, density, specific volume.

**Energy**

**Mechanical energy** is the sum of the kinetic energy as
well as potential energy of gravity.

Mechanical energy as well as internal energy may be evaluated only if the reference state is established. There is necessary to choose a convenient reference state and assign a value of zero for a convenient property or properties at that state.

**Internal energy U**

This is energy of atoms, molecules and parts of molecules, which constitute the physical body. The internal energy covers:

– **Nuclear
energy**: energy associated with the strong bonds within the nucleus of the
atom itself.

– **Chemical
energy**: energy associated with the atomic bonds in a molecule.

– **Thermal
energy**: is the sum of the kinetic energies of the molecules in translate
motion, rotational motion and oscilation as well as potential energies.

**Thermodynamic
processes.**

Any change that a system undergoes from one equilibrium state to another is called a process, and the series of states through which a system passes during a process is called the path of the process. Any change that a system undergoes from one equilibrium state to another is called an equilibrium process, and the series of states through which a system passes during a process is called the path of the process. To describe a process completely, one should specify the initial and final states of the process, as well as the path it follows, and the interactions with the surroundings.

**Heat Q** is a part of the thermal energy
that is transferred through the system boundary without mass transfer as a result
of temperature difference. Heat may not be considered as a kind of energy. Heat
is a kind of thermal energy transfer. Heat is a process function. For various
processes the amount of heat absorbed by the system or transferred to the
surroundings is different. Heat delivered to the system is treated is assumed
as positive while heat transferred from the system to the surroundings is
assumed as negative.

**Technical work Lt**

The technical work is sum of the three absolute works: work of the delivery of substance inside the open system; work of process that is performed inside the system; work of transfer of substance from the system to the surroundings.

**Enthalpy H** is sum of the internal energy and
the so called transport energy pV.

Enthalpy is a function of state.

**The First Law of
Thermodynamics**
states that heat is a form of energy, and thermodynamic processes are therefore
subject to the principle of conservation of energy. This means that heat energy
cannot be created or destroyed. It can, however, be transferred from one
location to another and converted to and from other forms of energy.

“The First Law says that the internal energy of a system has to be equal to the work that is being done on the system, plus or minus the heat that flows in or out of the system and any other work that is done on the system”

**Definition of perfect
gas:** Fulfill gas
laws: Clapeyron, Avogadro and Dalton. Constant specific heats.

**Semi-perfect gases: **Fulfill gas laws: Clapeyron,
Avogadro and Dalton. The specific heat depend on temperature for given process
and substance.

**Equipartition theorem**

Internal energy is shared equally among all of its various forms; as a consequence – the average kinetic energy per degree of freedom in the translational motion of a molecule should equal that of its rotational motions.

**Isochoric process:** V = const; v = const. Heating and cooling
of gas (vapour) stored in the closed vessel.

**Isothermal process:** T = const