Fundamentals of THERMODYNAMICS

Introduction• Thermodynamics is science of energy transfer and its effects on

properties.

• Main aim is to convert disorganized form of energy into organized form of energy in an efficient manner.

• Based on the macroscopic approach which does not require knowledge of behavior of individual particles and is called classical thermodynamics.

System, Surroundings, and Boundary• A thermodynamic system is defined as quantity of matter or a

region in space chosen for study.

• The region outside the system is called surroundings.

• The real or imaginary surface that separates the system from its surroundings is called boundary.

• Universe = System + Surroundings

Types of System• Closed System

• Open System

• Isolated System

Closed System• A closed system consists of fixed amount of mass and no

mass may cross the system boundary but energy in form of heat and work may cross the system boundary.

• The closed system boundary may move.

• Examples of closed systems are sealed tanks and piston cylinder devices without valves.

Open System or Control Volume• An open system has mass as well as energy crossing the

boundary, called a control surface.

• Examples of open systems are pumps, compressors, turbines, valves and heat exchangers.

Isolated system• An isolated system is one in which there is no interaction

between the system and surroundings.

• It is of fixed mass and energy, and there is no mass or energy transfer across the system boundary.

• Examples of isolated system are universe and hot coffee in a well insulated flask.

Closed, Open, and Isolated Systems

Types of System

Energy Transfer

Mass Transfer

Examples

Closed System Yes No Gas in a sealed container

Open System Yes Yes Turbines, pumps, valves etc.

Isolated System

No No Universe, Thermoflask

Properties of a System• Any measurable characteristic of a system in equilibrium is called a

property.

• The property is independent of the path used to arrive at the system condition.

• Properties are point functions.

• Properties are exact differentials.

• Properties may be intensive or extensive.

Extensive Properties• Extensive properties depends on size or mass of the system.

• Some extensive properties are:

a. Mass

b. Volume

c. Total Energy

d. Electric Charge

e. Magnetization

Intensive Properties• Intensive properties are independent of size or mass of the system.

• Some intensive properties are:

a. Pressure

b. Temperature

c. Density

d. Velocity

e. Viscosity

Important points w.r.t Properties• Extensive properties per unit mass are intensive properties. For

example, the specific volume v, is defined as

v = = = = Intensive

• Specific Properties are intensive properties.

Thermodynamics Equilibrium A system is said to be in thermodynamic equilibrium if it maintains

a. Thermal Equilibrium ( Equality of Temperature )

b. Mechanical Equilibrium ( Equality of Forces / Pressure )

c. Chemical Equilibrium ( Equality of Chemical Potential )

State, Path, and Process• Condition of a system as defined by properties of system is known

as state of a system.

• Series of state of system through which process occurs is known as path of a system.

• Any change of state of a system is known as process.

• Some of the processes are-

Process Property held constant

Isobaric Pressure

Isothermal Temperature

Isochoric Volume

Isentropic Entropy

Thermodynamic cycle• A system is said to have undergone a cycle if the initial and final

points are same.

• Minimum number of processes required for a cycle are 2.

• For a cycle change in property is equal to zero.

Pure Substance• A substance is said to be a pure substance if it is

a. Homogeneous in Chemical Composition.

b. Homogeneous in Chemical Aggregation.

• Examples of pure substance are atmospheric air, steam-water mixture and combustion products of a fuel.

• Phase ( solid, liquid, gas ) is not considered while determining pure substance.