Thermo dynamics

Ever wondered why Thermo Dynamics is named so?

THERMO → Heat, Dynamics → Motion or flow

Basically, thermodynamics deals with all changes in energy or transfers of energy that accompany physical and chemical processes.

Important terms in Thermo Dynamics:  

  1. System, surrounding and Boundary: A system is defined as specific part of matter which is under experimental investigation and the rest of the universe i.e., all matter except system is called as “surrounding”. Boundary separates system and surrounding.
  2. Types of system: There are 3 types of system on basis of system and surroundings.

Types of system

Isolated System Closed System

Open System

1) No interaction with surroundings. 1) Interaction with surroundings is possible.

1) Interaction with surroundings is completely possible.

2) Exchange of matter and energy are not allowed i.e.,

ΔE = 0,

but Δm = 0

2) Exchange of energy with surrounding is allowed but not the matter

ΔE ≠ 0,

but Δm = 0

2) Exchange of energy as well as matter is  allowed

ΔE ≠ 0,

but Δm ≠ 0

  1. Type of system on basis of composition:
  •  Homogeneous system: A system is completely uniform throughout i.e., it is made of one phase only.
    Ex: a) A pure single solid, b) Mixture of gases etc.,
  • Heterogeneous system:  Made of multiple phases.
    Ex: a) Two or more immiscible liquids, b) Solid in water etc.
  1. Thermo dynamic properties – 2 types:

Thermo dynamics


1) This properties depend on quantity of matter present in the system.

1) This properties independent of quantity of matter present in the system.

2) Eg: Mass, Volume, Number of moles

2) Eg: Density, Pressure, Temperature, M.P, B.P, Specific heat, Refractive Index.

  1. State functions and Path functions:

     a. State functions:

  • Fundamental properties which determine the state of system are referred as “state functions”.
  • The change of in the state properties depends only on initial and final states of system.
    Eg: Pressure, Temperature, Volume, Enthalpy(H), Free energy (G), Entropy (S), Internal Energy (E), Number of moles (n).

     b. Path functions:

  • Quantities depending on path of a function are “path functions” or “path variables”.
    Eg: Heat, Work
  1. Types of processes: Change form one state to other is called “process”.

a. Isothermal process

b. Isochoric process

c. Isobaric process

d. Adiabatic process

e. Cyclic process

f. Reversible process

g. Irreversible process

a. Isothermal process: Temperature remains fixed i.e., operation at constant temperature

i.e., dT = 0


b. Isochoric process: Volume is kept constant i.e., operation at constant volume

i.e., dV = 0

we know, work = PdV

∴ Work = 0 for isochoric process.

c. Isobaric process: Pressure is kept constant i.e., operation is done at constant pressure

i.e., Δp = 0

d. Adiabatic process: This process is carried out under no exchange of heat. No exchange of heat takes place between system and surrounding

i.e., dq = 0

Eg: Thermos Flask. The temperature of system varies

e. Cyclic process: System undergoes number of processes and finally comes to the original position. (i.e., change in internal energy is zero)

f. Reversible process: This process occurs in finitesimally slowly. It is considered that this process proceeds from initial state to final state through an infinite series of small changes work obtained is maximum

g. Irreversible Process: Process goes from initial state to final state and can’t be reversed. This process is spontaneous in nature. All natural processes are irreversible in nature.