Thermodynamics

Thermodynamics is a branch of science which deals with exchange of heat energy between bodies and conversion of the heat energy into mechanical energy and vice-versa.

Some definitions

(a)Thermodynamics system

(i) It is  a collection of an extremely large number of atoms or molecules.

(ii) It is confined with in certain boundaries.

(iii) Anything outside the thermodynamics system to which energy or matter is exchanged is called its surroundings.

(iv) Thermodynamics system may be of three types:

·         Open system: It exchange both energy and matter with the surroundings.

·         Closed system: It exchange only energy(no matter) with the surroundings.

·         Isolated system: It  exchange nither energy nor  matter with the surroundings.

(b) Thermodynamics variables and equations of states: A thermodynamics system can be described by specifying its pressure , volume, temperature , internal  energy and the number of moles. These parameters are called thermodynamics variables. The relation between the thermodynamics variables (P, V, T) of the system is called equation of state.

For u moles of an ideal gas , equation of state is PV = uRT and for 1 mole an ideal gas equations is   PV = RT.

(c) Thermodynamics equilibrium: In steady state thermodynamics variables are independent of time and the system is said to be in state of thermodynamics  equilibrium. For a system to be in thermodynamics equilibrium , following conditions must be fulfilled.

(i) Mechanical equilibrium : There is no unbalanced force between the system and its surroundings.

(ii) Thermal equilibrium : There is a uniform temperature in all parts of the system and is same as that of surrounding.

(iii) Chemical equilibrium: There is a uniform chemical composition through out the system and the surroundings.

(d) Thermodynamics process: The process of change of state involves change of thermodynamics variables such as pressure P, volume V, and temperature T of the system. The process is known as thermodynamics process. Some important process are:

·         Isothermal process : Temperature remain constant.

·         Adiabatic process: NO transfer of heat.

·         Isochoric (isovolumic process): Volume remain constant.

·         Cyclic and non-cyclic process: Incyclic process inital and final state are same while in non-cyclic process these state are different.

·         Reversible and irreversible process.

(e) Indicator diagram : Whenver the state of gas (P,V,T) is changed , we say gaseus system is undergone thermodynamics process. The graphics representation of the change in state of a gas by a thermodynamics process is called indicator diagram. Indicator diagram is plotted generally in pressure and volume of gas.

Zeroth law of Thermodynamics

If a system A and B are each in thermal equilibrium with a third system C, then A and B are in the thermal  equilibrium with each other.

·         The zeroth law leads to the concepts of temperature. All  bodies in thermal equilibrium must have a comman property which has the same value for all of them. This property is called the temperature.

·         The zeroth law came to light long after the first and seconds laws of thermodynamics has been discovered and numbered. It is so because it logically the first and second of thermodynamics.