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# Preparation Tips for Concept: The Thermodynamics of Physics Class 11?

Thermodynamics is a very scoring subject. It is all about MCQ Practice. After completing the basics, practice the MCQs and study every question of the module thoroughly. About the time required to complete the thermodynamics chapter of physics of class 11, it depends on person to person because everyone’s learning abilities is not the same.

Notes on class 11 chapter 6- Chemical Thermodynamics

Thermodynamics

Thermodynamics is defined as the study of the flow of mass, heat and energy.

Terminology of thermodynamics

• System: That part of the universe which can be observed is known as the system.
• Surrounding: The remaining part of the universe except the part which is not under observation is called as surroundings.

Or in other words,

Universe = System + Surrounding

• Types of the system:

-Open system: Where there is both flow of mass and heat energy, it is known as open system. For example, the human body

-closed system: It is that system where there is flow of heat energy with constant mass.

Example: Pressure cooker

-Isolated system: It is that system where none of the flow takes place.

State of the system

It is that system which can be defined and changed with regard to the changes in state variables i.e. P, V, T and n. These variables describe the conditions of the system. If there is any change in any one of them, then there will also be a change in the system.

Properties of the system:

• Intensive properties- Properties which are dependent upon concentration and which are not dependent on mass or the total number of particles in the system are called intensive properties which include pressure, refractive index, density, etc.
• Extensive properties- Properties which are dependent on the mass or the total number of particles in the system are called extensive properties which include volume, total energy, etc.

State and path function:

• State function- The state function is independent of the path it follows but is dependent upon the initial and final states when there is a change in the system. Examples are internal energy, enthalpy, etc.
• Path function- The path function is dependent upon the path which it follows when there are changes in the system. Examples are work, heat, etc.

Thermodynamic equilibrium

Thermodynamic equilibrium is the system which is in equilibrium and where the states variables do not change. Below are three types of equilibrium:

• Mechanical equilibrium- Mechanical equilibrium takes place when there is absence of mechanical motion, constant pressure and volume.
• Thermal equilibrium- Thermal equilibrium takes place due to the constant heat and temperature with regard to time.

Internal energy

Internal energy can be defined as the sum total of the parts of energy which are acted upon by the internal factors of the system. It is denoted by U or E.  The system which is under observation behaves like an ideal gas system dependent only on kinetic energy. Thus, it is the function of temperature as

That is why, the internal energy is said to be state function.

Modes of energy transport

• Heat- when there are temperature differences in the system and surroundings, then transfer of energy takes place which is known as heat (Q). When the system gets heated up, the kinetic energy of the molecules also increases which leads to the increase in the internal energy.
• Work- The energy which is needed to overcome the external forces on the system is called as work (W). When a system increases, the internal energy is lessened. When the system contracts, the internal energy increases.

The first law of thermodynamics

According to the first law of thermodynamics, energy can neither be created nor destroyed.

The signs of convections are as follows:

Reversibility

The process changes its direction by infinitesimal change in the system or surrounding. Then goes back to its initial state through the original path. For reversibility to occur, no dissipative forces must be there and the state must be quasi-static.

• Quasi-static state- In this state, the system is in static state at all times but not in reality. The motion is very slow. So, the system appears to be in equilibrium with the surroundings.

Expansion work

The work which is done as a result of changes in the volume of the system is known as expansion work. Whether it is expansion or contraction, the external pressure is taken as the driving force.

Cyclic process

In cyclic process, the process goes back to its original and initial state.

Enthalpy

Enthalpy is that thermodynamic state function where the total energy is stored in the system and the energy which is required to do the work.