Thermodynamics

Thermodynamics

  • Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy and matter.

Laws of Thermodynamics

  • The 0th law of thermodynamics states that if two separate systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other. This forms the basis of temperature measurement.

  • The first law of thermodynamics, also known as Law of Energy Conservation, states that energy cannot be created or destroyed in an isolated system.

  • The second law of thermodynamics claims that the entropy of an isolated system always increases. This law shows the asymmetry between forward and backward time directions.

  • The third law of thermodynamics states that the entropy of a perfect crystal at absolute zero is exactly equal to zero.

Heat and Work

  • Heat is the transfer of energy due to a temperature difference. It is denoted by ‘Q’.

  • Work is the transfer of energy by any process other than heat. It can be calculated using the formula W = Fd, where F is force and d is distance moved in direction of force.

  • Both heat and work are ways in which a system can transfer energy.

  • The total energy of a system is conserved. If the system does work on its surroundings or gives off heat, its internal energy will decrease.

Entropy

  • Entropy (S) is a measure of the randomness or disorder of a system. It increases as a system’s temperature increases.

  • Entropy is also a state function, meaning its value depends only on the state of the system and not on how that state was achieved.

Heat Engines

  • A heat engine is a device that converts heat to work. It operates between two heat reservoirs. Heat is absorbed from the high temperature source, and part of this energy is converted into work- the rest is rejected to the low temperature sink.

  • The efficiency of a heat engine is defined as the useful work done compared with the heat input. It is given by efficiency = (Work output / Heat input) x 100%.

  • The Second Law of Thermodynamics imposes a limit on the maximum possible efficiency of a heat engine.

Carnot Cycle

  • The Carnot Cycle is the ideal operating cycle for a heat engine and it consists of two isothermal processes and two adiabatic processes.

  • The engine with the Carnot cycle has the highest efficiency of any heat engine operating between two given temperatures.

  • This cycle helps understand the maximum possible efficiency a heat engine can achieve.