In thermodynamics, energy is a fundamental concept that refers to the capacity of a system to do work or transfer heat. It is a scalar quantity associated with the state of a system and is conserved, meaning it cannot be created or destroyed but can be converted from one form to another.
Work and heat are two ways in which energy can be transferred to or from a system:
Work: In thermodynamics, work is defined as the process of transferring energy to or from a system by means of a force acting through a displacement. It is the mechanical transfer of energy that occurs due to the application of external forces on a system. For example, when a gas expands and pushes a piston, it performs work on the surroundings. Work is represented by the symbol "W" and is expressed in units of energy (such as joules).
Heat: Heat, on the other hand, is the transfer of thermal energy between systems at different temperatures. It occurs due to the temperature difference between the system and its surroundings. Heat transfer can happen through conduction, convection, or radiation. In thermodynamics, heat is represented by the symbol "Q" and is also expressed in units of energy (such as joules).
Energy can exist in various forms, and these different forms can be converted from one to another. Some common forms of energy encountered in thermodynamics include:
Kinetic Energy: This is the energy associated with the motion of an object. In thermodynamics, it is often related to the motion of molecules in a system.
Potential Energy: This is the energy associated with the position or configuration of an object. It includes gravitational potential energy and elastic potential energy, among others.
Internal Energy: This is the total energy possessed by a system due to the motion, position, and interaction of its molecules or particles. It includes both the kinetic and potential energies at the microscopic level.
In thermodynamics, the first law of thermodynamics, also known as the law of energy conservation, states that the change in the internal energy of a system is equal to the heat added to the system minus the work done by the system:
ΔU = Q - W
where ΔU is the change in internal energy, Q is the heat added to the system, and W is the work done by the system. This equation shows how energy can be transferred between a system and its surroundings through heat and work.