The first law of thermodynamics, also known as the law of energy conservation, is a fundamental principle in thermodynamics. It states that energy cannot be created or destroyed within an isolated system. Instead, energy can be converted from one form to another or transferred between the system and its surroundings in the form of heat or work.
The first law of thermodynamics can be mathematically expressed as:
ΔU = Q – W
- ΔU represents the change in internal energy of the system,
- Q denotes the heat added to the system, and
- W represents the work done on or by the system.
This equation essentially states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system or vice versa.
The internal energy of a system refers to the total energy possessed by the system, including the kinetic energy of its particles, the potential energy associated with their interactions, and any other forms of energy contained within the system.
Heat (Q) is the transfer of energy between two objects due to a temperature difference. When heat is added to a system, it increases the internal energy, causing the system to gain energy. On the other hand, when heat is removed from a system, it decreases the internal energy, causing the system to lose energy.
Work (W) is the energy transfer that occurs due to a force acting over a distance. Work can be done on a system (positive work) or done by a system (negative work). When work is done on a system, it increases the internal energy, and when work is done by a system, it decreases the internal energy.
The first law of thermodynamics establishes the principle of energy conservation and the interconversion of different forms of energy. It allows for the analysis of energy flow and transformations in various thermodynamic processes, such as heat engines, refrigeration systems, chemical reactions, and power generation. This law forms the basis for understanding energy transfer, energy balance, and the efficiency of energy conversion systems.