According to first law of thermodynamics what is the value of change in internal energy
Answers
The first law of thermodynamics refers to the change of internal energy of the open system, between its initial and final states of internal equilibrium.
The first law of thermodynamics can be captured in the following equation, which states that the energy of the universe is constant. Energy can be transferred from the system to its surroundings, or vice versa, but it can't be created or destroyed.
First Law of Thermodynamics: deltaEuniv = deltaEsys + deltaEsurr = 0
A more useful form of the first law describes how energy is conserved. It says that the change in the internal energy of a system is equal to the sum of the heat gained or lost by the system and the work done by or on the system.
First Law of Thermodynamics: deltaEsys = q + w
The sign convention for the relationship between the internal energy of a system and the heat gained or lost by the system can be understood by thinking about a concrete example, such as a beaker of water on a hot plate. When the hot plate is turned on, the system gains heat from its surroundings. As a result, both the temperature and the internal energy of the system increase, and deltaE is positive. When the hot plate is turned off, the water loses heat to its surroundings as it cools to room temperature, and deltaE is negative.
The relationship between internal energy and work can be understood by considering another concrete example: the tungsten filament inside a light bulb. When work is done on this system by driving an electric current through the tungsten wire, the system becomes hotter and deltaE is therefore positive. (Eventually, the wire becomes hot enough to glow.) Conversely, deltaE is negative when the system does work on its surroundings.
The sign conventions for heat, work, and internal energy are summarized in the figure below. The internal energy and temperature of a system decrease (deltaE < 0) when the system either loses heat or does work on its surroundings. Conversely, the internal energy and temperature increase (deltaE > 0) when the system gains heat from its surroundings or when the surroundings do work on the system.