The First Law of Thermodynamics states that the total energy of a closed system remains constant, meaning that the sum of the internal energy (U) of the system...
The First Law of Thermodynamics states that the total energy of a closed system remains constant, meaning that the sum of the internal energy (U) of the system and the work (W) done on the system is always equal to zero.
The First Law can be expressed mathematically as follows:
where:
is the change in energy
is the work done on the system
is the heat energy absorbed or released by the system
The First Law can be applied to various systems, including a gas, a solid, or a mixture of gases. The law can also be applied to systems undergoing different processes, such as an adiabatic expansion or a compression.
For example, when a gas expands against a vacuum, the work done on the gas is positive, meaning that the gas is doing work on the surroundings. This positive work is equal to the negative change in internal energy of the gas, which results in a net decrease in the total energy of the system. As a result, the total energy of the gas remains constant.
Another example is when a solid melts at a constant temperature. The internal energy of the solid is increasing as heat is being supplied to it, so the work done by the surroundings on the solid is positive. However, the negative change in internal energy of the solid results in a net decrease in the total energy of the system, maintaining a constant energy value