First Law of Thermodynamics

The word thermodynamics is the combination of therm and dynamics. The word “therm” stands for thermal. In simple words, thermal means heat. The word “dynamics” relates to the branch of mechanics. Thermodynamics states the relationship between heat, temperature, work, and energy. There are four laws of thermodynamics. However, this article will only cover the first law of thermodynamics.

First law of thermodynamics

The first law of thermodynamics relates internal energy and work done by a system to the heat supplied to it. The law affirms that heat is a form of energy. Thermodynamic processes come under the principle of conservation of energy, which refers to the fact that heat can neither be created nor destroyed. However, it can change from one form to another. Hence, the first law of thermodynamics is also the law for the conservation of energy. 

According to the first law of thermodynamics, if we give energy to an isolated system, some energy will come to use to change the system’s internal energy. However, the remaining energy will come to use in doing work.

The mathematical representation is ΔU = q + W

Where,

ΔU is the change in the internal energy of the system.

q is the algebraic sum of heat transfer. The heat transfer is between the system and the surroundings.

W is the work interaction of the system with its surroundings.

Applications of the first law of thermodynamics

After the concept of thermodynamics was established, many applications of thermodynamics were discovered. It helped invent many new devices and improved the workings of some pre-existing systems. The law is the basis of any machine or device that involves heat and work transfer processes, such as refrigerators, boilers, compressors, rockets, turbines, light bulbs, etc. The most common application of the first law of thermodynamics in our surroundings is in heat engines.

The working of an engine

Engines are all around us, in cars, bikes, trucks, aeroplanes etc. These engines work on the basis of the first law of thermodynamics. An engine includes a chamber, a piston, and an opening from where gas enters the chamber. A system near the engine creates sparks, and fuel starts burning in a small amount.

The fuel used in these engines is generally petrol, diesel, or kerosene. These fuels burn very rapidly and get converted into gas. The chamber’s small size helps trap the gas, which increases pressure. This pressure moves the piston, which further helps in the movement of the vehicle. Ultimately, you can observe the conversion of thermal energy into mechanical energy.

Heat engines

Heat engines also work on the principle of the first law of thermodynamics by transforming heat into work. The most common application of the first law of thermodynamics is in steam engines, commonly used in trains. At one time, steam engines were also used to make cars, which now commonly work on gasoline or diesel engines. However, as diesel and gas engines generate electricity using heat, they also use the first law of thermodynamics.

The working of a steam engine

A steam engine includes a big chamber, a compressor, and pistons. First, coal starts burning in a big chamber, which heats the water and creates vapours or steam. Then, the steam compresses into a compressor. The pressure of the steam moves the piston of the engine. This results in the movement of the train. The conversion here is from heat energy to mechanical energy.

The working of cooling machines

The working of refrigerators and ACs is also based on the first law of thermodynamics. Most cooling systems are based on a closed system. First, a gas present in the cooling systems, mostly hydrofluorocarbons (HFCs), compresses in a compressor. This compression increases the internal temperature of the gas. Then, the compressed gas is released into an ample space. This space can be a refrigeration area (as in the case of refrigerators) that suddenly decreases the gas temperature to extremely cold. This is how most cooling systems work.

Conclusion

The first law of thermodynamics relates internal energy and work done by a system to the heat supplied to it. The law is the basis of any machine or device that involves heat and work transfer processes, such as refrigerators, boilers, compressors, rockets, turbines, light bulbs, etc. The law is the basis of many principles in physics and chemistry.