1st Law of Thermodynamics - The first law is related to the conservation of energy in simple words and explains that energy can neither be created nor destroyed, but can be converted from a shape to another. The law of thermodynamics defines the relationships between physical quantities, namely temperature, energy and entropy. The relationship of these physical quantities can be given in different ways relating to the Work, Internal Energy of a system [1].Applications of the 1st law of thermodynamics: Heat engine - Heat engines are designed based on the 1st law, it is a idealization of a set of processes used by spark-ignition internal combustion engines. Engines ingest a mixture of fuel and air, which is then compressed by a cylinder-piston arrangement, which causes the fuel to react, thus effectively adding heat by converting chemical energy into thermal energy, which leads to the expansion of combustion products, and then expel the combustion products and replace them with a new charge of fuel and air. Therefore the chemical reaction is converted into rotational motion along with the heat released into the environment [3].Refrigerators - The second major application of the 1st Law where the goal of a refrigerator is to lower the internal energy of a body at low temperature and transfer that energy to the higher temperature environment [3]. To do this you need to work. The medium for energy exchange is a working fluid that circulates in a circuit through a series of devices. These devices exploit to increase and eliminate energy from the working fluid. As the refrigerant circulates around the circuit, its internal energy is alternately raised and lowered by a series of devices. Turbine: Turbine engines are widely used for jet propulsion and f...... middle of paper..... .es upwards and removes all the exhaust gases inside the pressure cylinder constant. Carnot Cycle - The Carnot cycle shows that heat is absorbed from the high temperature reservoir and rejected into the low temperature reservoir, which can be considered the foundation of the second law of thermodynamics. The law states that the smooth movement of heat occurs from the high-temperature reservoir to the low-temperature reservoir, and to move it from the low-temperature reservoir to the high-temperature reservoir requires external work to be performed [1]. Diesel Engine: Diesel engine is an application of the 2nd law of thermodynamics. It is similar to the Otto cycle, the fuel used is different, which makes the engine work different, the thought output is rotational motion. The compression ratio is much higher than any other since no spark plug is used, only the adiabatic compression ratio leads to combustion of the fuel [4].