## an introduction

The science of thermodynamics, or what is known as thermodynamics, is one of the branches of statistical mechanics, which studies changes in thermal energy resulting from changing some physical quantities of this system, such as: change in pressure, volume, and temperature, in addition to studying the potential energy within this system, that is, the energy stored within atoms and molecules. Such as chemical energy stored within ionic bonds and co-bonds, and nuclear energy contained in heavy and unstable atoms such as uranium.

The science of thermodynamics studies and clarifies how heat and energy are transferred from one body to another, and how these are transformed into other forms such as the change of thermal energy into mechanical energy, which is used, for example, in steam machines and internal combustion engines such as car engines, and also studies how to convert thermal energy into electrical energy. As it happens in solar power plants, dams and rivers, through this article we will learn about one of the laws of thermodynamics, which is the second law of thermodynamics, learn about the variables on which this law depends, and show the most important results we obtained from this law in nature.

## Second Law of Thermodynamics

The laws of thermodynamics study physical systems in which changes in energy occur due to the influence of the surroundings in it, in addition to changes in other physical quantities such as heat and pressure. Examples of spontaneous and non-spontaneous changes are when a hot body cools, it happens automatically, while the process of converting a cold body to hot does not happen automatically, but we need energy to heat it, and also when we put gas in an empty place, this gas expands, but the opposite does not happen, meaning that Gas does not shrink automatically when placed in an empty container. Another example is that when chemicals interact with each other, these reactions go to equilibrium and the opposite does not happen.

## Formula for the second law of thermodynamics

Through these observations, the German scientist Rudolf Clausius formulated the second law of thermodynamics, which depends on the spontaneous change in any system associated with a specific physical quantity called entropy. The German scientist found that any system that wants to reach equilibrium automatically or in which natural processes occur Automatically, the entropy of this system either remains constant or increases, and the German scientist showed through mathematical equations that the entropy is a measure of the irregularity of the system and the increase in chaos in it, where he found that the change in entropy with respect to time in any system increases, for example when the sugar inside a certain liquid, the sugar molecules will spread and distribute in the liquid evenly, and in return, the chaos and irregularity increases in this case, the sum of the entropy of each substance separately (the sugar plus a liquid) is less or equal to the entropy of the mixture (when sugar is dissolved in the liquid), and the results which we get from the second law of thermodynamics:

• No machine can be built in perpetual motion.
• There is no spontaneous change that transfers heat from the cold object to the hot object or the cold object becomes hot spontaneously.
• All processes in which mixing occurs between two or more systems are irreversible, i.e. the entropy of the mixture is constantly increasing, and any process in which there is a loss of energy resulting from friction is also an irreversible process.

The second law of thermodynamics

writing – on the date : – Last updated: 2022-06-19 01:18:01