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  • Print publication year: 2019
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15 - Thermodynamics



In our day-to-day life, we come across several instances in which one form of energy is converted into another form. When you rub your hands they become hot; similarly, if a piece of metal is hammered, it becomes hot. In both the above examples, mechanical energy is converted into heat energy. On the other hand, you are well aware that when water is heated, steam is generated, which is used to move turbines for the generation of electricity. Here, heat energy produces mechanical work. There can be numerous examples for the conversion of one form of energy into another. The science that deals with the interconversion of heat to work or any other form of energy is termed as thermodynamics. The term is self-indicative of what is happening – “thermo” is from temperature, which means energy and ‘dynamics’ pertains to motion or work. Chemical thermodynamics is a portion of thermodynamics that deals with the study of the processes in which chemical energy is involved.

The principles of interconversion of energy in various forms are summarized in the three basic laws of thermodynamics. The first law is a statement of the law of conservation of energy, that is, energy cannot be created or destroyed, it can merely be converted from one form to another. The second law of thermodynamics explains the occurrence of various reactions spontaneously. It introduces the concept of ‘entropy’ or ‘disorder’ or ‘randomness’ to predict the spontaneous occurrence of chemical reactions. The third law of thermodynamics relates, among other things, to the experimental approach to absolute zero.

Thermodynamics is a powerful tool for chemists. It studies the relationship between the effects of temperature on physical systems at the macroscopic scale. It helps in predicting whether a reaction will occur or not. It also helps to predict the direction in which a chemical reaction will occur.

However, thermodynamics does not show how fast a reaction will proceed. Let us now deal with the fundamental concept of thermodynamics.

Terminology of Thermodynamics

It is necessary to define certain terms and expressions commonly used in thermodynamics.

(I) System and surroundings

System A thermodynamic system may be defined as that portion of the universe which is under observation or study.