Reversibile and Irreversibile Processes ¶ These statements emerged out years of experience gained by engineers trying to efficiently convert heat to work using devices commonly called as heat engines and those working to extract heat from cooler bodies and transferring them to hotter bodies using devices called as heat pumps (refrigerator). The wonderful thing about these statements are that they have never been found violated till now. Therefore they have no proof and must be accepted as it is. These new laws, happen to be purely empirical in nature and are postulated as statements of denial (what can not be done). The second law of thermodynamics gives us those rules, to plug the gaps that are left by the first law. So we need to come up with a better understanding or rules that can help us on situations such as the above. Limits to Efficiency: While it is possible to convert all work to energy, but all heat does not seem to ever get converted to work. An ocean at ambient temperature may have a lot of thermal energy, but steam generated in boiler can much more easily move turbines and produce work. Quality of Energy: In addition it is also observed that all energy is just not the same in terms of the ease with which it lends itself for exploitation say extraction of useful work. But a body lying on the ground will not pick heat from environment and elevate itself spontaneously. Similarly, if a body falls to ground its kinetic energy would convert to heat and get wasted. Pressurised air in a tank will always escape to atmosphere when the valve is opened, but atmospheric air will never on its own compress and store itself in the tank. The reverse process of surroundings lossing heat and the body becoming hotter would never occur spontaneously. For example, A hot body looses heat when kept in cold surroundings spontaneously. Spontaneity/directionality of processes : We observe that some processes occur spontaneously while their reverse counterparts do not. The inadequacy of first law comes to the fore as we make the following observations in life. In everyday life we observe that certain processes and their behaviour can not fully be explained by the first law of thermodynamics.
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