The invention of the steam engine is generally accepted as being one of the most significant factors responsible for unleashing the industrial revolution. However, subsequent technological advances were critically dependent on increasing the efficiency of machines, that is, increasing the delivery of mechanical energy per unit of input thermal energy. These considerations led to investigations into quantifying parameters of the basic laws of thermodynamics involving transformation of thermal energy to mechanical energy. The phenomenon of heat transfer is inherent in the conceptual formulation of energy in the context of thermodynamics. The transfer of heat (Q) can be quantified by the system temperature (T) and a property (S) that defines the change of state of the whole system (i.e., Q = T.S or S = Q/T). Whilst T can be readily measured, S is essentially a conceptual entity that is qualitatively defined by all the individual parts of the system (down to the microparticles) that constitute the system structure. This implies that if there is no change in the system structure, there is no change in the order of the system parts, and so there is no energy transfer. Hence, the corollary is that when energy (heat) is transferred, there is, by necessity, a change in structural elements of the whole system, and the changes can be at either the macroscale or the microscale, or both. Thus, transfer of energy is always associated with an increase in disorder of the system due to the system undergoing transformation. This was the basic notion that led to the original definition of the parameter S as "entropy" by Rudolph Clausius in 1865, using the original Greek roots τροπ? for "transformation" 1. Indeed, for the physical universe, this is fundamental to the second law of thermodynamics, which states that entropy (or disorder) always increases with time.
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