Second law of thermodynamics Entropy [Mechanical engineering]

# Second law of thermodynamics Entropy

Entropy and the Second Law of Thermodynamics

The second law of thermodynamics (the entropy law or law of entropy) was formulated in the middle of the last century by Clausius and Thomson following Carnot's earlier observation that, like the fall or flow of a stream that turns a mill wheel, it is the "fall" or flow of heat from higher to lower temperatures that motivates a steam engine. The key insight was that the world is inherently active, and that whenever an energy distribution is out of equilibrium a potential or thermodynamic "force" (the gradient of a potential) exists that the world acts spontaneously to dissipate or minimize. All real-world change or dynamics is seen to follow, or be motivated, by this law. So whereas the first law expresses that which remains the same, or is time-symmetric, in all real-world processes the second law expresses that which changes and motivates the change, the fundamental time-asymmetry, in all real-world process. Clausius coined the term "entropy" to refer to the dissipated potential and the second law, in its most general form, states that the world acts spontaneously to minimize potentials (or equivalently maximize entropy), and with this, active end-directedness or time-asymmetry was, for the first time, given a universal physical basis. The balance equation of the second law, expressed as S > 0, says that in all natural processes the entropy of the world always increases, and thus whereas with the first law there is no time, and the past, present, and future are indistinguishable, the second law, with its one-way flow, introduces the basis for telling the difference.
The active nature of the second law is intuitively easy to grasp and empirically demonstrate. If a glass of hot liquid, for example, as shown in Figure 3, is placed in a colder room a potential exists and a flow of heat is spontaneously produced from the cup to the room until it is minimized (or the entropy is maximized) at which point the temperatures are the same and all flows stop.

A glass of liquid at temperature TI is placed in a room at temperatureTII such that . The disequilibrium produces a field potential that results in a flow of energy in the form of heat from the glass to the room so as to drain the potential until it is minimized (the entropy is maximized) at which time thermodynamic equilibrium is reached and all flows stop. refers to the conservation of energy in that the flow from the glass equals the flow of heat into the room. (From Swenson, 1991a. Copyright 1991 Intersystems Publications. Adapted by permission).

Figure 4 shows various other potentials and the flows they would produce. Of important theoretical interest for this paper is the fact that Joule's experiment (Figure 2) while designed to

Further examples of potentials that follow from nonequilibrium distributions of energy. Whenever energy (in whatever form) is out of equilibrium with its surroundings, a potential exists for producing change that, following the second law, is spontaneously minimized.

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### FAQ ##### How does the second law of thermodynamics (entropy) apply to burning biomass? | Yahoo Answers

The same way burning anything does...the heat energy is lost to the environment and becomes high entropy unrecoverable and useless energy. So the low entropy potential energy contained in the mass morphs into the high entropy radiant and heat energy.
But that's true of all combustion. The fuel makes no difference. ##### second law of thermodynamics- entropy..? | Yahoo Answers

You should have an ideal gas formula which will find the entropy change between two states, knowing the P & T for both states.
If a process occurs with no heat transfer, entropy wouldn't change if the process is reversible. In such a situation, the entropy production = the entropy change. In the case that it claims entropy is "destroyed", the process is impossible.
In the case of heat transfer, you need to integrate the Temperature wrt each joule of heat added. This finds the reversible change in entropy. Subtract this from the real change in entropy to find the entropy generation.…