# Thermodynamics

Energy is an indirectly observed quantity that is often understood as the ability of a HYPERLINK “http://en.wikipedia.org/wiki/Physical_system” \o “Physical system” physical system to do HYPERLINK “http://en.wikipedia.org/wiki/Work_%28physics%29” \o “Work (physics)” work on other physical systems (Source 3). However, this must be understood as an overly simplified definition, as the laws of HYPERLINK “http://en.wikipedia.org/wiki/Thermodynamics” \o “Thermodynamics” thermodynamics demonstrate that not all energy can perform work. Energy quality is a measure of the capacity of a type of energy to do useful work. High-quality energy has a great capacity to do useful work because it is concentrated. Examples of high-quality energy include very high-temperature heat, concentrated sunlight, high-speed wind, and the energy released when we burn gasoline or coal. By contrast low-quality energy is so dispersed that it has little capacity to do useful work. For example, when heat is dispersed in the moving molecules of a large amount of matter, its temperature decreases so dramatically that its energy quality is poor. Energy changes are governed by two scientific laws: the laws of thermodynamics.

The laws of HYPERLINK “http://en.wikipedia.org/wiki/Thermodynamics” \o “Thermodynamics” thermodynamics define fundamental physical quantities ( HYPERLINK “http://en.wikipedia.org/wiki/Temperature” \o “Temperature” temperature , HYPERLINK “http://en.wikipedia.org/wiki/Energy” \o “Energy” energy , and HYPERLINK “http://en.wikipedia.org/wiki/Entropy” \o “Entropy” entropy ) that characterize HYPERLINK “http://en.wikipedia.org/wiki/Thermodynamic_system” \o “Thermodynamic system” thermodynamic systems (Kondepudi, 2008). The laws describe how these quantities behave under various circumstances, and forbid certain phenomena (such as HYPERLINK “http://en.wikipedia.org/wiki/Perpetual_motion” \o “Perpetual motion” perpetual motion ).

The first law of thermodynamics states that energy is neither created nor destroyed when converted from one form to another. Heat and work are forms of energy transfer. HYPERLINK “http://en.wikipedia.org/wiki/Conservation_of_energy” \o “Conservation of energy” Energy is invariably conserved but the internal energy of a closed system changes as heat and work are transferred in or out of it. The HYPERLINK “http://en.wikipedia.org/wiki/First_law_of_thermodynamics” \o “First law of thermodynamics” first law of thermodynamics may be stated thus:

Increase in internal energy of a body = heat supplied to the body – work done by the body.

For a HYPERLINK “http://en.wikipedia.org/wiki/Thermodynamic_cycle” \o “Thermodynamic cycle” thermodynamic cycle , the net HYPERLINK “http://en.wikipedia.org/wiki/Heat” \o “Heat” heat supplied to the system equals the net HYPERLINK “http://en.wikipedia.org/wiki/Work_%28thermodynamics%29” \o “Work (thermodynamics)” work done by the system. It is not possible to construct a perpetual motion machine which will continuously do work without consuming energy.

Essentially, this law tells us that we will never get more energy out of a chemical or physical change than we put in.

The second law of thermodynamics states that the HYPERLINK “http://en.wikipedia.org/wiki/Entropy” \o “Entropy” entropy of closed systems never decreases, because closed systems spontaneously evolve towards HYPERLINK “http://en.wikipedia.org/wiki/Thermal_equilibrium” \o “Thermal equilibrium” thermal equilibrium – the …
Posted by: Naida Carew

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