Equilibrium Thermodynamics (Latin: aequalis = level and libra = weight or balance + Greek: thermos = heat and dynamis = power) is the systematic study of transformations of matter and energy in systems as they approach equilibrium. The word equilibrium implies a state of balance. Equilibrium thermodynamics, in origins, derives from analysis of the Carnot cycle. Here, typically a system, as cylinder of gas, is set out of balance via heat input from a combustion reaction. Then, though a series of steps, as the system settles into its final equilibrium state, work is extracted. A heat engine is an engine that uses heat to produce mechanical work by carrying a working substance through a cyclic process. ... Combustion or burning is an exothermic reaction between a substance (the fuel) and a gas (the oxidizer), usually O2, to release heat. ...

In an equilibrium state there are no unbalanced potentials, or driving forces, within the system. A central aim in equilibrium thermodynamics is: given a system in a well-defined initial state, subject to accurately specified constraints, to calculate what the state of the system will be once it has reached equilibrium. An equilibrium state is obtained by seeking the extrema of a thermodynamic potential function, whose nature depends on the constraints imposed on the system. In thermodynamics, four quantities, measured in units of energy, are called thermodynamic potentials: where T = temperature, S = entropy, p = pressure, V = volume Differential definitions The following differential relations hold for the four potentials: If we write the above four equations generally as Then it is seen that yielding expressions for...

Equilibrium thermodynamics differs from non-equilibrium thermodynamics, in that, with the later, the state of the system under investigation will typically not be uniform but will vary locally in those as energy, entropy, and temperature distributions as gradients are imposed by dissipative thermodynamic fluxes. In equilibrium thermodynamics, by contrast, the state of the system will be considered uniform throughout, defined macroscopically by those quantities as temperature, pressure, or volume. Here, typically, systems are studied as they change from one state to another. Non-equilibrium thermodynamics is a branch of thermodynamics concerned with studying time-dependent thermodynamic systems, irreversible transformations and open systems. ...

Sources

Adkins, C.J. (1983). Equilibrium Thermodynamics, 3rd Ed. Cambridge: Cambridge University Press.

Cengel, Y. & Boles, M. (2002). Thermodynamics – an Engineering Approach, 4th Ed. (textbook). New York: McGraw Hill.

Kondepudi, D. & Prigogine, I. (2004). Modern Thermodynamics – From Heat Engines of Dissipative Structures (textbook). New York: John Wiley & Sons.

Perrot, P. (1998). A to Z of Thermodynamics (dictionary). New York: Oxford University Press.