Editing Quasistatic process (section)

{{short description|Thermodynamic process in which equilibrium is maintained throughout the process's duration}}
{{Thermodynamics|cTopic=[[Thermodynamic system|Systems]]}}

In [[thermodynamics]], a '''quasi-static process''', also known as a '''quasi-equilibrium process''' (from Latin ''quasi'', meaning ‘as if’<ref>Lewis, C.T., Short, C. (1879). ''A Latin Dictionary'', Clarendon Press, Oxford, page 1507.</ref>), is a [[thermodynamic process]] that happens slowly enough for the system to remain in internal physical (but not necessarily chemical) [[thermodynamic equilibrium]]. An example of this is quasi-static expansion of a mixture of hydrogen and oxygen gas, where the [[volume]] of the system changes so slowly that the [[pressure]] remains uniform throughout the system at each instant of time during the process.<ref>{{Cite book|title = An Introduction to Thermal Physics|last = Schroeder|first = Daniel|publisher = Addison Wesley Longman|year = 2000|isbn = 0-201-38027-7|location = United States|pages = 20–21}}</ref> Such an idealized process is a succession of physical equilibrium states, characterized by infinite slowness.<ref>Rajput, R.K. (2010). ''A Textbook of Engineering Thermodynamics'', 4th edition, Laxmi Publications (P) Ltd, New Delhi, pages 21, 45, 58.</ref>

Only in a quasi-static thermodynamic process can we exactly define [[intensive quantities]] (such as pressure, [[temperature]], [[specific volume]], [[specific entropy]]) of the system at any instant during the whole process; otherwise, since no internal equilibrium is established, different parts of the system would have different values of these quantities, so a single value per quantity may not be sufficient to represent the whole system. In other words, when an [[Fundamental thermodynamic relation|equation for a change in a state function]] contains ''P'' or ''T'', it implies a quasi-static process.