Isothermal Process
When a thermodynamic system undergoes a physical change in such a way that its temperature remains constant, then the change is known as isothermal changes.
(1) Essential condition for isothermal process
(i) The walls of the container must be perfectly conducting to allow free exchange of heat between the gas and its surrounding.
(ii) The process of compression or expansion should be so slow so as to provide time for the exchange of heat.
Since these two conditions are not fully realised in practice, therefore, no process is perfectly isothermal.
(2) Equation of state : In this process, P and V change but T = constant i.e. change in temperature T = 0.
Boyle's law is obeyed i.e. PV= constant P1V1 = P2V2
(3) Example of isothermal process : Melting of ice (at 0°C) and boiling of water (at 100°C) are common example of this process.
(4) Indicator diagram : According to PV = constant, graph between P and V is a part of rectangular hyperbola. The graphs at different temperature are parallel to each other are called isotherms.
(i) Slope of isothermal curve : By differentiating PV = constant. We get