What the difference between 'steady state' and 'equilibrium'?

Answer 1

At equilibrium all chemical potential gradients are zero. Moreover, the principle of microscopic reversibility guarantees that, at equilibrium, the rate at which any process proceeds in the "forward" direction is exactly balanced by the rate of that process in the "reverse" direction. This holds for every individual process, and means that at equilibrium there can be no net flux through any enzyme, any ion channel, or any transport protein. This is easy to understand intellectually because a nonzero chemical potential difference is absolutely required to drive a net flux. But steady state and equilibrium are so commonly used as if they were synonyms, that you will likely have to think about these points for hours before you can parry the objections of scientists who are sure of their misinformation.

A widely misunderstood example is provided by the transport of ions across the plasma membrane of a cell. Take Na+ as an example. Because, in the normal state of the cell, there is no net flux of Na+ across the cell membrane, and because the Na concentration in the cytosol is not changing with time, this condition is sometimes thought to be an equilibrium state. It is not. It is a steady state. The fact that [Na+] is constant is sufficient to define a steady state, but is insufficient to distinguish a steady state from an equilibrium. That is because an equilibrium is a special case of a steady state; an equilibrium is a steady state that is achieved when all chemical potential gradients have decayed to zero and there are no further net movements of molecules via any process. This is in marked contrast to the steady state of Na in a living cell. Here, there is a substantial net flux of Na into the cell through Na channels in the cell membrane, and there is an opposite but equal net flux of Na extruded from the cell by the action of the Na+K+ATPase. There is a nonzero chemical potential gradient consisting of both chemical and electrical terms that propells Na+ into the cell, and there is a nonzero chemical potential gradient including a term for the hydrolysis of ATP that pumps Na+ from the cell. Neither the ion channels nor the Na pump can qualify as processes at equilibrium; there are net Na fluxes through both. The fact that there is no net flux across the membrane is simply a corrollary of the steady state, not an indication of equilibrium. This is because the equilibrium condition is a statement about processes, not about state variables. Consequently, equilibrium is attained only when there are no net fluxes through ion channels and no net fluxes through the pumps. Equilibrium is thus achieved only when the cell is dead. Far from being synonyms, the difference between steady state and equilibrium is the difference between life and death.

Answer 2

A body is said to be in stable equilibrium if after a slight tilt it returns to its previous position. For example. Consider a book lying on a table. Tilt the book slightly about its one edge by tilting the book from the opposite side , it will return to its previous position as sets fre. Such a state of the body is called stable equilibrium.

If a body doesnot return to its previous position when sets free after a slightest tilt is said to be in unstable equilibrium. For example . take a pencil and try to keep it in a vertical position on its tip. Whenever you will leave it the pencil topples over its tip and falls down. This is called unstable equilibrium.

Unstable equilibrium is an oxymoron and therefore is a contradiction of terms.

Answer 3

Stable air is generally cool and dry and does not rise easily. It generally leads to clear weather. Unstable air is warm an moist an so rises easily. Because of this unstable air often leads to the formation of thunderstorms.