Advancement, Stress, and Chemical Equilibrium
Changes in temperature, number of moles, or volume which cause as system to be disturbed from equilibrium are sometimes called STRESS. How reactant and product concentrations change as a response to a stress is has long been a topic of study by Chemists. Below is a qualitative(no numbers) treatment of this topic.
["Le Chatelier's Principle", J. Chem.
Ed., 57 417 (1980)]
"General Chemistry" P&H 6th
"When an equilibrium system is subjected to a change in temperature, pressure, or concentration of a reacting species, the system reacts in a way that partially offsets the change while reaching a new state of equilibrium"
"The Extraordinary Chemistry of Ordinary Things" C.H. Snyder
"Placing a stress on an equilibrium causes the equilibrium to shift so as to relieve the stress"
"Principles of Modern Chemistry", Oxtoby & Natrieb 2nd
"A system in equilibrium that is subjected to stress will react in a way that counteracts the stress"
"Chemistry the Molecular Science", Olmstead & Williams
"When a change is imposed on a system at equilibrium, the system will react, if possible, in a direction that reduced the amount of change"
If an equilibrium is established at a given temperature and more reactant is added to the vessel at constant volume, the rate of ammonia formation collisions will increase, but the rate of destruction of product will reamin the same, so the equilibrium concentration of ammonia (product) will go up. If we add H2 to a reaction at equilibrium, the concentrations will change like this:
What happens if I2 (gas) is added at constant total volume?
What happens if I2 (solid) is added at constant total volume?
Reactants or products in a pure phase do not enter into the equilibrium expression.
Liquid Water <--> Water Vapor
Keq = Kp = pvap
The vapor pressure of a liquid is independent of the amount of the liquid (pure phase)
What happens to the system if the volume is increased at constant temperature?
What happens to the system if the temperature is increased at constant volume?
Of course, each of the above examples can be treated quantitatively...