CHEMICAL EQUILIBRIUM 233 



in the conditions (temperature and pressure or concentration), 

 even if slight, produces a corresponding change hi the state of the 

 system, and does this by favoring or disfavoring one of the two 

 opposing tendencies or activities. Such a change is called a dis- 

 placement of the equilibrium, for the system settles down in a new 

 state of equilibrium with new proportions of the two sets of sub- 

 stances, corresponding to the changed conditions. Thus, in the 

 present instance, a change from 345, where there is 80 per cent 

 of the material in the form of steam and chlorine, to 384 results 

 in the diminution of this proportion to 75 per cent. The equilib- 

 rium is affected by changes in concentration also, as we shall 

 presently see. 



Now, the foregoing facts show that the key to understanding 

 chemical activities, their magnitudes, their changes, and especially 

 their practical results, must lie in knowing how changes in the 

 conditions affect them. Hence, to the chemist, familiarity with the 

 influence of conditions on chemical phenomena must be of the 

 greatest practical importance. 



The " conditions " to be considered are familiar, temperature, 

 and concentration or, in the case of a gas, partial pressure. The 

 " activity " of an action is accurately measured by the speed with 

 which the action proceeds. Thus, if the foregoing section be 

 re-examined, it will be seen that we spoke throughout of the speed, 

 rather than of the tendency or activity, 



Finally, temperature and other conditions influence also the 

 activities in, and therefore the speeds of, those actions which pro- 

 ceed to completion, and are not reversible. Hence, unless our 

 statements are expressly restricted to reversible actions and to 

 states of equilibrium, they apply to all chemical changes. 



The Influence of Concentration. In the first place, let us 

 assume that the temperature is constant, and let us confine our 

 attention for the present to the influence of concentration upon a 

 chemical reaction. We have seen (p. 231) that the speed of a 



