Equilibrium and Rate Equations

The reversible reaction A 44- B can be thought of as being composed of two processes, the forward and reverse. These take place simultaneously with velocity v, thus 

Because the time change of the activity coefficient is small, the velocity equations are always expressed in concentrations rather than in activities. At equilibrium the two velocities are equal, therefore no net chemical change takes place and (c.f. 

time is introduced as a new variable to the definition of chemical processes including the equilibrium ones. Although the absolute value of K may be the same we can talk about fast or slow equilibria, meaning that the rate constants kf and kr 

Reactions involving two or more species are reactions of second- and higher-order. Thus for irreversible reaction A + 2B — C, the rate law is 

Note that the rate of disappearance of B is two times as high as that of species A and C, hence the 1/2 coefficient. The reaction is also second-order in B because 

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