<P> The reaction rate or rate of reaction is the speed at which reactants are converted into products . For example, the oxidative rusting of iron under Earth's atmosphere is a slow reaction that can take many years, but the combustion of cellulose in a fire is a reaction that takes place in fractions of a second . For most reactions, the rate decreases as the reaction proceeds . </P> <P> Chemical kinetics is the part of physical chemistry that studies reaction rates . The concepts of chemical kinetics are applied in many disciplines, such as chemical engineering, enzymology and environmental engineering . </P>

What is the definition of rate of reaction