yes. "A 0-order reaction has a rate which is independent of the concentration of the reactant(s)" "A reaction is zero order if concentration data are plotted versus time and the result is a straight line. The slope of this resulting line is the negative of the zero order rate constant k. " http://www.chem.purdue.edu/gchelp/howtosolveit/Kinetics/KineticsArt/A_vs_t_zero_order.JPG "Reversed Haber process: 2NH3(g) -> 3H2(g) + N2(g) It should be noted that the order of a reaction cannot be deduced from the chemical equation of the reaction!!" http://en.wikipedia.org/wiki/Rate_equation A + B + C + D -> Products | 2NH3(g) -> 3H2(g) + N2(g) "Reactions in heterogenous system usually follow zero order kinetics. In such a system the reactants are adsorbed on the surface of a solid catalyst. At low concentrations of the reactant, the rate of the reaction depends on the fraction of the surface covered by the reactant. However, at higher concentrations the surface of the catalyst becomes fully covered and any further increase in the concentration of the reactants does not affect the rate of the reaction. One very common example, is the decomposition of ammonia (NH3) on finely divided platinum (e.g., 4). At very low pressures of ammonia, the decomposition reaction has rate r given by.. rate = k1[NH3] --------- 1+k2[NH3] .... but at low pressures, k2 [NH3] term does not count as it is very less than one. Under such condition, the reaction is first order in ammonia." http://www.tutorvista.com/content/chemistry/chemistry-iv/chemical-kinetics/isolation-method.php