The only unfamiliar aspect about this rate equation is the dx/dt style of writing rates. This equation should be translated as: "The rate of disappearance of H₂ and the rate of disappearance of I₂, both are half the rate of appearance of HI (since two HI molecules are produced), and each of these is proportional to the product of H₂ and I₂ concentrations.

The order of an experimental rate equation describes how the rate depends on the power of the concentration terms. The rate of breakdown of carbon-14 is proportional to the first power of C-14 concentration, so the reaction is first order. The hydrogen-iodine reaction rate depends on the product of two concentrations, so the reaction is second order in overall concentration.

One also can focus on the individual reactants, and say that the HI reaction is separately first order in H₂ and I₂ concentrations, since these each occur in the rate equation with a firstpower dependence.