what is the spectator ion in a reaction
Spectator ion A spectator ion is an ion that exists as a reactant and a product in a chemical equation. A spectator ion can, therefore, be observed in the reaction of aqueous solutions of sodium carbonate and copper(II) sulfate but does not affect the equilibrium:
Order of reaction A reaction is said to be second order when the overall order is two. The rate of a second-order reaction may be proportional to one concentration squared   r = k [ A ] 2   {\displaystyle r=k[A]^{2}\,} , or (more commonly) to the product of two concentrations   r = k [ A ] [ B ]  {\displaystyle r=k[A][B]\,} . As an example of the first type, the reaction NO2 + CO â†’ NO + CO2 is second-order in the reactant NO2 and zero order in the reactant CO. The observed rate is given by   r = k [  NO 2    ] 2   {\displaystyle r=k[{\ce {NO2}}]^{2}\,} , and is independent of the concentration of CO.[9]