In this paper, we present a numerical technique to solve two mathematical models corresponding to two problems in the field of chemistry. One of these problems delves into the dynamic interplay of carbon substrates and oxygen concentrations within a microbial floc particle. Another problem relates to the chemical reaction of carbon dioxide CO2 and phenyl glycidyl ether in solution. The proposed method is based on Haar wavelet functions. This method reduces the problems mentioned to sets of algebraic equations. The method is straightforward, and numerical results validate its effectiveness. To demonstrate its efficiency, we have compared the numerical results to some existing results.