In a chemical reaction, the reaction rate is influenced by various factors, including the concentration of reactants. The reaction between hydrogen gas H2 and iodine gas I2 to form hydrogen iodide gas 2HI can be represented by the following equation:H2 + I2 2HIThe effect of changing the concentration of reactants on the reaction rate depends on the mechanism of the reaction, whether it is a single-step or a multi-step mechanism.1. Single-step mechanism: In a single-step mechanism, the reaction occurs in one elementary step. The rate law for this reaction can be represented as:Rate = k[H2][I2]where k is the rate constant, and [H2] and [I2] are the concentrations of hydrogen and iodine, respectively. In this case, the reaction rate is directly proportional to the concentration of both reactants. If the concentration of either reactant increases, the reaction rate will also increase.2. Multi-step mechanism: In a multi-step mechanism, the reaction occurs through a series of elementary steps. Each step has its own rate law, and the overall reaction rate depends on the slowest step rate-determining step . For example, the reaction between hydrogen and iodine can occur through a two-step mechanism:Step 1: H2 + I2 HI + HI slow, rate-determining step Step 2: HI + HI 2HI fast The rate law for the rate-determining step is:Rate = k[H2][I2]In this case, the reaction rate is still directly proportional to the concentration of both reactants. However, the overall reaction rate may be influenced by the intermediate species HI and the rate constants of each step.In conclusion, for both single-step and multi-step mechanisms in the reaction between hydrogen gas and iodine gas to form hydrogen iodide gas, the reaction rate is directly proportional to the concentration of the reactants. However, in a multi-step mechanism, the overall reaction rate may be influenced by the intermediate species and the rate constants of each step.