The reaction between hydrogen gas H2 and chlorine gas Cl2 to form hydrogen chloride HCl is a complex process that occurs in multiple steps. The overall reaction can be represented as:H2 + Cl2 2 HClThe mechanism of this reaction involves three steps:1. Initiation: Cl2 2 Cl homolytic cleavage of the Cl-Cl bond to form two chlorine radicals 2. Propagation: H2 + Cl HCl + H chlorine radical reacts with hydrogen molecule to form HCl and a hydrogen radical 3. Termination: H + Cl HCl hydrogen and chlorine radicals react to form HCl The rate-determining step RDS is the slowest step in a reaction mechanism, which ultimately determines the overall rate of the reaction. In the case of the reaction between hydrogen and chlorine gas, the rate-determining step is the propagation step Step 2 . This is because the initiation step Step 1 is relatively fast due to the presence of light or heat, which can easily break the Cl-Cl bond, and the termination step Step 3 is also fast as it involves the recombination of two radicals.The rate constant k of the rate-determining step is influenced by changes in temperature and pressure. According to the Arrhenius equation, the rate constant is related to temperature as follows:k = Ae^-Ea/RT where A is the pre-exponential factor, Ea is the activation energy, R is the gas constant, and T is the temperature in Kelvin. As the temperature increases, the rate constant k also increases, leading to a faster reaction rate.The effect of pressure on the rate constant is more complex and depends on the specific reaction conditions. In general, for a bimolecular reaction like the propagation step in this mechanism, an increase in pressure can lead to an increase in the rate constant due to the increased frequency of collisions between reactant molecules. However, this effect may be less significant if the reaction is already occurring at a high rate or if other factors, such as temperature, are more dominant in determining the reaction rate.