The rate of reaction affects the selectivity of a chemical reaction by determining the relative amounts of different products formed during the reaction. Selectivity is the preference for the formation of one product over another in a chemical reaction. In many cases, a reaction may have multiple pathways leading to different products, and the rate at which each pathway proceeds can influence the selectivity of the reaction.To manipulate the reaction conditions to favor a specific product, chemists can alter factors such as temperature, pressure, concentration of reactants, and the use of catalysts. By adjusting these conditions, it is possible to change the rate of reaction for specific pathways, thus affecting the selectivity of the reaction.A specific example to illustrate this concept is the reaction of propylene C3H6 with hydrogen H2 to form propane C3H8 and propylene dimer C6H12 . This reaction can proceed via two different pathways:1. Hydrogenation of propylene to form propane C3H8 2. Dimerization of propylene to form propylene dimer C6H12 Both pathways are exothermic, but the hydrogenation pathway has a lower activation energy than the dimerization pathway. At low temperatures, the hydrogenation pathway is favored due to its lower activation energy, leading to a higher selectivity for propane formation. However, as the temperature increases, the rate of the dimerization pathway increases more rapidly than the hydrogenation pathway, leading to a higher selectivity for propylene dimer formation.To favor the formation of propane, a chemist could perform the reaction at a lower temperature, which would slow down the dimerization pathway and increase the selectivity for the hydrogenation pathway. Alternatively, a catalyst could be used to selectively lower the activation energy of the hydrogenation pathway, further increasing the selectivity for propane formation.In summary, the rate of reaction affects the selectivity of a chemical reaction by determining the relative amounts of different products formed. By manipulating reaction conditions such as temperature, pressure, concentration of reactants, and the use of catalysts, chemists can influence the rate of reaction for specific pathways and favor the formation of a desired product.