AP Chemistry Unit 5 - Kinetics

University:
Kentucky State University
Course:
CHE 101 | General Chemistry I
Academic year:

2022
Views:

402

Pages:

3
Author:

se2bagjuf

Unit 5 - Kinetics Concentration of reactants, presence of catalysts, temperature, pressure and surface area affect reaction rate by changing the rate of collisions. Rate laws - 𝑟𝑎𝑡𝑒 = 𝑘[𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡 1]𝑚 [𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡 2]𝑛 . .., m and n must be determined by experimental data, overall order=m+n…, rate constant=k, To solve for order, find two trials in which one reactant’s concentration remains constant and determine the ratio between the other reactant’s concentration and rate(1:2 = 2nd order). See relative rate vs. concentration below. To solve for rate constant, plug in any trial into the rate law. Pay attention to the units of the rate constant! Use overall order to determine the units as shown below! In a reaction with many steps, the slowest step(given) determines the rate law. Rate laws cannot have an intermediate species, so you must use other steps to rewrite intermediates. Not all chemical reactions can occur in one step so we must look at the series of steps. Each step in a mechanism is called an elementary reaction. Species that are in elementary reactions but are not in the final overall equation are called intermediates (they are in the products in one equation and then appear as reactants in another- this causes them to cancel). Whenever dealing with mechanisms the slowest step is the rate determining step, the rate of that particular step determines the rate of the entire reaction. Remember when there is more of a substance in a reaction it will increase the rate of the reaction because it will take longer for the reaction to be complete. In the image above, the correct kinetics equation would be rate=k[H2][ICl] because step 1 was the rate-determining step. Collision Model - In a reaction the particles in the reactants must successfully collide in order to produce products. The bonds need to be broken. Successful collisions have the right amount of energy and the correct orientation that allows the bonds to rearrange in the required manner. Other factors that affect reaction rate: reactant concentration, pressure, temperature, surface area, and catalyst. Here’s a chart that explains and summarizes these factors: For reactions with multiple steps, the taller hump from bottom to top is the slowest step because it requires the most activation energy. Catalysts provide a reaction mechanism with lower activation energy, so it has a shorter hump and reaches the potential energy of products faster.