CHEM 1120 1st Edition Lecture 5 Outline of Current Lecture 1 Chemical kinetics 2 Factors that affect reaction rates 3 Types of rates measured 4 Average rates and plotting data gathering information from plotted data 5 Concentration and Rate Laws Current Lecture Chapter 14 Chemical Kinetics Chemical Kinetics o when we study the rate or speed at which a chemical process occurs o Also has to deal with reaction mechanism a molecular level view of the path from reactants to products o Examples of Chemical Kinetics speed of reaction at which an apple goes bad speed at which oxidation occurs on steel 14 1 Factors that affect reaction rates o Physical state The more readily the reactants collide the more rapidly they react Homogeneous reactions are often faster Heterogeneous reactions that involve solids are faster if the surface area is increased ex a fine powder reacts faster than a pellet or tablet These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o o o example fine powder vs solid block vs gas vs liquid Reactant concentration Increasing reactant concentration generally increases reaction rate Since there are more molecules more collisions occur example dilute vs concentrated Reaction Temperature Reaction rates generally increase with increasing temperature Kinetic energy of molecules is related to temperature At higher temperatures molecules move more quickly example boiling eggs Catalysts Affect rate without being in the overall balanced equation Affect kinds of collisions changing the mechanism individual reactions that are part of the pathway from reactants to products Critical in many biological reactions example alcohol sensitivity related to aldehyde dehydrogenase or car catalytic converters 14 2 Rate is a change in concentration over a time period Types of rates measured o Average rate Final minus initial concentration time Rate of reaction averaged over a period of time Slide 22 o Instantaneous rate Slope of the tangent line o Initial rate The instantaneous rate at time zero Often the rate of interests for chemists Average rate of appearance Average rate of disappearance Plotting rate data o Gives us more information about rate o Instantaneous rate Slope of curve at one point in time Relative rates o Rate is dependent on stoichiometry Average rate for loss of reactants Average rate for formation of products o Average rate change in c change in t o Reaction rate o The change in concentration per unit time taking into account stoichiometry and reaction directions 14 3 Concentration and Rate Laws Rate k A m B n o K rate constant depends on temp o Expoonets define the order of the reaction m is the order of the reaction with respect to A n is order of reaction with respect to B m n is the overall reaction order m and n are both usually integers o o Often found that m and n do not need to equal a and b AND must be determined Reaction order