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Chemical Kinetics w Reaction rate - the change in concentration of reactant or product per unit time.

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Presentation on theme: "Chemical Kinetics w Reaction rate - the change in concentration of reactant or product per unit time."— Presentation transcript:

1 Chemical Kinetics w Reaction rate - the change in concentration of reactant or product per unit time.

2 Factors Affecting Rates w Temperature w Concentration of reactants w Particle size w Presence of a catalyst

3 Rates w Average rates - the difference in concentration over a set amount of time. Table 12.2 w Instantaneous rates - calculated from the slope of the line tangent to the curve at a certain point.

4 Reaction rates w Rates are not constant. w Rates vary with time because concentrations vary with time.

5 Rate Laws w Rate = k[A] n [B] m [C] p w k = rate constant w n,m,p = order ; must be determined by experiment.

6 Differential rate law w Expresses how a rate depends on concentration. w Often this is just called the rate law.

7 Integrated rate law w Expresses how the concentration depends on time.

8 Reaction Mechanism w The series of elementary steps by which a reaction occurs. w An elementary step is a step whose rate law can be determined from its molecularity.

9 Molecularity w The number of species that must collide to produce the reaction in that step. w Unimolecular involves one molecule. w Bimolecular and termolecular involve 2 and 3 species respectively

10 Intermediate w A species that is neither a reactant or a product. This species is produced and consumed in the reaction.

11 Rate Determining Step w This is the slowest step of the mechanism. The reaction can only proceed as fast as this rate determining step will allow.

12 Requirements of Mechanisms w The sum of the elementary steps must give the overall balanced equation. w The mechanism must agree with the experimentally determined rate law. The rate determining step.

13 Collision model for kinetics w Reactant molecules must collide in order to react. w Concentration w Particle size w Temperature w Molecular orientation

14 Requirements for reaction w The collision energy must equal or exceed the activation energy. w The orientation of the reactants must allow the formation of new bonds.


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