Chemical Kinetics The Study of Reaction Rates

Why Such a Vast Difference in Reaction Rates? Reaction speeds can range from the very slow (rotting of wood; rusting of iron) to the very fast (explosion of a firecracker). We want to understand the factors that control reaction rates.

Factors Affecting Reaction Rate Concentration (for substances in solution) –Higher conc. results in a faster reaction Pressure (for gases) –Higher pressure results in a faster reaction Surface Area (for solids) –Higher surface area results in a faster reaction

Factors Affecting Reaction Rate Temperature –The higher the temperature, the faster the reaction Presence (or absence) of a Catalyst –Reaction is faster with a catalyst Nature of the Reactants –Some substances are more reactive than others

Factors Affecting Reaction Rate: What’s Behind Them? Molecules must collide to react –Increasing the number of collisions per unit time increases the rate Molecules must have correct orientation and sufficient energy (activation energy) –Increasing the probability that a collision will be “successful” increases the reaction rate This means increasing the collision energy, or decreasing the barrier to reaction