Factors affecting reaction rates

Monday 1 May 2023

ConcentrationThe higher the level of concentration (or

pressure in gases) the faster the reaction.This is due to increased collisions between

reacting particles.

Factors affecting reaction rates

Surface area in solidsThe larger the surface area of a solid the

faster the reaction. Finely divided substances have much larger surface areas than large chunks of a solid.

This is due to increased collisions between reacting particles.

Factors affecting reaction rates

TemperatureThe higher the temperature the faster the

reaction.This is due to increased and more energetic

collisions between reacting particles.A 10oC rise in temperature often results in a

doubling of the reaction rate.Key point: at a higher temperature more

molecules have energy greater than the activation energy.

Factors affecting reaction rates

Maxwell Boltzman distribution

Temperature effect

Only molecules with enough activation energy will react to form the products.

Temperature effects explained

The Arrhenius equation

The Arrhenius equation

CatalystsCatalysts increase the rates of chemical

reactions.This is due a lowering of the activation

energy for the reaction.Catalysts are not consumed in the reaction so

in theory they can be used over and over again. In practice they are often contaminated and/or some is lost in a process.

Factors affecting reaction rates

Catalyst effect

Catalyst effect

Catalyst effect

Hetrogeneous catalysts

Hetrogeneous catalysts

Homogeneous catalysts

Homogeneous catalysts

Relating mechanisms to the rate determining step

SN 1

Hydrolysis of halogenoalkanesThis is a SN2 reaction:

SN 2

Reaction of iodine with propanone

Reaction of iodine with propanone