Rate of Reaction

Five Factors that affect the

Rate of Reaction

SCH4U UNIT 3 - Reaction Kinetics

Five Factors that affect theRate of Reaction

Temperature Concentration/Pressure Surface Area Catalysts/Inhibitors Chemical Nature of Reactants

Collision Theory Particles in a chemical system are in constant

motion with their Kinetic Energy (KE) proportional to their temperature.

A chemical reaction involves the collision of particles.

EFFECTIVE collisions have sufficient energy and correct orientation so that bonds are broken and new bonds are formed.

INEFFECTIVE collisions result in an elastic collision but no chemical rxn.

Collision Theory

The RATE OF REACTION depends on the frequency of collisions and the fraction of effective collisions.

Temperature As the temperature increases the

average Kinetic Energy increases. Collisions will be more frequent and

collisions will have have higher energy. Increased frequency and energy

increase the rate of reaction.

http://comp.uark.edu/~jgeabana/mol_dyn/KinThI.html

Recall

Temperature

As the temperature is increased from T1 to T2 the KE of the particles increases and more particles achieve the activation energy REACTION

Concentration

As the number of particles increases the number of collisions increases (constant volume).

Increased collisions increased Rate of Reaction.

An increase in pressure will result in a decrease in volume or an increase in temp. [VP/T = constant]

Surface Area Reagents must come in contact to

react. The greater the surface area the more collisions between reagents.

Surface AreaFASTEST Reaction Gas - Gas reactions Aqueous reactions Solid in a liquid Solid - Solid

SLOWEST

Powdered solids can be explosive

Catalysts

Stabilizes the activated complex which reduces the activation energy of the reaction.

With a lower activation energy, more particles have the required amount of energy to react.

Catalysts

Ex. Pt Catalyst of C2H4 + H2 C2H6

Catalyst

Catalysts and Inhibitors

Enzymes are proteins with catalytic activity.

Inhibitors, directly or indirectly, block the active site of the catalyst inhibiting the catalyst.

Nature of the Reactants

Rate depends on reactivity of reactants.

Ex. Au <<< less reactive than Na.

Some reactions are complex multi-step processes.