Rate of Reaction Five Factors that affect the Rate of Reaction SCH4U UNIT 3 - Reaction Kinetics

Five Factors that affect the Rate of Reaction l Temperature l Concentration/Pressure l Surface Area l Catalysts/Inhibitors l Chemical Nature of Reactants

Collision Theory l Particles in a chemical system are in constant motion with their Kinetic Energy (KE) proportional to their temperature. l A chemical reaction involves the collision of particles. l EFFECTIVE collisions have sufficient energy and correct orientation so that bonds are broken and new bonds are formed. l INEFFECTIVE collisions result in an elastic collision but no chemical rxn.

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

Temperature l As the temperature increases the average Kinetic Energy increases. l Collisions will be more frequent and collisions will have have higher energy. l Increased frequency and energy increase the rate of reaction.

Recall

Temperature As the temperature is increased from T 1 to T 2 the KE of the particles increases and more particles achieve the activation energy  REACTION

Concentration l As the number of particles increases the number of collisions increases (constant volume). l Increased collisions increased Rate of Reaction. l An increase in pressure will result in a decrease in volume or an increase in temp. [VP/T = constant]

Surface Area l Reagents must come in contact to react. The greater the surface area the more collisions between reagents.

Surface Area FASTEST Reaction l Gas - Gas reactions l Aqueous reactions l Solid in a liquid l Solid - Solid SLOWEST l Powdered solids can be explosive

Catalysts l Stabilizes the activated complex which reduces the activation energy of the reaction. l With a lower activation energy, more particles have the required amount of energy to react.

Catalysts

Ex. Pt Catalyst of C 2 H 4 + H 2  C 2 H 6

Catalyst

Catalysts and Inhibitors l Enzymes are proteins with catalytic activity. l Inhibitors, directly or indirectly, block the active site of the catalyst inhibiting the catalyst.

Nature of the Reactants l Rate depends on reactivity of reactants. Ex. Au <<< less reactive than Na. l Some reactions are complex multi-step processes.