By

Mohd Ruzaini Ridhwan

6.5 Explaining and Applying Chemical

Kinetics

The frequently of collisions and

The fraction of those collision that are effective

Rate of Reaction occurs depends on two CRITERIA:

The minimum kinetic energy required to convert kinetic energy to activation energy during the formation of the

activated complex

Threshold Energy

Molecules are not all moving at the same speed; some are

moving quickly and some slowly, but most are in the

mid-range of kinetic energy.

Maxwell-Boltzmann Distribution

Particles require a minimum activation energy and correct alignment for a collision to be effective. The collision must provide sufficient energy to cause the breaking and forming of bond, producing new particles.

Many reactions occurs as a sequence of elementary steps that make up the overall reaction mechanism.

Factor such as the atomic structure of the reactant and the nature of their bonds, as well as the type of reaction occurring.

The rate of any depends on the nature of the chemical substance reacting, because both the strength of bond(s) to be broken and the location of the bond(s) in the particle structure effect the likelihood that any given collision is effective

Theoretical Effect of Chemical Nature of Reactant

An increase in initial reactant concentration or in reactant surface are increase the rate of a reaction because the total number of collision possible per unit time increase proportionately.

A higher concentration of reactant means a greater number of particles per unit volume, which are more likely to collide as they move randomly within a fixed space.

The rate of reaction is generally directly proportional to the concentration of a reaction.

Theoretical Effect of Concentration and Surface Area

Meanwhile, surface area only applies to heterogeneous reaction, such as gas react with solid or solid with a liquid. Surface area affects a collision frequently because reactants can collide only at the surface where the substances are in contact. The surface are of solid is fixed while the are of surface exposed for given quantity depends on how finely divided the sample of solid is.

Theoretical Effect of Concentration and Surface Area

A rise in temperature increase the rate of a reaction for two reasons: the total number of collision possible per unit time is increased slightly; and, more importantly, the fraction of collision that are sufficiently energetic to be effective is increased dramatically.

Theoretical Effect of Temperature

A catalyst increase the rate of reaction by providing an alternative pathway, with lower activation energy, to the same product formation. A much larger fraction of collisions is effective following the changed reaction mechanism. Catalysts are involved in the reaction mechanism at some point, but are regenerated before the reaction is complete.

Theoretical Effect of Catalysis

Heterogeneous catalyst – a catalyst in a reaction in which the reaction in which the reactants and the catalyst are in the different physical states

Homogeneous catalyst - a catalyst in a reaction in which the reaction in which the reactants and the catalyst are in the same physical states

Types of Catalyst

THE END