KINETICS CHAPTER 6

BT TIER 1 & 2 -Define Kinetics -Define the term rate of the reaction -Define rate -Define the term activation energy Ea -Describe the units used to express rate -Describe the kinetic theory in terms of the movement of particles whose average kinetic energy is proportional to temperature in Kelvins -Describe the collision theory -Describe the effect of a catalyst on a chemical reaction - Describe the Maxwell-Boltzmann distribution curve

KINETICS: The study of how fast a reaction occurs, how rate is measured, describe what happens on the molecular level and what factors effect the rate. RATE OF REACTION: a measure of the amount of reactants being converted to products per unit of time. The unit for the rate of a reaction is (mol dm -3 s -1 ) or moles per cubic decimeter per sec.) RATE: something measured per unit of time. Example of a runners performance per unit of time. ACTIVATION ENERGY: energy a reactant must acquired in order to achieve a transition state from which products can form. DEFINITIONS

Describe the kinetic theory in terms of the movement of particles whose average kinetic energy is proportional to temperature in Kelvins Since molecules are in constant motion, they have kinetic energy(energy of motion). As energy is added to the molecules in the form of increasing temperature, the molecules gain more kinetic energy. Even though, not all molecules in a substance have the same kinetic energy, the average of the kinetic energy of all the molecules is measured by measuring the temperature of the substance.

Describe the Maxwell-Boltzmann distribution curve Because not all gas particles have the same kinetic energy at a given temperature, a curve of the number of particles that have a particular kinetic energy against the kinetic energy value is used to represent a graphic representation of this model. This graph is known as the Maxwell-Boltzmann distribution curve. (Figure to the right) The area under the curve represents the total number of particles in the sample

THE COLLISION THEORY The collision theory describes the rate of reaction as being dependent on the frequency of the collision of molecules possessing : The area beneath each curve represents the number of molecules having certain kinetic energy. Since the area beneath the curve T2 is wider than area of T1, it can conclude that there is more number of molecules possessing kinetic energy equal to or greater than activation energy (Ea) at a higher temperature. kinetic energy greater than the activation energy having the correct orientation (collision geometry) AND

ROLE OF A CATALYST A catalyst is a substance used to increase the rate of a reaction without actually being used up. Most catalyst work by providing an alternate route for the reaction, which lowers the activation energy. The number of molecules having energy greater than this lowered activation energy increases, and thus the number of effective collisions increases.

Enzymes are catalysts that controlled biological reactions. Below are 2 models that show how enzymes act to control a reaction rate.