Course Name: Catalysis and Catalytic Processes Course Code : CHPE550 Dr. Qazi Nasir Office No: 5D-40, College of Engineering qazinasir@unizwa.edu.pk

Rate Law Homogenous reaction Reaction which involves only one phase Heterogeneous reaction Reaction which involves more then one phase Irreversible reaction Reaction which proceeds only in one direction Reversible reaction Reaction which can proceed in either direction

Rate Law Molecularity of reaction The number of atoms, ions or molecules involved in reaction step Unimolecular reaction Bimolecular Termolecular reaction

Rate Law Relative rates of reaction Can be obtained from the ratio of stoichiometric coefficients

Rate Law Example If NO2 is formed at a rate of 4 mol/m3/s The rate of formation of NO The rate of disappearance of NO is The rate of disappearance of O2 is

Rate Law The reaction order and the rate law The rate of disappearance of A, -rA depends on temperature and composition. It can written as product of rate constant kA & function of concentration of various species Rate law of kinetic expression

Rate Law Power Law models Dependence of the reaction rate (-rA) on concentration fn(Cj) is determined by experimental observation Alternatively, power law models are used The exponents of concentration is reaction order

Rate Law Power Law models Units of –rA are in terms of concentration per unit time but units of specific reaction rate kA depends on reaction order Consider the following reaction

Rate Law Elementary reaction The one that evolves a single step such as biomolecular reaction The stoichiometric coefficient in this reaction are identical to the power it the rate law Nonelementary reaction

Rate Law Nonelementary reaction Large number of both homogenous and heterogeneous reactions don not follow simple rate laws Homogeneous Reactions The over all order does not have to be an integer

Rate Law Nonelementary reaction Heterogeneous Reactions In many gas-solid reaction, it is often practice to write rate laws in terms of partial pressures rather than concentration e.g. hydrodemethylation of toluene (T) to form benzene (B) and methane (M) over solid catalyst The rate of disappearance of toluene per mass of catalyst, -r’T, follows Langmuir-Hinshelwood kinetics and rate law found experimentally to be

Rate Law Nonelementary reaction Heterogeneous Reactions Where KB and KT are the adsorption constants with units of kPa-1 (atm-1) and specific reaction rate has units Rate of reaction in terms of concentration rather then partial pressure can be written as

Rate Law The Reaction Rate Constant The reaction rate constant k is not truly a constant It merely independent of concentration It is almost strong function of temperature It may be function of total pressure (gas phase-R) In liquid system it is function of other parameter e.g. ionic strength, choice of solvent

Rate Law The Reaction Rate Constant Swedish chemist Arrhenius first suggested the temperature dependence of the specific reaction rate, kA could be correlated in equation

Rate Law Activation Energy Most atoms and molecules undergoes reaction, there is an activation energy Couples of reason The molecules need energy to distort or stretch their bonds so that they break them to form new bonds The steric and electron repulsion forces must be overcome as the reacting molecules come close together

Rate Law Activation Energy One way to view the barrier to a reaction is through the use of the reaction coordinates The coordinates denotes the potential energy of the system as a function of the progress along the reaction path as we go from reactant to an intermediate to product

Rate Law Activation Energy

Rate Law Activation Energy Example: Determination of the Activation Energy Calculate the activation energy for the decomposition of benzene Diazonium chloride to give chlorobenzene and nitrogen using the table information

Rate Law Activation Energy The equation that best fit the data The slope of the line Example 3-1 Page 95

Batch System Batch reactor are primarily used for the production of specialty chemicals and to obtained reaction rate data in order to determine reaction rate laws and rate law parameters such as k, the specific reaction rate

Batch System At time t=0, open the reactor and place a number of moles of species A, B, C, D and I (NAO, NBO, NCO, NDO and Nt) into the reactor

Batch System At time t=0, open the reactor and place a number of moles of species A, B, C, D and I (NAO, NBO, NCO, NDO and Nt) into the reactor

Batch System Equation of Batch Concentrations The concentration of A is the moles of A per unit volume CA = NA/V. Similarly, for other components