Kinetics of an Adiabatic Reaction

Objectives

The objectives of this experiment are to determine, and compare with literature data, the following parameters for an adiabatic-exothermic liquid-based reaction by observing the temperature rise during reaction

1. Overall reaction stoichiometry
2. Reaction enthalpy ΔΗ
3. Arrhenius parameters, Pre-exponential factor A and activation energy E

Theory

Neglecting heat losses and changes in volumetric heat capacity with system composition, the rate of temperature rise is proportional to the rate of reaction, which in turn is proportional to the rate of change in concentration of each reactant species.

Since reaction ceases with complete consumption of any one reactant, the maximum heat generation, per mole of reactants supplied, occurs when there is no excess of any reactant. Thus the overall stoichiometry may be determined by finding the mixing ratio of reactants which gives the maximum temperature rise at constant initial molarity and constant volume.

For the reaction:

                                                                   (I)

Which occurs without volume change of the reaction mixture, the kinetics of all species are related to r, the species independent reaction rate:

                                               (II)

For an adiabatic reaction, the rate of temperature change is given by energy balance:

                                                                                          (III)

Integrating and applying initial boundary condition and also eliminating r using equation (II):

                                                                             (IV)

For the case that A is totally consumed C_A=0 and T=T_f, then:

                                                                                   (V)

Assuming the reaction is irreversible and first order with respect to each reactant, the kinetic rate expression becomes:

                                                              (VI)

Where A΄ is the pre-exponential factor and E is the activation energy of the Arrhenius equation.