Heterogeneous Catalysis

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HETEROGENEOUS CATALYSIS

D. C. AGUILAR AND B. N. SANCHEZ
INSTITUTE OF CHEMISTRY, COLLEGE OF SCIENCE
UNIVERSITY OF THE PHILIPPINES, DILIMAN QUEZON CITY, PHILIPPINES RECEIVED MARCH 17, 2008

ABSTRACT

Catalysis which involves the use of a catalyst in a different phase from the reactants is known as heterogeneous catalysis. Catalysts are known to enhance rates of reaction without being consumed and they also reduce activation energies. The hydrogen peroxide decomposition reaction catalyzed in the presence of black, insoluble MnO2 solids has been investigated in this experiment. Parts 1A and 2A of the experiment are carried out at 25°C and 4°C, respectively. The same method and temperatures has been employed for the B part; only, the amount of KMnO4 added is twice the amount added in A. The calculated activation energy for B part is much lower than that of A part having a value of 24.91 kJ/mol. The calculated Arrhenius constant A, is also lower in B having a value of 34.84s-1. Results have shown that the higher the concentration of the catalyst used, the lower the activation energy, thus, the faster the reaction.

INTRODUCTION

A potential barrier called the activation energy must first be overcome by the reactants in order to become products. In the decomposition reaction of hydrogen peroxide, the barrier might be a state in which the oxygen-hydrogen bonds of one hydrogen peroxide molecule are being stretched as –OH bonds on an adjacent molecule are being formed [4]. This can be shown by the figure below.

The rate of the reaction depends on the magnitude of the activation barrier between the reactants. Here, the species with the highest energy is called the transition state. The Arrhenius equation k = Ae– Ea/RT, shows that the fraction of molecules having enough energy to overcome a potential energy barrier of magnitude Ea depends exponentially on the ratio of the activation to the thermal energy [4]. This...
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