Abstract

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The inhibitive action of ethanol leaf extract of Sorghum bicolor has been studied using the weight loss method at the temperature range of 305 K to 315 K. The inhibitive action was observed to increase with increase in concentration of the extract, but decreased with increase in temperature. The decrease in the inhibitive action with rise in temperature is suggestive of physisorption. The evaluated heat of adsorption, Qads, ranged from -72.50 kJ/mol to -126.76 kJ/mol and the negative values are indication that the adsorption of inhibitor onto the coupon surface is exothermic. The values of activation energy, Ea, range from 105.89 to128.60 kJ/mol in the presence of the extract, clear indication of Chemisorption. Enthalpy of adsorptionΔH°, values range from 17.61 kJ/mol to 88.40 kJ/mol with values in the presence of the extract being higher than the free solution. Adsorption of leaf extract of Sorghum bicolor best fitted into the Frumkin, El-Awady isotherms and Adejo-Ekwenchi isotherm models. The decrease in value of parameter b in Adejo-Ekwenchi isotherm with increase in temperature confirmed that the adsorption mechanism was physisorption.

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