Determining the change in enthalpy for the combustion of Mg using solution calorimetry and heat summation.

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Determining the change in enthalpy for the combustion of Mg using solution calorimetry and heat summation.

Abstract

Hess's law of heat summation states that the value of ?H for a reaction is the same whether it occurs directly or as a series of steps. This principle was used to determine the change in enthalpy for a highly exothermic reaction, the combustion of magnesium metal. Enthalpy changes for the reactions of Mg in HCl (aq) and MgO (s) in HCl (aq) were determined experimentally, then added to that for the combustion of hydrogen gas to arrive at a value of

-587 kJ/mol Mg. Compared with the accepted value of -601.8 kJ/mol Mg, our experimental error was 2.46%.

Introduction

In this investigation the change in enthalpy will be determined from the following equation: 2Mg + O2 ? 2MgO, but in an indirect manner. Magnesium metal burns with a bright extremely hot flame to produce magnesium oxide. It would be difficult to measure the heat of the reaction since the reaction is rapid and occurs at a high temperature (LeMay et al, 1996). So, to determine the change in enthalpy we will