... a high temperature (LeMay et al, 1996). So, to determine the change in enthalpy we will employ Hess's Law of heat summation: It states that the value of ?H for a reaction is the same whether it occurs directly or as a series of steps (LeMay et al, 1996). We will perform the two following reactions: Mg + 2HCl ? MgCl2 + H2 and MgO + 2HCl ? MgCl2 + H2O, determine their enthalpy changes (?Hs), and they will then be "added" to that of a given equation, the combustion of water, H2 + 1/2 O2 ? H2O ?H=-285.5 kJ/mol. In this investigation we will be working with potentially dangerous chemicals and safety precautions must be made. Magnesium oxide is a respiratory and eye irritant, the dust must not be inhaled and all work with MgO should be conducted in the fume hood ( Cartwright, 2002). Hydrochloric acid is extremely ...

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