Magnesium Oxide Experiment

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In part C, the enthalpy of formation of magnesium oxide was found by adding together three reactions, as shown in the table below. Experiments were performed to obtain the ΔHrxn value of the first two reactions in the table, which were reactions 4 and 5 respectively in the experimental section, while the ΔHrxn for the third reaction in the table was provided. Using the ΔT obtained experimentally, heat energy (q) was determined using the equation q = mCΔT + CΔT where q was the heat, m was the mass of the solution, ΔT was the change in temperature, C was the specific heat of water, and C was the calorimeter constant. The mass was calculated by multiplying the density of the solution, which was 1.01 g/mL, by the volume of solution. When these …show more content…
It was then added to the equation for reaction 5 and the third equation in the table. The following three equations were added to produce the final equation:
MgCl2(aq) + H2O(l) ⟶ MgO(s) + 2 HCl(aq)
Mg (s) + 2 HCl(aq) ⟶ MgCl2(aq + H2(g)
H2 (g) + ½ O2 (g) ⟶ H2O (l)
The enthalpies of these equations were then added to produce a final value of -602.98 kJ/mol. The two reactions in part C were also observed to be exothermic as the system, consisting of the reactants for each reaction, released heat, which was absorbed by the surrounding solution and calorimeter. This absorption of heat by the surroundings was indicated by an increase in temperature of the surroundings, which was recorded during the experiment. Further, the measured heat energy and ΔHrxn of each individual reaction were found to be negative, which indicated that heat was released during these reactions. If 6 M HCl was added instead of 2 M HCl in reaction 5, the reaction would be violently exothermic and release a large amount of heat that causes an explosion. This was highlighted as a safety risk of the experiment. The several data points that illustrated the increase in temperature were graphed as
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It can be calculated y subtracting the sum of enthalpies of formation of reactants from the sum of enthalpies of formation of the products. The enthalpy of formation is the ΔHrxn when 1 mole of a compound is formed from its elements in their standard states at 25℃ at 1 atm.2 The change in enthalpy per mole of a reaction was illustrated by part B of the experiment, because the change in enthalpy per mole of HCl or NH4OH was calculated. The standard molar enthalpy of formation was illustrated by part C of this experiment, because the various reactions added up to a reaction that led to the creation of 1 mole MgO from its elements at their standard states. Hence, the ΔHrxn in this reaction represented the enthalpy of

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