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Chemistry Lab. Deducing Enthalpy of Combustion of Magnesium Oxide with Hesss Law

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Lab 7: Deducing Enthalpy if Combustion of Magnesium Oxide with Hess's Law Background: Hess's law enables us to determine enthalpy of a reaction. It states that the enthalpy of a reaction is independent of the route taken to yield the products. Therefore, through this, it is possible for us to obtain enthalpies of reaction, which are otherwise difficult to measure by using the enthalpies of reactions. Aim/ Purpose: To deduce the enthalpy of the oxidation of Magnesium by means of Hess's law and the measured enthalpy's of reaction of Magnesium with Hydrochloric acid, and reaction of Magnesium Oxide with Hydrochloric acid and the formation of water. Hypothesis: A prediction was made that the value of reaction enthalpy of oxidization of Magnesium would be approximately -601.8 KJ/ mol, which is the accepted value. (Source of accepted value of oxidization of Magnesium: IUPAC) Apparatus: * Standard Thermometer * 1 M HCl * Magnesium Oxide (MgO) ...read more.


+ H2(g) Processed Data: Table 2. Processed data for the Mg(s) + 2 HCl(aq) --> MgCl2(aq) + H2(g) and MgO(s) + 2HCl(aq) --> MgCl2(aq) + H2O(l) MgO Mg Temperature Change (C ) 7.4 18.8 Moles of HCl 0.04830 0.04779 Moles of 0.01290 0.00864 Limiting Reagent Mg MgO Reaction Enthalpy (KJ/ mol) -115.8 - 434.6 Reaction Enthalpy for Mg(s) + 1/2 O2 (g) --> MgO (s) reaction = -591.4 KJ/ mol Percent Error: (601.8-604.6/601.8) * 100 = 0.46 % Calculations for acquired Processed Data: Using the following reactions, Hess' Law was applied to find out reaction enthalpy of MgO was found indirectly. Also using this formula for reaction enthalpy: ?H= (-Q / n) * Mg(s) + 1/2 O2 (g) --> MgO (s) * MgO(s) + 2HCl(aq) --> MgCl2(aq) + H2O(l) * Mg(s) + 2 HCl(aq) --> MgCl2(aq) + H2(g) * H2(g) + 1/2 O2 (g) --> H2O(l) Temperature change= final temperature - initial temperature = 27.6 -21.6 = 7.4 Moles of HCl = (ml of HCl /1000) ...read more.


Therefore, the Hypothesis proved to be correct, since we got an almost close value. Evaluation: The almost perfect results with a 0.46 % error in this experiment can proved to be a great result for the determination of enthalpy of oxidization of Magnesium. Numerous errors could have been affected the results achieved in this experiment. The likeliness of heat loss from the probe itself and heat loss into the system could affect the enthalpy of reaction of MgO and Mg with HCl. Another error could be that the specific heat capacity used was for water when in the liquid was solution had other impurities in it, which could have resulted in the slightly off results. These errors could be avoided in other experiments by making use of an insulated cup and by considering the proper specific heat capacity of solutions used in the experiment. The lab also faced the plight of not being experimented under standard conditions. ?? ?? ?? ?? Samhitha Kumbhajadala Lab Partners: Sung Jin Kim Mr. Kuijlaars Chemistry HL 3rd March 2012 ...read more.

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