hess law - Purpose: In this calorimetry experiment, the...

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Purpose: In this calorimetry experiment, the heat of formation of magnesium oxide was determined using calorimetry and Hess’s law. The results obtained during the experiment were compared to the known H f of MgO was used to calculate the percent error of the experiment. Procedure: The calorimeter was assembled by placing two Styrofoam cups one inside the other, this served as the thermally insulated container. The cover for the calorimeter consisted of corrugated cardboard with a hole in the center big enough for a thermometer to fit though, this was to measure the temperature change of the system. The experiment started with reaction A: Mg (s) + 2HCl → MgCl 2(aq) + H 2(g) Accurately measure 50ml of 1.00M HCL solution in a graduated cylinder. Pour the HCL into the calorimeter and place the cover and thermometer through the hole and record the initial temperature of the HCL, monitor for several minutes. Accurately weigh 0.2g (to the nearest milligram) of magnesium metal turnings. When the metal turnings were added to the calorimeter the cover was put in place quickly and the heterogeneous solution was stirred continuously to increase the rate of the reaction. Temperature was closely monitored for several minutes until the maximum temperature was reached and the final temperature was recorded. Reaction B: MgO (s) + 2HCl (aq) → MgCl 2(aq) + H 2 O (l) Accurately measure 50ml of 1.00M HCL solution in a graduated cylinder. Pour the HCL into the calorimeter and place the cover and thermometer through the hole and record the initial temperature of the HCL, monitor for several minutes. Accurately weigh 0.5g (to the nearest milligram) of MgO. When the MgO was added to the calorimeter the cover was put in place quickly and the solution was stirred continuously to increase the rate of the reaction. The temperature was monitored closely for several minutes until the maximum temperature was reached and the final temperature was recorded. Results and calculations: Reaction A: Mg (s) + 2HCl → MgCl 2(aq) + H 2(g) (Average) change in temperature: 19.7 C Mass of the system: H: = 509.55kJ/mol = -509.55kJ/mol Reaction B: MgO (s) + 2HCl (aq) → MgCl 2(aq) + H 2 O (l) Average change in temperature: 4.6 C Mass of the system: H: = 79.60kJ/mol = -79.60 kJ/mol Mg (s) + 2HCl (g) → MgCl 2(aq) + H 2(g) H A = -509.55kJ/mol H
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This note was uploaded on 01/30/2012 for the course CHEMISTRY 212 taught by Professor Ha during the Spring '11 term at George Mason.

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hess law - Purpose: In this calorimetry experiment, the...

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