Calorimetry 1: The Enthalpy of Formation of MgO Overview Getting Started Techniques Procedure FAQ Full Lab Manual Introduction & Goals Chemistry & Background Key Questions Prelab Problems Safety Procedure In Your Write-up Experiments Index ChemLab Home		Prelab Problems 1. Use the values in Table 1 to calculate a literature value of the enthalpy change for the reaction Mg(s) + 2 HCl(aq) MgCl2(aq) + H2(g) Your value should be for the reaction, as written, with one mole of magnesium solid reacting with two moles of aqueous hydrochloric acid. 2. In an adiabatic calorimetry experiment, 100 mL of 0.500 M HCl was added to 100 mL 0.500 M NaOH to produce 200 mL 0.25 M NaCl. A temperature increase of 3.38 °C was measured. Calculate the heat of reaction associated with this process at 25 °C from the data in Table 1, for one mole of reactant and for the reaction conditions used. Use this value to calculate the heat capacity of the system, Ctotal. 3. In an adiabatic calorimetry experiment, a 0.1277 g Mg ribbon was added to 200 mL 0.500 M HCl following the procedure outlined above. A temperature increase of 2.98 °C was measured. The heat capacity of the product solution and the calorimeter was 846.0 J °K-1. Calculate for this reaction, as performed, and a molar . Compare the latter to the literature value. 4. A pair of students measured the temperature change for the reaction of Mg and HCl and calculated the molar for the reaction. They made the mistake of measuring 100 mL of HCl solution (as in the HCl + NaOH reaction), rather than 200 mL (needed for the Mg + HCl reaction). They calculated a molar for the Mg + HCl reaction that was about twice what they expected based on the literature value. Why did the mistake in solution volume result in a value that is too large, by a factor of two? Be specific in your explanation and be sure you don't make this mistake! 5. You will use the web applet, Enthalpy and Hess's Law to complete this prelab problem. Use the Test Reactions part of the applet to find the set of reactions you will sum to find the heat of formation of MgO. Then use the Enthalpy Diagrams portion of the applet to construct a diagram showing the enthalpy difference between the reactants and products of this set of reactions. Sketch your completed enthalpy diagram with accurate values, to receive credit for this prelab problem.
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