Question

5. Suppose you place 0.500 g of Mg metal in a coffee cup calorimeter. You add 100.0 mL of 1.00 M HCl. The mass of the HCl solution is 100.112 g. The reaction that occurs is as follows: Mg (s) + 2 HCl (aq) MgCl2 (aq) + H2 (g) The initial temperature of the HCl solution is 22.2°C and the final temperature after the reaction is complete is 44.8°C. The specific heat of water is 4.184 J/gK, and magnesium is the limiting reactant.

a. How much heat is given off (generated) in this reaction?

b. What is the enthalpy change (H) for the reaction per mole of magnesium?

Answer 1

Mg(s) + 2HCl(aq) -------> H2(g) + MgCl2(aq)

Molar mass og Mg = 24.3 g / mol,

moles of 0.5 g of Mg = 0.5/24.3 = 0.02058 moles Mg
Heat of rxn = [ delta H ] / mole Mg

                  = (100.112*4.184*(44.8-22.2)) /0.02058

                  = - 459982 J

                  = -449.982 KJ/mol

Heat given off from the reaction = -9466.43 J

                                                   = -9.46643 KJ