Magnesium metal was added to a coffee-cup calorimeter containing 145.0 mL of 0.500 M hydrochloric acid. The temperature increased by 1.5 °C. What mass of metal was placed in the calorimeter? Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g), ΔHrxn = -44 kJ The heat capacity and density of solution in the calorimeter is the same as those for water: 4.184 J/(g·°C) and 1.00 g/mL. You can ignore change in the mass of solution caused by adding the magnesium and by escape of the hydrogen.