A 0.1326 g sample of magnesium was burned in an oxygen bomb calorimeter. The total heat capacity of the calorimeter plus water was 5,760 J/°C. If the temperature rise of the calorimeter with water was 0.570°C, calculate the enthalpy of combustion of magnesium. Mg(s)+ 1/2O₂(g)$\rarr$ MgO(s)

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Quizplus · Accepted Answer

The enthalpy of combustion is calculated using the formula: q = C * ΔT, where q is the heat absorbed, C is the heat capacity, and ΔT is the temperature change. Here, q = 5,760 J/°C * 0.570°C = 3,283.2 J. Converting to kJ gives 3.2832 kJ. The molar mass of Mg is 24.305 g/mol, so the moles of Mg burned is 0.1326 g / 24.305 g/mol = 0.00546 mol. The enthalpy of combustion per mole is then 3.2832 kJ / 0.00546 mol = -601.5 kJ/mol, which rounds to -602 kJ/mol.

A 01326 G Sample of Magnesium Was Burned in an Oxygen