In a calorimeter, a 1.0 g sample of magnesium is burned to form MgO. In doing so, 25.5 kJ of energy is released. What is the Heat of Combustion in kJ/mol of magnesium?

Answer 1

First, convert from grams to moles of magnesium (unit conversion. Divide the mass (in grams) by the amu of magnesium (in g/mol) to get mol (g*(mol/g)=mol)). Then divide the energy released (in kJ) by the moles of magnesium used to get kJ/mol

Answer 2

Calculate the # moles of Mg.

1.0 gm / 24.305 g/mole = 0.0411 moles

The 25.5 kj was released in burning 0.0411 moles, so the kj/mole is

25.5 kj / 0.0411 moles = 620 kj / mole