Question

Consider the following reaction and answer the three questions that follow.

 2 Mg (s) + O2 (g) → 2 MgO (s)             ΔH = -1204 kJ

Calculate the amount of heat transferred when 31.67 g of Mg (s) reacts with an excess amount of oxygen gas at a constant pressure.

Answer 1

MM(Mg) = 24.31 g/mol

n(Mg) $= \frac{31.67}{24.31} = 1.30 \;mol$

Energy released by 2 moles of Mg =1204 kJ

Energy released by 1.30 moles of Mg $= \frac{1204 \;kJ}{2} \times 1.3 = 782.6 \;kJ$

Answer: 782.6 kJ