Consider the reaction in a commercial heat pack: 4 Fe (s) + 3 O2 (g) ® 2 Fe2O3 (s) DH = - 1652 kJ a) How much heat is released when 1.00 g iron is reacted with excess O2? b) What mass of O2 must react with iron in order to generate 2150 kJ of heat?

a) - 7.395kJ of energy are released.

b) 125g of O₂ must react.

Explanation:

Based on the reaction:

4 Fe (s) + 3 O₂ (g) → 2 Fe₂O₃ (s) ΔH = - 1652 kJ

4 moles of iron with an excess of oxygen release - 1652kJ of energy

a) The heat released is:

1.00g Fe (molar mass: 55.845g/mol)

1.00g * (1mol / 55.845g) = 0.0179 moles de Fe.

As 4 moles release - 1652kJ, 0.0179 moles release:

0.0179 mol Fe * (-1652kJ / 4mol Fe) = - 7.395kJ of energy are released.

b) As 3 moles of oxygen produce - 1652kJ, 2150kJ are released when react:

2150kJ * (3 mol O₂ / 1652kJ) = 3.9 moles of O₂

As molar mass of O₂ is 32g/mol, mass of 3.9 moles of O₂ is:

3.9 mol O₂ * (32g / mol) = 125g of O₂ must react.