Question

What is the standard enthalpy change for the following reaction, where 2 moles of solid iron (Fe) reacts with 1 mole of oxygen gas (O2) to produce 2 moles of solid iron (III) oxide (Fe2O3)? 4Fe(s) + 3O2(g) -> 2Fe2O3(s)

Answer 1

To calculate the standard enthalpy change for this reaction, we need to know the standard enthalpies of formation  Hf  for the reactants and products involved in the reaction. The standard enthalpy of formation is the change in enthalpy when one mole of a substance is formed from its constituent elements in their standard states.The standard enthalpy of formation for elemental substances, such as Fe s  and O2 g , is zero because they are in their standard states.The standard enthalpy of formation for Fe2O3 s  is -824.2 kJ/mol.Now, we can use the following equation to calculate the standard enthalpy change for the reaction:H =  [Hf products ] -  [Hf reactants ]For our reaction:H = [2   -824.2 kJ/mol ] - [4  0 kJ/mol + 3  0 kJ/mol]H =  -1648.4 kJ  - 0H = -1648.4 kJThe standard enthalpy change for the given reaction is -1648.4 kJ.