calculate the standard enthalpy change for the reaction 2Al(s) + Fe2O3(s)------2Fe(s) + Al2O3(s)
given that
2Al(s) + 3/2O2(g)----Al2O3(s) DeltaHrxn = -1669.8kJ/mol
2Fe(s) + 3/2O2(g)------Fe2O3(s) deltaHrxn= -822.2kJ/mol

Question

calculate the standard enthalpy change for the reaction   2Al(s) + Fe2O3(s)------>2Fe(s) + Al2O3(s)   
given that
2Al(s) + 3/2O2(g)---->Al2O3(s)  DeltaHrxn = -1669.8kJ/mol
2Fe(s) + 3/2O2(g)------>Fe2O3(s) deltaHrxn= -822.2kJ/mol

anonymous · Answer

|dw:1349929294082:dw|
 Using Hess's Law, you can add together the two reactions. Since the second one is flipped, the sign must also be flipped. The 3/2 O2 cancel because they are on both sides of the equation, and then you just add the enthalpies.