[faye]

How does the enthalpy change for the reverse  :s-sault:reaction compare to the enthalpy change of the forward reaction? WHat is a forward and reverse reaction??  :confused1:

[jdurg]

Let's say you had 2H₂(g) + O₂(g) -> 2H₂O(g).  The forward reaction is the reaction of hydrogen and oxygen forming water, and the reverse reaction is water forming hydrogen and oxygen.  The enthalpy change for the reverse reaction is the same magnitude, but different sign.  So if the forward reaction had an enthalpy change of -900 kJ/mol, the reverse would have an enthalpy change of +900 kJ/mol.