Question

If you need to reverse the following reaction and multiply it by 2 in order for it to be an intermediate reaction in a Hess's law problem, what would be the final value for the enthalpy of reaction you use for this intermediate reaction? C2H4 + 3 O2 2 CO2 + 2 H2O, H = -1410 kJ

Answer 1

The reaction is:
C₂H₄ + 3O₂ → 2CO₂ + 2H₂O; ΔH = 1410 kJ

When we reverse this reaction, the sign of the enthalpy  change, ΔH, will be changed. The enthalpy change for the reversed reaction would be 1,410 kJ.
Next, we must also multiply the reaction by 2, so the final enthalpy change for the reverse reaction will be:

ΔH = 2,820 kJ