Use Hess’ Law to determine the standard enthalpy change for the following reaction. Target C3H8 (g) + 5O2 (g) 3C (s) + 4H2 (g) C (s) + O2(g) H2 (g) + ½ O2 (g) 3CO2 (g) + 4H2O (l) Hrxn=??? C3H8 (g) CO2 (g) H2O (l) Hf= -104kJ Hf= -394kJ Hf= -286kJ What is the standard enthalpy of formation for a substance? NOTE: The standard enthalpy of formation of any element in its standard state = ______ WHY?? Look closely at the Hess’ Law example above and you will see that Hrxn = ____________________________ - ______________________________ A new equation: Hrxn = ___________________________ - ______________________________ Now use this equation to solve the problem above.