Question

Learning Goal: To understand how to use Hess's law to find the enthalpy of an overall reaction The change in enthalpy, AH is the heat absorbed or produced during any reaction at constant pressure. Hess's law states that AH for an overall reaction is the sum of the AH values for the individual reactions. For example, if we wanted to know the enthalpy change for the reaction 3Mn +302+3MnO2 we could calculate it using the enthalpy values for the following individual steps Step 1: 4A1+302+2A1,03 Step 2:3Mn + 2Al2O3+3MnO2 + 4A1 Overall: 3Mn +302+3MnO2 If the enthalpy change is -3352 kJ/mol for step 1 and 1792 kJ/mol for step 2, then the enthalpy change for the overall reaction is calculated as follows: AH = -3352 + 1792 = -1560 kJ/mol It is also important to note that the change in enthalpy is a state function, meaning it is independent of path. In other words, the sum of the AH values for any set of reactions that produce the desired product from the starting materials gives the same overall ΔΗ.

sorry i was confused here is the correct photo

Answer 1

(b) for step 4H=ove hence Rx - Exothermic Step 2 is exothermic because the energy released when carbon-oxygen bonds form greater than Energy consumed when carbon-carbonand oxygen-oxygen bonds are broken.