Consider the following intermediate chemical equations.
What is the enthalpy of the overall chemical reaction
-4,580 kJ
-1,300 kJ
1,300 kJ
4,580 kJ

Explanation:

According to Hess’s law, you can calculate the enthalpy  of the overall chemical reaction by adding enthalpy changes of the intermediate reactions, at the same temperature.

First, you must find how the intermediate equations form the overall equation.

Here, the overall equation is:

To obtain it you can swift both the first and second intermediate equations and sum them. When you swift a chemcial equation, the corresponding enthalpy change has the opposite sign:

Change

     to

Change

    to

Now add the two transformed equations: