Exercise 2 solution

Overall energy change = energy in (breaking bonds) minus energy out (making bonds). Negative means energy leaves the system.

Reaction X: 1000 - 1250 = -250 kJ. Negative, so EXOTHERMIC.
Reaction Y: 900 - 700 = +200 kJ. Positive, so ENDOTHERMIC.
(All numbers are invented teaching values; calculated in Python.)

Profile for X (invented): reactants 0, peak +60, products -250 kJ/mol.
Activation energy = peak minus reactants = 60 - 0 = 60 kJ/mol.
The overall change is -250 kJ/mol, a different question from the 60 kJ/mol barrier.

Extra (my own reading of the picture) (check): the reverse barrier would be 60 - (-250) = 310 kJ/mol.