Classify each of the following as exothermic or endothermic:
a. C3H8(g) + 5O2(g) -->3CO2(g) + 4H2O(g) + 2220 kJ
b. 2Na(s) + Cl2(g) --> 2NaCl(s) + 819 kJ
c. PCl5(g) + 67 kJ --> PCl3(g) + Cl2(g)