Classify the following chemical reactions as endothermic or exothermic.

Question

PCl3 (s) + Cl2 (g) → PCl5 (s) + energy

2KNO3 (s) + energy → 2KNO2 (s) + O2 (g)

NH4NO2 + energy → N2 (g) + 2H2O (g)

2H2 (g) + O2 (g) → 2H2O (l) + energy

a.exothermic

b.endothermic

Answer 1

If energy is added to the system (a reactant), it is endothermic.

If energy is released from the system (a product), it is exothermic.

You should be able to answer this now.

Hint: answer to the first question is (a) exothermic since energy is a product