Which of the following is/are endothermic compound(s)? — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

An endothermic compound is one that has a positive standard enthalpy of formation (ΔfH° > 0). Let's evaluate:<br>(a) $NO$(g): Formation reaction 1/2 $N_2$(g) + 1/2 $O_2$(g) → $NO$(g) is endothermic (ΔfH° = +90.25 kJ/mol) due to the high bond energy of the $N_2$ triple bond.<br>(b) $CO_2$(g): ΔfH° = -393.5 kJ/mol (exothermic, so it is an exothermic compound).<br>(c) $CO$(g): ΔfH° = -110.5 kJ/mol (exothermic).<br>(d) $NH_3$(g): ΔfH° = -46.1 kJ/mol (exothermic).<br>Therefore, only $NO$(g) is an endothermic compound. (The answer key on page 5.35 confirms the answer is (a)).