Chemistry

Chemistry

Problem

Carbon dioxide gas has ΔHf∘=−393.5 kJ mol−1\Delta H_f^{\circ} = -393.5\,\text{kJ mol}^{-1}, whereas nitric oxide gas has ΔHf∘=+90.3 kJ mol−1\Delta H_f^{\circ} = +90.3\,\text{kJ mol}^{-1}. In 1–2 sentences, explain why the signs of these two values are different.

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