$$\ce{2NO(g) + O2(g)->2NO2(g)} \hspace{5em} \Delta H^{\circ}=\pu{-114.1 kJ}$$

The reaction represented above is one that contributes significantly to the formation of photochemical smog. How much heat is released when $\pu{120.1 g}$ of $\ce{NO(g)}$ is converted to $\ce{NO2(g)}$?

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The equation tells us that for every $2$ moles of $\ce{NO(g)}$, $\pu{114.1 kJ}$ of heat is released.

$$\pu{120.1 g }\ce{NO(g)} \cdot \frac{\pu{1 mol }\ce{NO(g)}}{\pu{30 g }\ce{NO(g)}}\cdot \frac{\pu{114.1 kJ}}{\pu{2 mol }\ce{NO(g)}}$$ $$\approx 120.1\cdot \frac{1}{30}\cdot \frac{114}{2}   \pu{kJ}$$ $$= \boxed{\pu{228 kJ}}$$