AP Chemistry / Unit 6: Thermochemistry
6.8 Enthalpy of Formation
Notes
$\Delta H_f^\circ$: enthalpy change to form 1 mol from elements in standard states (elements = 0).
$$\Delta H^\circ_{rxn}=\sum\Delta H_f^\circ(\text{products})-\sum\Delta H_f^\circ(\text{reactants})$$
Practice
$\Delta H_f^\circ$ of $O_2(g)$:
An element in its standard state.
$\Delta H_f^\circ$: $CO_2=-394$, $CO=-111$ kJ/mol. For $\displaystyle CO+\frac{1}{2}O_2\to CO_2$, $\Delta H=$
$-394-(-111)$.
The formula is products minus:
Products − reactants.
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