AP Chemistry
6.9 Hess’s Law
6.8 Enthalpy of Formation
6.6 Introduction to Enthalpy of Reaction
A student investigates the thermochemistry of ethanol, \(\text{C}_2\text{H}_5\text{OH}(l)\), by analyzing its combustion reaction under standard conditions according to the balanced equation below:
\[ \text{C}_2\text{H}_5\text{OH}(l) + 3\,\text{O}_2(g) \rightarrow 2\,\text{CO}_2(g) + 3\,\text{H}_2\text{O}(l) \quad \Delta H_{\text{comb}}^\circ = -1370\text{ kJ/mol}_{\text{rxn}} \]
The student compiles standard enthalpies of formation in the table below.
Based on the balanced equation and the data in the table, what is the standard enthalpy of formation, \(\Delta H_f^\circ\), of \(\text{C}_2\text{H}_5\text{OH}(l)\)?
\[ \text{C}_2\text{H}_5\text{OH}(l) + 3\,\text{O}_2(g) \rightarrow 2\,\text{CO}_2(g) + 3\,\text{H}_2\text{O}(l) \quad \Delta H_{\text{comb}}^\circ = -1370\text{ kJ/mol}_{\text{rxn}} \]
The student compiles standard enthalpies of formation in the table below.
| Substance | State | \(\Delta H_f^\circ\ (\text{kJ/mol})\) |
|---|---|---|
| \(\text{CO}_2(g)\) | Gas | \(-390\) |
| \(\text{H}_2\text{O}(l)\) | Liquid | \(-290\) |
| \(\text{O}_2(g)\) | Gas | \(0\) |
Based on the balanced equation and the data in the table, what is the standard enthalpy of formation, \(\Delta H_f^\circ\), of \(\text{C}_2\text{H}_5\text{OH}(l)\)?
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