AP Chemistry
6.6 Introduction to Enthalpy of Reaction
A student compares three fuels to determine which releases the greatest amount of heat per gram combusted under standard conditions. The complete combustion of each fuel is represented by the general process:
\[ \text{Fuel} + \text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)} + \text{H}_2\text{O(l)} \]
The table below provides the molar mass and standard molar enthalpy of combustion, \(\Delta H^\circ_{\text{comb}}\), for each fuel.
Which of the following correctly ranks the fuels in order of the quantity of heat released per gram of fuel combusted, from greatest to least?
\[ \text{Fuel} + \text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)} + \text{H}_2\text{O(l)} \]
The table below provides the molar mass and standard molar enthalpy of combustion, \(\Delta H^\circ_{\text{comb}}\), for each fuel.
| Fuel | Chemical formula | Molar mass (\(\text{g/mol}\)) | \(\Delta H^\circ_{\text{comb}}\) (\(\text{kJ/mol}\)) |
|---|---|---|---|
| Methane | \(\text{CH}_4\) | \(16\) | \(-880\) |
| Ethanol | \(\text{C}_2\text{H}_5\text{OH}\) | \(46\) | \(-1380\) |
| Octane | \(\text{C}_8\text{H}_{18}\) | \(114\) | \(-5472\) |
Which of the following correctly ranks the fuels in order of the quantity of heat released per gram of fuel combusted, from greatest to least?
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