Methanol, CH3 OH, a compound that can be made relatively...

Methanol, $\mathrm{CH}_{3} \mathrm{OH},$ a compound that can be made relatively inexpensively from coal, is a promising substitute for gasoline. The alcohol has a smaller energy content than gasoline, but, with its higher octane rating, it burns more efficiently than gasoline in combustion engines. (It has the added advantage of contributing to a lesser degree to some air pollutants.) Compare the enthalpy of combustion per gram of $\mathrm{CH}_{3} \mathrm{OH}$ and $\mathrm{C}_{8} \mathrm{H}_{18}$ (isooctane), the latter being representative of the compounds in gasoline. $\left(\Delta_{j} H^{\circ}=-259.3 \mathrm{kJ} / \mathrm{mol} \text { for isooctane }\right)$

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Key Concepts

Molar Mass Calculation

Molar mass is the mass of one mole of a substance and is crucial for converting an energy value given per mole (such as the enthalpy of combustion) into an energy per mass basis. This conversion enables a fair comparison between substances with different molecular weights based on their energy content per gram.

Energy Density

Energy density represents the amount of energy stored per unit mass of a fuel. Calculating the enthalpy of combustion per gram provides a measure of energy density, which is fundamental in assessing the practical utility and efficiency of fuels, as it directly influences how much energy can be delivered by a given mass of fuel.

Enthalpy of Combustion

This concept refers to the energy released when one mole of a substance is completely oxidized under standard conditions. It is a key thermodynamic property used to evaluate how much heat a fuel will produce during combustion, and understanding it aids in comparing the efficiency of different fuels.

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