Question

Ethanol is added to gasoline to produce E-15 and E-85. It promotes more complete combustion of the gasoline and is an octane booster. Compare the heats of combustion of 2,2,4-trimethylpentane (1304 kcal/mol) and ethanol (327 kcal/mol). Which has the higher heat of combustion in kcal/mol?

Answer 1

Answer:

2,2,4-trimethylpentane has the higher heat of combustion in kcal/mol.

Explanation:

Heat of combustion is defined as heat evolved on combustion of 1 mole of a substance.

2,2,4-trimethylpentane has the higher heat of combustion in kcal/mol.

Heat combustion of 2,2,4-trimethylpentane =  (1304 kcal/mol) and

$C_8H_{18}+\frac{25}{2}O_2\rightarrow 8CO_2+9H_2O,\Delta H=-1,304 kcal/mol$

1 mole of 2,2,4-trimethylpentane on combustion gives 8 mole sof carbon dioxide gas and 9 moles of water.

Heat combustion of ethanol = (327 kcal/mol)

$C_2H_5OH+3O_2\rightarrow 2CO_2+3H_2O,\Delta H=-327kcal/mol$

1 mole of ethanol on combustion gives 2 moles of carbon dioxide gas and 3 mole of water.

Heat combustion of ethanol < Heat combustion of 2,2,4-trimethylpentane