Combustion and the Relative Stabilities of Alkanes

December 31,1995. Since that lime, first hydrochlorofluorocarbons (HCFCs) and later hydrofluorocarbons (HFCs) have been developed as CFC replacements. The HCFCs are destroyed by Ught at lower altitudes than CFCs, and thus pose lesser threats to the ozone layer. They are scheduled to be phased out of use by 2030. HFC-134a has become a popular CFC substitute in refrigerators and air conditioners in the United States. HFCs are not ozone depletors but are potent greenhouse gases and thus are not long-term solutions as CFC replacanents. 

Both products in the combustion of alkanes have a very low energy content, and hence their formation is associated with a large negative A/T, released as heat. 

The heat released in the burning of a molecule is called its heat of combustion, AH b-Many heats of combustion have been measured with high precision, thus allowing comparisons of the relative energy content of the alkanes (Table 3-7) and other compounds. 

Heats of Combustion [kcal mol (kj mol ), Normalized to 25 C] of Various Organic Compounds 

CH3CH2OH (gas) CH3CH2OH (liquid) C12H22O11 (solid) Ethanol Ethanol Cane sugar (sucrose) -336.4 (-1407.5) -326.7 (-1366.9) -1348.2 (-5640.9) 

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