Methanol (`CH_3OH` ), ethanol (`C_2H_5OH` ), propanol (`C_3H_7OH` ) and butanol (`C_4H_9OH` ) are the first four alcohols and contain 1, 2, 3 and 4 carbon atoms, respectively. These alcohols undergo exothermic combustion, that is, release energy when burned. We can burn a known quantity of these alcohols in a spirit burner and use the energy generated to heat the water. By knowing the change in water temperature, we can calculate the heat of combustion...
Methanol (`CH_3OH` ), ethanol (`C_2H_5OH` ), propanol (`C_3H_7OH` ) and butanol (`C_4H_9OH` ) are the first four alcohols and contain 1, 2, 3 and 4 carbon atoms, respectively. These alcohols undergo exothermic combustion, that is, release energy when burned. We can burn a known quantity of these alcohols in a spirit burner and use the energy generated to heat the water. By knowing the change in water temperature, we can calculate the heat of combustion of each of these alcohols.
Here is a summary of heat of combustion on per carbon atom basis:
Alcohol No of carbon atoms heat of combustion (kJ/mol) per carbon atom basis (kJ/mol)
Methanol 1 726 726
Ethanol 2 1367 683.5
Propanol 3 2021 673.7
Butanol 4 2676 669
Thus, we can see that as the number of carbon atoms increase, the amount of heat released (per carbon atom basis) decreases. We can also infer that the difference reduces as we go towards higher carbon alcohols. For example, on per carbon atom basis, ethanol releases 10 kJ/mol extra heat as compared to propanol. However, when comparing propanol and butanol, a difference of only about 5 kJ/mol (per carbon atom basis) is obtained.
Thus, fuels with lesser carbon numbers generate more energy, although the difference reduces as we use alcohols with more carbon atoms.
Hope this helps.
No comments:
Post a Comment