Combustion of Alkanes

Alkanes are hydrocarbons that contain only single bonds between carbon atoms. They are also known as saturated hydrocarbons. Alkanes are used as fuels because they burn readily in the presence of oxygen, producing carbon dioxide and water. The combustion of alkanes is an exothermic reaction, which means that it releases energy in the form of heat and light.

Stoichiometry of Combustion

The stoichiometry of combustion is the study of the relationship between the amount of fuel and oxygen required for complete combustion to occur. The balanced chemical equation for the combustion of an alkane is:

CnH2n+2 + (3n+1/2)O2 → nCO2 + (n+1)H2O

This equation shows that one mole of an alkane reacts with (3n+1/2) moles of oxygen to produce n moles of carbon dioxide and (n+1) moles of water. The ratio of the volumes of the reactants and products is also important in stoichiometry, as gases occupy different volumes under the same conditions of temperature and pressure.

Solution

According to the given information, 5 L of an alkane requires 25 L of oxygen for complete combustion. Therefore, the ratio of the volumes of alkane to oxygen is:

5 L alkane : 25 L oxygen = 1 : 5

This means that for every one volume of alkane, five volumes of oxygen are required for complete combustion. Using the balanced chemical equation above, we can see that the alkane must have the formula C3H8, which is propane.

C3H8 + 5O2 → 3CO2 + 4H2O

Conclusion

In conclusion, the alkane that requires 25 L of oxygen for complete combustion when 5 L of it is burned is propane (C3H8). This is because the ratio of the volumes of alkane to oxygen is 1:5, which corresponds to the stoichiometry of propane combustion.