You must write them completely like this CnH2n + 2 + 3n +1/2O2-----> nCO2 + n+1H2O

Here are the balanced chemical equations for the complete combustion of each class of organic compounds:

• Alkane ($\text{C}_n\text{H}_{2n+2}$):

  $$\text{C}_n\text{H}_{2n+2} + \frac{3n+1}{2}\text{O}_2 \longrightarrow n\text{CO}_2 + (n+1)\text{H}_2\text{O}$$

• Alkene ($\text{C}_n\text{H}_{2n}$):

  $$\text{C}_n\text{H}_{2n} + \frac{3n}{2}\text{O}_2 \longrightarrow n\text{CO}_2 + n\text{H}_2\text{O}$$

• Alkyne ($\text{C}_n\text{H}_{2n-2}$):

  $$\text{C}_n\text{H}_{2n-2} + \frac{3n-1}{2}\text{O}_2 \longrightarrow n\text{CO}_2 + (n-1)\text{H}_2\text{O}$$

• Benzene ($\text{C}_6\text{H}_6$):

  $$\text{C}_6\text{H}_6 + \frac{15}{2}\text{O}_2 \longrightarrow 6\text{CO}_2 + 3\text{H}_2\text{O}$$

• Alcohol ($\text{C}_n\text{H}_{2n+2}\text{O}$):

  $$\text{C}_n\text{H}_{2n+2}\text{O} + \frac{3n}{2}\text{O}_2 \longrightarrow n\text{CO}_2 + (n+1)\text{H}_2\text{O}$$

• Alkanoic acid (Carboxylic acid) ($\text{C}_n\text{H}_{2n}\text{O}_2$):

  $$\text{C}_n\text{H}_{2n}\text{O}_2 + \frac{3n-2}{2}\text{O}_2 \longrightarrow n\text{CO}_2 + n\text{H}_2\text{O}$$

• Aldehyde ($\text{C}_n\text{H}_{2n}\text{O}$):

  $$\text{C}_n\text{H}_{2n}\text{O} + \frac{3n-1}{2}\text{O}_2 \longrightarrow n\text{CO}_2 + n\text{H}_2\text{O}$$

• Ketone ($\text{C}_n\text{H}_{2n}\text{O}$):

  $$\text{C}_n\text{H}_{2n}\text{O} + \frac{3n-1}{2}\text{O}_2 \longrightarrow n\text{CO}_2 + n\text{H}_2\text{O}$$