NCERT · Class 10 · Science · Carbon and its CompoundsExplain the chemical properties of carbon compounds with respect to (i) Combustion, (ii) Oxidation, (iii) Addition reaction, and (iv) Substitution reaction. Give chemical equations for each.

Chemical Properties of Carbon Compounds

(i) Combustion

• Explanation: Carbon compounds generally burn in air (oxygen) to release carbon dioxide gas, water vapor, along with a large amount of heat and light. Saturated hydrocarbons usually burn with a clean, blue flame in sufficient air, while unsaturated hydrocarbons burn with a yellow, smoky flame due to incomplete combustion.
• Chemical Equation: $$\text{CH}_4 (g) + 2\text{O}_2 (g) \rightarrow \text{CO}_2 (g) + 2\text{H}_2\text{O} (g) + \text{Heat and Light}$$

(ii) Oxidation

• Explanation: Carbon compounds can be easily oxidized when heated with oxidizing agents like alkaline potassium permanganate ($\text{KMnO}_4$) or acidified potassium dichromate ($\text{K}_2\text{Cr}_2\text{O}_7$). During this process, alcohols are converted into carboxylic acids.
• Chemical Equation: $$\text{CH}_3\text{CH}_2\text{OH} \xrightarrow[\text{or acidified } \text{K}_2\text{Cr}_2\text{O}_7]{\text{Alkaline } \text{KMnO}_4 + \text{Heat}} \text{CH}_3\text{COOH} + \text{H}_2\text{O}$$

(iii) Addition Reaction

• Explanation: Unsaturated hydrocarbons (alkenes and alkynes) add hydrogen in the presence of catalysts such as nickel (Ni) or palladium (Pd) to form saturated hydrocarbons (alkanes). This process is known as hydrogenation (addition reaction).
• Chemical Equation: $$\text{CH}_2=\text{CH}_2 + \text{H}_2 \xrightarrow{\text{Ni catalyst}, \text{Heat}} \text{CH}_3-\text{CH}_3$$

(iv) Substitution Reaction

• Explanation: Saturated hydrocarbons are generally unreactive in the presence of most reagents. However, in the presence of sunlight, chlorine can replace hydrogen atoms one by one in a saturated hydrocarbon, known as a substitution reaction.
• Chemical Equation: $$\text{CH}_4 + \text{Cl}_2 \xrightarrow{\text{Sunlight}} \text{CH}_3\text{Cl} + \text{HCl}$$