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When a gaseous olefinic hydrocarbon is b...

When a gaseous olefinic hydrocarbon is burnt completely in excess of `O_(2)`, a contraction in volume equal to double to the volume of hydrocarbon is noticed then hydrocarbon will be

A

`C_(2)H_(2)`

B

`C_(2)H_(4)`

C

`C_(2)H_(6)`

D

`C_(3)H_(8)`

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we need to analyze the combustion reaction of an olefinic hydrocarbon and the resulting volume changes. Here’s a step-by-step solution: ### Step 1: Understand the combustion reaction When a hydrocarbon (olefinic) burns in excess oxygen, it produces carbon dioxide and water. The general combustion reaction for an olefinic hydrocarbon (C_nH_m) can be represented as: \[ C_nH_m + O_2 \rightarrow CO_2 + H_2O \] ### Step 2: Write the balanced equation For a typical olefinic hydrocarbon like ethylene (C₂H₄), the combustion reaction can be written as: \[ C_2H_4 + O_2 \rightarrow 2CO_2 + 2H_2O \] ### Step 3: Determine the volume of reactants and products According to the problem, the contraction in volume is equal to double the volume of the hydrocarbon. Let’s assume we have 1 volume unit of C₂H₄: - Volume of C₂H₄ = 1 unit - From the balanced equation, we need 3 units of O₂ (1 unit of C₂H₄ requires 3 units of O₂ for complete combustion). - Products formed: 2 units of CO₂ and 2 units of H₂O (the volume of water vapor can be considered as equal to its gaseous state). ### Step 4: Calculate the total volume before and after combustion **Before combustion:** Total volume = Volume of C₂H₄ + Volume of O₂ = 1 + 3 = 4 units **After combustion:** Total volume = Volume of CO₂ + Volume of H₂O = 2 + 2 = 4 units ### Step 5: Analyze the contraction in volume The problem states that there is a contraction in volume equal to double the volume of the hydrocarbon. If we started with 1 unit of C₂H₄, the contraction in volume would be: Contraction = 2 × Volume of C₂H₄ = 2 × 1 = 2 units. ### Step 6: Determine the final volume after contraction If we started with 4 units and there is a contraction of 2 units, the final volume after combustion would be: Final volume = Initial volume - Contraction = 4 - 2 = 2 units. ### Step 7: Conclusion Given that the contraction observed is consistent with the combustion of C₂H₄, we conclude that the hydrocarbon in question is **C₂H₄ (ethylene)**. ### Final Answer: The hydrocarbon will be **C₂H₄ (ethylene)**. ---
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