Q.34 What volume of oxygen is required for complete combustion of 5cm3 C2H2
C) 5cm
B) 12.5cm
D) 13.5cm
Answers
Answer:
B. 12.5cm
Explanation:
Look at the equation for the reaction. C2H2 + O2 = CO2 + H2O, before balancing. But we need to put numbers in there to balance it out. The two carbons need a total of 4 oxygen atoms to balance them; the two hydrogens need one atom of oxygen. So one molecule of acetylene needs 5 atoms of oxygen for full combustion. Oxygen comes in biatomic molecules O2, so one has to double both sides; the equation comes out to 2C2H2 + 5O2 = 4CO2 +2H2O.
OK, we have the equation. Now, the number of molecules in a volume of gas is directly proportional to the volume; the actual number of molecules is extremely high and also irrelevant. There are 2.5 times as many oxygen molecules in the equation as acetylene, so the volume of oxygen is 2.5 times that of the acetylene. 5x2.5=12.5, so the answer is 12.5cm.
Answer:
The correct answer is option B) 12.5 cm³.
Solution:
The combustion reaction of C₂H₂ is as follows,
2C₂H₂ + 5O₂ 4CO₂ + 2H₂O
Here we can see that for combustion of 2 moles of C₂H₂, 5 moles of O₂ are required.
Number of moles of oxygen required for combustion of 1 mole of C₂H₂, n = 5/2 = 2.5 moles
We know that 1 mole of gas contains 22.4 L of gas.
∴ Volume of O₂ required for combustion of 22.4 L of C₂H₂ = 2.5×22.4
= 56 L
Volume of O₂ required for combustion of 1 L of C₂H₂, V = 56/22.4 = 2.5 L
Volume of oxygen required for combustion of 5 cm³ (5 L) of C₂H₂ = 2.5×5
= 12.5 L
= 12.5 cm³
Hence, volume of oxygen required for complete combustion of 5 cm³ of C₂H₂ is 12.5 cm³.
So, option B) is the correct answer.
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