In a closed vessel at STP, 50L of CH4 is ignited with 750L of air (containing 20% O2). The number of moles of O2 remaining in the vessel on cooling to room temperature is closest to:
A
5.8
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B
2.2
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C
4.5
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D
6.7
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Solution
The correct option is B2.2 At STP, 22.4 L of any gas =1 mole.
50L of CH4=50L22.4L/mol=2.23 moles.
750L of air =750L22.4L/mol=33.48 moles.
The air contains 20% O2. The number of moles of O2=33.48×20100=6.697 moles.
CH4+2O2→CO2+2H2O
2.23 moles of CH4 will react with 2×2.23=4.46 moles of O2.
6.697−4.46≃2.2 moles of O2 will remain in the vessel on cooling to room temperature.