Q. Find the amount of oxygen gas $\left(O_{2}\right)$ measured at a temperature of $0^{o}C$ and pressure of 1 atm, which is needed for the combustion of 1 L of propane gas $\left(C_{3} H_{8}\right)$ measured under the same temperature and pressure conditions.

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A

7 L

B

6 L

C

5 L

D

10 L

Solution:

Writing the equation of combustion of propane $\left(C_{3} H_{8}\right)$ , we get
$\text{C}_{3}\text{H}_{8} & + & 5\text{O}_{2} & \rightarrow & 3\text{CO}_{2} & + & 4\text{H}_{2}\text{O} \\ \text{1 vol} & & \text{5 vol} & & & & \\ 1 \, \text{L} & & \text{5 L} & & $
From the above equation we find that we need 5 L of oxygen at NTP to completely burn 1 L of propane at NTP
If we change the conditions for both the gases from NTP to same conditions of temperature and pressure. The same results are obtained. i.e. 5 L is correct answer.

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