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GATE 2025 AE – Question 33

Propulsion · Gas turbine combustors: types, combustion and stoichiometric fuel-to-air ratio · 1 mark · Multiple choice

A gaseous fuel mixture comprising 3 moles of methane and 2 moles of ammonia is combusted in X moles of pure oxygen in stoichiometric amount. Assuming complete combustion, with only CO$_2$, H$_2$O and N$_2$ in the product gases, the value of X is ___.

$3\,CH_4 + 2\,NH_3 + X\,O_2 \rightarrow$ Products (CO$_2$, H$_2$O, N$_2$)

  1. 7.5
  2. 5.5
  3. 8.5
  4. 9.5

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Correct answer: (A) 7.5

Explanation

Carbon: 3 mol of CO$_2$, which takes 6 mol of O. Hydrogen: $3 \times 4 + 2 \times 3 = 18$ atoms make 9 mol of H$_2$O, which takes 9 mol of O. The nitrogen goes to N$_2$ and takes no oxygen. In all 15 mol of O atoms are needed, which is $X = 7.5$ mol of O$_2$.