JEE Main 2016 · 10 Apr · Shift 1 · Chemistry Q35

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ChemistrySingle correct+4 / -1Question 35 of 90

If 100 mole of $\ce{H2O2}$ decompose at 1 bar and 300 K, the work done (kJ) by one mole of $\ce{O2(g)}$ as it expands against 1 bar pressure is :
$\ce{2H2O2(l) <=> 2H2O(l) + O2(g)}$
(R = 8.3 J K $^{-1}$ mol $^{-1}$ )

62.25

124.50

249.00

498.00

Answer and worked solution

Official answer: B

100 mol of $\ce{H2O2}$ gives 50 mol of $\ce{O2}$ , which does $W=nRT=50\times8.3\times300=124.5$ kJ against 1 bar.

The question says "by one mole of $\ce{O2}$ ", which would be 2.49 kJ (not an option); the derived key takes the intended quantity to be the work done by all the oxygen formed.

Topics:First law and enthalpy

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JEE Main 2016 · 10 Apr · Shift 1, Chemistry question 35