JEE Advanced 2015 · Paper 2 · Chemistry Q27

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ChemistryInteger+4Question 27 of 60

A closed vessel with rigid walls contains 1 mol of $^{238}_{92}\mathrm U$ and 1 mol of air at 298 K. Considering complete decay of $^{238}_{92}\mathrm U$ to $^{206}_{82}\mathrm{Pb}$ , the ratio of the final pressure to the initial pressure of the system at 298 K is

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Answer and worked solution

Official answer: 9

Decay chain. $^{238}\mathrm U\to{}^{206}\mathrm{Pb}$ loses 32 mass units, i.e. 8 α-particles (and 6 β⁻). The α-particles become 8 mol of He gas.

Pressure ratio. Initially there is 1 mol of gas (air; U is solid). Finally there are $1+8=9$ mol. At constant $T$ and $V$ , the ratio is 9.

Answer: 9

Topics:Radioactive decay kinetics

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JEE Advanced 2015 · Paper 2, Chemistry question 27