A mixture of hydrogen and chlorine kept in a closed flask at a constant temperature was irradiated w

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A mixture of hydrogen and chlorine kept in a closed flask at a constant temperature was irradiated with scattered light. After a certain time, the chlorine content decreased by 20% compared with that of the starting mixture and the resulting mixture had the composition as follows: 60 volume % of chlorine, 10 volume % of hydrogen, and 30 volume % of hydrogen chloride. Determine the composition of the initial gaseous mixture

Accepted Answer

Sol. Key concept: Gas-volume stoichiometry at the same temperature and pressure.The reaction is H₂ + Cl₂ → 2HCl. Two volumes of reactants form two volumes of product, so the total gas volume is unchanged. Take the final mixture as 100 volume units: 60 Cl₂, 10 H₂ and 30 HCl.Producing 30 units of HCl consumes 15 units each of H₂ and Cl₂. Therefore, the starting volumes were 10 + 15 = 25 units H₂ and 60 + 15 = 75 units Cl₂.$$\% H_{2} = 25\%,\ \ \ \ \% Cl_{2} = 75\%$$Check: chlorine decreased by 15/75 × 100 = 20%, as required. Thus (d). This volume method also avoids the algebraic transcription errors in the earlier solution.

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