Question

5. A open ended mercury manometer is used to measure the pressure cxerting by a trapped gas as shown in the figure. Initially manometer shows no difference in mercury level in both columnas shown in diagram After sparking 'NHs' dissociated according to following given reaction NH, (g) N (g) H, (g) If pressures of NH decreases to 0.9 atm. Then difference in mercury level is (assume temperature is constant during entire process.) (A) 228 mm Hg (BJ 38 mm Hg (C) 76 mm Hg (D) 152 mm Hg

JEE/Engineering Exams

Chemistry

Solution

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Initial pressure of A is equal to atmospheric pressure which is ( 760 mathrm{mm} ) Hg. At equilibrium, the pressures of ( A, B ) and ( C ) are 0.8,0.3 and 0.2 atm respectively. The total pressure at equilibrium is ( 0.8+0.3+0.2=1.3 ) atm Thus the total pressure increased by 0.3 atm. This corresponds to ( 0.3 times 760 mathrm{mm}=228 mathrm{mm} mathrm{Hg} )