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MCAT Chemistry Question — Pressure

Sodium nitrate and ammonium sulfate react at 230ºC to yield sodium sulfate, nitrous oxide, and water vapor. If the total pressure of the products is 1.8 atm, what is the partial pressure of the nitrous oxide?

The reaction is as follows:

2 NaNO3 + (NH4)2SO4 → Na2SO4 (aq) + 2 N2O (g)+ 4H2O (g)  (230—300° С)


A. 0.5 atm

B. 0.6 atm

C. 0.9 atm

D. 1.8 atm

Click for Explanation

A. 0.5 atm, incorrect, this would indicate that 2/7 of the pressure comes from 2 moles of nitrous oxide in the presence of 4 additional moles of water vapor and 1 mole of aqueous sodium sulfate (liquid).

B. 0.6 atm, correct, 2 moles nitrous oxide and 4 moles of water vapor in the products indicate that 1/3 of the pressure is from the nitrous oxide

C. 0.9 atm, incorrect, this answer incorrectly shows that 1/2 the pressure is from nitrous oxide, but the correct ratio is determined by the molar ratio of gas products

D.1.8 atm, incorrect, this would indicate that all pressure is from the nitrous oxide

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