# A mixture of 1.56 g Na2O2 and 8.28 g Ag2CO3 was calcined at 900 ∘C in an evacuated 200 ml

A mixture of 1.56 g Na2O2 and 8.28 g Ag2CO3 was calcined at 900 ∘C in an evacuated 200 ml ampoule and cooled to 25 ∘C. Calculate the final pressure in the ampoule.

At high temperatures, the reaction of decomposition of silver carbonate into metallic silver and gases will take place:
2Ag2CO3 = 4Ag + 2CO2 + O2.

Sodium peroxide, in turn, will interact with carbon dioxide:

2Na2O2 + 2CO2 = 2Na2CO3 + O2.

Let’s find the number of moles of all reaction elements:

n (Ag2CO3) = m / M = 8.28 / 276 = 0.03 mol.

Accordingly, from 2 molecules of silver carbonate, 1 molecule of O2 and 2 CO2 is formed, and during decomposition, 0.03 mol of CO2 and 0.015 mol of O2 are formed.

n (Na2O2) = m / M = 1.56 / 78 = 0.02 mol.

This means that 0.02 mol of CO2 will react with 0.02 mol of peroxide with the release of 0.01 mol of O2.

The total composition of the gas mixture: 0.01 mol CO2 + 0.025 mol O2 = 0.035 mol.

Let’s find the pressure from the Mendeleev-Clapeyron equation:

PV = nRT, P = nRT / V.

P = 0.035 • 8.31 • (25 + 273) / 0.0002 = 433366.5 Pa = 433.4 kPa or 4.3 atm.

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