Question

A 3.31-g sample of lead nitrate, Pb(NO3)2, molar mass = 331 g/mol, is heated in an evacuated cylinder with a volume of 2.53 L. The salt decomposes when heated, according to the equation:
2Pb(NO3)2(s)-->2PbO(s) + 4NO2(g) + O2(g)
Assuming complete decomposition, what is the pressure in the cylinder after decomposition and cooling to a temperature of 300. K? Assume the PbO(s) takes up negligible volume.

Answer 1

Answer:

0.486atm is the pressure of the cylinder

Explanation:

1 mole of Pb(NO₃)₂ descomposes in 4 moles of NO2 and 1 mole of O2. That is 1 mole descomposes in 5 moles of gas.

To find the pressure of the cylinder, we need to find moles of gas produced, and using general gas law we can determine the pressure of the gas:

Moles Pb(NO₃)₂ and moles of gas:

3.31g * (1mol / 331g) = 0.01 moles of Pb(NO₃)₂.

That means moles of gas produced is 0.05 moles.

Pressure of the gas:

Using PV = nRT

P = nRT/V

Where P is pressure (Incognite)

V is volume (2.53L)

R is gas constant (0.082atmL/molK)

T is absolute temperature (300K)

And n are moles of gas (0.05 moles)

P = 0.05mol*0.082atmL/molK*300K / 2.53L

P = 0.486atm is the pressure of the cylinder