Pressure caused by explosion in closed container

[Reluctant Atom]

Homework Statement

(C2H4NO6, EGDN) is an explosive with perfect attributes. We fill 20% of a sealed container with an EGDN. Assume that EGDN explodes and the created gas bahaves according to ideal gas law. What is the excess pressure in the sealed container?

My problem: I don't know where to utilize the fact that only 20% of the container has been filled with the explosives.

Known data
ρ = 1.49 g/cm³
T = 1006 °C
maximum pressure of a container: 395 Bar
M(EGDN) = 152 g/mol
R_Specific = 8.314 J / K . mol

Homework Equations

pV = nRT
n = m/M
ρ = m/V

The Attempt at a Solution

pV = nRT / substitute n = m/M
pV = m . R/M . T / get V to the right side
p = m/V . R/M . T / substitute ρ = m/V
p = ρ . R/M . T

ρ = 1.49 g/cm³ = 1490 kg/m³
R = 8.314 J / K . mol = 8.314 kg m² / (s² . K . mol)
M = 152 g/mol = 0.152 kg/mol
T = 1006 °C = 1 279.15 K

p = 104 249 546.8 kg / (m . s²) = Pa
p = 1042.495468 Bar

1042.495468 Bar - 395 Bar = 647,495468 Bar

I don't know where to apply the information that only 20% of the container has been filled with EGDN.

 

[TSny]

Hello, Reluctant Atom and welcome to PF!

The Attempt at a Solution

pV = nRT / substitute n = m/M
pV = m . R/M . T / get V to the right side
p = m/V . R/M . T / substitute ρ = m/V

Is the red volume the same as the blue volume? (Is the given density of EGDN the density for the liquid state or the gas state?)

 

[Reluctant Atom]

Hello, Reluctant Atom and welcome to PF!
Is the red volume the same as the blue volume? (Is the given density of EGDN the density for the liquid state or the gas state?)

I believe the density is of the EGDN in liquid state. It hasn't been clarified in the assignment either. Just stated that the density of EGDN is 1.49 g/cm³ and I have no further information about what gas does the EGDN produce after explosion or its density.

 

[TSny]

I believe the density is of the EGDN in liquid state. It hasn't been clarified in the assignment either. Just stated that the density of EGDN is 1.49 g/cm³ and I have no further information about what gas does the EGDN produce after explosion or its density.

Yes, the density given is for the liquid state. This would be the mass divided by the liquid volume. The volume in the liquid state is different than the volume in the gas state.

 

[Patrikp]

This is a problem from competition that is not over yet.

 

[TSny]

This is a problem from competition that is not over yet.

OK, thanks for the information.
I will not provide any further help on this question.