why is it that food containers expand when they spoil? If the container is a closed system and matter can’t be created, what causes an increased pressure?



why is it that food containers expand when they spoil? If the container is a closed system and matter can’t be created, what causes an increased pressure?

In: Biology

Bacteria in the food creates gas as a byproduct. The gas is less dense than the solid matter. This gas takes up more space and causes the container to expand.

The matter isn’t destroyed or spawned from the void. It is solids/ liquids converted into a gas. Think how fires put off smoke. That is wood being turned into a gas. That’s why when a fire is done burning the ash takes up so little space. All the mass was converted to a gas and dissipated away

Bacteria in the container eat solids and liquids (which are more dense) and produce gases, which are much less dense. No atoms are being created, but the bonds between them are broken down and then rearranged into bacteria farts.

“Less dense” means that the same amount of atoms in gas form now take up a lot more space than the liquids and solids they were before. Or at least they *would* take more space…but in a sealed can the amount of space is fixed. The can is already full to begin with! So the only possibility is increasing pressure in the space available.

Gases, solids and liquids have different typical densities. Solids and liquids are relatively comparable and depend mostly on the material, gases (ideally) do not depend on what they’re made of, only of the temperature and pressure. (In reality, some gases take up less space than simple models would imply, but this is beyond the scope of this discussion)

Assuming one lump of matter becomes just one lump of gas, it will desire greater volume. Since volume is constant, it will result in increased pressure instead.

Once the increased pressure (many lumps of solids/liquid become gases) surpasses that which the container can well, contain – it will either deform until the pressure reduces (Higher volume -> lower pressure for when temperature and quantity remain the same), or if it cannot deform any longer – it will burst.

Above, we assumed only that one lump of solid gives an “equal” lump of gas.

But many times, a solid decomposes into multiple lumps of gas.

You are probably familiar with hypo, the bleaching and cleaning agent – correct? Its real name is sodium hypochlorate. There is a similar chemical known as Sodium Chlorate – a common herbicide.

Sodium chlorate is made of one lump of sodium, one lump of chlorine and three lumps of oxygen, all contained within a single molecule.

If you take 2 lumps of sodium chlorate and heat it to a high temperature, it will produce two lumps of table salt and three lumps of breathable oxygen gas. As a solid, its volume won’t change much… but the pressure will suddenly skyrocket in a closed container.

No matter was produced, simply existing matter was rearranged into different combinations (table salt and breathable oxygen), and this rearrangement led to a far more gases than previously. And more gas leads to higher pressure… And higher pressure leads to expansion or explosion.

Now, re-read the above but replace lump with “moles” and you’ll get the ‘chemicall correct, if simplified answer’.

As for the ideal model…

It says:

Volume is: directly proportional with temperature, quantity and indirectly proportional with pressure

Meaning: Increasing the temperature will increase volume, Increasing the quantity (not mass!) will increase volume. Whereas, to increase pressure volume must be reduced.

in short, pV=nRT where p is pressure, volume is v, n is quantity, R is an empirical constant and T is absolute temperature (kelvin scale).