Why does gunpowder explode more violently when contained?

Question

I want an in depth answer to this one, please.

Answer 1

First of all, gunpowder doesn't explode, it burns. Also whether contained or not contained it burns at the same rate. When you burn gunpowder you release a set amount of energy that has to be transferred to the surroundings. Much of this energy is given off in the form of heat. As air heats up, it's pressure increases. When the pressure gets high enough, it can tear apart lots of things and that is what causes the "explosion". In the open, there is so much air, that you couldn't possibly heat it up enough to create the pressures needed to create significant damage. In a closed situation, with very little air to heat up, the pressures skyrocket and the high pressure is what causes the explosion.

Answer 2

PV = nRT; where P = pressure, V = volume, n = number of moles of gas, R = Reynolds number (a constant), and T = temperature in Kelvin.

Inside a container, the volume of a gas is held constant; so V = constant = k. Then we have P = (R/k)nT = CnT; where C = R/k = constant. Thus, pressure in a confined space is predicated on the moles of gas and the temperature of that gas.

Because the number of moles of gas is expanding and the temperature is rising as the gunpowder burns, the pressure inside the grenade, firecracker, or tin can must be rising. Finally, P > rupture pressure and the container ruptures. The gas pulses as it rushes into the atmosphere and that pulse makes the explosive sound (kaboom).

Without the confinement V <> constant; so PV = nRT and P = nRT/V; so as n and T go up to make the pressure rise, the volume can expand forcing the pressure back down. In the end, the P stays pretty steady and certainly not high or sudden enough to make a bang. The gunpowder just fizzles away.

By the way, there is fast burning gunpowder that will explode when uncontained. Such powder burns along a line where the burn rate travels at or near the speed of sound. That speed of the burn alone is explosive and makes a big noise like an explosion sounds.

Answer 3

Gunpowder burns very quickly and produces a large amount of gas in a small time period. If it is uncontained, then this gas can fill the surrounding atmosphere unhindered. If it is contained then this gas rapidly fills up the container and increases the pressure very quickly. This pressure quicly exceeds the integrity of the container and causes it to break, like a baloon popping, but on a grander scale. This abrupt release of pressure creates a shock wave in the air (all the energy is released at once, so this creates a pulse of sound energy which is of a greater amplitude than if it were uncontained).

Answer 4

If you just laid some out and put a match to it, it would just burn. If it's confined, like it a bullet casing, it explodes.

Answer 5

jeremy already answered correcty also in closed container the proces go through ADIABATIC CHANGE which is faster leading to more exlosive change of entropy then open which is bit ISOTHERMAL thus leads to smooth entropy change and most energy is transfered into work.