Categories
Miscellaneous Graphics

The Chemistry of Gunpowder

Chemistry of Gunpowder v3

With the Fourth of July and American Independence Day on the horizon, a somehow topical post seemed in order. Having already examined the chemical compounds that give fireworks their colours in a previous graphic, I decided to examine another important firework component here: the first chemical explosive, gunpowder, also commonly referred to as black powder.

Until the mid-19th Century, gunpowder was the only known chemical explosive. Its use can be traced much earlier than this, however, and there are historical accounts of its use in fireworks in China as far back as 1200AD. In subsequent centuries it had military applications in rifles and cannons, but in these it has long since been replaced by modern, smokeless powders. The fireworks industry is one of the last major industries that still uses traditional black powder.

Rather than being one particular compound, gunpowder is actually a mix of three different components. It consists of potassium nitrate (75% by weight), charcoal (15% by weight), and sulfur (10% by weight). Each of these components plays an important role in the combustion of gunpowder.

Potassium nitrate, also known as ‘saltpetre’, or ‘saltpeter’, decomposes at high temperature to provide oxygen for the reaction. This means that gunpowder doesn’t need to be exposed to air to burn – and is why smothering fireworks won’t stop them burning! The charcoal is often represented simply as being a source of carbon, which acts as a fuel, though it’s actually a broken down form of cellulose, with the approximate empirical formula C7H4O. Finally, the sulfur can also act as a fuel, though its inclusion has more to do with the fact that it undergoes exothermic reactions (reactions that give off heat) at relatively low temperatures, providing more energy and lowering the ignition temperature of the charcoal.

It’s worth noting that just mixing these three constituents together isn’t enough to produce good quality gunpowder; they must be thoroughly mixed, moistened and ground to produce a reactive mixture. Deviations from the ideal ratio given above are sometimes utilised to alter the burning behaviour of the mixture, and the addition of small amounts of water to the mixture can also be used to extend the burning time.

The precise reactions of gunpowder are difficult to elucidate. Rather than being a simple single reaction, the combustion of gunpowder consists of many differing complex reactions. It’s possible, however, to provide simplified equation that provides an overall idea of the products of the various reactions, as shown in the graphic. A mixture of solid and gaseous products are produced by the reactions, along with a very small amount of water.

The obvious use for black powder in firework is as the ‘lift charge’, which propels the firework into the air. The fuse, which allows the delay before the bursting of the firework, and the bursting charge itself, will also utilise gunpowder. The burning of the charcoal in gunpowder is often the source of the sparkling tails of fireworks as they ascend. The gases produced by the combustion reaction are the causes of the propellant effect, and the eventual bursting of the firework.

In some cases, safer alternatives to gunpowder that are more stable and easier to handle are now used in modern fireworks. However, many still utilise gunpowder, continuing a centuries old custom.

DOWNLOAD

SUBSCRIBE

The graphic in this article is licensed under a  Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. See the site’s content usage guidelines.

References & Further Reading

25 replies on “The Chemistry of Gunpowder”

True or false: the combustion of hydrocarbons forms liquid water (which of course immediately vaporizes at the elevated temperature of the flame)? Serious question. I’ve seen it both ways and gotten in arguments with people about it.

I’d say true – in all honesty the state of the water produced isn’t something that occurred to me to consider until just now! I know that I certainly teach it as being liquid water that’s produced initially, before it’s vaporised. Although I’m guessing the argument is that at higher combustion temperatures, for heavier hydrocarbons, it’s produced as vapour? What’s your take on it?

I also say true, it forms liquid water. It doesn’t matter, as it gets vaporized anyway, but I’m sure thermodynamically it matters. It probably matters when calculating the effective amount of heat produced and subsequent work that can be done.

Liquid and vapor and gas are aggregate states, which describe a system of many many molecules. If an isolated molecule of hydrocarbon burns into, say, 7 molecules of water, these 7 molecules are too few to be described as any aggregate state.
But if we describe aggregate states in units of energy per molecule, each molecule of water produced during HC burn will have enough energy to be over critical temperature of 647 K. Thus, the water will never be liquid.

Liquid and vapor and gas are aggregate states, which describe a system of many many molecules. If an isolated molecule of hydrocarbon burns into, say, 7 molecules of water, these 7 molecules are too few to be described as any aggregate state. But if we describe aggregate states in units of energy per molecule, each molecule of water produced during HC burn will have enough energy to be far over critical temperature of 647 K. Thus, the water will never be liquid.

[…] 2. The source of that potassium nitrate (aka saltpetre or KNO3), carbon and sulfur is … gunpowder (aka black powder), which is made of 75 percent KNO3, 15 percent carbon (e.g. from charcoal) and 10 percent sulfur. It’s literally an explosive mixture. (Sources: Staff of Eugene’s Science Factory, HowStuffWorks.com’s How Fireworks Work and Compound Interest via Oregon Museum of Science and Industry) […]

Once gunpowder is burned or used what is the chemical breakdown of the residue? Like when bullet is show, what is the chemical makeup of the residue in the casing?

So, I’m aware this is a tad old, but my chemistry teacher recommended this to me, and if you’ve the time to answer a question, I’d be most appreciative.
My question is this: Is the chemical reaction given in the graphic complete? From what I understand, there are numerous extra reagents at play here. If that is the case, can you tell me what compounds those are, and what affect they have on the gasses that are released in this reaction?

More than happy to answer questions! As the graphic states, the equation given is a simplified one; really, there are a myriad of reactions occurring during the combustion of black powder. A more complete (but still simplified) equation for the combustion is given by the attached image, from M S Russell’s ‘The Chemistry of Fireworks’. This is an overall equation, taking into account a number of different reactions which occur during the burning of black powder.

He also goes into a little detail about some of the individual reactions – the book is free to view (for that portion at least) on Google Books. The link’s provided in the references above.

The above equation is to complicated to understand i thought that is why once a persona short by gun is going to die.
But my question is that from above equation which chemical formula once contact with blood it kill blood cell?

Without the constant burning of black powder, could everyone, still occupy the land in which they currently live on?

I beg to differ. Could the burning of black powder be for the sole purpose that none matter entities can exist?

What type of reaction is this? Synthesis, decomposition, single/double replacement, or combustion?

It’s quite a complex reaction, so probably quite difficult to simplify and categorise as a single type. I’d honestly be at a loss to class it as one particular type of reaction, there’s a lot going on. Potassium nitrate thermally decomposes, the oxygen generated by this decomposition then proceeds to react in a combustion reaction with the carbon, to give but two examples.

Hi, I’m working on making a trickling device for re loaders to use. Can you tell me are there any substitute substances that can be used for testing to replace gunpowder with. We don’t want to use it in a work environment so we’d like a substitute product that has the same weight and size per grain as gunpowder. If you are unaware of any perhaps you could even me give me the size and weight of the grain? Thanks for any help- it really would be appreciated.

By any chance, does anyone know the ignition temperature of gunpowder with and without sulfur? The graphic says sulfur lowers ignition temp, so, what does it lower it to and what would the ignition temp be without it?

Comments are closed.