Chemical warfare is the fact we use chemical weapons to fight instead of more conventional projectiles, explosives or even more futuristic energy weapons
Chemical weapons uses various kind of products to produce their effects, they exists in various forms shapes and sizes. They can be man portable devices up to large scale weapons, some of them are weapons of mass destruction (WMD).
They can be radioactive, biological or chemical, many weapons exists in games from conventional flamethrowers, molotov cocktails and pepper sprays, up to more original Acid guns, Sleeping gas launchers, Petrifying guns, Bio rifles, Chemical bombs and Radioactive cannons. Some of them are deadly while some others are non lethal.
These weapons while they are very efficient against specific organic targets, they are inefficient or poorly effective against certain immune enemies. There is also often specific protections to counter them like Hazmats, Fireproof suits, gas masks, Rubber Suits and such things sometimes warn by the enemy...
These weapons exists in various forms, they use often Liquids or Gases as an ammunition, the liquids can sometimes stay in the ground or simply disappear and the gas can sometimes generate a deadly cloud that can discourage enemies to go in or highly damage them. Petrifiers, Acid pulverizers, Liquid Nitrogen launchers, Flamethrowers (in both forms), Electric Gel launcher, Nerve gas launcher, Pepper sprays, Radioactive Liquids, Poison gas launchers Radioactive Pulverizers, Sleeping gas launchers are part of this category. There is sometimes a single Chemical Thrower can use multiple functions second the loaded canister, a few games uses weapons of that kind like BioShock and Prey.
Some weapons uses projectiles with chemical products some of them uses syringe like projectiles, and some others uses bullets or shells to throw poison bullets or simply the chemical product like the dragon breath shotgun shells. So most conventional guns can be a chemical weapon with that kind of process, but some others like dart guns are often dedicated chemical weapons.
These weapons uses explosive charges to deliver their chemical content, it often happen that the player can pass a zone where he or enemies thrown chemical explosives, the weapons can go from Bombs, Grenades, and of course explosive launchers such as grenade and rocket launchers.