While many chemical reactions are critical to life—the conversion, for instance, of nutrients to water and carbon dioxide, a process that also yields the energy used to fuel cells—still others are quite dangerous. Many toxin-liberating or potentially explosive chemical reactions aren't encountered outside the controlled environment of a laboratory, as the required reagents are rare or controlled, but even household substances, if mixed in the wrong combinations, can liberate poisonous vapors. It's a good idea to be aware of such reactions, and to avoid them at all costs.
Bleach and Acid
Household bleach is a ubiquitous and useful cleaning agent, but it's quite reactive and produces toxic fumes if combined with acids such as vinegar. If exposed to acid, the chlorine-containing molecule that comprises bleach, called sodium hypochlorite, reacts to produce highly toxic chlorine gas. According to the Material Safety Data Sheet, chlorine gas causes respiratory, skin, and eye burns. Exposure to small amounts is damaging and can produce difficulty breathing and permanent respiratory impairment. Significant exposure results in death.
Bleach and Ammonia
Ammonia is a form of base, the chemical opposite of an acid. Household bleach reacts with ammonia, common in many cleaning agents such as window solution, to produce a series of toxic gases. The principle among these is chloramine, which is highly caustic. According to the Material Safety Data Sheet, exposure produces respiratory, skin, and eye burns. Blood poisoning can result from moderate doses, and large doses produce cyanosis, bluing of the skin caused by lack of oxygen in the blood, and death.
Oven Cleaner and Acid
Most oven cleaner is composed of concentrated sodium hydroxide, a powerful chemical base. Bases react explosively with acids, and oven cleaner is no exception. The products of these reactions may be quite inert; sodium hydroxide, for instance, reacts powerfully with the common chemical hydrochloric acid to produce nothing more than table salt and water. The intense heat and energy yielded by the reaction, however, can result in explosions. Household acids, like vinegar, will explode if mixed with oven cleaners, particularly if the reaction takes place at high temperature, such as inside an oven.
Peach and cherry pits, as well as apple seeds, contain small amounts of the chemical sodium cyanide. Although this compound is not dangerous on its own, when mixed with acid, it reacts to produce a highly toxic gas called hydrogen cyanide. According to the Material Safety Data Sheet, hydrogen cyanide exposure interrupts the ability of the cells to convert nutrients to energy, and results in cellular starvation and rapid death. Significant consumption of cyanide-containing seeds and pits results in a chemical reaction between the sodium cyanide in the seeds and the hydrochloric acid in the stomach, producing large amounts of hydrogen cyanide gas that escape the stomach through the esophagus and can be inhaled. Although it's unlikely that a few apple seeds would produce symptoms of cyanide poisoning, it's best to avoid habitual consumption of fruit pits.