5.2.2 Carbon Monoxide

[Music]

[Applause]

[Music]

[Presenter] Most chemical reactions are pretty predictable. If we know what substances we start with, we know what substances will be formed, and we'll get the same result every time those substances react.

But sometimes the very same reactants can yield different products. There are reactions where the temperature can affect which substances are formed, and there are reactions where it matters whether we use a larger or smaller amount of one of the reactants.

That’s the case with the graphite and oxygen example. Usually, when there is plenty of oxygen, carbon and oxygen will form carbon dioxide when the graphite burns. When there is less available oxygen, like when the reaction takes place in an area with limited air supply, another reaction will occur as well, where another product is formed. In this substance, each carbon atom is attached to one oxygen atom instead of two. Instead of carbon dioxide, carbon monoxide is formed, where “mono” means one. The name of the compound is contracted from mono oxide to monoxide.

Carbon dioxide and carbon monoxide. They sound almost the same, and both are made up of carbon and oxygen, but there is an important difference between them. Carbon dioxide is naturally present in the atmosphere. There’s not much—only four hundredths of one percent—but it’s vital for all plant life. The air you exhale contains about a hundred times that amount, about four percent carbon dioxide. If there is a lot of carbon dioxide in a room, the air feels bad, but it is not dangerous to inhale.

Carbon monoxide, on the other hand, is poisonous for humans and animals. If the air you inhale contains as little as one percent carbon monoxide, that’s enough to kill you within minutes. Carbon monoxide is formed not only when pure graphite burns. Other combustible substances that contain carbon, such as petrol, oil, plastic, or wood, can also form carbon monoxide.

It’s called incomplete combustion and occurs as soon as the oxygen level gets too low. In a house fire, the carbon monoxide produced is particularly dangerous. It can make the people in the house unconscious before they have time to get out, or they can even die in their sleep without even noticing there is a fire. In a fire, there is a greater risk of dying from carbon monoxide poisoning than from the flames.

Good job they had a working smoke detector.

It’s a simplification to say that when carbon compounds burn, we get either carbon dioxide or carbon monoxide. In reality, both reactions take place at the same time. Less oxygen results in more carbon monoxide. Chemical reactions can give different products even though we start with the same reactants, and in this case, where carbon reacts with oxygen, this difference can mean life or death.

[Music]