The study of coordination chemistry is significant in Chemistry Topics as it investigates the bonding and reactivity of metal complexes with ligands.
What are Combustible and Non-Combustible Substances ?
The burning of a substance in the oxygen of air in which heat and light are produced, is called combustion. So, in most simple words, ‘combustion’ means ‘burning’. In this Chapter we will study the chemical process of combustion (or burning) and the types of flames produced during this process.
A chemical process in which a substance reacts with the oxygen (of air) to give heat and light is called combustion.
The light which is given off during combustion can be in the form of a ‘flame’ or as a ‘glow’. For example, wood burns by producing a flame (see Figure).
But charcoal burns by producing light in the form of glow. The substance which undergoes combustion is said to be combustible. It is also called a fuel. We will now give some examples of combustion.
(i) Combustion of Magnesium. If a magnesium ribbon is heated, it starts burning (or undergoes combustion). When a magnesium ribbon burns, it combines with the oxygen of air to form magnesium oxide, and liberates heat and light. The combustion of magnesium can he written as follows:
Thus, the burning of magnesium in air to produce heat and light is a combustion process. In this reaction, magnesium is a combustible substance.
(ii) Combustion of Charcoal. Charcoal is mainly carbon. If we hold a piece of charcoal with a pair of tongs and heat it on the flame of a burner, it starts burning (or undergoes combustion).
When charcoal burns, then the carbon of charcoal combines with the oxygen of air to form carbon dioxide. A lot of heat is produced in this combustion reaction but only a little light is produced (which makes the charcoal glow). The combustion of charcoal can be written as follows :
Coal also contains a lot of carbon. So, coal also burns in air producing carbon dioxide, heat and light. Thus, charcoal and coal are combustible substances.
In both the examples of combustion given above, we find that oxygen is necessary for combustion (or burning) to take place. Actually, oxygen is a supporter of combustion. In most of the cases of combustion, oxygen is provided by the air around us. So, in a way, air is also a supporter of combustion.
This is because air contains oxygen. So, whether we write oxygen as supporter of combustion or air as supporter of combustion, it will mean the same thing.
Food is a fuel for our body. During respiration, the digested food (like glucose) is broken down by reaction with oxygen in the body cells to produce carbon dioxide, water and heat energy. This heat energy is utilised by our body. Thus, respiration is a kind of slow combustion of food which takes place in the body to produce heat energy.
We have all seen the brown rust present on iron nails and other iron objects. The rust is formed when iron slowly combines with the oxygen present in air (in the presence of moisture) to form iron oxide. The process of rusting of iron is an example of slow combustion. The rusting liberates very little heat but no light.
The sun produces heat and light. The heat and light produced in the sun are not due to ordinary combustion (which takes place in the presence of oxygen of air). In the sun, heat and light are produced due to nuclear reactions (in which hydrogen is converted into helium with the release of heat and light).
Combustible and Non-Combustible Substances
Take a piece of paper. Apply a lighted matchstick to this piece of paper. We will find that the piece of paper starts burning. We say that the piece of paper burns (or the piece of paper undergoes combustion). We now take a piece of stone and apply a lighted matchstick to it.
We will find that the piece of stone does not burn. We say that the piece of stone does not undergo combustion. This means that all the substances around us do not burn (or do not undergo combustion). So, there are two types of substances around us:
- Combustible substances, and
- Non-combustible substances.
Those substances which can burn are called combustible substances. In other words, those substances which can undergo combustion are called combustible substances. Some of the combustible substances are : Paper, Cloth (Fabrics), Straw (Dry grass), Cooking gas (LPG), CNG, Kerosene oil, Wood, Charcoal, Coal, Cow-dung cakes, Petrol, Diesel, Alcohol, Matchstick and Magnesium ribbon, etc. A combustible substance is also called a fuel.
Those substances which do not burn are called non-combustible substances. In other words, those substances which do not undergo combustion are called non-combustible substances.
Some of the non-combustible substances are : Stone, Glass, Cement, Bricks, Soil, Sand, Water, Iron nails, Copper objects and Asbestos, etc. From this discussion we conclude that some of the substances around us are combustible whereas others are non-combustible.