Chemical reactions are what makes the world around us tick. The reactions going on inside your body ensure that you metabolise the food you consume, make use of the oxygen you inhale and produce substances that are essential to survival, and chemical reactions are essential to industry and many other elements of life. However, from the perspective of the chemistry student tackling seemingly abstract chemical equations and lab-controlled reactions, it can be difficult to understand the genuine use (or indeed, uselessness) of different chemical reactions. There are inherent issues with calling a reaction “useless,” but they can be basically classified regardless.
Useful reactions: Biological reactions
All living organisms use chemical reactions as a source of energy and to release energy from food or materials they consume. Two examples of these types of useful reactions are photosynthesis, in which carbon dioxide and water are combined – with the help of energy from the Sun – to form glucose (the key biological “fuel”) and oxygen, and respiration, in which glucose is broken down using oxygen to form carbon dioxide and water (essentially releasing the energy stored in the glucose “fuel”). These steps are made up of several intermediate reactions, which are equally important to the functioning of organisms.
Useful reactions: Energy-releasing reactions
Chemical reactions are either endothermic or exothermic, which means they either take in energy or give out energy. Reactions which release energy can be important sources of power, and there are many different examples of these reactions. One example is the reaction between carbon dioxide and lithium nitride, which transforms the gaseous carbon dioxide into a solid product and releases a great deal of energy in the process.
Reactions aren’t really “useless”
Before considering “useless” reactions, it’s important to consider how the idea applies to chemistry as a whole. All chemical reactions start with source materials (the “reactants”) and finish with products. These products may not be immediately useful in the same way glucose or the energy produced by other reactions is, but there is always something that can be done with a product. This means that saying a reaction is “useless” is fundamentally flawed, since every reaction leads to products (and either releases or absorbs energy), which could be used in numerous ways.
Useless reactions: Rusting
The rusting of iron is a familiar reaction which doesn’t have much practical value. This basically occurs when iron is exposed to oxygen and water, leading to the creation of a compound containing iron, oxygen and varying amounts of water. Since this weakens and damages the iron, there is limited practical use for the reaction.
Useless reactions: Neutralisation
Acids and bases react together in a “neutralisation” reaction, in which the free hydrogen ions present in the acid combine with the free hydroxide ions present in the base to produce water and a salt. Acids and bases have interesting chemical properties, so turning them into plain water isn’t exactly “useful,” although you do get a salt out of it. In the case of hydrochloric acid and sodium hydroxide reacting together, you get water and sodium chloride (more commonly known as table salt), but in others the metal salts you obtain aren’t as readily useful.