Chemical Reactions

Chemical changes are usually irreversible, you can't get easily back to the original materials (e.g. you can't un-cook an egg). However, some are easily reversed like the reaction of nitrogen and hydrogen to form ammonia and the color changes of universal indicator.

At first, chemical reactions can appear difficult to understand but basically all that happens is that the atoms of the starting materials are rearranged to form the finishing material(s). So in other words, whatever atoms are there to start with will be there at the end but the molecular structure will be in a different arrangement. The starting materials of any chemical reaction are called the reactants and the finishing materials are called the products.

Chemical reactions are described by chemical equations. Word equations are easier than balanced symbol equations but if you just remember the basics that you need to end up with exactly the same atoms as you started with, things begin to fall into place.

In high school, you need to know about a number of chemical reactions, which can be a bit worrying as there are lots to remember. Wrong! Of course, there are some specific ones to learn like the Haber process, but on the whole, you just need to learn a few basic rules - that's what's great about science, learn a few rules and it becomes a whole lot easier. One example is the reaction of strong acids with metal carbonates - these react to form a salt, water and carbon dioxide. Armed with that rule, you can easily predict the result of adding any of the strong acids to any metal carbonate - that one simple rule saves you learning dozens of individual chemical reactions.

Take this quiz on chemical reactions and see if you know some of the rules governing the molecular structures in the resulting products.