GCSE Chemistry Practice Test: Chemical Reactions - Molecular Structure Changes — Flashcards

Chemical reactions are changes to the arrangement of atoms and the molecular structure of materials. They are all around us. We can see some reactions such as fireworks and explosions. Many are very useful, like cooking and combustion. Others are more vital but are not quite as obvious such as photosynthesis and respiration. Without these reactions there would be no life on Earth - in fact there would be no universe as we know it. Everything would be made of elements and nothing would ever change. 

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 colour 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.

You must know important chemical reactions like the Haber process, and a few basic rules. 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.