Dr Hall's Chemistry Blog (copy)

\(\require{mhchem}\) Reduction can be: removal of oxygen; addition of hydrogen; gain of electrons. We often want to reduce metal ores to get the useful metals from them. Oxidation can be: addition of oxygen; removal of hydrogen; loss of electrons. A substance that reduces another substance is a reducing agent . And guess what? A substance that oxidises another substance is an oxidising agent . Reduction and oxidation always go hand in hand. If a reducing agent like \(\ce{H2}\) acts on a substance (let's say oxygen \(\ce{O2}\)), oxygen is reduced, but in doing so hydrogen is oxidised. $$\ce{hydrogen + oxygen -> water}$$ $$\begin{equation} \ce{2H2(g) + O2(g) -> 2H2O(g)} \end{equation}\label{water}$$ (I've made the water a gas here because when you burn hydrogen in oxygen, things get hot, and the water is produced as vapour.) If we look at equation \(\eqref{water}\) from the point of view of oxygen, we can think of oxygen as the oxidising agent which oxidises hydrogen,...

We must have the same number of atoms on both sides of a chemical equation's arrow. Why? If we didn't we would be creating or destroying atoms, and that's not possible. The Law Of Conservation Of Mass tells us that matter (in this case atoms) cannot be created nor destroyed. So when we count up the number of atoms on each side of the arrow, they must be the same . Also, the number of atoms of each element must be the same. In a chemical reaction, the atoms are rearranged, but they can't change from one element to another. A carbon atom in a reactant on the left side of the arrow remains a carbon when it changes to a product on the right side of the arrow. It doesn't suddenly become a different element. Sidenote: when we have radioactive elements, changes happen in the nucleus of the atom that mean that an atom of a radioactive element can decay to form a different element. And in stars, at immense temperatures, the nuclei of two atoms may fuse together to make a he...