The big number written in front of a molecule (coefficient) shows how many of that molecule there are. All the atoms in the products come from the atoms in the reactants. The reactants are on the left ...

For a reaction to occur, the reactants must have enough energy to overcome a barrier so as to reach the transition state and consequently form products (Fig. 1). The reactants all possess ...

You can tell this because the products have less energy than the reactants, and the arrow showing the overall change in energy points downwards. In the profile for an endothermic reaction ...

It is more obvious in reactions that do not go to completion that the reaction is reversible. This is the case when the reaction mixture contains both reactants and products.

Heterogeneous catalysis is a type of catalysis in which the catalyst occupies a different phase from the reactants and products. This may refer to the physical phase — solid, liquid or gas ...