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 ...

The atoms in the reactants are: 1 calcium atom, 2 chlorine atoms, 2 sodium atoms, 2 hydrogen atoms, 2 carbon atoms, and 6 oxygen atoms The atoms in the products are: 1 calcium atom, 2 chlorine atoms, ...

When hydrogen reacts with oxygen, water is made. What are the names of the reactants and products in this reaction?

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 ...