1st of all, reactants are needed,that is one or more elements chemically combined to form a compound which is called the product.
In post 2,for example,
H2+O2 is called the reactants
while H2O is the product of the 'chemical combination'.
we have to write an equation to recognize its reactants and products..........
eg. Mg+ O2----------> 2MgO
Usually, you have to know that in a chemical equation enter reactants and products are coming out.
You also need to know the chemical formulae for reactants and products.
For the beginning, you'll create a skeletal chemical equation, taht is not balanced.
For instance, a skeletal equation is:
H2 + O2 -> H2O
In equation enters 2 reactants: 2 atoms of hydrogen and 2 atoms of oxygen
The product resulted from equation is water. The product has only one atom of oxygen. This means that the equation is unbalanced and it has to be balanced.