Here is a way that you can use matrices and your TI calculator to balance most chemical equations including the one from the post.

__P4 + __H2O + __P2I4 ------> __PH4I + __H3PO4
 we produce a matrix as follows where you line up the formulas on the first row, and the elements on the first column, then fill in the table with the number of each element present in each formula.  The reactants are input as positive values and products as negative values

Example Limiting Reactant Calculation: A 2.00 g sample of ammonia is mixed with 4.00 g of oxygen.  Which is the limiting reactant and how much excess reactant remains after the reaction has stopped? First, we need to create a balanced equation for the reaction: 4 NH3(g) + 5 O2(g)4 NO(g) + 6 H2O(g)

Empirical formulas and molecular formulas are types of chemical formulas.Chemical formulas represent the composition of a substance with atomic symbols.Empirical formulas show the simplest whole number ratio of these atoms.Molecular formulas show the actual ratio of atoms in the compound.Here is an example:Glucose is the a simple sugar whose molecular formula is C6H12O6Its empirical formula would be CH2O which would be its molecular formula divided by the smallest whole number 

Stoichiometryⁱ is the quantitative relationship among reactants and products in a chemical reaction.

Stoichiometry is derived from two Greek words: stoicheion (meaning "element") and metron (meaning "measure").

You often are required to calculate quantities of reactants or products.

Stoichiometry calculations are based on the fact that the number of atoms are conserved in a chemical reaction. The number and kinds of atoms before and after the reactions are always the same. Therefore we have to balance any chemical equation.

How to determine a molecular formula from an empirical formula?

In order to determine a molecular formula of an unknown compound from its empirical formula, you must know the molecular weight of the compound.