Grade 8 Chemistry: Chemical Bonding: Chemical Equations: Balancing Equations, Predicting Products, and Writing Compounds

In a chemical reaction, the quantity of each element does not change. Thus, each side of the equation must represent the same quantity of any particular element. In case of net ionic reactions, the same charge must be present on both sides of the unbalanced equation. By changing the scalar number for each molecular formula, the equation may be balanced.

Question:
How to write the balanced chemical equation of P4 and H2 ?
(and why it's PH3 and not H3P).

Phosphine ( IUPAC name phosphane )

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Periodic table of electronegativity of Elements by Pauling scale:

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