Question

How many moles of $ \text{P} 4 $ are needed to react with 9 moles of $ Mg $ ?
 $ 6{\text{Mg}} + {{\text{P}}_4} \to 2{\text{M}}{{\text{a}}_3}{{\text{P}}_2} $

Answer 1

Hint: The addition of stoichiometric coefficients to the reactants and products includes balancing chemical equations. This is important because on the reactant side and the product side of the equation, a chemical equation must obey the law of mass conservation and the law of constant proportions, i.e., the same number of atoms of each element must exist.

Complete Step-by-Step Solution
Let us mention the given chemical reaction
 $ 6{\text{Mg}} + {{\text{P}}_4} \to 2{\text{M}}{{\text{a}}_3}{{\text{P}}_2} $
According to the reaction, we can observe that $ 1 $ mole of $ {{P}_{4}} $ reacts with $ 6 $ moles of $ Mg $
This means that $ 1 $ mole of $ {{P}_{4}} $ is required for every $ 6 $ moles of $ Mg $
And we need to find the number of moles of $ {{P}_{4}} $ required for $ 9 $ moles of $ Mg $
We can find the desired solution by simple unitary method.
 $ 6 $ moles of $ Mg $ requires $ 1 $ mole of $ {{P}_{4}} $
 $ 9 $ moles of $ Mg $ will require $ \dfrac{1}{6}\times 9 $ moles of $ {{P}_{4}} $
Upon solving, we get
 $ 9 $ moles of $ Mg $ will require $ 1.5 $ moles of $ {{P}_{4}} $ .

Additional Information
We know that $ 1 $ mole of any substance means $ 6.022\times {{10}^{23}} $ entities of that substance. A mole is defined in the field of chemistry as the quantity of a substance containing exactly $ 6.022\times {{10}^{23}} $ 'elementary entities' of the substance given.
The number $ 6.022\times {{10}^{23}} $ is commonly referred to as the constant of Avogadro and is often denoted by the ' $ {{N}_{A}} $ ' symbol. Atoms, molecules, monatomic/polyatomic ions, and other particles can be the fundamental entities (such as electrons) that can be represented in moles.

Note
Even one gram of a pure element is known to contain an enormous number of atoms when dealing with particles at an atomic (or molecular) level. This is where it is widely used to use the mole concept. It focuses primarily on the unit known as a mole, which is a very large number of particles counted.