stoichiometric coefficient

The number of molecules of a reactant taking part in a reaction is known as Stoichiometric coefficient.

In a balanced reaction, both sides of the equation have the same number of elements. The stoichiometric coefficient is the number written in front of atoms, ion and molecules in a chemical reaction to balance the number of each element on both the reactant and product sides of the equation. Though the stoichiometric coefficients can be fractions, whole numbers are frequently used and often preferred. These stoichiometric coefficients are useful since they establish the mole ratio between reactants and products. In the equation:

2 Na (s) + HCl(aq) → 2NaCl (aq) + H₂(g)

we can determine that 1 mole of HCl will react with 2 moles of Na(s) to form 2 moles of NaCl(aq) and 1 mole of H₂(g). If we know how many moles of Na we start out with, we can use the ratio of 2 moles of NaCl to 2 moles of Na to determine how many moles of NaCl were produced or we can use the ration of 1 mole of H2 to 2 moles of Na to convert to NaCl. This is known as the coeffient factor. The balanced equation makes it possible to convert information about one reactant or product to quantitative data about another element. Understanding this is essential to solving stoichiometric problems!

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