Stoichiometric Calculations

What Is Stoichiometry?

Stoichiometry is the evaluation of products and reactants that are part of a chemical reaction. The term “stoichiometry” is derived from the Greek words, “stoicheion” and “metry” meaning element and measuring, respectively.

Stoichiometry Formulas

1. The law of conservation of mass is the base concept of stoichiometry; the mass of reactants is equal to the mass of products. This shows the relation between the quantities of products and reactants’ quantities, usually written in the ratio of positive integers.
2. If you have the number of individual elements, you can easily calculate the amount of the product. When you have the number of reactants, finding the number of products is easy.
3. Here, to find the stoichiometry, we need a balanced chemical formula of the reaction. The stoichiometric equation will have the same amount of elements on both sides.
4. Stoichiometric Coefficient- The stoichiometric coefficient, otherwise called the stoichiometric number, denotes the molecules participating in a reaction. For any balanced reaction, there is an equal number of elements on either side of the equation.
5. So basically, the stoichiometric coefficient is the number that is written in front of molecules, atoms, or ions. It helps in establishing the molar ratio between reactants to the products. It can be written in whole numbers or as fractions.

Stoichiometric Calculations based on chemical formulas

The stoichiometric calculations are based on certain factors. Also given are some stoichiometric calculations examples.

Formula Mass

• The sum of the atomic mass of each element of the molecule in a substance
• For example formula mass of NA₂S is written as 2(23) + 1(32) = 78

Avogadro number

Avogadro’s number is the number of particles in one mole of a substance. To be precise, It is defined as the number of atoms in 12g of C-12. Avogadro’s number is always valued as 6.02214076 × 10²³.

Molar Mass

• It is the total mass of the atoms that form a molecule in g/mol
• The mole ratio of reactants and products is explained as: 2Na + 2HCl → 2NaCl + H₂
• We see that 2 moles of sodium (Na) are reacting with 2 moles of hydrochloric acid (HCl) to form 2 moles of sodium chloride (NaCl) and 1 mole of hydrogen gas (H₂)