Stoichiometry And Stoichiometric Calculations

A chemical equation can be divided into two parts. The reactants appear on the left-side of the equation. The products appear on the right side of the equation.

Law of Conservation of Mass states that in all physical and chemical changes, the total mass of the reactants is equal to the total mass of the products.

A chemical equations in which the number of atoms of each element in reactants side is equal products side, called a balanced chemical equation.

Ex: Given balanced equation for the reaction of combustion of propane.

    C₃H_8(g) + 5O_2(g)                →                   3CO_2(g) + 4H₂O_(l)
  
    Carbon     -3 atoms                                   Carbon     -3 atoms
    Hydrogen  -8 atoms                                  Hydrogen  -8 atoms
    Oxygen      -10 atoms                               Oxygen      -10 atoms

Steps to be followed in balancing a chemical equation:

• Write the chemical formula for the reactants and products.
• Balance the number of atoms of each element on both sides of the equation. 

A balanced equation is useful in determing the quantitative relationship between the reactants and products in terms of number of moles, molecules, atomic masses and volumes. The calculation of quantitative relationships of the reactants and products in a balanced chemical reaction is known as ‘stoichiometry’.

The coefficients in a balanced chemical equation are called stoichiometry coefficients. The concentration of a solution can be expalined through four methods. They are mass percent, mole fraction, molarity and molality.

The mass percent of a solution is determined by dividing the mass of the solute by the mass of the solution and multiplying it by hundred.
 
Mass Percentage = Mass of Solute / Mass of Solution x 100

Mole fraction is the ratio of number of moles of a particular component to the total number of moles of the solution.

Mole fraction = number of moles of component/ total number of moles

Molarity (M) is defined as the number of moles of solute in one litre of solution.

Molarity (M) = No. of moles of solute / Volume of solution in litres

Molality (m) is defined as the number of moles of a solute present in 1 kg of solvent.

Molarity (m) = No. of moles of solute / Mass of solvent in kg