Chemical Formulae, Equations and Calculations

Chemical Formulae

A chemical formula represents the types and numbers of atoms in the smallest unit of a substance.
The elements in a compound are represented by their chemical symbols, as found in the periodic table.
Subscript numbers are used to indicate the number of atoms of each element in a compound.
For example, Water is represented as H₂O, where 2 is the subscript representing two hydrogen (H) atoms bonded with one oxygen (O) atom.

Chemical Equations

A chemical equation represents a chemical reaction using the chemical formulas of the reactants and products.
Reactants are the substances that are changed in the reaction, and are written on the left of the equation.
Products are the substances that are produced in the reaction, and are written on the right of the equation.
The two sides of the equation are separated by an arrow (→) that signifies the direction of the reaction.
For example, the reaction of hydrogen with oxygen to form water is represented as: 2H₂ + O₂ → 2H₂O.

Balancing Chemical Equations

In a balanced chemical equation, the number of atoms for each element is the same on the reactant side as on the product side, demonstrating the law of conservation of mass.
To balance an equation, numbers called coefficients are placed in front of the chemical formulas in the equation, altered until each type of atom is balanced.

Moles and Calculations

The mole is the unit used to count entities at the atomic and molecular scale.
One mole of any substance contains Avogadro’s number (6.022 × 10²³) of entities (atoms, molecules, ions, etc.).
The molar mass of a substance is the mass in grams that one mole of that substance would have. It is numerically equal to the substance’s relative atomic or molecular weight.
Stoichiometry involves the calculation of quantities in chemical equations.
By using the coefficients in a balanced chemical equation, you can predict the amount of product that will be formed and the amount of reactant needed.

Limiting Reactant and Yield Calculations

The limiting reactant is the reactant that is completely used up in a reaction and determines the maximum amount of product that can be formed.
The yield of a reaction refers to the amount of product obtained.
Theoretical yield is the maximum amount of product that could be formed from the reactant amounts.
Actual yield is the amount of product actually obtained, which is often less than the theoretical yield due to side reactions or incomplete reactions.
The percentage yield is calculated by (actual yield / theoretical yield) * 100% and represents the efficiency of a reaction.