Chemical Formula and Chemical Equations
- The chemical formula of a substance is a representation of the substance using symbols.
- Two atoms of hydrogen combine together to form a molecule of hydrogen. A molecule of hydrogen is represented by H2.
- One atom of oxygen combines with two atoms of hydrogen to form one molecule of water. A molecule of water is represented by the chemical formula H2O.
Combining Power (Valency)
- The ability of atoms of elements to combine with hydrogen is referred to as their combining power or valency.
- One atom of oxygen can combine with two atoms of hydrogen, H2O. Oxygen here is said to have the combining power of two.
- One atom of nitrogen can combine with three atoms of hydrogen, NH3. Nitrogen here is said to have the combining power of three.
- Chemical formula, like chemical symbols, are written in a particular way to obey certain rules.
- In a compound, where we have more than one type of atom chemically combined, the formula of such a substance is again written to express the type and number of atoms present.
- Chemical formulas always have both letters and numbers; a combination of letters and numbers representing symbols and the number of atoms in the molecule that are used. For example:
- CH4 (Methane) – This contains one carbon atom (C) combined with four atoms of hydrogen (H).
- C4H10 (Butane) – This contains four atoms of carbon combined with ten atoms of hydrogen.
- A chemical equation is used to describe the initial substance and end products in a chemical reaction.
Rules to be Followed in Writing and Balancing a Chemical Equation
- The reactants and products must be known.
- Write a word equation.
- Write the formula of all the reactants and all the products.
- Check the number of each type of atom of the reactant(s) and the product(s).
- Balance the equation by supplying coefficients that will make the number of atoms of each element, in the reactants and products, the same. For example:
- H2 + O2 → H2O
2H2 + O2 → 2H2O
- N2 + H2 → NH3
N2 + 3H2 → 2NH3
- KClO3 → KCl + O2
2KClO3 → 2KCl + 3O2
- H2 + O2 → H2O