Chemical Formulae

chemical formulae 

A representation of a chemical substance using letters for atom and subscript numbers to show the numbers of each type of atoms that are present in the substance

Compound can be represented by two types: 

1. Empirical formula 

2. Molecular formula

Relationship between the number of moles, number of particles, mass and the volume of gas

Relationship between the number of moles, number of particles, mass and the volume of gas 

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The Mole and the Volume of Gas

The volume occupied by one mole of the gas is called molar volume

One mole of any gas always has the same volume under the same temperature and pressure

The molar volume of any gas is 22.4 dm³ at STP or 24 dm³ at room condition

Relationship between the number of moles and the volume of gas

Example 

How many moles of ammonia gas, NH₃ are present in 600 cm³ of the gas measured at room conditions? [Molar volume: 24 dm³ mol^-1 at room condition]

The number of moles of ammonia gas, NH₃

 600 cm³ /1000 = 0.6 dm³

=       0.6 dm³

    24 dm³ mol^-1

= 0.025 mol

The Mole and the Mass of Substances

The mass of one mole of any substance is called molar mass

Units: g mol^-1

The molar mass of substances are numerically equal to relative mass

Relationship between the number of moles and the mass of a substance

Example

What is the mass 0.1 mol of magnesium? [Relative atomic mass: Mg=24]

Molar mass of Mg = 24 g mol^-1

      Mass of Mg = 0.1 mol × 24 g mol^-1 

                 = 2.4g