What is the general formula for alkanes?

The general formula for alkanes is CnH2n+2.

Alkanes are a type of hydrocarbon, which means they are composed solely of hydrogen and carbon atoms. The general formula for alkanes, CnH2n+2, reflects this composition. In this formula, 'n' represents the number of carbon atoms in the molecule. The number of hydrogen atoms is always twice the number of carbon atoms, plus two.

For example, if an alkane has 3 carbon atoms (n=3), it will have 2(3)+2 = 8 hydrogen atoms. This corresponds to the alkane propane, which has the molecular formula C3H8. Similarly, if an alkane has 5 carbon atoms (n=5), it will have 2(5)+2 = 12 hydrogen atoms. This corresponds to the alkane pentane, with the molecular formula C5H12.

This formula is a simple way to understand the structure of alkanes. Alkanes are characterised by single bonds between the carbon atoms and the hydrogen atoms, forming a saturated hydrocarbon. This means that the carbon atoms are bonded to the maximum number of hydrogen atoms possible, hence the term 'saturated'.

The general formula for alkanes also helps to explain their physical properties. For instance, as the number of carbon atoms (n) increases, the boiling point of the alkane also increases. This is due to the increased number of electrons leading to stronger London dispersion forces, a type of intermolecular force, between the alkane molecules.

IB Chemistry Tutor Summary: The formula CnH2n+2 represents alkanes, showing they're made of hydrogen and carbon. 'n' is the carbon count, with hydrogen being double this plus two. For example, propane (C3H8) has 3 carbons and 8 hydrogens. Alkanes, with only single bonds, are saturated, meaning they're fully bonded to hydrogen. As carbon numbers increase, so does the boiling point due to stronger forces between molecules.