Final answer:
Butane boiling involves overcoming London dispersion forces, which are weaker intermolecular attractions between nonpolar alkane molecules. The energy for boiling comes from heat which increases the molecules' kinetic energy. Intermolecular forces are generally less energetic to overcome than the intramolecular forces that hold a molecule together.
Step-by-step explanation:
When butane boils, the intermolecular forces between the butane molecules are overcome. These forces are known as London dispersion forces, which are the only significant intermolecular forces for nonpolar molecules like alkanes. The energy required to overcome these interactions comes from the heat supplied to the butane, which increases the kinetic energy of the molecules.
In general, intermolecular forces are weaker than intramolecular forces, such as covalent bonds within a molecule. This is why boiling, which involves overcoming intermolecular forces, typically requires less energy than breaking chemical bonds within the molecule.
The actual boiling points of various alkanes demonstrate the impact of molecular mass and shape on the strength of London dispersion forces. For instance, n-butane with its extended shape has stronger intermolecular interactions and a higher boiling point compared to its isomer 2-methylpropane, which is more compact.