Which of the following would you expect to have the highest boiling point? C8H18, CH4, C4H10, C2H6, C3H8
Generally speaking, boiling points increase as carbon chain length increases. This is because there are more atoms present in the hydrocarbon molecule and therefore more intermolecular forces (eg Van der Waals') that must be overcome. In addition the now heavier molecule requires greater energy (heat) to make the phase change to a gas. However, branching decreases boiling point; branched hydrocarbons cannot pack together as closely as unbranched ones, and so intermolecular forces are less strong.
Basing on this, the C8H18 should have the highest boiling point, followed by C4H10, C3H8, C2H6 and CH4.
Hope this helps
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