solids and gases?

Question

explain why C20H40 is a solid at 25 degrees while C4H8 is a gas at the same temperature

Answer 1

The C20H40 has higher intermolecular forces which pull it together tighter than the C4H8.

This is due to "London-Dispersion forces".
In a nutshell anything with more electrons (a higher mass) will be more attracted to each other because random momentary (split second) shifts in the electrons cause the molecules to be temporarily polar. The polar regions attract (negative to positive charge and vice versa) and it holds itself together.

The C4H8 has these forces too but it has less electrons which means these forces aren't as strong.

More electrons=more ability for the electrons to 'shift' = more polarizable = more attraction for each other = higher boiling point

Hope this helps!

Answer 2

That's because C(20)H(40) is a bigger molecule, there are lots of more secondary forces sticking the molecule togheter and making bonds.
Thus, its more dense (much more, making it solid).

Buthane (c4h8) is a smaller molecule, less secondary forces and thus, less dense (meaning: gas).

Answer 3

different compounds have different melting points and boiling points.
these are determined by the intermolecular structures and forces of the molecules. The first compound you mentioned has hydrogen bonds, which are a very powerful force.

Answer 4

because as carbo+hydrogen+oxy have higher boiling point thus are solids