Is this a combination of Boyle's and Charle's law or simply one of them? I'm confused as to which applies. I don't feel I fully understand the implications of both laws individually and I'm wondering why it's easy to take a gas like butane and liquify it under pressure at "normal" temperatures and why other gasses need to be cooled to extremely low temperatures or very high pressures to liquify. I understand that temperature, pressure and volume are all related, I just don't know which rules apply and how... and how they all interact. And how do these laws apply to changes of state from gas to liquid?

I'm sure this is stuff I forgot from 10th grade but I'd love to hear an explanation again.

Is this a combination of Boyle's and Charles' Laws or simply one of them? 

I'm confused as to which applies. I don't feel I fully understand the implications of both laws individually and I'm wondering why it's easy to take a gas like butane and liquefy it under pressure at "normal" temperatures and why other gases need to be cooled to extremely low temperatures or very high pressures to liquefy. 

I understand that temperature, pressure and volume are all related, I just don't know which rules apply and how and how they all interact. How do these laws apply to changes of state from gas to liquid?

I'm sure this is stuff I forgot from 10th grade but I'd love to hear an explanation again.