Hello, I am watching this video to try and better understand Gibb's Phase rule The part of interest starts at 4:30 I like that he is using a visual to explain, which is very helpful. When there is 1 phase and one component, there are 2 degrees of freedom. This means two variables can be changed. This is clear when he shows the gas phase of the P-T diagram where changing either the temperature or pressure remains in the same region as a gas. He also shows when there are 3 phases, which is at the triple point, you have zero degrees of freedom. He shows the triple point on the P-T diagram, and if you change the either the temperature or pressure, you will no longer be at the triple point, hence will not have 3 phases. What seems to break down for me is when there are 2 phases. Thus there is one degree of freedom. He shows the line between the liquid and gas phase, and seems to justify that you can change either P or T, but not both, and you will still have two phases. However, when I look at it, it seems like if you change either P or T, then you will leave that gas/liquid phase line. It seems like you would need to change P and T precisely to remain on the line, thus having 2 degrees of freedom.