Is the lid too tight?

Macbooks usually have that one hand opening I think. So your hinges could be binding and need replaced. Or they have come loose, the screws could be slightly stripped but if your comfortable enough opening it up remove the screws keeping track of where they go, remove the frame around the screen and first off check every screw connecting the hinges to the top and bottom and make sure they're tight with no play at all. Then there should be a screw goin through the middle connecting the top and bottom of the hinges together. It'll have washers, spring, etc and usually is a hex head or different type of screw head then the rest. Take a fine tip marker first and draw a small line from right to left across the head of the screw and the washers etc after it. This is your reference line so you can always start over. Loosen the screw very little at a time until it opens smoother. You should not have to fully rotate these screws even half way around. Very little goes a long way. This is from my experience with laptops in general, not macbooks so I hope it's similar. Hope this helps.