Question: So I am struggling with trying to understand what electric potential is and I wondering if this statement is correct based on my readings:

"Electric potential is the electric potential energy a charge would have if you were to place a charge at that point."
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Is that correct? Because if we have two plates where one is positive and one negative with a space between them, the electrical potentials of the positive and negative plates combine, so we know that near the negative plate and far from the positive plate, the electrical potential is very low, but far from the negative plate and near the positive plate that electrical potential is very high (Khan Academy).

Thoughts?

Answer: 
Above the critical temperature and pressure (126K), nitrogen is a supercritical fluid (has properties of both a gas and a liquid).

If it started half full of liquid, then you're asking at what pressure is the density half of liquid nitrogen. That's about 800 kg/m^3. 
Using <http://www.peacesoftware.de/einigewerte/stickstoff_e.html> it appears that 450 bar at 15 degrees C will be sufficient. You can play around with finding similar at other temperatures.
The nitrogen is above its critical temperature when it is at room temperature. It doesn't contain the standard liquid or vapor phases at that point. It would be only one phase, which would be a supercritical fluid. See <https://en.wikipedia.org/wiki/Supercritical_fluid>