Another thing to get out of the way before we get too far along, is what we mean by a positive or negative electrical potential.
The way these things are generally done is to consider the OUTSIDE of the cell to be sort of “neutral” (a ground, if that helps). So if the inside is more positive than the outside, then the voltage potential difference is positive, and if the inside is more negative, then the voltage potential difference is negative.
This means that as K+ leaves the cell, it makes the inside slightly more negative than the outside, and hence there will be a negative potential difference, which will tend to pull the K+ back in. The concentration difference for K+ will also mean that K+ will continue to leak to the outside of the cell.
Got it? Understanding which way the potential difference goes will help a lot in the next section, so re-read if you need to!