The position where Chelsea is currently is in the premier league stand, their is no guarantee thst Chelsea will surely secure the fourth position because their are teams under Chelsea that their points are even close to Chelsea, so any mistake from Chelsea these clubs can take over the fourth position. Chelsea has a lot of job to do to win every of their games till the end of the season.
As for the first position and second position, it has been secured already by Liverpool and arsenal, no team can get to this point in this season . I think where the competition is now , the third position and the fourth position.
Mathematically first position can still change that's why Liverpool isn't yet declared champions because mathematically it's still possible to overtake them. As for second spot, the point difference between second and third is 4 points and we all know that it very possible to overtake. 2 consecutive slips from a particular team and the other team that's 4 points behind wins that two games, the position will definitely change and the team that was 3rd will move to second and vice versa.