Chest/Key Exchange

Not entirely sure if this is the right board, but I was wondering what the chances might be of potentially exchanging keys for chests and vice versa? I'm getting a LOT of key fragments lately (not sure why, TBH, I'm only Honor 2), and I have no chests for them (and no RP to buy chests). I'm not good enough at the game to get S grades on champions I don't main. T.T