A lump is usually a raised area or a bump in a surface. "When I hit my head on the board, it left a lump." A chunk is a piece that has been separated from a larger piece. "When the dog bit me, he took a chunk of my skin out." A block is usually a specific portion of something. "We put a block of ice in the cooler" A hunk is normally a large "chunk". "A hunk of that iceberg broke off and formed another iceberg" Some of these words also have other meanings, but in this context, I hope that makes it clear.

They all do and have separate meanings as Larry said but can also mean the same, as in a lump of coal, a chunk of coal, a block of coal and a hunk of coal. I have called pieces of coal all these terms.