We buy a block of baking chocolate of 5 kg around 10 pounds. When we want to use the chocolate it's always a hassle to break off a piece. It's a block 5 cm thick (2 inches). I need a easier way to break off just the amount we need.
I think you will get better suggestions on Seasoned Advice (the Stack exchange for professional and amateur chefs).
But apart from chopping off a large chunk by using a knife/chisel and a blunt tool like a hammer, you could also heat the knife and melt-cut the piece you want (I don't see a problem with doing it, although there might be, because of the nature of chocolate).
Use a chocolate slicer
Chocolate slicers are specially designed to chop chocolate. One can be purchased on Amazon, or at a cooking supply store. It looks like a tiny pitchfork and is usually around $5. This is a good method if you find it takes too much force to cut the chocolate with a knife. A chocolate chipper requires less force and power. This might just be a worthwhile investment if you regularly cut chunks of chocolate. Ice axes look similar and do the same job.
I can think of 2 options.
Add your own indentations. That is, figure out the size you need, and score it to that size with a serrated knife (like a large bread knife). It should break off very easily that way.
Another option is to chip the whole giant block into small pieces, which you can store in tightly-sealed plastic bags or plastic containers. Then, when you need a certain weight, just pour out the right amount of the small chips you made.