Please help! A chemist adds 6.5 L of concentrated (12 M) hydrochloric-acid solution to 15 L of water. What is the new solution’s concentration?

Aphysical change is one that you can put in and remove like a ham sandwich. the stuff you put in there can be changem its not permanet. a chemical change is on that can't be change thats permanet. like when you make a cake and bake it. you can't get those ingredients back.