Why are we using dilute acids for reaction? Why can't we use concentrated acids for reaction?
It only affects the rate of reaction. With concentrated acids such as hydrochloric, the reaction is very vigorous and the contents become hot. This increases the rate even more, and the contents can froth. With diluted acid, the reaction is much more controlled.
Note that concentrated sulphuric and nitric acids do not give much hydrogen. Both are reduced by metals, sulphuric giving sulphur dioxide and nitric giving nitrogen dioxide.