How does concentration affect the reaction rate when a metal and acid react?
Rate of a chemical reaction is ALWAYS proportional to the concentration of reactants (in your case concentrations of metal and acid). However, actual relation depends on rate and stoichiometry of reaction.
The rate(speed) of a reaction is directly related to the concentration of the enzyme. As the concentration of the enzyme increases, the speed of a reaction will increase. This is because the more concentrated the enzyme concentration, the more particles there are to collide and react. There will be a stronger concentration of enzyme to react with the substrate.