A chemical reaction means that the substrate is converted to product (new substance) over time, the amount of substrate is reduced. Concentration will increase
Chemical reaction means that the precursor to the products (new) Over time, the quantity of the precursor are reduced. The quantity of new substances are added.
This means that the chemical reactions substances begin to change to a product (new Substances) over time. quantity of substances will be reduced to abide by new substances will increase volume.