Mass conservation is a fundamental principle in science stating that mass cannot be created or destroyed in a closed system. This means that the total mass of substances involved in a chemical reaction or physical process remains constant, even if they change form. For example, when wood burns, the mass of the ash, gases, and heat produced equals the mass of the original wood and oxygen consumed. This principle is crucial in various fields, including chemistry, physics, and engineering. It helps scientists and engineers predict how materials will behave in reactions and processes, ensuring efficient designs and safe practices in industries like chemical engineering and environmental science.