A chemical reaction is a process where substances transform into new substances. During these transformations, mass is conserved. This means the total quantity of matter remains constant, neither increasing nor decreasing.
Defining the Law of Conservation of Mass
The Law of Conservation of Mass states that in any chemical reaction, mass is neither created nor destroyed. Instead, the substances involved merely change their form or arrangement. This principle means that the total mass of the starting materials, known as reactants, will precisely equal the total mass of the substances produced, called products.
French chemist Antoine Lavoisier is widely credited with formulating and demonstrating this law in the late 18th century. His work was pivotal in transforming alchemy into modern chemistry by emphasizing precise measurements. Observing this conservation requires a “closed system,” meaning no matter can enter or leave during the process.
The Atomic Basis of Mass Conservation
The conservation of mass is explained by atomic theory. Chemical reactions involve the rearrangement of atoms, not their creation, destruction, or transformation into different types of atoms. The atoms present in the initial reactants break their existing bonds and form new bonds to create the product substances.
Consider atoms as building blocks, similar to LEGO bricks. Just as bricks are reconfigured, the total number and type of atoms remain constant before and after a chemical reaction. Because atoms retain their mass, the combined mass of all atoms involved remains constant throughout the reaction. This atomic rearrangement ensures the overall mass of the system is conserved.
Practical Demonstrations of Mass Conservation
Observing the Law of Conservation of Mass in everyday chemical reactions often requires a closed system to capture all reactants and products. For example, when wood burns, it appears to lose mass, leaving only ash. However, burning wood combines with oxygen to produce ash, carbon dioxide, and water vapor. If all reactants and gaseous products were measured in a sealed container, the total mass before and after burning would be identical.
Another demonstration involves mixing baking soda and vinegar. These substances react to produce carbon dioxide gas, causing bubbling. If performed in an open container, the gas escapes, leading to an apparent mass decrease. However, if the reaction occurs in a sealed container, like a bottle with a balloon capturing the gas, the total mass remains the same, demonstrating mass conservation.