All physical things around us, from the air we breathe to the solid ground beneath our feet, are made of matter. This matter possesses a fundamental property known as mass, which quantifies the amount of substance present in an object.
Understanding the Law of Conservation of Mass
A foundational principle in chemistry is the Law of Conservation of Mass, sometimes referred to as the Lavoisier-Lomonosov Law. This scientific law states that matter cannot be created or destroyed in an isolated system. Instead, the total mass of the reactants before a chemical reaction must equal the total mass of the products after the reaction.
This principle emphasizes that all the atoms present at the beginning of a chemical process are still present at the end. They simply rearrange themselves into different combinations. The Law of Conservation of Mass allows scientists to predict and understand the quantitative aspects of chemical reactions. It provides a basis for balancing chemical equations, ensuring that the number of atoms of each element is the same on both sides of the equation.
Defining Chemical Changes
Chemical changes involve a transformation at the molecular level, resulting in the creation of entirely new substances. Unlike physical changes, which alter a substance’s form but not its chemical identity, chemical reactions break existing chemical bonds and form new ones. This rearrangement of atoms leads to the formation of products with distinct chemical and physical properties from the original reactants.
For example, when wood burns, it undergoes a chemical change, transforming into ash, smoke, and gases like carbon dioxide and water vapor. These new substances have properties vastly different from the original wood. Similarly, the rusting of iron is a chemical change where iron reacts with oxygen and water to form iron oxides, a new substance with different characteristics than pure iron.
How Mass Stays Constant in Reactions
The constancy of mass during a chemical reaction stems from the fundamental principle that atoms themselves are not altered. When substances react, the atoms present in the starting materials merely rearrange their connections to form new molecules. The total count and type of each atom remain precisely the same before and after the reaction occurs.
For instance, if a reaction begins with 10 carbon atoms and 20 oxygen atoms, the products will collectively contain exactly 10 carbon atoms and 20 oxygen atoms, albeit bonded differently. Because atoms are neither created nor destroyed, the total mass of all atoms involved remains unchanged. The law applies universally to all chemical reactions, from simple acid-base neutralizations to complex biochemical processes within living organisms.
Observing Mass Conservation in Everyday Chemistry
Observing the conservation of mass in everyday chemical reactions often requires careful consideration, especially when gases are involved. For instance, combining baking soda (sodium bicarbonate) and vinegar (acetic acid) in an open container appears to result in a loss of mass as carbon dioxide gas escapes.
However, if this reaction occurs within a sealed system, like a closed bottle, the total mass of the bottle and its contents remains unchanged before and after the vigorous bubbling subsides. The gas produced is simply contained within the system.
Another example is the burning of a candle, which might seem to contradict the law as the candle visibly shrinks. In reality, the wax reacts with oxygen from the air to produce carbon dioxide and water vapor, both of which are gases that dissipate into the surroundings. If one could capture and measure the mass of all the gaseous products, along with any solid residue, the total mass would precisely equal the initial mass of the candle and the oxygen consumed from the air.