Question

State and explain the law of conservation of mass.

Short answer

The law of conservation of mass states that mass cannot be created or destroyed in a chemical reaction, so the mass of the reactants equals the mass of the products.

Step-by-step solution

Understanding the Law of Conservation of Mass

The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. This means that the mass of the reactants (the substances that start the reaction) must equal the mass of the products (the substances that are produced by the reaction). The total mass remains constant throughout the reaction.

Applying the Law to Chemical Equations

When writing a balanced chemical equation, the law of conservation of mass requires that the number of atoms of each element must be the same on both sides of the equation. Balancing a chemical equation means ensuring that the number of atoms for each element are equal on the reactant side and the product side, which implies that mass is conserved.

Practical Implications of the Law

In practice, this law implies that in a closed system, the total mass measured before and after a chemical reaction must be the same. This conservation applies despite changes in the form of substances or their states; for example, a solid reactant may produce liquid or gas products, but the total mass will remain unchanged.

Key concepts

Chemical Reactions

Chemical reactions involve the transformation of substances through the breaking and forming of chemical bonds. During these processes, reactants, which are the starting materials, convert to products, with new chemical properties and compositions. A simple example is the reaction between vinegar and baking soda which produces carbon dioxide gas, water, and a salt.

Understanding the nature of chemical reactions is foundational to chemistry, as they are the mechanisms by which substances interact with one another. These reactions are governed by certain rules and principles, one of which is the subject of your textbook exercise: the law of conservation of mass.

Although some reactions may seem to produce materials out of thin air, such as the sudden appearance of a gas, the law assures us that if you were to carefully capture and measure all the substances involved, including those seemingly invisible gases, their total mass would precisely match the mass of the original reactants.

Balanced Chemical Equations

Just like a seesaw at equilibrium, a balanced chemical equation ensures that the mass on one side is equivalent to the mass on the other. This is a visual and mathematical representation of the law of conservation of mass. It's crucial to ensure that for every element involved in the reaction, the number of atoms on the reactant side (before the reaction) and the product side (after the reaction) are identical.

In writing out a chemical equation, the reactants are listed on the left-hand side, products on the right, and an arrow points from reactants to products to indicate the direction of the reaction. If the equation is not balanced, coefficients (numbers placed before molecules) are used to multiply the number of those molecules, adjusting the equation until balance is achieved. An important tip is to start balancing elements that appear in the fewest compounds and save hydrogen and oxygen for last, as they're often found in several compounds within a reaction.

Conservation Principles in Chemistry

The conservation principles in chemistry are fundamental guidelines about how matter and energy behave during chemical processes. The law of conservation of mass is a cornerstone among conservation principles, anchored in the understanding that mass cannot be created or destroyed. This principle is essential, not just in academic exercises, but in practical chemistry applications, like chemical engineering, pharmacology, and environmental science.

Aside from mass, other conserved quantities include energy (law of conservation of energy) and electric charge (law of conservation of charge). When teaching these principles, it's crucial to stress that conservation does not imply that substances cannot change form—only that the total amount of the conserved quantity remains the same throughout the process. In the context of a chemistry lab or industry, precisely knowing these principles allows scientists and engineers to predict the outcomes of reactions and design processes that are safe, efficient, and sustainable.