Problem 51 - Chemistry The Molecular Science

Question

Explain in your own words, by writing a short paragraph, how the atomic theory explains conservation of mass during a chemical reaction and during a physical change.

Step-by-Step Solution

Answer

Atomic theory explains that atoms rearrange without changing mass in both chemical reactions and physical changes, so mass is conserved.

Step 1: Understanding Atomic Theory

Atomic theory posits that all matter is composed of small, indivisible particles called atoms. Each atom of an element has the same mass, and these atoms rearrange during chemical reactions or physical changes but are neither created nor destroyed.

Step 2: Conservation of Mass in Chemical Reactions

In a chemical reaction, the bonds between atoms in the reactants are broken, and new bonds are formed to create the products. However, the total number of each type of atom remains the same, ensuring that the mass of the reactants equals the mass of the products, aligning with the law of conservation of mass.

Step 3: Conservation of Mass in Physical Changes

During a physical change, such as a change in state (e.g., solid to liquid), the chemical identity of the substance remains the same, with no atoms being added or removed. Thus, the total mass before and after the change remains constant, preserving mass according to atomic theory.

Key Concepts

Atomic Theory

Atomic theory is a fundamental scientific concept that explains the nature of matter. It states that all matter is made up of tiny particles called atoms. These atoms are indivisible in chemical processes, meaning they cannot be created or destroyed in ordinary chemical reactions.

• Atoms are the smallest unit of an element that retains all of the chemical properties of that element.
• According to atomic theory, each element consists of a specific type of atom that is unique in mass and properties.

This theory is essential for understanding why during a chemical reaction, the total mass of the substances involved remains unchanged. Atoms merely rearrange but their fundamental characteristics like mass and type remain constant, according to the laws of chemistry and physics.

Chemical Reactions

Chemical reactions involve the rearrangement of atoms to form new substances. During this process, the bonds between atoms in the reactants are broken and new bonds are formed to create the products.

• Despite these changes, the total number of every type of atom remains the same before and after the reaction.
• This is because chemical reactions adhere to the law of conservation of mass.

Thus, the mass and number of atoms of the products are the same as that of the reactants. This is a key point in ensuring that mass is conserved when transformations occur at the atomic level.

Physical Changes

Physical changes, unlike chemical reactions, do not alter the chemical identity of a substance. Instead, they involve changes in the state or physical appearance. For example, melting ice changes water from a solid to a liquid, but its molecular structure remains unchanged.

• During these changes, the atoms of the substance don't change but may rearrange within their existing structures.
• Importantly, no atoms are added or removed in the process.

Thus, the mass before and after a physical change stays consistent, aligning with the principles of atomic theory and the law of conservation of mass. This illustrates how mass is preserved even when the physical form of a substance changes.