Problem 10 - Chemistry Matter and Change

Question

A Classify each example as a physical change or a chemical change. \begin{equation} \begin{array}{l}{\text { a. crushing an aluminum can }} \\ {\text { b. recycling used aluminum cans to make new aluminum cans }} \\ {\text { c. aluminum combining with oxygen to form aluminum oxide }}\end{array} \end{equation}

Step-by-Step Solution

Answer

a. Physical change; b. Physical change; c. Chemical change.

Step 1: Understanding Physical Change

A physical change involves a change in physical properties (such as shape, state, or size) but does not change the substance's chemical identity. Crushing an aluminum can is an example of a physical change because it alters the can's shape without altering the substance itself.

Step 2: Analyzing the Reconstitution Process

Recycling used aluminum cans involves melting them and reshaping them into new cans. This is considered a physical change because aluminum's chemical structure remains unchanged. The process involves changes in form and state but not in the chemical composition.

Step 3: Identifying Chemical Change

A chemical change involves a chemical reaction, resulting in the formation of one or more new substances with different properties. When aluminum combines with oxygen to form aluminum oxide, its chemical structure changes, indicating a chemical change as a new compound (aluminum oxide) is created.

Key Concepts

Physical Change

Physical changes are all about altering the form or appearance of a material without changing its actual chemical substance. This means the chemical makeup of the material remains the same, even as its physical properties like shape, size, or state alter.
For instance, when you crush an aluminum can, you're not changing what the can is made of — just how it looks. It compresses and maybe looks different, but it's still aluminum through and through.

• Shape, size, or state changes
• No new substances formed
• Reversible changes are often a sign of physical change

Overall, physical changes are superficial but sometimes quite important in processes like recycling, which involves melting and reshaping materials without altering their basic chemistry.

Chemical Change

Chemical changes are more profound. They happen when the substances involved undergo a transformation at the molecular level, leading to the production of one or more distinct substances. Essentially, it's a change in what the single entities of the materials actually are.
One classic example is when aluminum reacts with oxygen in the air to form aluminum oxide. This transformation means new bonds are created between different elements, altering what's fundamentally present.

• Formation of new substances
• Irreversible changes are common
• Changes in energy (like heat or light) often accompany chemical changes

Identifying chemical changes means looking for these clues that signal a shift in the essential makeup of the original materials.

Chemical Reaction

Chemical reactions are the processes by which chemical changes occur. They involve rearranging atoms in molecules and can be thought of as the pathways that lead to new substances forming.
In our example, aluminum combining with oxygen is a classic chemical reaction. During this process, aluminum and oxygen atoms reconfigure to create a new substance: aluminum oxide.

• Involve reactants and products
• Often require an energy source to proceed
• Can be represented by chemical equations

The general formula is:\[ \text{Reactants} \rightarrow \text{Products} \]
Understanding chemical reactions helps us see how complex and varied the world of chemistry is, with each reaction telling a unique story of transformation.