Problem 10 - Chemistry Matter and Change

Question

A Classify each example as a physical change or a chemical change. a. crushing an aluminum can b. recycling used aluminum cans to make new aluminum cans c. aluminum combining with oxygen to form aluminum oxide

Step-by-Step Solution

Answer

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

Step 1: Example 1: Crushing an aluminum can

In this example, we need to determine whether crushing the aluminum can is a physical or chemical change. When crushing the can, we are only changing its shape, but not its chemical properties. Therefore, it is a physical change.

Step 2: Example 2: Recycling used aluminum cans to make new aluminum cans

In this example, we need to determine whether recycling aluminum cans to make new ones is a physical or chemical change. During the recycling process, the aluminum cans are melted down and reformed into new cans. Although this process involves the melting of aluminum, its chemical composition remains the same. Therefore, this is a physical change.

Step 3: Example 3: Aluminum combining with oxygen to form aluminum oxide

In this example, we need to determine whether the formation of aluminum oxide is a physical or chemical change. When aluminum reacts with oxygen, it forms a new substance called aluminum oxide. This reaction changes the chemical composition of the reacting substances, forming a new compound. Thus, this is a chemical change. In conclusion: a. Crushing an aluminum can is a physical change. b. Recycling used aluminum cans to make new aluminum cans is a physical change. c. Aluminum combining with oxygen to form aluminum oxide is a chemical change.

Key Concepts

Chemical Reactions

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another.

Consider the example of aluminum reacting with oxygen to form aluminum oxide. This process illustrates a fundamental chemical reaction where the properties of the starting materials—aluminum and oxygen—are fundamentally different from the properties of the resulting compound. Notably, chemical reactions always involve a change in the molecular structure of the substances involved, which results in the production of one or more new substances with different properties.

Signs of a Chemical Change

• Color change.
• Production of a gas (bubbling and fizzing).
• Formation of a precipitate (a solid that separates from a solution).
• Temperature change (heat is either absorbed or released).

Chemical changes are usually irreversible, meaning it's often challenging or impossible to return the new substances back to their original form. This distinguishing factor is crucial for understanding the differences between chemical and physical changes.

Properties of Matter

Matter can be described by its properties, which are separated into physical and chemical categories.

Physical properties include characteristics such as color, density, volume, and mass, as well as the state of matter (solid, liquid, or gas). These properties can be observed or measured without changing the composition of the material. Hence, when you crush an aluminum can, you're only altering its shape and volume, not its chemical identity or composition.

The chemical properties describe a substance's ability to undergo certain chemical changes or reactions. The formation of aluminum oxide from aluminum and oxygen is, therefore, a change in chemical properties. In this process, the original properties of aluminum are lost as it becomes a different substance with distinct chemical properties.

Understanding the properties of matter is essential when distinguishing between physical and chemical changes, as it allows us to predict the behavior of materials under different conditions, and recognize when a new substance has been formed.

Recycling Process

The recycling process illustrates one of the most common examples of a physical change in the context of sustainability.

Using the example of recycling aluminum cans, we can see that the cans are collected, sorted, and then melted down to be formed into new cans or other products. Throughout this process, although the aluminum is subjected to high temperatures and mechanical treatments, its chemical composition remains unchanged. The melting and reshaping of aluminum into new forms are purely physical changes.

Steps in the Recycling Process

• Collection and transportation of recyclable materials.
• Sorting materials by type and quality.
• Cleaning to remove any contamination.
• Processing and re-manufacturing into new products.

This cycle is not only a model of efficiently using resources but also a clear representation of how physical changes can be harnessed in a way that benefits both the environment and the economy. In a world increasingly concerned with resource preservation, the recycling process has become a cornerstone of waste management and sustainability.