Question

State whether each of the following is a physical or a chemical change: (a) cutting aluminum foil (b) caramelizing sugar (c) adding air to a tire (d) igniting a sparkler

Short answer

(a) Physical, (b) Chemical, (c) Physical, (d) Chemical.

Step-by-step solution

Define Physical and Chemical Changes

A physical change is a change in the physical properties of a substance without altering its chemical composition, such as changes in state, shape, or size. A chemical change involves a chemical reaction, resulting in the formation of one or more new substances with different properties.

Analyze Cutting Aluminum Foil

Cutting aluminum foil involves changing the size and shape of the aluminum, but its chemical structure remains the same. Therefore, cutting aluminum foil is a physical change.

Analyze Caramelizing Sugar

Caramelizing sugar involves heating sugar to break down its molecular structure, forming new substances like caramel. This is a chemical change because it results in a chemical reaction that produces a new substance.

Analyze Adding Air to a Tire

Adding air to a tire increases the volume of air inside the tire, but neither the air nor the tire undergoes a change in chemical composition. This is a physical change.

Analyze Igniting a Sparkler

Igniting a sparkler involves burning, resulting in a chemical reaction that produces light, heat, and new substances (oxides). This is a chemical change due to the formation of new products.

Key concepts

Physical Change

Physical changes are shifts in the form or appearance of a material that do not alter its underlying composition.
For example, when you cut aluminum foil, you are changing its size and shape. Yet the aluminum remains aluminum; its molecules are still the same.
Physical changes can include:

• Changes in state, such as water freezing into ice
• Alterations in shape, like bending metal
• Modifications in size, such as tearing paper into smaller pieces

These transformations are usually reversible, meaning the original material can be restored if desired. In cutting the aluminum foil, although it looks different, it still possesses the same elemental structure.

Chemical Change

Chemical changes result in new substances with different properties from the starting materials. This process involves breaking bonds and forming new ones as elements and compounds react.
An example of a chemical change is caramelizing sugar. When sugar is heated, its molecular structure breaks down, resulting in new compounds, which give caramel its distinct color and flavor.
Important characteristics of chemical changes include:

• A change in color, like silver tarnishing
• The production of gas, for instance, when vinegar reacts with baking soda
• Emission of light or heat, such as in fireworks

These changes are often irreversible, as the original substance is fundamentally altered.

Chemical Reaction

Chemical reactions are processes in which the atoms of one or more substances are rearranged to create new substances.
In the igniting of a sparkler, a chemical reaction occurs, resulting in heat, light, and new compounds, like metal oxides. This transformation is a type of combustion, where a fuel reacts with oxygen to release energy.
Key indicators of a chemical reaction include:

• Changes in temperature or light, as with a burning candle
• Formation of precipitates, solids formed from a liquid reaction
• Development of new odors, which can signal the creation of new chemical entities

Such reactions are central to understanding chemical changes, as they explain how substances interact and transform.