Question

What is the difference between a physical change and a chemical change? List some examples of each.

Short answer

A physical change affects the form of a substance but not its composition, for example, melting ice. A chemical change alters the substance's chemical structure, forming new products, such as burning wood.

Step-by-step solution

Identify the Characteristics of a Physical Change

Understand that a physical change involves a change in one or more physical properties, but no change in the fundamental components that make up the substance. This means the substance undergoes a change in size, shape, state, or other physical properties, but its chemical structure does not change. Examples of physical changes include melting, freezing, shredding, and dissolving.

Recognize the Characteristics of a Chemical Change

Acknowledge that a chemical change involves a change in the chemical makeup of the substance. In a chemical change, new substances with new chemical properties are formed. This may involve a reaction that results in a change in color, temperature, or the production of light, heat, gas bubbles, or a precipitate. Examples of chemical changes include rusting, burning, decomposing, and fermenting.

List Examples of Physical Changes

Provide examples of physical changes such as ice melting into water, breaking a piece of glass, and dissolving sugar in water. Here, ice to water changes the state but not the chemical structure (H2O), the glass shards are still glass, and the dissolved sugar is still sugar, just dispersed in water.

List Examples of Chemical Changes

Provide examples of chemical changes like an iron nail rusting (forming iron oxide), a wood log burning (turning into ash and releasing carbon dioxide and water vapor), milk souring (where bacteria convert lactose into lactic acid), and silver tarnishing (forming silver sulfide when exposed to sulfur compounds in the air).

Key concepts

Physical Properties

When we talk about physical properties, we're referring to characteristics of a substance that can be observed or measured without changing its composition. These are aspects like color, density, volume, mass, boiling point, and melting point, to name a few.

One key thing to remember is that when a physical change occurs, such as when ice melts or paper is shredded, these properties might be altered, but the substance's chemical identity remains the same. So, ice, whether solid or liquid, is still H2O, and paper, no matter its size, is still paper.

Chemical Reactions

Moving on to chemical reactions, these are processes where the substances involved undergo a change in their chemical structure, resulting in the formation of new substances with different properties.

During a chemical reaction, atoms are rearranged through breaking and forming bonds, which is quite an event on the molecular level! Indicators of a chemical reaction include a change in color, temperature, or the production of light, heat, gas, or a precipitate. It's an entire transformation and not just a superficial change.

Examples of Physical Changes

Let's dive into some examples of physical changes. Imagine a block of ice melting into a puddle, a pile of paper strips after using a shredder, or sugar disappearing into a cup of coffee – these are all classic cases of physical changes.

Other examples might include:

• Clay being molded into a new shape
• A can being crushed
• Water vapor condensing on a cold surface

In all these instances, the materials involved undergo a change in form or state, yet their underlying chemical composition remains untouched.

Examples of Chemical Changes

Now, let's explore examples of chemical changes, which are all about creating something new on a molecular level. Picture a rusty bicycle chain, the embers of a campfire, or bread rising in the oven.

Additional examples include:

• Vinegar mixing with baking soda to produce carbon dioxide gas
• A silver necklace developing a black tarnish
• Food being digested in the stomach

In these situations, the original substances have reacted to form new compounds, showcasing all the drama of chemical reactions with their new properties and compositions.